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Fundamental of fixed prosthodontics
 

Fundamental of fixed prosthodontics

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Procedimientos principales para elaborar una protesis fija en clinica y laboratorio

Procedimientos principales para elaborar una protesis fija en clinica y laboratorio

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    Fundamental of fixed prosthodontics Fundamental of fixed prosthodontics Document Transcript

    • Fundamentals ofFixedProsthodonticsThird EditionHerbert T. Shillingburg, Jr, DDSSumiya Hobo, DDS, MSD, PhDLowell D. Whitsett, DDSRichard Jacobi, DDSSusan E. Brackett, DDS, MSquinlc/zeneebooh/
    • Library of Congress Cataloging-in-Publication DataFundamentals of fixed prosthodontics / Herbert T. Shillingburg Jr... [et al.]. — 3rd edp. cm.Rev. ed of: Fundamentals of fixed prosthodontics / Herbert T.Shillingburg, Jr., Sumiya Hobo, Lowell D. Whitsett. 2nd ed 1981.Includes bibliographical references and index.ISBN0-86715-201-X1. Prosthodontics. I. Shillingburg, Herbert T.[DNLM: 1. Denture, Partial, Fixed. 2. Prosthodontics-methods.3 Denial Prosthesis Design. WU 515 F981 1996]RK651 F86 1997617.69—dc20DNLM/DLCfor Library of Congress 96-24703CIPQuintessence Publishing Co, Inc551 North Kimberly DriveCarol Stream, IL 60188-1881All rights reserved. This book or any part thereof may not be reproduced, stored in a retrieval s1or transmitted in any form or by any means, electronic, rnechamcal, photocopying, or otherwiseout prior written permission of the publisher.Production Manager Timothy M. BobbinsCover Design: Jennifer A. SabellaPrinting and binding: The Ovid Bell Press, Fulton, MOPrinted in the USA on recycled paper
    • ContentsPrefaceAcknowledgments1 An Introduction to Fixed Prosthodontics2 Fundamentals of Occlusion3 Articulators4 Interocclusal Records5 Articulation of Casts6 Treatment Planning for Single-Tooth Restorations7 Treatment Planning for the Replacement of Missing Teeth8 Fixed Partial Denture Configurations9 Principles of Tooth Preparations10 Preparations for Full Veneer Crowns11 Preparations for Partial Veneer Crowns12 Preparations for Intracoronal Restorations13 Preparations for Extensively Damaged Teeth14 Preparations for Periodontaily Weakened Teeth15 Provisional Restorations16 Fluid Control and Soft Tissue Management. . .1. .11. .25. .35. .47. .73. .85.105.119.139.155.171.181.211.225.257
    • 17 Impressions18 Working Casts and Dies19 Wax Patterns20 The Functionally Generated Path Technique .21 Investing and Casting22 Finishing and Cementation23 Esthetic Considerations24 All-Ceramic Restorations25 Metal-Ceramic Restorations26 Pontics and Edentulous Ridges27 Solder Joints and Other Connectors28 Resin-Bonded Fixed Partial Dentures.281.309.335.355.365.385.419.433.455.485.509.537Index .
    • PrefaceFixed prosthodontics is the art and science of restor-ing damaged teeth with cast metal, metal-ceramic,or all-ceramic restorations, and of replacing missingteeth with fixed prostheses. Successfully treating apatient by means of fixed prosthodontics requires athoughtful combination of many aspects of dental treat-ment: patient education and the prevention of furtherdental disease, sound diagnosis, periodontal therapy,operative skills, occlusal considerations, and sometimes,placement of removable complete or partial prosthesesand endodontic treatment.Restorations in this field of dentistry can be the finestservice rendered for dental patients, or the worst disser-vice perpetrated upon them. The path taken dependsupon ones knowledge of sound biological and mechan-ical principles, the growth of manipulative skills to imple-ment the treatment plan, and the development of a criti-cal eye and judgment for assessing detail.As in all fields of the healing arts in recent years, therehas been tremendous change in this area of dentistryImproved materials, instruments, and techniques havemade it possible for todays operator of average skills toprovide a service whose quality is on par with that pro-duced only by the most gifted dentist of years gone by.This is possible, however, only if the dentist has a thor-ough background in the principles of restorative dentistryand an intimate knowledge of the techniques required.This book was designed to serve as an introduction tothe area of restorative dentistry dealing with fixed partialdentures and cast metal, metal-ceramic, and all-ceramicrestorations. It should provide the background knowl-edge needed by the novice, as well as be a refresher forthe practitioner or graduate student.To provide the needed background for formulatingrational judgments in the clinical environment, there arechapters dealing with the fundamentals of treatmentplanning, occlusion, and tooth preparation. In addition,sections of other chapters are devoted to the fundamen-tals of the respective subject. Specific techniques andinstruments are discussed because dentists and dentalstudents must deal with them in their daily work.Alternative techniques are given when there are multi-ple techniques widely used in the profession. Frequently,however, only one technique is presented Cognizance isgiven to the fact that there is usually more than oneacceptable way of accomplishing a particular operation.However, in the limited time available in undergraduatedental training, there is usually time for the mastery ofonly one basic technique for accomplishing each of thevarious types of treatmentAn attempt has been made to provide a sound workingbackground in the various facets of fixed prosthodontictherapy. Current information has been added to cover theincreasing use of new cements, new packaging andtechniques for the use of impression materials, andchanges in the management of soft tissues for impres-sion making. New articulators, facebows, and conceptsof occlusion needed attention, along with precise ways ofmaking removable dies. The increased usage of peri-odontally weakened teeth required some tips on han-dling teeth with exposed root morphology or molars thathave lost a root.Different ways of handling edentulous ridges withdefects have given the dentist better control of the func-tional and esthetic outcome; no longer must metal orceramics be relied on to somehow mask the loss of boneand soft tissue. The pages devoted to the technique forfabricating gold pontics with cemented, customized, pre-fabricated porcelain facings have been deleted.The increased emphasis on esthetic restorations hasnecessitated expanding the subject of all-ceramic andmetal-ceramic restorations from one chapter to threechapters. A chapter has been added to cover resin-bonded fixed partial dentures, a treatment modalitywhose strengths and shortcomings we are coming torecognize. Changes are based on recent research andon the experiences of the authors and their associates inthe treatment of patients and the teaching of students.Updated references are used to document the ratio-nale for using materials and techniques and to familiarizethe student with the literature in the various aspects offixed prosthodontics. If more background information onspecific topics is desired, several books are recom-mended:For a detailed treatment of the subject of dental mate-rials, refer to Dr Kenneth Anusavices book, PhillipsScience
    • of Dental Materials. For an in-depih study of occlusion,see Dr Peter Dawsons Evaluation, Diagnosis, andTreatment of Occlusat Problems (2nd ed) or Dr Jeffrey P.Okesons Management of Temporomandibular Disordersand Occlusion (3rd ed). The topic of tooth preparationsis discussed in greater detail in Fundamentals of ToothPreparations by Shillmgburg, Jacobi, and Bracket!. Fordetailed coverage of occlusal morphology used in wax-ing restorations, consult Guide to Occlusal Waxing byShillingburg, Wilson, and Morrison. A wealth of informa-tion concerning both the fabrication of porcelain restora-tions and the materials aspect of porcelain can be foundin Dr John McLeans excellent works, The Science andArt of Dental Ceramics, Volumes I and II; in MetalCeramics—Principles and Methods of Makoto Yama-moto; and in Introduction to Metal Ceramic Technologyby Dr W. Patrick Naylor.Two fine restorative dentists had an important influenceon this book. Dr Robert Dewhirst and Dr Donald Fisherhave been teachers, colleagues, and most important,friends. Many of their philosophies have steered usthrough the past 25 years. The UCLA Fixed Prostho-dontics Syllabus, authored and edited by Dr Fisher andcoauthored by Drs Dewhirst and Shillingburg in 1968,was the foundation upon which the first edition of thisbook was based in 1976.
    • Chapter 1An Introduction to Fixed ProsthodonticsThe scope of fixed prosthodontic treatment canrange from the restoration of a single tooth to therehabilitation of the entire occlusion. Single teethcan be restored to full function, and improvement in cos-metic effect can be achieved. Missing teeth can bereplaced with fixed prostheses that wilf improve patientcomfort and masticatory ability, maintain the health andintegrity of the dental arches, and, in many instances,elevate the patients self-image.It is also possible, by the use of fixed restorations, torender supportive and long-range corrective measuresfor the treatment of problems related to the temporo-mandibular joint and its neuromuscular components. Onthe other hand, with improper treatment of the occlusion,it is possible to create disharmony and damage to thestomatognathic system.TerminologyA crown is a cemented extracoronal restoration that cov-ers, or veneers, the outer surface of the clinical crown. Itshould reproduce the morphology and contours of thedamaged coronal portions of a tooth while performing itsfunction. It should also protect the remaining tooth struc-ture from further damage.If it covers all of the clinical crown, the restoration is afull or complete veneer crown (Fig 1-1). It may be fabri-cated entirely of a gold alloy or some other untarnishablemetal, a ceramic veneer fused to metal, an all-ceramicmaterial, resin and metal, or resin only. If only portions ofthe clinical crown are veneered, the restoration is calleda partial veneer crown (Fig 1-2).Intracoronal cast restorations are those that fit withinthe anatomic contours of the clinical crown of a tooth.Inlays may be used as single-tooth restorations for prox-imo-occlusal or gingival lesions with minimal to moderateextensions. They may be made of gold alloy (Fig 1-3, A)or a ceramic material (Fig 1-3, B). When modified with anocclusal veneer, the intracoronal restoration is called anonlay and is useful for restoring more extensively dam-aged posterior teeth needing wide mesio-occluso-distalrestorations (Fig 1-4).Another type of cemented restoration has gained con-siderable popularity in the past 10 years. The all-ceram-ic laminate veneer, or facial veneer (Fig 1-5), is used insituations requiring an improved cosmetic appearanceon an anterior tooth that is otherwise sound. It consists ofa thin layer of dental porcelain or cast ceramic that isbonded to the facial surface of the tooth with an appro-priate resin.The fixed partial denture is a prosthetic appliance,permanently attached to remaining teeth, which replacesone or more missing teeth (Fig 1-6). Although the term ispreferred by prosthodontists, this type of restoration haslong been called a bridge. "Bridge" is still in commonenough usage that in the most recent listing of ADAinsurance codes and nomenclature (1991), componentsof this restoration are catalogued under "bridge," and theterm "fixed partial denture" does not appear in the list.1A tooth serving as an attachment for a fixed partial den-ture is called an abutment. The artificial tooth suspendedfrom the abutment teeth is a pontlc. The pontic is con-nected to the fixed partial denture retainers, which areextracoronal restorations that are cemented to the pre-pared abutment teeth. Intracoronal restorations lack thenecessary retention and resistance to be utilized as fixedpartial denture retainers. The connectors between thepontic and the retainer may be rigid (ie, solder joints orcast connectors) or nonngid (ie, precision attachmentsor stress breakers).DiagnosisA thorough diagnosis must first be made of the patientsdental condition, considering both hard and soft tissues.This must be correlated with the individuals overall phys-ical health and psychological needs. Using the diagnos-tic information that has been gathered, it is then possibleto formulate a treatment plan based upon the patientsdental needs, mitigated to a variable degree by his or
    • n Introduction to Fixed Prosthodonticsooth. The e:Fig1•2face is LA. of 1isuaparti;thecllly lefher medical, psychological, and personal circumstances.There are five elements to a good diagnostic workup irpreparation for fixed prosthodontic treatment:1,2.3.4,5.HistoryTMJ/occlussIntraoral exaDiagnostic cFull mouth nil evaluationmination:astsidiographsHistoryIt is important that a good history be taken before the ini-tiation of treatment to determine if any special precau-tions are necessary. Some elective treatment might beeliminated or postponed because of the patients physi-cal or emotional health. It may be necessary to premed-icate some patients for certain conditions or to avoidmedication for others
    • Fig 1-5 A laminatP veiwr is a thin layer ofporcelain or cast ceramic that is bonded tothe facial surface of a tooth with resin.Connector PonticFig 1-6 The components of a fixed partial deruurc.It is not within the scope of this book to describe all theconditions that might influence patient treatment.However, there are some which occur frequently enoughor pose a great enough threat to the patients or dentistswell-being that they merit discussion. A history of infec-tious diseases such as serum hepatitis and acquiredimmunodeficiency syndrome must be known so that pro-tection can be provided for other patients as well asoffice personnel.There are numerous conditions of a noninfectiousnature that also can be important to the patients well-being If a patient reports a previous reaction to a drug,it should be determined whether it was an allergic reac-tion or syncope resulting from anxiety in the dental chair.If there is any possibility of a true allergic reaction, anotation should be made on a sticker prominently dis-played on the outside of the patients record, so that theoffending medication will never be administered or pre-
    • o Fixed Prosthodontic:scribed. Local anesthetics and antibiotics are the mostcommon offenders.The patient might also report a reaction to a dentalmaterial. Impression materials and nickel-containingalloys are leading candidates in this area. Do not engagein any "do-it-yourself" allergy testing to corroborate thepatients recollection of previous problems. It is possibleto initiate a lile-threatening anaphylactic reaction if youchallenge the patients immune system with an allergento which he or she has been previously sensitized.The patient should be asked about medication cur-rently being taken All medications should be identifiedand their contraindications noted before proceeding withtreatment. Question the patient about current medica-tions at each subsequent appointment so that you willhave up-to-date information on the medication regimen.Patients who present with a history of cardiovascularproblems may require special treatment. No patient withuncontrolled hypertension should be treated until theblood pressure has been lowered. Generally, a systolicreading above 160 mm of mercury or a diastolic readingabove 95 preempts dental treatment and should because for referring the patient to his or her physician forevaluation and treatment.2Patients with a history ofhypertension or coronary artery disease should notreceive epinephrme. since this drug has a tendency bothto increase heart rate and elevate blood pressure.An individual with a prosthetic heart valve, a history ofprevious bacterial endocarditis, rheumatic fever withvalvular dysfunction, most congenital heart malforma-tions,34or mitral valve prolapse with valvular regurgita-tion3-5should be premedicated with amoxicillin or, in thecase of allergy, erythromycin or clindamycin following the1991 guidelines set by the American Heart Associ-ation.34Alternative regimens with other antibioticsadministered by injection could be required. Patients withcardiac pacemakers311or prosthetic joints6probably willnot require prophylaxis. It is best to check with thepatients physician if there is any question whether pro-phylactic antibiotics should be employed at all, or if analternative antibiotic regimen should be utilizedA patient who is on an antibiotic regimen prescribed toprevent the recurrence of rheumatic fever is not ade-quately premedicated to prevent bacterial endocardi-tis.3-4Tetracyclines and sulfonamides are also not recom-mended."Many patients with prosthetic heart valves are onCoumadm, an anticoagulant These patients physiciansshould be consulted before beginning any proceduresthat will cause even minor bleedingEpilepsy is another condition whose existence shouldbe known. It does not contraindicate dentistry, but thedentist should know of its history in a patient so thatappropriate measures can be taken without delay in theevent of a seizure while the patient is in the chair Stepsshould also be taken to control anxiety in these patients.Long, fatiguing appointments should be avoided to min-imize the possibility of precipitating a seizure.Diabetic patients are predisposed to periodontalbreakdown or abscess formation.7A well-controlled dia-betic may receive routine dental treatment. Those whoare poorly controlled, tending toward elevated bloodsugar, or hyperglycemia, could be adversely affected bythe stress of a dental appointment to the point of fallinginto a diabetic coma.Hypoglycemia can also cause problems. A controlleddiabetic (on medication) who has missed a meal or hasnot eaten for several hours may suddenly feel light-head-ed and appear intoxicated These patients usually carrysome quick source of sucrose, such as candy, whichshould be administered. For this reason, dental treatmentfor the diabetic should interfere as little as possible withthe patients dietary routine, and the patients stress levelshould be reduced. Any questions about the patientsability to cope with dental treatment, and whether he orshe is properly controlled, should be referred to a physi-cian before proceeding.The prolonged presence of xerostomia, or dry mouth,is conducive to greater carious activity and is thereforeextremely hostile to the margins of cast metal or ceramicrestorations. Patients who have had large doses of radi-ation in the oral region may have drastically diminishedsalivary flow.8It can also occur as a component ofSjogrens syndrome, an autoimmune, collagen disease.9It is frequently seen in conjunction with other autoimmunediseases, such as rheumatoid arthritis, lupus erythe-matosus, and scleroderma.!0There are also some 375 drugs capable of producingmild to severe xerostomia." Anticholinergics, anorectics,and antihypertensives may produce this effect.Antihistamines comprise the largest group of such drugs,and chronic allergy sufferers who use them over a pro-longed time may suffer from a dry mouth.The patient should be given an opportunity to describethe exact nature of the complaint that has brought him orher to the dental office for treatment. Attitudes about pre-vious treatment and the dentists who have rendered itoffer an insight into the patients level of dental aware-ness and the quality of care expected. This will help thedentist to determine how much education the patient willrequire and how amenable the patient will be to cooper-ating with a good home-care programAn effort should be made to get an accurate descrip-tion of the patients expectations of the treatment results.Particular attention should be paid to the cosmetic effectanticipated. A judgment must be made as to whether thepatients desires are compatible with sound restorativeprocedures. Possible conflicts in this area, as well as inthe realm of personality, should be noted. The option ofnot providing care may need to be exercised with somepatientsTMJ/Occlusal EvaluationPrior to the start of fixed prosthodontic procedures, thepatients occlusion must be evaluated to determine if it is
    • Fig 1-7 The joints are palpateto detect iigns of dysfurFig 1-8placingmandil•YlieThe masse>ter muscle tarover the lateralp;ilpaiod oxtr;:[orally1LIS Ofbythehealthy enough to allow the fabrication of such restora-tions. If the occlusion is within normal limits, then all treat-ment should be designed to maintain that occlusal rela-tionship. However, if the occlusion is dysfunctional insome manner, further appraisal is necessary to deter-mine whether the occlusion can be improved prior to theplacement of the restorations or whether the restorationscan be employed in the correction of the occlusal prob-lem.Does the patient suffer from frequent occasions ofhead, neck, or shoulder pain? If so, an attempt must bemade to determine the origin of such pain. Many patientssuffer from undiagnosed muscle and/or joint dysfunctionof the head and neck region, and such a history that hasnot been adequately diagnosed should be investigatedfurther.Next is an assessment of the temporomandibular jointsthemselves. Healthy temporomandibular joints functionquietly with no evidence of clicking, crepitation, or limita-tion of movement on opening, closing, or moving lateral-ly. Palpation of the joints as the patient opens and closesshould reveal the existence of any signs of dysfunction(Fig 1-7). Many patients suffer from muscle pain as aresult of parafunctional jaw activity related to stress orsensitivity to faults in their occlusion. Habits such asclenching the teeth and "playing with the bite" during thecourse of the daily routine may result in fatigue and mus-cle spasm. Observe the physical appearance and activ-ities of this type of patient. Many times they will have asquare-jowled appearance, with masseter muscles thatare overdeveloped from hyperactivity. They may beclenching their teeth even as they converse with you.A brief palpation of the masseter (Fig 1-8), temporalis(Fig 1-9), medial pterygoid (Fig 1-10), lateral pterygoid(Fig 1-11), trapezius (Fig 1-12), and sternocleidomastoid(Fig 1-13) muscles may reveal tenderness The patientmay demonstrate limited opening due to spasm of themasseter and/or temporal muscles. This can be noted byasking the patient to open "all the way" (Fig 1-14). If itappears that the opening is limited, ask the patient to usea finger to indicate the area that hurts. If the patienttouches a muscle area, as opposed to the temporo-mandibular joint, there is probably some dysfunction ofthe neuromuscular system (Fig 1-15).Evidence of pain or dysfunction in either the temporo-mandibular joints or the muscles associated with thehead and neck region is an indication for further evalua-tion prior to starting any fixed prosthodontic procedures.
    • <oFixedProsthodonticsFig 1-13 The siemoc leidumastoid muscle is grasped betweethe thumb and forefingers on the side of the neck. The muscle LJbe accentuated by a slight turn of the patients head.Intraoral ExaminationWhen the patients mouth is examined, there are severalobservations to be made. The first of these is thepatients general oral hygiene. How much plaque can befound on the teeth, and in what areas? What is the gen-eral periodontal condition?Check for a band of attached gingiva around all teeth,particularly around teeth to be restored with crownsMandibular third molars frequently do not have attachedgingiva around the distal segment (30% to 60%}, Aprospective abutment that lacks the necessary attachedtissue is a very poor candidate to receive a crown. Theprospects of chronic inflammation occurring in responseto any minute marginal irregularity in the crown are quitehighThe presence or absence of inflammation should benoted along with gingival architecture and stippling. Theexistence of pockets should be entered in the record andtheir location and depth charted. The presence andamount of tooth mobility should also be recorded, withspecial attention paid to any relationship with occlusafprematurities and to potential abutment teethExamine edentulous ridges and note the relationship
    • g 1-14 The diwhen the patientpartway (B), the ir>ce between maxillary and mandibular incinstmcted to open "all the way" (A). If the patieise should be determined.Fig 1-15 Kopeninjuse a finger lo indiof spaces if there are more than one. What is the condi-tion of prospective abutment teeth? Mote the presenceand location of caries. Is it localized or widespread? Arethere large numbers of gingival lesions and decalcifica-tion areas? The amount and location of caries, coupledwith an evaluation of plaque retention, can offer someprognosis for new restorations that will be placed. It willalso help to determine the preparation designs to be used.Previous restorations and prostheses should be exam-ined carefully. This will make it possible to determinetheir present suitability or their need to be replaced. It willalso offer some prognosis for future work to be done.Finally, an evaluation should be made of the occlusion.Are there large facets of wear? Are they localized orwidespread? Are there any nonworking interferences?The amount of slide between the retruded position andthe position of maximum intercuspation should be noted.Is the slide a straight one, or does the mandible deviateto one side or the other? The presence or absence ofsimultaneous contact on both sides of the mouth shouldbe observed. The existence and amount of anterior guid-ance is also important. Restorations of anterior teethmust duplicate existing guidance or, in some patients,replace that which has been lost through wear or trauma.Diagnostic CastsDiagnostic casts are an integral part of the diagnosticprocedures necessary to give the dentist as complete aperspective as possible of the patients dental needs. Toaccomplish their intended goal, they must be accuratereproductions of the maxillary and mandibular arches,made from distortion-free alginate impressions. Thecasts should contain no bubbles as a result of faultypouring, nor positive nodules on the occlusal surfacesensuing from air entrapment during the making of theimpression.To gain the most from the diagnostic casts, theyshould be mounted on a semiadjustable articulator.When they have been positioned with a facebow and thearticulator adjustments have been set by the use of lat-eral interocclusal records, or check bites, a reasonablyaccurate simulation of jaw movements will be possible.The articulator settings should be included in thepatients permanent record to facilitate resetting theinstrument when restorations are fabricated for this
    • o Fixed Prosthodor,patient at some future date Finally, the mandibular castshould be set in a relationship determined by thepatients optimum condylar position (with the disc inter-posed) to better enable a critical occlusal analysis.Articulated diagnostic casts can provide a great dealof information for diagnosing problems and arriving at atreatment plan. They allow an unobstructed view of theedentulous spaces and an accurate assessment of thespan length, as well as the occlusogingival dimension.The curvature of the arch in the edentulous region can bedetermined, so that it will be possible to predict whetherthe pontic(s) will act as a lever arm on the abutmentteeth.The length of abutment teeth can be accuratelygauged to determine which preparation designs will pro-vide adequate retention and resistance. The true inclina-tion of the abutment teeth will also become evident, sothat problems in a common path of insertion can beanticipated, Mesiodistal drifting, rotation, and faciolingualdisplacement of prospective abutment teeth can also beclearly seen.A further analysis of the occlusion can be conductedusing the diagnostic casts. A thorough evaluation of wearfacets—their numbers, size, and location—is possiblewhen they are viewed on casts. Occlusal discrepanciescan be evaluated and the presence of centric prematuri-ties or excursive interferences determined. Discre-pancies in the occlusal plane become very apparent onthe articulated casts. Teeth that have supererupted intoopposing edentulous spaces are easily spotted, and theamount of correction needed can be determined.Situations calling for the use of pontics which are wideror narrower than the teeth that would normally occupythe edentulous space call for a diagnostic wax-up.Changes in contour plus widening or narrowing of anabutment tooth can also be tried and evaluated on aduplicate of the original cast. This enables the dentistand the patient to see how a difficult treatment will lookwhen finished. The diagnostic wax-up, done in ivory wax,allows the patient to see all of the compromises that willbe necessary.It is far better to discover that the projected result isunsatisfactory to the patient before treatment is begun. Ifthe patient is satisfied and the work proceeds, the wax-up will help the dentist plan and execute the preparationsand the provisional, or temporary, restorations.Full-Mouth RadiographsRadiographs, the final aspect of the diagnostic proce-dure, provide the dentist with information to help corre-lale all of the facts that have been collected in listening tothe patient, examining the mouth, and evaluating thediagnostic casts. The radiographs should be examinedcarefully for signs of caries, both on unrestored proximalsurfaces and recurring around previous restorations. Thepresence of penapical lesions, as well as the existenceand quality of previous endodontic treatments, should benoted.General alveolar bone levels, with particular emphasison prospective abutment teeth, should be observed Thecrown-root ratio of abutment teeth can be calculated. Thelength, configuration, and direction of those roots shouldalso be examined. Any widening of the periodontal mem-brane should be correlated with occlusal prematurities orocclusal trauma. An evaluation can be made of the thick-ness of the cortical plate of bone around the teeth and ofthe trabeculation of the bone.The presence of retained root tips or other pathosis inthe edentulous areas should be recorded. On many radi-ographs it is possible to trace the outline of the soft tis-sue in edentulous areas so that the thickness of the softtissue overlying the ridge can be determined.Protection AgainstInfectious DiseasesProtecting against cross-contamination of patients andpreventing exposure of office staff to infectious diseaseshave become major concerns in dentistry in recentyears. In particular, patients should be queried about apast history of either serum hepatitis (hepatitis B virus, orHBV) or human immunodeficiency virus (HIV). AlthoughAIDS has received the greatest publicity and has gener-ated near hysteria. HBV is the major infectious occupa-tional hazard to health-care professionals.12- There is no evidence that either disease is contractedby casual contact with an infected person. However, thenature of dental procedures does produce the risk ofcontact with blood and tissues. A safe, effective vaccineagainst hepatitis B is available and is recommended bythe Centers for Disease Control13."14and the ADA Councilon Dental Therapeutics15for all dental personnel whohave contact with patients.While special precautions should be observed whentreating patients with a history of either disease, everypatient should be treated as being potentially infectious.Rubber gloves, a surgical mask or full-length plastic faceshield, protective eyeglasses (if a shield is not used), anda protective uniform are recommended for the dentistand all other office personnel who will be in contact withthe patient during actual treatment (Fig 1-16).Concern for these matters does not end at the door tothe operatory. Any item contaminated with blood or sali-va in the operatory, such as an impression, is just as con-taminated when it is touched outside the operatory. Thedays of casually munching on Doritos while waxing andhandling a cast recently extracted from a bloody impres-sion are a thing of the past. The specifics of decontami-nating impressions will be covered in Chapter 17.
    • Protection Against Infectious DiseasesReferencesFig 1-16 Rubber gloves, a sur;important for safeguarding denial officSteps must be taken in a receiving area of the labora-tory to isolate and decontaminate items coming from thedental operatory.15An infection-control program shouldbe established to protect laboratory personnel frominfectious diseases, as well as to prevent cross-contami-nation that could affect a patient when an appliancereturns from the laboratory to the operatory for insertionin the patients mouth.16There is more to dental laborato-ry work than manipulating inert gypsum, wax. resins,metal, and ceramics.91-97I. Malamed SF: Blood pressure evaluation and the preventionof medical emergencies in dental practice. J Prev Dent1980; 6:183-198.i. Dajani AS, Bisno AL, Chung KJ, et al: Prevention of bacter-ial endocarditis—Recommendations by the American HeartAssociation. JAMA 1990; 264:2919-2922.X. Council on Dental Therapeutics. American HeartAssociation: Preventing bacterial endocarditis—A state-ment ior the dental professional. J Am Dent Assoc 1991;12287-92.5 Bracked SE: Infective endocarditis and mitral valve pro-lapse—The unsuspected risk. Oral Surg Oral Med OralPathol 1982; 54:273-276.i. Council on Dental Therapeutics: Management of dentalpatients wiih prosthetic joints. J Am Dent Assoc 1990;121 537-538. Schlossman M, Knowler WC, Pettit DJ, Genco RJ: Type 2diabetes mellitus and periodontal disease. J Am Den!Assoc 1990; 121:532-536.i. Frank RM, Herdly J, Phillipe E: Acquired dental defects andsalivary gland lesions after irradiation tor carcinoma. J AmDent Assoc 1965; 70:868-883.). Bertram U: Xerostomia—Clinical aspects, pathology andpathogenesis. Ada Odontol Scand 1967; 25 (suppl49):1-126). Daniels T, SNverman S, Michalski JP, Greenspan JS,Silvester RA, Talal N: The oral components of Sjogrens syn-drome. Oral Surg Oral Med Oral Pathol 1975; 39:875-885.I. Sreebny LM, Schwartz SS: A reference guide to drugs anddry mouths. Gerodontology 1986; 5:75-98.>. Joint Advisory Notice. Protection Against OccupationalExposure to Hepatitis B Virus (HBV) and HumanImmunodeficiency Virus (HIV). Washington, DC, USDepartment of Labor, US Department of Health and HumanServices, Oct 19, 1987.I Centers for Disease Control: Hepatitis B virus vaccine safe-ty—Report of an inter-agency group- Morbidity and MortalityWeekly Report 1982; 31:465-467.1. Centers for Disease Control: The safety of hepatitis B virusvaccine Morbidity and Mortality Weekly Report 1983132:134-136.i. Council on Dental Materials, Instruments and Equipment;Council on Dental Practice, Council on Dental Therapeutics:Infection control recommendations for the dental office andthe dental laboratory J Am Den! Assoc 1988; 116:241-248.5. National Board for Certification of Dental Laboratories:Infection Control Requirements for Certified DentalLaboratories. Alexandria, VA, National Association of DentalLaboratories, 1986.
    • Chapter 2Fundamentals of OcclusionUnfortunately, the occlusion of teeth is frequentlyoverlooked or taken for granted in providingrestorative dental treatment for patients. This maybe due in part to the fact that the symptoms of occlusaldisease are often hidden from the practitioner not trainedto recognize them or to appreciate their significance. Thelong-term successful restoration of a mouth with castmetal or ceramic restorations is dependent upon themaintenance of occlusal harmony.While it is not possible to present the philosophies andtechniques required to render extensive occlusal recon-struction in this limited space, it is essential that the read-er develop an appreciation for the importance of occlu-sion. The perfection of skills required to provide sophisti-cated treatment of complex occlusal problems may takeyears to acquire. However, the minimum expectation ofthe competent practitioner is the ability to diagnose andtreat simple occlusal disharmonies. He or she also mustbe able to produce restorations that will avoid the cre-ation of iatrogenic occlusal disease.Centric RelationIn restoraiive Ireatment, the goal is to create occlusalcontacts in posterior teeth that stabile, instead of creat-ing deflective contacts that may destabilize, themandibular position. The occlusion in a restorationshould be made in harmony with the optimum condylarposition, centric relation: an anteriorly, superiorly bracedposition along the articular eminence of the glenoidfossa, with the articular disc interposed between thecondyle and eminence.1This position of the condyles in the glenoid fossae hasbeen discussed and debated for years. It is used in den-tistry as a repeatable reference position for mountingcasts in an articulator.23The term attempts to define theoptimum relative position between all of the anatomiccomponents. Ideally, that condylar position is also coin-cident with maximum intercuspation of the teeth.4For the concept of centric relation to be meaningful,the basic anatomy of the temporomandibular joint mustbe understood (Fig 2-1). The bone of the glenoid fossa isthin in its most superior aspect and is not suited to be astress-bearing area. However, the slope of the eminencein the anterior aspect of the fossa is composed of thickcortical bone that is capable of bearing stress.The articular disc is biconcave, is devoid of nerves andblood vessels in the central area, and is tough—muchlike a piece of shoe leather. It has a few muscle fibersattached in the anterior aspect from the superior head ofthe lateral pterygoid muscle. The disc is attached to thecondyle on its medial and lateral aspects and should beinterposed between the condyle and articular eminenceas function occurs. The condyie is not spherical, but hasan irregular, elliptical shape. This shape helps to distrib-ute stress throughout the temporomandibular joint ratherthan concentrating it in a small area.Many methods have been used to guide the mandibleinto an "ideal" position Earlier concepts of centric rela-tion involved the most posterior condylar position in thefossa. The condyle was sometimes forcefully manipulat-ed into the rearmost, uppermost, and midmost positionwithin the glenoid fossa, called the "RUM" position,"-7using chinpoint guidance. However, when the condyle isretruded, it may not be seated onto the central area of thearticular disc. Instead it may be on the highly vascularand innervated retrodiscal tissues (the bilaminar zone)posterior to the disc (Fig 2-2).s This can occur if the hor-izontal fibers of the temporomandibular ligament havebeen unduly traumatized so that they no longer supportthe condyle in a more anterior, physiologic position. It ispresently thought that rather than being a physiologicposition, it is frequently an abnormal, forced position,which could create unnecessary strain in the temporo-mandibular joint. In this circumstance, the disc is dis-placed anteriorly, and clicking of the joint is frequentlyobserved as the patient opens and closes.The more recent concept describes a physiologicposition regarding musculoskeletal relationships of thestructures9(Fig 2-3). It is not a forced position, but is gen-tly guided by the operator using the bilateral method10orby allowing natural muscle action to place the condyle ina physiologically unstrained position.11
    • Fundamentals ofOcciusioiFig 2-1 Some of the components of thetemporomandibular joint are A, articulareminence; C, condyle; D, articular disc; E,external auditory meatus; L, lateral ptery-goid muscle; R, retrodiscal tissue (bilaminatzone); S, thin superior wall of the glenoidfossa.Fig 2-2 In a dysfunctional joint with aninternal derangement, the condyle is dis-placed posterior to the disc at the intercus-pal position (A). After initial rotationalopening, the condyle is still posterior to thedisc (B). In translation of the mandible tomaximum opening, the condyle recapturesthe disr., clicking into position as it does (Q.
    • Mandibular MovementrFig 2-3 In a healthy joint, the condyle isin d superoanterior position in the fossawith the articular disc interposed when theteeth are in maximum intercuspation {A}. Jnthe initial stage of opening, the condylerotates in position, with the disc remainingstationary [B). In maximum opening, thecondyle translates forward, with the discstill interposed (Q.Mandibular MovementMandibular movement can be broken down into a seriesof motions that occur around three axes.1. Horizontal axis (Fig 2-4). This movement, in the sagit-tal plane, happens when the mandible in centric rela-tion makes a purely rotational opening and closingborder movement around the transverse horizontalaxis, which extends through both condyles.2. Vertical axis (Fig 2-5). This movement occurs in thehorizontal plane when the mandible moves into a lat-eral excursion. The center for this rotation is a verticalaxis extending through the rotating or working-sidecondyle.3. Sagittal axis (Fig 2-6). When the mandible moves toone side, the condyle on the side opposite from thedirection of movement travels forward. As it does, itencounters the eminentia of the glenoid fossa andmoves downward simultaneously. When viewed in thefrontal plane, this produces a downward arc on theside opposite the direction of movement, rotatingabout an anteroposterior (sagittal) axis passingthrough the other condyle.Various mandibular movements are composed ofmotions occurring concurrently about one or more of theaxes. The up and down motion of the mandible is a com-bination of two movements. A purely "hinge" movementoccurs as the result of the condyles rotating in the lowercompartments of the temporomandibular joints within a10- to 13-degree arc, which creates a 20- to 25-mm sep-aration of the anterior teeth (Fig 2-3, B). This phenome-non was the basis for the "terminal hinge axis" theory inthe early 1920s by McCollum 2Kohno verified the pres-
    • Fig 2-4 Thea hinge axis opening..Fig 2-6 The mandible also rotates arone side drops down during a lateral eence of a transverse horizontal axis, which he termed the"kinematic axis."12There is also some gliding movementin the upper compartment of the joint if the mandibledrops down farther (Fig 2-3, C). Then the axis of rotationshifts to the area of the mandibular foramen, as thecondyles translate forward and downward while continu-ing to rotate.When the mandible slides forward so that the maxillaryand mandibular anterior teeth are in an end-to-end rela-tionship, it is in a protrusive position. Ideally, the anteriorsegment ot the mandible will travel a path guided by con-tacts between the anterior teeth, with complete disocclu-sion of the posterior teeth (Fig 2-7)Mandibular movement to one side will place it in aworking, or laterotrusive, relationship on that side and anonworking, or mediotrusive, relationship on the oppositeside; eg, if the mandible is moved to the left, the left sideis the working side, and the right side is the nonworkingside (Fig 2-8). In this type of movement, the condyle onthe nonworking side will arc forward and medially (Fig 2-8, A). Meanwhile, the condyle on the working side willshift laterally and usually slightly posteriorly (Fig 2-8, B).The bodily shift of the mandible in the direction of theworking side was first described by Bennett.13The angleformed in the horizontal plane between the pathway ofthe nonworking condyle, the mandibular lateral transla-tion, and the sagittal plane, is called the Bennett angle(Fig 2-9). The presence of an immediate or early lateraltranslation, or side shift, has been reported in 86% of thecondyles studied.14In addition to confirming the pre-dominant presence of the early lateral translation,Lundeen and Wirth, using a mechanical apparatus,showed its median dimension to be approximately 1.0mm with a maximum of 3.0 mm.15Hobo and Mochizuki,using an electronic measuring device, found a lowermean value of 0.4 mm for the immediate lateral transla-tion, with a high of 2.6 mm.1617Following the immediate lateral translation, there is afurther gradual shifting of the mandible, progressive lat-eral translation, which occurs at a rate proportional to theforward movement of the nonworking condyle.19At onetime this was known as "progressive side shift" or"Bennett side shift." Lundeen and Wirth found slight vari-ation in the direction of the progressive lateral translationor Bennett angle, with a mean value of 7.5 degrees.15Hobo and Mochizuki found a much greater variation,ranging from 1 5 to 36 degrees, with a mean value of12.8 degrees.1617
    • „ t condyle (A] moves forward and inward, while the leftcondyle (li) will shift slightly in a lateroposterior direction. In thisexample, the left side is the working side (W), and the right side isthe nonworking side (NW).The Determinants of Mandibular MovementThe two condyles and the contacting teeth are analogousto Ihe three legs of an inverted tripod suspended fromthe cranium. The determinants of the movements of thattripod are, posteriorly, the right and left temporo-mandibular joints; anteriorly, the teeth of the maxillaryand mandibular arches; and overall, the neuromuscularsystem.19The dentist has no control over the posterior determi-nants, the temporomandibular joints; they are unchange-able. However, they influence the movements of themandible, and of the teeth, by the paths that thecondyles must travel when the mandible is moved by themuscles of mastication. The measurement and repro-duction of those condylar movements is the basis for theuse of articulators.The anterior determinant, the teeth, provides guidanceto the mandible in several ways. The posterior teeth pro-vide the vertical stops for mandibular closure. They alsoguide the mandible into the position of maximum inter-cuspation, which may or may not correspond with theoptimum position of the condyies in the glenoid fossae.The anterior teeth (canine to canine) help to guide themandible in right and left lateral excursive movementsand in protrusive movements. Anterior teeth are espe-cially suited for guidance by virtue of11. Canines having the longest, strongest roots in theirrespective arches2. The load being reduced by distance from the fulcrum(Class III lever)3. The proprioceptive threshold and concomitant reflex-es reducing the load 7a-?Fig 2-9 In the nonworking condyle (NW), the "traditional"Bennett angle (SCB) measures the angle from the sagittal plane tothe endpoint of the movement of the condyle center. The Bennettangle used in articulators with an immediate lateral translationcapability (SPB) is measured from the sagittal plane after theimmediate or early lateral translation (I) has occurred. The trans-verse horizontal axis (THA), or hinge axis of purely rotationalmovement extends through both condyles. The working-sidecondyle (W), slides laterally, or outward, in laterotrusion.Dentists have direct control over the tooth determinantby orthodontic movement of teeth; restoration of the ante-rior lingual or posterior occlusal surfaces; and equilibra-tion, or selective grinding, of any teeth that are not in aharmonious relationship. Intercuspal position and anteri-or guidance can be altered, for better or for worse, byany of these means.
    • Fundamentals o! OcclusioiFig 2-10 The farther anterior a tooth is located, the less the iience of the temporomandibular joint (TMJ) and the greaterinfluence of the anterior guidance (AG).The closer a tooth is located to a determinant, themore that it will be influenced by that determinant (Fig 2-10). A tooth placed near the anterior region will be influ-enced greatly by anterior guidance and less by the tem-poromandibular joint. A tooth in the posterior region willbe influenced partially by the joints and partially by theanterior guidance.The neuromuscular system, through proprioceptivenerve endings in the periodontium, muscles, and joints,monitors the position of the mandible and its paths ofmovement. Through reflex action, it will program themost nearly physiologic paths of movement possibleunder the set of circumstances present. Dentists haveindirect control over this determinant. Procedures doneto the teeth may be reflected in the response of the neu-romuscular system.One of the objectives of restorative dentistry is to placethe teeth in harmony with the temporomaridibular jointsThis will result in minimum stress on the teeth and joints,with only a minimum effort expended by the neuromus-cular system to produce mandibular movements. Whenthe teeth are not in harmony with the joints and with themovements of the mandible, an interference is said toOcclusal InterferencesInterferences are undesirable occlusal contacts that mayproduce mandibular deviation during closure to maxi-mum intercuspation or may hinder smooth passage toand from the intercuspal position. There are four types ofocclusal interferences.1. Centric2. Working3. Nonworking4. ProtrusiveThe centric interference is a premature contact thatoccurs when the mandible closes with the condyles intheir optimum position in the glenoid fossae (Fig 2-11). Itwill cause deflection of the mandible in a posterior, ante-rior, and/or lateral direction.23A working interference may occur when there is con-tact between the maxillary and mandibular posteriorteeth on the same side of the arches as the direction inwhich the mandible has moved (Fig 2-12). If that contactis heavy enough to disocclude anterior teeth, it is aninterference MA nonworking interference is an occlusal contactbetween maxillary and mandibular teeth on the side ofthe arches opposite the direction in which the mandiblehas moved in a lateral excursion (Fig 2-13). The non-working interference is of a particularly destructivenature.36-?8The potential for damaging the masticatoryapparatus has been attributed to changes in themandibular leverage, the placement of forces outsidethe long axes of the teeth, and disruption of normal mus-cle function.29The protrusive interference is a premature contactoccurring between the mesial aspects of mandibularposterior teeth and the distal aspects of maxillary poste-rior teeth (Fig 2-14). The proximity of the teeth to the mus-cles and the oblique vector of the forces make contactsbetween opposing posterior teeth during protrusionpotentially destructive, as well as interfere with thepatients ability to incise properlyNormal Versus Pathologic OcclusionIn only slightly more than 10% of the population is therecomplete harmony between the teeth and the temporo-mandibular joints.30This finding is based on a concept ofcentric relation in which the mandible is in the mostretruded position. With the present concept of thecondyles being in the most superoanterior position withthe disc interposed, the results could be different.Nonetheless, in a majority of the population, the positionof maximum intercuspation causes the mandible to bedeflected away from its optimum position.In the absence of symptoms, this can be consideredphysiologic, or normal. Therefore, in the normal occlu-sion there will be a reflex function of the neuromuscularsystem, producing mandibular movement that avoidspremature contacts. This guides the mandible into aposition of maximum intercuspation with the condyle in aless than optimal position. The result will be either somehypertonicity of nearby muscles or trauma to the tem-poromandibular joint, but it is usually well within mostpeoples physiologic capacity to adapt and will notcause discomfort.However, the patients ability to adapt may be influ-enced by the effects of psychic stress and emotional ten-sions on the central nervous system.31By lowering thethreshold, frequently parafunctional jaw activity such as
    • Msndibulsr MovementFig 2-11 A centric occlusal interfer-ence often occurs during mandibularclosure between maxillary mesial-facingcusp inclines and mandibular distal-fac-ing inclines. As a result, the mandible isdeflected anteriorly.Fig 2-12 A working interference mayoccur between maxillary lingual-facingcusp inclines and mandibular buccal-facing cusp inclines on the workingside.clenching or bruxing occurs, and a normal occlusion canbecome a pathologic one (Fig 2-15). Simple musclehypertonicity may give way to muscle fatigue and spasm,with chronic headaches and localized muscle tender-ness, or temporomandibular joint dysfunction may occur.Pathologic occlusion can also manifest itself in the phys-ical signs of trauma and destruction. Heavy facets ofwear on occlusal surfaces, fractured cusps, and toothmobility often are the result of occlusal disharmony. Theremary periodontal lesion However, when occlusal traumais present, there will be more severe periodontal break-down in response to local factors than there would be ifonly the local factors were present.32Habit patterns may develop in response to occlusaldisharmony and emotional stress. Bruxism and clench-ing, the cyclic rubbing together of opposing occlusal sur-faces, will produce even greater tooth destruction andmuscle dysfunction.
    • FundamentalsofOcciusio,maxillary posterior teeth contact mesialfacing inclines of mandibular posterioiteelh during a protrusive movement.When the acute discomfort of a patient with a patho-logic occlusion lias been relieved, changes that will pre-vent the recurrence of symptoms must be effected in theocclusal scheme. Care must also be taken when provid-ing occlusal restorations for a patient without symptoms.The dentist must not produce an iatrogenic pathologicocclusion.In the placement of restorations, the dentist must striveto produce for the patient an occlusion that is as nearlyoptimum as his or her skills and the patients oral condi-tion will permit. The optimum occlusion is one thatrequires a minimum ot adaptation by the patient. The cri-teria for such an occlusion have been described by1. In closure, the condyles are in the most superoanteri-or position against the discs on the posterior slopes ofthe eminences of the glenoid fossae. The posteriorteeth are in solid and even contact, and the anteriorteeth are in slightly lighter contact.2. Occlusal forces are in the long axes of the teeth.3. In lateral excursions of the mandible, working-sidecontacts (preferably on the canines) disocclude orseparate the nonworking teeth instantly.4. In protrusive excursions, anterior tooth contacts willdisocclude the posterior teeth.5 In an upright posture, posterior teeth contact moreheavily than do anterior teeth.
    • m of the OcclusionIDEALATHRESHOLDIDEALBv LOWERED THRESHOLDvnsymptoms <• r - • -IDEAL j —ci Decrees) dishnrrnonyi to preventFig 2-15 There may betolerated by the pi bf f hocclusal disharmony (shaded bar) that is not ideal but isuse it is below his or her threshold of perception and dis-ered, the disharmony which had been previouslyn the patient (B) Treatment is then rendered by firsttolerated by the patient because it is below his or her threshold of perception and dis-comfort iA). If the threshold is lowered, the disharmony which had been previouslytolerated may produce symptoms in the patient (B). Treatment is then rendered by firstraising the patients threshold and then decreasing or eliminating the disharmony (C).Organization of the OcclusionThe collective arrangement of the teeth in function isquite important and has been subjected to a great dealof analysis and discussion over the years. There arethree recognized concepts that describe the manner inwhich teeth should and should not contact in the variousfunctional and excursive positions of the mandible. Theyare bilateral balanced occlusion, unilateral balancedocclusion, and mutually protected occlusion.Bilateral Balanced OcclusionBilateral balanced occlusion is based on the work of vonSpee34and Monson.35It is a concept that is not used asfrequently today as it has been in the past. It is largely aprosthodontic concept which dictates that a maximumnumber of teeth should contact in all excursive positionsof the mandible. This is particularly useful in completedenture construction, in which contact on the nonworkingside is important to prevent tipping of the denture.35Subsequently, the concept was applied to natural teeth incomplete occlusal rehabilitation. An attempt was made toreduce the load on individual teeth by sharing the stressamong as many teeth as possible.3*1It was soon discov-ered, however, that this was a very difficult type ofarrangement to achieve. As a result of the multiple toothcontacts that occurred as the mandible moved throughits various excursions, there was excessive frtctionalwear on the teeth 37Unilateral Balanced OcclusionUnilateral balanced occlusion, which is also commonlyknown as group function, is a widely accepted and usedmethod of tooth arrangement in restorative dental proce-dures today. This concept had its origin in the work ofSchuyler38and others who began to observe the destruc-tive nature of tooth contact on the nonworking side. Theyconcluded that inasmuch as cross-arch balance was notnecessary in natural teeth, it would be best to eliminateall tooth contact on the nonworking side.Therefore, unilateral balanced occlusion calls for allteeth on the working side to be in contact during a later-al excursion. On the other hand, teeth on the nonworkingside are contoured to be free of any contact. The groupfunction of the teeth on the working side distributes theocclusal load The absence of contact on the nonworkingside prevents those teeth from being subjected to thedestructive, obliquely directed forces found in nonwork-ing interferences. It also saves the centric holding cusps,ie, the mandibular buccal cusps and the maxillary lingualcusps, from excessive wear. The obvious advantage isthe maintenance of the occlusion.The functionally generated path technique, originallydescribed by Meyer,39is used for producing restorationsin unilateral balanced occlusion. It has been adapted byMann and Pankey for use in complete-mouth occlusalreconstruction.40.41Mutually Protected OcclusionMutually protected occlusion is also known as canine-protected occlusion or organic" occlusion. It had its ori-gin in the work of DAmico,« Stuart,4^44Stallard and
    • Stuart,??and Lucia-5and the members of theGnathological Society They observed that in manymouths with a healthy periodontium and minimum wear,the teeth were arranged so that the overlap of the anteri-or teeth prevented the posterior teeth from making anycontact on either the working or the nonworking sidesduring mandibular excursions. This separation fromocclusion was termed disocclusion. According to thisconcept of occlusion, the anterior teeth bear all the loadand the posterior teeth are disoccluded in any excursiveposition of the mandible. The desired result is anabsence of frictional wear.The position of maximum intercuspation coincides withthe optimal condylar position of the mandible. All poste-rior teeth are in contact with the forces being directedalong their long axes. The anterior teeth either contactlightly or are very slightly out of contact (approximately25 microns), relieving them of the obliquely directedforces that would be the result of anterior tooth contact.As a result of the anterior teeth protecting the posteriorteeth in all mandibular excursions and the posterior teethprotecting the anterior teeth at the intercuspal position,this type of occlusion came to be known as a mutuallyprotected occlusion. This arrangement of the occlusion isprobably the most widely accepted because of its easeof fabrication and greater tolerance by patients.However, to reconstruct a mouth with a mutually pro-tected occlusion, it is necessary to have anterior teeththat are periodontally healthy. In the presence of anteriorbone loss or missing canines, the mouth should probablybe restored to group function (unilateral balance). Theadded support of the posterior teeth on the working sidewill distribute the load that the anterior teeth may not beable to bear. The use of a mutually protected occlusion isalso dependent upon the orthodontic relationship of theopposing arches In either a Class II or a Class III mal-occlusion (Angle), the mandible cannot be guided by theanterior teeth. A mutually protected occlusion cannot beused in a situation of reverse occlusion, or cross bite, inwhich the maxillary and mandibular buccal cusps inter-fere with each other in a working-side excursion.Effects of Anatomic DeterminantsThe anatomic determinants of mandibular movement, ie,condylar and anterior guidance, have a strong influenceon the occlusal surface morphology of the teeth beingrestored. There is a relationship between the numerousfactors, such as immediate lateral translation, condylarinclination, and even disc flexibility, and on the cuspheight, cusp location, and groove direction that areacceptable in the restoration. It is beyond the scope ofthis text to discuss all of the nearly 50 rules that havebeen written on the subject of determinants."6Thosewhich have the greatest effect on morphology should beMolar DisocclusionWhen subjects with normal occlusions perform repeatedlateral mandibular movements, they will not trace thesame path on electronic recordings, presumably be-cause of the flexible nature of the articular disc. The mea-sured deviation averages 0.2 mm in centric relation, 0.3mm in working, and 0.8 mm in both protrusive and non-working movements.47To avoid occlusal interferencesand nonaxially directed forces on molars during eccen-tric mandibular movements, molar disocclusion mustequal or surpass these observed deviations in mandibu-lar movement.Healthy natural occlusions exhibit clearances that willaccommodate these aberrations. Measurements of dis-occlusions from the mesiobuccal cusp tips of mandibu-lar first molars in asymptomatic test subjects with goodocclusions showed separations averaging 0.5 mm inworking, 1.0 mm in nonworking, and 1.1 mm in protrusivemovements.48Therefore, one of the treatment goals inplacing occlusal restorations should be to produce aposterior occlusion with buffer space that equals or sur-passes the deviations resulting from natural variationsfound m the temporomandibular joint.Condylar GuidanceChief among those aspects of condylar guidance thatwill have an impact on the occlusal surface of posteriorteeth are the protrusive condylar path inclination andmandibular lateral translation.The inclination of the condylar path during protrusivemovement can vary from steep to shallow in differentpatients It forms an average angle of 30.4 degrees withthe horizontal reference plane (43 mm above the maxil-lary central incisor edge).1617If the protrusive inclinationis steep, the cusp height maybe longer. However, if theinclination is shallow, the cusp height must be shorter(Fig 2-16).Immediate mandibular lateral translation is the lateralshift during initial lateral movement. If immediate lateraltranslation is great, then the cusp height must be shorter(Fig 2-17). With minimal immediate translation, the cuspheight maybe made longer.Ridge and groove directions are affected by thecondylar path, particularly the lateral translation. Theeffects are observed on the occlusal surface of amandibular molar and premolar with the paths traced bythe lingual cusps of the respective opposing maxillaryteeth. The working path is traced on the mandibular toothin a lingual direction, and the nonworking path is in a dis-tobuccal direction. The nearer the tooth is to the working-side condyle anteroposteriorly, the smaller the anglebetween the working and nonworking paths (Fig 2-18).The farther the tooth is placed from the working-sidecondyle, the greater the angle between the working andnonworking condyles. When immediate lateral translationis increased, the angle also becomes more oblique.
    • Effects o/ Anatomic DeterminantsFig 2-16 A shallow protrusive condylar inca steeper path permits the cusps to be longeiin requires short cusps (A), whileFig 2-17 A pronounced immedthat the cusps he short (A), whiallows the cusps to be longer (B).
    • Fundamentals of OcctusuFig 2-19 A pronteeth to have longer cusps (A). Acusps (B).teeth permits posterioroverlap requires shorterFig 2-20 A pronounced horizontal overlap of the anterior ieeth requirecusps on the posterior teeth (A). A minimum anterior horizontal overlap pernposterior cusps to be longer (B|.Anterior GuidanceDuring protrusive movement of the mandible, the incisaledges of mandibular anterior teeth move forward anddownward along the lingual concavities of the maxillaryanterior teeth. The track of the incisal edges from maxi-mum intercuspation to edge-to-edge occlusion is termedthe protrusive incisal path. The angle formed by the pro-trusive incisal path and the horizontal reference plane isthe protrusive incisal path inclination, which ranges from50 to 70 degrees.4950While conventionally regarded asindependent factors, there is evidence to suggest thatcondylar inclination and anterior guidance are linked, ordependent factors.51"63In a healthy occlusion, the anteri-or guidance is approximately 5 to 10 degrees steeperthan the condylar path in the sagittal plane. Therefore,when the mandible moves protrusively, the anterior teethguide the mandible downward to create disocclusion, orseparation, between the maxillary and mandibular poste-rior teeth. The same phenomenon should occur duringlateral mandibular excursions.The lingual surface of a maxillary anterior tooth hasboth a concave aspect and a convexity, or cmgulum. Themandibular incisal edges should contact the maxillarylingual surfaces at the transition from the concavity to theconvexity in the centric relation position. The concavityrepresents a uniform shape in all subjects.54Anterior guidance, which is linked to the combinationof vertical and horizontal overlap of the anterior teeth,can affect occlusal surface morphology of the posteriorteeth. The greater the vertical overlap of the anteriorteeth, the longer the posterior cusp height may be. Whenthe vertical overlap is less, the posterior cusp heightmust be shorter (Fig 2-19). The greater the horizontal
    • it Anatomic DeterminantsFig 2-21 While a shallow protrusive path vence of minimal anterior guidance (A), the poanterior guidance is increased (Bj.1short cusps in the pres-can be lengthened if theA pronounced immediate lateral)r guidance is increased (B).overlap of the anterior teeth, the shorter the cusp heighimust be. With a decreased horizontal overlap, the poste-rior cusp height maybe longer (Fig 2-20).By increasing anterior guidance to compensate forinadequate condylar guidance, it is possible to increasethe cusp height. If the protrusive condylar inclination isshallow, requiring short posterior cusps, the cusps maybe lengthened by making the anterior guidance steeper(Fig 2-21). In like manner, increasing anterior guidancewill permit the lengthening of cusps that would otherwisehave to be shorter in the presence of a pronouncedimmediate lateral translation (Fig 2-22).References1. Nomenclature Committee of the Academy of DentureProsthetics: Glossary of Prosthodontic Terms, ed 5. StLouis, CV Mosby Co, 1987, p 152 McCollum BB Stuart CE- Gnathology—A Research ReportSouth Pasadena, Calif, Scientific Press, 1955, pp 91-123.3 Lucia VO Modern Gnathological Concepts. St Louis, CVMosby Co, 1961, pp 15-22.4 Dawson PE Evaluation, Diagnosis, and Treatment ofOcclusal Problems. St Louis, CV Mosby Co, 1974, p 293.5. Kornfeld M: Mouth Rehabilitation. S1 Louis, CV Mosby Co,1967, p34.6. Bauer A, Gutowski A: Gnathology Berlin, QuintessencePubl Co. 1975, pp 65-91.7. Huffman R, Regenos J- Principles of Occlusion, ed 8.Columbus, H & R Press, 1980, pp VA1-VB39.
    • 9. McNeill C: The optimum temporomandibular joint condyleposition in clinical practice. Int J Periodont Rest Dent 1985;5(6):53-76.}. Dawson PE: Evaluation, Diagnosis, and Treatment ofOcclusai Problems. St Louis, CV Mosby Co, 1961, pp48-79.I. Brill N, Lammie GA. Osborne J. Perry HT: Mandibular posi-tions and mandibular movements. Br Dent J 1959:106:391-400.I. Kohno S: Analyse der kondylenbewegung in der sagit-tlebene. Dtsch ZahnMrtzl Z1974, 27.739-743.3. Bennett NG: A contribution to the study of Ihe movements ofthe mandible. Proc Roy Soc Med, Odont Sec 1908; 1:79-95(reprinted in J Prosthel Dent 1958; 8:41-54).1. Aull AE: Condylar determinants of occlusai patterns. Part I.Statistical report on condylar path variations. J ProsthetDent 1965, 15:826-835.5. Lundeen HC, Wirth CG: Condylar movement patternsengraved in plastic blocks. J Prosthet Dent 1973130:866-875.3. Hobo S, Mochizuki S: Study of mandibular movement bymeans of an electronic measuring system, Part I J JpnProsth Soc 1982; 26:619-634.i. Hobo S, Mochizuki S: Study of mandibular movement bymeans of an electronic measuring system, Part II. J JpnProsth Soc 1982, 26.635-653.3. Nomenclature Committee of the Academy of DentureProsthetics: Glossary of Prosthodontic Terms, ed 5. St Louis,CV Mosby Co, 1987, p 31.3. Guichet NF1Occlusion. Anaheim, CA, The DenarCorporation, 1970, p 13.). Manly RS, Pfaffmann C, Lathrop DD, Kayser J: Oral senso-ry thresholds of persons with natural and artificial dentitions.JDentHes 1952; 31:305I. Williamson EH, Lundquist DO: Anterior guidance: Its effecton electromyographic activity of the temporal and massetermuscles. J Prosthet Dent 1983, 49:816.> Manns A, Chan C, Miralles R: Influence of group functionand canine guidance or electromyographic activity of ele-vator muscles. J Prosthet DenM9B7; 57:494-501.I. Dawson PE: Temporomandibular joint pain-dysfunctionproblems can be solved. J Prosthet Dent 1973; 29:100-112.1. Dawson PE: Evaluation, Diagnosis, and Treatment o!Occlusai Problems. St Louis, CV Mosby Co, 1961, p 299.5. Ramfjord SP: Dysfunctional temporomandibular joint andmuscle pain. J Prosthet Dent 1961; 11:353-374,5. Stallard H, Stuart CE: Eliminating tooth guidance in naturaldentitions. J Prosthet Dent <S§-; 11:474-479. Schuyler CH: Factors contributing to traumatic occlusion. JProsthet DenM961, 11:708-715,i. Yuodelis RA, Mann WV: The prevalence and possible role ofnonworking contacts in periodontal disease. Periodontics1965; 3:219-223.). Whitsett LD, Shillingburg HT, Duncanson MG: The nonwork-ing interference. J OHIa Dent Assoc 1974; 65:5-8.). Posselt U: Studies in the mobility of the human mandible.Ada Odontol Scand 1952; 10 (suppl 10) 1-109.I. Ramfjord SP, Ash MM: Occlusion, ed 2. Philadelphia WBSaunders Co, 1971, p 104>. Glickman I, Smulow JB. Alterations in the pathway of gmgi-val inflammation into the underlying tissues induced byexcessive occlusai iorces. J Periodontol 1962; 337-13.i. Okeson JP: Management of Temporomandibular Disordersand Occlusion. St Louis, CV Mosby Co, 1989, p 113.1. von Spee FG: The gliding path of the mandible along theskull. Archiv fAnatuPhys 1890; 16:285-294. (Translated byBiedenbach MA, Hotz M, Hitchcock HP: J Am Dent Assoc1980; 100:670-675).5. Monson GS: impaired function as a result of a closed bite. JAm Dent Assoc 1921; 8:833-839.5. Schuyler CH Fundamental principles in the correction ofocclusai disharmony, natural and artificial. JAm Dent Assoc1935; 22:1193-1202. Stuart CE, Stallard H: Principles involved in restoring occlu-sion to natural teeth. J Prosthet Dent I960; 10:304-313.i. Schuyler CH: Factors of occlusion applicable to restorativedentistry. J Prosthet Dent 1953; 3:772-782.). Meyer FS1Can the plain line articulator meet all thedemands of balanced and functional occlusion in allrestorative work? J Colo Dent Assoc 1938; 17:6-16.). Mann AW, Pankey LD: Oral rehabilitation: Part I. Use of theP-M instrument in treatment planning and in restoring thelower posterior teeth. J Prosthet Dent 1960: 10:135-150.I. Pankey LD, Mann AW: Oral rehabilitation: Part II.Reconstruction of the upper teeth using a functionally gen-erated path technique. J Prosthet Dent 1960, 10:151-162... DAmico A: Functional occlusion of the natural teeth of man.J Prosthet Dent 1961; 11:899-915.J Stuart CE: Good occlusion ior natural teeth. J Prosthet Dent1964; 14:716-724.I Stuart CE: Why dental restorations should have cusps JSouth Calif Dent Assoc 1959; 27:198-200.j. Lucia VO The gnathological concept of articulation. DentClin North Am 1962; 6:183-197.I Katz GT: The Determinants of Human Occlusion. LosAngeles, Marina Press, 1972, p vi.. Oliva RA, Takayama H. Hobo S: Three-dimensional study ofmandibular movement using an automatic electronic mea-suring system. J Gnathol 1986, 51115-182.1. Hobo S, Takayama H: Pilot study—analysis and measure-ment of the amount of disclusion during lateral movement. JJpn Prosth Soc 1984; 29:238-239.i Gysi A, Kohler L- Handbuch der Zahnehikunde Berlin &Vienna, Scheff, 1929, IVliciJlat . Dent Cosmos 1910;. Takayama H, Hobo S. The derivation of kinematic formulaefor mandibular movement Int J Prosthodont 1989;2:285-295.. Takayama H, Hobo S: Experimental verification of the kine-matic formulae for mandibular movement (unpublisheddata),I. Takayama H, Hobo S: Kinematic and experimental analysesof mandibular movement for clinical application. Prec MachIncorp Life Supp Tech 1989; 2:229-304.k Kubein-Meesenburg D, Naegeri H, Meyer G, Buecking W:Individual reconstruction of palatal concavities J ProsthetDen! 1988: 60:662-672
    • Chapter 3ArticulatorsAn articulator is a mechanical device that simulatesthe movements of the mandible (Fig 3-1). The prin-ciple employed in the use ol articulators is themechanical replication of the paths of movement of theposterior determinants, the temporomandibular joints.The instrument is then used in the fabrication of fixed andremovable dental restorations that are in harmony withthose movements.The outer limits of all excursive movements made bythe mandible are referred to as border movements. Allfunctional movements of the mandible are confined to thethree-dimensional envelope of movement contained with-in these borders.1The border movements are of signifi-cance in discussing articulation because they are limitedby ligaments. As such, they are highly repeatable anduseful in setting the various adjustments on the mechan-ical fossae of an articulator. The more nearly the articula-tor duplicates the border movements, the more nearly itwill simulate the posterior determinants of occlusion. Asa result, the harmony between the restoration fabricatedand the posterior determinants, ie, the temporomandibu-lar joints, will be improved.Articulators vary widely in the accuracy with which theyreproduce the movements of the mandible. At the lowerend of the scale is the nonadjustable articulator. It is usu-ally a small instrument that is capable of only a hingeopening The distance between the teeth and the axis ofrotation on the small instrument is considerably shorterthan it is in the skull, with a resultant loss of accuracy.As the mandible moves up and down in the retrudedposition, the cusp tip of a mandibular tooth moves alongan arc in a sagittal plane, with the center for that rotationlocated at the transverse horizontal axis, which passesthrough the condyles (Fig 3-2). If the location of the axisof rotation relative to the cusp tip differs markedly fromthe patient to the articulator, the radius of the arc of clo-sure of the cusp tip may be different, producing an error.Drastic differences between the radius of closure on thearticulator and in the patients mouth can affect theplacement of morphologic features such as cusps,ridges, and grooves on the occlusal surface.The casts mounted on a smaller articulator will have amuch shorter radius of movement, and a tooth will travela steeper arc during closure of the small articulator (Fig3-3). If the casts are mounted at an increased dimensionof occlusion (ie, a thick interocclusal record), the teethwill occlude in a different intercuspal position on the artic-ulator than in the mouth.2A slight positive error resultingin a deflective occlusal contact could develop betweenthe mesial incline of the maxillary teeth and the distalincline of the mandibular teeth.3The mediolateral location of the centers of rotation (ie,the intercondylar distance) will change the radius of toothmovement, which in turn will affect the arc traveled by atooth cusp in the horizontal plane during a lateral excur-sion of the mandible. On a small hinge articulator, the dis-crepancy between the arcs traveled by a cusp on theinstrument and in the mouth can be sizable, particularlyon the nonworking side (Fig 3-4). The result is anincreased possibility of incorporating a nonworkingocclusal interference into the restoration.A semiadjustable articulator is an instrument whose larg-er size allows a close approximation of the anatomic dis-tance between the axis of rotation and the teeth. If casts aremounted with a facebow using no more than an approxi-mate transverse horizontal axis, the radius of movementproduced on the articulator will reproduce the tooth closurearc with relative accuracy, and any resulting error will beslight (Fig 3-5). Placing the casts a small distance closer toor farther from the condyles through the use of an approx-imate transverse horizontal axis will produce an error ofonly a small magnitude during lateral excursions (Fig 3-6).The semiadjustable articulator reproduces the direc-tion and endpoint, but not the intermediate track of somecondylar movements. As an example, the inclination ofthe condylar path is reproduced as a straight line onmany articulators, when in fact it usually traverses acurved path. On many instruments, the lateral translation,or Bennett movement, is reproduced as a gradually devi-ating straight line, although several recently introducedsemiadjustable articulators do accommodate the imme-diate lateral translation.Intercondylar distances are not totally adjustable onsemiadjustable articulators. They can be adjusted tosmall, medium, and large configurations, if at allRestorations will require some intraoral adjustment, but itshould be inconsequential if the restoration is fabricatedcarefully on accurately mounted casts. This type of artic-ulator can be used for the fabrication of most single unitsand fixed partial dentures.
    • / /1uxtLiLiniiiiinn Bnmandible closes around the hinge a>nandibular tooth moves along an arcFig 3-3 The large dissimilarity between the hinge axis of thsmall articulator (aha) and the hinge axis of the mandible (mhawi]l produce a large discrepancy between the arcs of closure of tharticulator (broken line! and of the mandihle (solid line}. I FroHobo et al.2)Fig 3-4 A majorcusp path on the si(From Hobo etaW
    • Fig 3-5 The dissimilarity between thehinge axis of the full-size semiadjustablearticulator (aha) and the mandibuLarhinge axis fmha) will cause a slight dis-crepancy between the arcs of closure ofthe articulator (broken line! and of themandible (solid line). (From Hobo etal.)The most accurate instrument is the fully adjustablearticulator. It is designed to reproduce the entire charac-ter of border movements, including immediate and pro-gressive lateral translation, and the curvature and direc-tion of the condylar inclination. Intercondylar distance iscompletely adjustable. When a kinematically locatedhinge axis and an accurate recording of mandibularmovement are employed, a highly accurate reproductionof the mandibular movement can be achieved.This type of instrument is expensive. The techniquesrequired for its use demand a high degree of skill and aretime consuming to accomplish. For this reason, fullyadjustable articulators are used primarily for extensivetreatment, requiring the reconstruction of an entire occlu-Arcon and Nonarcon ArticulatorsThere are two basic designs used in the fabrication ofarticulators: arcon and nonarcon. On an arcon articula-tor, the condylar elements are placed on the lower mem-ber of the articulator, just as the condyles are located onthe mandible. The mechanical fossae are placed on theupper member of the articulator, simulating the positionof the glenoid fossae in the skull. In the case of thenonarcon articulator, the condylar paths simulating theglenoid fossae are attached to the lower member of theinstrument, while the condylar elements are placed onthe upper portion of the articulator.To set the condylar inclinations on a semiadjustableinstrument, wax wafers called interocclusal records, orcheck bites, are used (see Chapter 4 for the technique)?re is only a slight difference between cusp paths oniculator (a) and those in the mouth (mf, even thoughitirig exhibits a slight discrepancy. iFrom Hobo et al.2fto transfer the terminal positions of the condyles from theskull to the instrument. These wafers are 3.0 to 5.0 mmthick, so that the teeth on the maxillary and mandibuiarcasts are separated by that distance when the condylarinatio eset.
    • g een the condylar inclination and the occlusal plane of the maxillary teethains constant between an open (A] and a closed (Bl arcon articulator Za, = Zar However, the anglechanges between an open (C) and a closed (D) nonarcon instrument Za2* Za4. For the amount of open-ing illustrated, there would be a difference of 8 degrees between the condylar inclination at an open posi-tion {where the articulator settings are adjusted! and a closed position at which the articulator is used.When the wafers are removed from an arcon articula-tor, and the teeth are closed together, the condylar incli-nation will remain the same. However, when the teeth areclosed on a nonarcon articulator, the inclination changes.becoming less steep (Fig 3-7). Arcon articulators havebecome more widely used because of their accuracyand the ease with which they disassemble to facilitate theocclusal waxing required for cast gold restorations. Thisvery feature makes them unpopular for arranging dentureteeth. The centric position is less easily maintained whenthe occlusion on all of the posterior teeth is being manip-ulated. Therefore, the nonarcon instrument has beenmore popular for the fabrication of dentures. Arcon artic-ulators equipped with firm centric latches that preventposterior separation will overcome many of these objec-tions.
    • r tal Axis RelationshipFig 3-8 After the transverse horizontalaxis locator is plated, the patient isassisted in opening and closing on thetransverse horizontal axis. An arcingmovement of the stylus on the side arm[A) indicates that it is not located overthe transverse horizontal axis. The sidearm is adjusted so the stylus will rotatewithout moving during opening andclosing (B). This indicates that it hasbeen positioned over the transverse hor-The Tooth-TransverseHorizontal Axis RelationshipTo achieve the highest possible degree of accuracy froman articulator, the casts mounted on it should be closingaround an axis of rotation that is as close as possible tothe transverse horizontal (hinge) axis of the patientsmandible. This axis is an important reference because itis repeatable. It is necessary to transfer the relationshipof the maxillary teeth, the transverse horizontal axis, anda third reference point from the patients skull to the artic-ulating device. This is accomplished with a facebow, aninstrument that records those spatial relationships and isthen used for the attachment of the maxillary casts to thearticulator.The more precisely located the transverse horizontalaxis, the more accurate will be the transfer and themounting of the casts. The most accurate way to deter-mine the hinge axis is by the "trial and error" methoddeveloped by McCollum and Stuart in 1921." A devicewith horizontal arms extending to the region of the ears isfixed to the mandibular teeth. A grid is placed under triepin at the end of the arm, just anterior to the tragus of theear. The mandible is manipulated to a retruded position,from which it is guided to open and close 10 mm. As itdoes, the pin will trace an arc (Fig 3-8). The arm is adjust-ed in small increments to move it up, down, forward, orback, until the pin simply rotates without tracing an arc.This is the location of the hinge axis, which may be pre-served for future reference by tattooing.The facebow is attached to the maxillary teeth, and theside arms are adjusted so the pin at the free (posterior)end of each side arm will touch the hinge axis mark on itsrespective side of the face (Fig 3-9) A third referencepoint is selected on the face and recorded by adjustinga pointer on the facebow. The facebow is removed fromthe patient and transferred to the articulator. The refer-ence pins on the facebow are placed over the axis ofrotation on the articulator condyles With the anterior ref-
    • Table 3-1 Accuracy ofArbitrary Hinge Axis Points51easuFoments and landmarks^r arbitrary hinge axis pointsArbitrary points within Iof kinematic hinge apoints (%)13r i in iront oi antericmeatus13 mm from foot of tragus to10 mm anterior to center of e.98.092.158.333.083.3Scballhorn7BeyroneLauntzen and Bcdnei1-Teteruckand Lundeen12Teteruek and tundeen2erence device providing the vertical orientation of thefacebow. it can then be used to accurately mount themaxillary cast on the articulator. This technique is mostcommonly used for facebow transfers to fully adjustablearticulators.A facebow that employs an approximate location ofthe hinge axis based on an anatomic average can alsobe used. This technique should provide enough accura-cy for the restoration of most mouths, if the occlusal ver-tical dimension is not to be altered to any significantextent. An error of 5.0 mm in the location of the trans-verse hinge axis location will produce a negligibleanteropostenor mandibular displacement of approxi-mately 0.2 mm when a 3.0-mm centric relation record isremoved to close the articulator5There are numerous techniques used for arbitrarilylocating the hinge axis to serve as the set of posterior ref-erence points for a facebow.^14A comparison of theaccuracy of arbitrary and kinematically located hingeaxis points is shown in Table 3-1.Facebows must have acceptable accuracy and besimple to apply or they will not be used routinely. Caliper-style ear facebows possess a relatively high degree ofaccuracy, with 75% of the axes located by it falling with-in 6 mm of the true hinge axis.12There are severalcaliper-style facebows (Fig 3-10). They are designed tobe self-centering, so that little time is wasted in centeringthe bite fork and adjusting individual side arms. Thetechnique for their use is described in Chapter 4Registration ofCondylar MovementsTo faithfully simulate the condylar movement on an artic-ulator, it is necessary to obtain a precise tracing of thepaths followed by the condyle. This can be achievedmost accurately by means of a pantographic recording,which will capture all of the characteristics of themandibular border movement from its retruded positionto its most forward and most lateral positions.The pantograph consists of two facebows. One isaffixed to the maxilla and the other to the mandible, usingclutches that attach to the teeth in the respective arches.Recording styli are attached to the one member, andsmall tables upon which the tracings are made areattached to the other member of the instrument, oppositethe styli. There are both horizontal and vertical posteriortables attached in the vicinity of the hinge axis on eachside of the pantograph. There are also two tablesattached to the anterior member of the bow, one oneither side of the midline (Fig 3-11).The mandible goes through a series of right and leftlateral, as well as protrusive, excursions. The styli on onefacebow scribe on the recording tables the paths fol-lowed by the condyles in each movement (Fig 3-12).When the pantograph is attached to the articulator, vari-ous adjustments are made until the movements of thearticulator will follow the same paths scribed on the trac-ings during mandibular excursions.The pantographic tracing can only be utilized to fulladvantage when used with a fully adjustable articulator.To adjust the settings of a semiadjustable articulator, waxinterocclusal records are used. The patient closes into aheat-softened wax wafer in a right lateral protrusive posi-tion and maintains that posture until the wax has hard-ened. The procedure is repeated with another wax waferfor a left lateral protrusive position. The wax wafers arethen placed, first one and then the other, on the articu-lated casts. After the right lateral wafer is used to adjustthe condylar inclination for the left condyle, the left later-al wafer is used to adjust the right condylar inclination.Complete details of the technique are described inChapter 4.
    • Registration of Condylar MoverFig 3-10 These ihree caliper-style facebows are among those in use at the pre:time: A, Quick-Mount facebow (Whip Mix Corp, Louisville, KY); B, Denat Slidemfacebow (Teledyne Water Pik, Fort Collins, CO); C, H-jnau Springbow face!(Teledyne Water Pik).
    • Fig 3-12 Tracings are shown for a pantograph in which all recording tables ...^ uu.uu.~~In the manHihlp and all stvli aw attarhpiH In fhn mav|J|a; Af left lateral excursion B rightFig 312 Tracings are shoto the mandible and all styllateral excursion; C, protrusid t o the m ; , e t ateral excursn. Styli are shown in their initial positii
    • References10 Launteen AG, Bodnet GH: Variations in location ot arb1. PosseH U: Physiology of Occlusion and Rehabilitation, ed 2. and true hinge axis points. J Prosthet Dent •Philadelphia, FA David Co, 1968, p 55. 11:224-229.2. Hobo S, Shillingburg HT, Whitsett LD- Articulalor selection 11- Gysi A: The problem of articulation. Dent Cosmos for restorative dentistry. J Prosthet Dent A97G; 36:35-43. 52:1-19.3. Hodge LC, Mahan PE: A study of mandibular moverfrom centric occlusion to maximum mtercuspatioProsthet Dent 9Q1 18:19-30. 13. Bergstrom G: On the reproduction of dental articulation by4 McCollum BB Stuart CE1Gnathology—A Research Report means of articulators—A kinematic investigation. AdaVentura, Calif, Scientific Press, 1955, p 39. Odontol Scand 1950, 9 (suppl 4)1-1315. Weinberg LA: An evaluation of the face-bow mounting. J 14. Guichet NF: Procedures lor Occlusal Treatment—AProsthet Dent 1961; 11:32-42. Teaching Alias. Anaheim, CA, The Denar Corporation, 1969,6. Kornfeld M. Mouth Rehabilitation—Clinical and Laboratory p 3 5Procedures ed2 St Louis CV Mosby Co 1974 pp48 336 15. Whitsett LO, Shillingburg HT, Keenan MP: Modifications of a7 Sr-haiihnrn Rrv A <nuriu nf thP arhitrar,, ranter anr! ihs km<= n e wsemi-adjustable articulator for use with a caiiper style/. bcnaimorn WJ. A study ot the arbitrary center ana tne Kine- . . . p a M n ™ ! / , ™ , 1Q77- ^ - I P iflmatic center of rotation for tace-bow mountings J Prosthet l d L B u™ - ° -""" ual" """" "*", a-o^-ooDent 1957; 7162-169.8. Beyron H1Orienteringsproblertioneroch bettstudier Sven Tai
    • Chapter 4Interocclusal RecordsAfter the maxillary cast has been accurately affixedto the articulator by using a facebow, the mandibu-lar cast must be oriented to the maxillary cast withequal exactitude to be able to diagnose the patientsocclusion.•£ Centric relation records are used to repli-cate, on the articulator, the relationship between the max-illary and mandibular arches that exists when thecondyles are in their most anterosuperior position in theglenoid fossae. Lateral interocclusal records are used toadjust the condylar guidance of the articulator. Then, it ispossible to observe tooth relationships and identifydeflective contacts and/or other occlusal discrepanciesfrom the casts on the articulator. When this informationhas been gathered and assessed, a determination canbe made as to what corrective measures, if any, will beperformed on the occlusion.A distinction must be made between mounting fordiagnosis and mounting for treatment. The attachment ofcasts to an articulator for diagnosis will be done with thecondyles in a centric relation position. When casts arearticulated for restoration of a significant portion of theocclusion, it also may be done with the condyles in thecentric relation position. However, the beginning operatorusually will be restoring only limited segments of theocclusion at one time. Mounting casts for restoration ofonly a small part of the occlusion generally will be donewith the teeth in a position of maximum intercuspation.Centric Relation Recorda physiologic anterosuperiarticular disc along the articularThe unguided method productposition," but it can be difficuresults because of the patientproprioception is minimized bya leaf gauge composed of sevstrips, which help to eliminatesponses. While the patient occlistrips are added one at a time irthe patient no longer feels anyThis permits the muscles to act fidyles to move into a physiolofmuscles will rotate the mandibleid position on theeminence.physiologic "muscleill to achieve consistentmuscle activity, Muscleseparating the teeth withsral 0.1-mm-thick plasticdirect proprioceptor re-ides with light pressure,i the anterior region untilposterior tooth contact,eely and allows the con-lie position,45Then theanteriorly and superiorly.Armamentarium1. Cotton rolls2. Pink baseplate wax3. Green stick compound4. Hollenback carver5. Scissors6. Aluwax7. Bite registration paste8. Cement spatula9. Disposable mixing pad10. Laboratory knife with no. 2!11. 28-gauge green wax12. Mo. 10 red-inked silk ribborTo mount the mandibular cast on the articulator, it is nec-essary to record the relationship of the dental arches toeach other. There are three techniques that are frequent-ly used in locating the centric relation position1chinpointguidance, bilateral manipulation, and the unguidedmethod. With a computer-assisted three-dimensionalmandibular recording device, Hobo and Iwata3analyzedcondylar position achieved by the three methods.Chinpoint guidance puts the condyles in the most poste-rior and superior position, while the bilateral and unguid-ed methods allow the muscles to guide the condyles intoTechniqueThe most consistent, repeatable results can be accom-plished by utilizing the technique of "bimanual manipula-tion" described by Dawson.67The neuromuscular sys-tem monitors all sensory impulses from the teeth andjaws and programs occlusal contact to occur where theprotective stimuli are minimal. This position, throughrepeated closures, becomes habitual and is maintainedat the expense of normal muscle function.8To enable thecondyles to be placed in an unstrained position, the mus-
    • Inteiocclusal RecordsFig 4-1 Ttie fingers are placed along the inferior border of the Fig 4-2 With the thumbs in position, the mandible is manipulat-mandible. ed into a centric relation position.Fig 4-3 The temporomandibular ligament (TML| acts as the pos-terior limit and fulcrum (F). The downward force of the thumbs andupward force of the fingers help to seat the condyles in the pos-terosuperior portion of the glenoid fossa (after Dawson7).culature must first be deprogrammed from its habitualclosing patternA simple means of doing this is to place a cotton rollbetween the anterior teeth and have the patient closewith the instructions, "Bite on your back teeth." Check tobe sure that there is no contact of the posterior teeth Ifthe cotton roll is placed as soon as the patient is seated,the operator and assistant can prepare the materials forthe subsequent interocclusal record during [he 5 minutesthat the patient remains closed. After this time, the "mem-ory" of the position in which the teeth intercuspate fullywill likely have been lost, and the mandible can bemanipulated more easily into its optimum position. Assoon as the cotton roll has been removed, begin themandibular manipulation. Do not allow the patient toclose the teeth together again, as this will allow the mus-culature to readapt to a tooth-guided closure.Seat the patient with the chair back approximately 45degrees from the floor. The head should be lilted backwith the chin up so that the face is parallel with the floorThis position tends to keep the patient from protrudingthe mandible. The dentist should take a position behindthe patient that will facilitate stabilization of the patientshead between the dentists rib cage and forearm. Thepatients head must not move while the mandible is beingmanipulated. Place all four lingers of each hand on the
    • lower border of ihe mandible, making sure that the fin-gertips are in direct contact with bone (Fig 4-1).Place the thumbs lightly over the mandibular symph-ysis so that they touch each other at the midline. Instructthe patient to open approximately 35 mm, and then askhim or her to relax the jaw as you close it, guiding themandible posteriorly into a terminal hinge relationshipwith a gentle motion (Fig 4-2). Observation of thepatients mandible will demonstrate that it shifts posteri-orly with this gentle motion.When the mandible has "dropped back," firm pressureis applied to seat the condyles anterosupenorly in theglenoid fossae (centric relation), An upward lifting forceis applied on the inferior border of the mandible by thefingers of each hand, while a downward force is appliedto the symphysis by the thumbs (Fig 4-3). With firm seat-ing pressure, once again open and close the mandible insmall increments of 2.0 to 5.0 mm while gradually closingthe mandible to the point of first tooth contact. Do notallow the mandible to deviate from this arc while closingThis position of initial tooth contact with the mandible inthe optimum position is the centric relation contact posi-tion(CRCP).Trim a piece of hard, pink baseplate wax to an archform, using the template as a guide (Fig 4-4). Minor mod-ifications to make it fit the arch may be necessary afterthe first try-in. Soften this preformed piece of baseplatewax in hot tap water. Place it against the maxillary archso that the anterior teeth are approximately 6.0 mm (1/4inch) inside the periphery of the wax. Carefully but firmlyapply finger pressure along the inferior surface of thesoftened wax so that indentations of alt of the maxillarycusp tips will be registered in the wax (Fig 4-5).Use a Hollenback carver or similar instrument to placea cut in the wax extending from the periphery of the waxsheet to the embrasure between the maxillary lateralincisor and canine on each side (Fig 4-6). Fold the waxdistal to the cuts onto the facial surfaces of the canines(Fig 4-7). These tabs will serve as an index to aid inreseating the baseplate wax record later.Remove the wax record from the mouth while it is stillsoft. Extend the initial cuts with scissors so that a wedge-shaped piece of wax is removed (Fig 4-8). This will pro-duce space for the compound occlusal programmer laterwhen the wax is reinserted in the mouth. Narrow the waxarch form in its buccolingual dimension by trimmingaway any wax that lies buccal to the buccal cusp tipsfrom the second molar to the first premolar (Fig 4-9). Take
    • •§-*•• Interocclusal Recordscare to retain the tabs that were folded onto the labial sur-faces of the canines. Remove any excess wax distal tothes >nd molarsLightly adapt a piece of 28-gauge green wax over bothquadrants of the maxillary teeth and again manipulate themandible to centric relation. At this position, tap the teethtogether lightly until perforations are made in the wax atCRCP. Remove and store the wax in a cup of cool water.An anterior programming device, or jig, is made toestablish a predetermined stop to vertical closure withthe condyles in optimum position.2The absence ofdeflecting incline tooth contact allows muscle function tobe reprogrammed to eliminate the adaptive arc of clo-sure. Soften a 2.5-cm (1.0-inch) length of green stickcompound in hot tap water and bend it into a "J." Placethe compound over the midline between the two maxil-lary central incisors with the short leg of the "J" on thefacial surface, extending approximately halfway betweenthe incisal edge and the gingiva While the compound isstill quite soft, quickly adapt it to the maxillary teeth in thefollowing three-step procedure:1. With your thumb, firmly adapt the facial portion of thecompound into the labial embrasure, while at thesame time thinning out the compound to an approxi-mate thickness of 2.0 mm.2. Place both thumbs on the facial and both index fin-gers on the lingual, with approximately 6.0-mm (1/4-inch) space between the tips. Squeeze tightly to moldthe compound to the lingual surface (Fig 4-10).3. While maintaining the finger posture and pressure inStep 2, push the fingertips closer together to form aspine of compound at approximately the midline. (Theentire process described should take no more than afew seconds, and the compound should still be softenough to further mold as the patients mandible isclosed ir ) it.)While the compound is still soft, repeat the mandibularposition previously rehearsed, guiding the patient into aretruded position while arcing the mandible closed untilthe mandibular incisors have made an indentation in thecompound and the posterior teeth are 1.0 mm out of con-tact. Cool the compound and confirm the accuracy of theprogramming device. There are two important points tobe checked at this time:1. Be certain that the condyles are in the optimum posi-tion in their fossae by lightly tapping the mandibularincisors into the compound. The patient should closeprecisely into the programming device with no deflec-tion.2. The patient must not be closed to the point of contactbetween the maxillary and mandibular teeth. Themandibular teeth should make contact only with thecompound programming device and be no closerthan 1.0 mm to the maxillary teeth anywhere.If the patients posture is maintained with the chairback and the chin up, the face will be parallel with thefloor and a well-adapted compound programmingdevice should stay firmly in place. It necessary, it can beheld in place by the patient, using his or her index finger(Fig 4-11). It need not be removed until the centric rela-tion registration has been completed.With the compound anterior programming device stillin place, slightly resoften the baseplate wax record andplace it in position, using the canine flaps as an index forcorrect placement. Carefully close the patients teeth intothe programmer, and note that the pink wax has beenadequately softened to allow complete closure into theprogrammer (Fig 4-12). Ideally, the mandibular molarsshould form slight indentations in the pink wax.If the increased vertical dimension of occlusion pro-duced by the anterior programming device is great
    • Fig 4-11 The patient holds the prograwhile the operator manipulates the mandenough to prevent contact of the mandibular posteriorcusp tips with the pink wax, it will be necessary to flow alayer of Aluwax (Bite and Impression Wax, Aluwax DentalProducts Co, Grand Rapids, Ml) onto the inferior surfaceof the wax arch form (Fig 4-13). This will increase thethickness and insure contact of the posterior teeth withthe record. Remove the wax arch form from the mouthand cool it by floating it in a cup of water Replace it in themouth to confirm that the wax did not distort while beingcooledMeasure out 6.0-mm (1/4-inch) lengths of zincoxide-eugenol bite registration paste base and acceler-ator (Bile Registration Paste [Type I, Hard], KerrManufacturing Co, Romulus, Ml) on a small mixing pad.Mix thoroughly with a cement spatula (Fig 4-14).Carefully place a small amount of registration paste onthe wax arch form over each area where a centric hold-ing cusp has indented the wax (Fig 4-15). Do not placelarge amounts of paste into the indentations, since it willhave to be removed later. The maximum allowableamount over each cusp is approximately the size of amatch head.Replace the wax in the mouth and have the patientclose until the mandibular incisors are firmly contactingthe programming device. Have the patient hold that posi-tion with moderate closing pressure until the registration
    • Interocclusal RecordsFig 4-14 One-quarter inch (6.O-1 igths of bite registration pastiTiing device and the pasftFig 4-17 Excess resistpaste is completely set (Fig 4-16). When it has set,remove the complete interocclusal record and com-pound programmer from the mouth. Use a sharp labora-tory knife to remove any excess registration paste thatextends more than 1.5 mm from the cusp tip in any direc-tion (Fig 4-17). Excess paste that has spread to occlusalanatomic grooves may prevent the casi from seatingcompletely into the record.The success of this technique is dependent upon theuse of very small quantities of bite registration paste.Because inexperienced operators have a tendency touse too large a quantity, it may be best to eliminate theuse of the paste completely when introducing the tech-nique to novices. In that case, the baseplate wax recordis well adapted to the maxillary teeth, and Aluwax isplaced on the underside of the baseplate wax to accom-modate the cusp tips of the mandibular teeth.
    • Maximum Intercuspation RecordWhile diagnostic mountings are done with the condylesin a centric relation position, casts that are to be used forthe fabrication of restorations for a small portion of theocclusion are attached to the articulator in a position ofmaximum intercuspation. Mounting them in a retrudedposition could result in a restoration with a built-in inter-ference.Armamentarium1. Plastic registration frame2. Scissors3. Polyvinyt siioxane registration material4. Impression material dispenser5. Laboratory knife with no. 25 blade6. Arbor bandTechniqueThe technique employed to index the intercuspal positionfor restoration fabrication produces an interocclusalrecord with the maxillary and mandibular teeth in totalcontact. Use a plastic registration frame (Triple-BiteImpression Tray, Premier, Inc. Philadelphia, PA) to carrythe registration material (Fig 4-18). Try it in the mouth onthe side with the prepared teeth (Fig 4-19). This willinsure that the patient is able to bring the posterior teethtogether completely with the frame in position. The pres-ence of both third molars on one side of the mouth willusually preclude the use of this device Note any areawhere the interarch film overlies unprepared teeth Afterremoving the frame from the mouth, trim away the filmthat covered the unprepared teeth (Fig 4-20].IPlace the twin-barrel cartridge of bite registrationmaterial (Stat B-R Registration Paste, Kerr ManufacturingCo) in the gun and lock on a new tip. Then mix the regis-tration material by expressing it from the dispenser withsteady pressure on the trigger. Apply the material evenlyto both top and bottom of the frame (Fig 4-21). Do notplace any in those areas where you have removed thesupporting film.Insert the loaded frame into the mouth, centering theloaded portion over the prepared tooth or teeth (Fig 4-22). Have the patient close firmly until all posterior teethare contacting normally. Part the lips and verify that thepatient has not closed in a protrusive or working relation-ship. Instruct the patient to keep the teeth together untilasked to open. Leave the record in place for 3 minutes.Remove the tray from the mouth, rinse it under runningtap water, and then dry it with an air syringe. Inspect it toinsure that you have captured all of the necessary teeth(Fig 4-23). Use a laboratory knife with a no. 25 blade to
    • tnterocclusal RecordsFig 4-21 Registration paste is injected over the lop and bottom of Fig 4-22 The loaded frame is placed ovur the prepaithe bite registration frame.cut ofl all excess above the edge of the frame (Fig 4-24).Cut off any material that extends over unprepared teethadjacent to the preparation(s).Remove excess thickness from the upper and lowersurfaces of the record using an arbor band on a lathe(Fig 4-25). On the unprepared teeth opposing the prepa-rations), remove enough material so that little more thanthe cusp tip indentations remain [Fig 4-26). Any materialthat reproduces edentulous ridges, gingival crevices, orthe central fossae of the occlusal surfaces is likely to pro-duce incomplete seating of a cast with imperfections inthose areas, so get rid of it. The overall thickness of therecord should be approximately 4.0 mm, with an equalamount having been removed from its upper and loweraspects.So that you will be able to verify seating of the castsinto the record, cut completely through its thicknessalong the buccal cusps of the mandibular teeth using alaboratory knife with a no. 25 blade (Fig 4-27). Cut all theway through the posterior member of the trame and dis-card the facial segment of the record.Set the record on the mandibular cast, making surethat it seats completely (Fig 4-28). Place the teeth of themaxillary cast completely into the index while articulatingthe teeth on the opposite side of the arch and those nearthe preparation(s) (Fig 4-29). At this point you will bestappreciate why the registration material must be rigidand brittle. If a flexible material were used, it would dis-tort when the casts were compressed and the resultantarticulation of casts would be inaccurate. Now use therecord to articulate the casts and mount the mandibularcast on the articulator (Fig 4-30).
    • Intercuspsfion Record
    • Interocclusal RecordsLateral Interocclusal RecordLateral interocclusal records, or check bites, are made inthe mouth for the purpose of capturing the position of thecondyles in their respective fossae. These records arethen used to set the condylar guides to approximate theanatomic limits of the temporomandibular joints Thisallows the maximum benefit from using an articulator,facilitating the fabrication of accurate restorations with aminimum of time required for intraoral adjustment whenthe restoration is cemented.Because the configuration of the temporomandibularjoint has a strong determining influence on the move-ments of the mandible, the occlusal morphology of anyrestoration placed in the mouth must be in harmony withthe movements of the mandible to prevent the initiation ofocclusal disharmony and trauma. Cusp placement, cuspheight, groove direction, and groove depth are all fea-tures ultimately affected by temporomandibular joint con-figuration.3Armamentarium1. Laboratory knife with no. 25 blade2. Horseshoe wax wafers3. Plaster bowlTechniqueGuide the patient into a CRCP closure and visually notethe position of the lower midline in relation to the maxil-lary teeth. Measure and mark with a pencil the points onthe maxillary teeth that would be opposite the lower mid-line if the patient moves the mandible 8 0 mm in both aright and left lateral excursion (Fig 4-31) With your handon the patients chin, have the patient open slightly.Guide the mandible approximately 8.0 mm to the rightand close it until the teeth lightly touch. Explain to thepatient that you are going to repeat this procedure withsome wax between the teeth and that you want him or herto bite down carefully until told to stop.Place a slightly warmed wax rim (Surgident CoprwaxBite Wafer, Miles Dental Products, South Bend, IN)against the maxillary teeth approximately 4.0 mm off cen-ter to the right. Support the wax with your hand and guidethe mandible to the right. Repeat the closure practicedpreviously until the teeth make indentations in the waxthat are approximately 1.0 mm deep (Fig 4-32). Cool thewax rim with compressed air and remove it from themouth Place it in a plaster bowl of cold tap water. Repeatthe steps with a second wax rim for the left side.
    • References1. Lucia VO. Centric relation, theory and practice J ProsthetDenM960; 10:849-856.2. Lucia VO. A technique for recording centric relation JProsthet Dent 1964; 14:492-505.3. Hobo S, Iwata T: Reproducibility of mandibular cenlricity inthree dimensions. J Prosthet Dent 1985; 53:649-654.4. Williamson EH, Sleimke RM, Morse PK, Swift TR; Centric rela-tion: A comparison of muscle-determined position and oper-ator guidance. AmJOrthod 1980, 77:133-145.5. McHorns WH: Centric relation defined. J Gnathol 1986;5:5-21.6. Dawson PE1Temporomandibular joint pain dysfunction prob-lems can be solved. J Prosthet Dent 1973; 29:100-112.7. Dawson PE1Evaluation, Diagnosis, and Treatment ofOcclusal Problems. St Louis, CV Mosby Co, 1974, p 58.8. Perry HT. Muscular changes associated with temporo-mandibular joint dysfunction. J Am Deri! Assoc 1957;54:644-653.9. Weinbe
    • Chapter 5Articulation of CastsTo properly evaluate a patients occlusion, it ismandatory that diagnostic casts be placed in anarticulator in approximately the same relationship tothe temporomandibular joints as exists in the patient.1Afacebow registration is used to mount the maxillary caston the articulator so that it is properly located bothanteroposteriorly and mediolaterally.23To be usedenough to make a real contribution to the improvement ofquality dentistry, a facebow and articulator that possessa modicum of accuracy, are simple to assemble and use,and can be set up relatively quickly should be selected.In a survey done in 1984, 36% of the responding NorthAmerican dental schools were using a Whip Mix articula-tor, 32% were using an arcon Hanau (with another 25%using a nonarcon model employing the same type ofcondylar track mechanism), and 28% were using aDenar semiadjustable articulator.4The percentages addup to more than 100 because some schools use morethan one articulator. Two of the three articulatorsdescribed in this chapter did not exist in 1984, but theydo represent the latest advances and the best featuresfor fixed prosthodontics offered by those manufacturersat the present time. Each of the sections on a face-bow-articulator combination is meant to stand alone; ie,everything the reader needs to know about the use of asystem is contained in that respective section The oneexception lies in the description of a mechanical anteriorguide. Although similar devices are available for all threearticulators, use of the mechanical anterior guide isdescribed only for the Hanau articulator.Fig 5-1 The components of a Quick Mount facebow aright): a bitefork, the facebow, and the nasion relator.that has been set to the same parameters 5There aremany advantages to this feature, including the ability tosend casts to the laboratory without sending the instru-Facebow Armamentariumebow (with bitefork,Whip Mix Facebowand Articulator1. Quick Mount fcand hex driver)2. Whip Mix articulator3. Plaster bowl4. Spatula5. Laboratory knife with no. 25 bla6. Trimmed maxillary cast7 Pink baseplate wax8 Mounting stoneThe technique for the Quick Mount facebow (Whip MixCorp. Louisville, KY) (Fig 5-1), an ear facebow that pos-sesses the qualities previously described, is presented.Following that is the technique for the use of the Whip Mix2200 series articulator, a semiadjustable instrument.Casts mounted on one of these articulators can be trans-ferred accurately to another instrument of the same typeFacebow RecordHeat a sheet of baseplate wax in hot tap water until itbecomes soft and flexible. Adapt the wax to the biteforkso that it is uniformly covered. Place the wax-coveredbitefork against the maxillary teeth. Center the shaft ofthe fork with the patients midline. Support the bitefork
    • Fig 5-2 The patient guides the earpieces vthe dentist inserts the bitefork shaft into the tcunder the facebow.Fig 5-4 Firm pressure is placed on the end of then,ision relator and the thumbscrew is tightened.
    • Whip Mix Facebow and Articvlatormand have the patient close lightly into the wax to obtainshallow impressions of only the cusp tips Cool the waxand remove the bitefork from the mouth. Trim awayexcess wax. Any areas where soft tissue was registeredon the wax must be completely removed.Set the maxillary cast in the bitefork registration to con-firm that the cast seats firmly in the index with no rockingor instability. If the cast does not seat, first check theocclusal surfaces of the cast to make sure there are nonodules of stone. If there are none, then either the regis-tration or the cast is distorted and should be remade.Place the bitefork back in the mouth and have thepatient close to hold it securely between the maxillaryand mandibular arches. Ask the patient to grasp botharms of the facebow and guide the plastic earpieces intothe external auditory meati, much as one would guide theearpieces of a stethoscope (Fig 5-2). At the same time,the operator should slide the toggle onto the shaft of thebitefork, making certain that the toggle is positionedabove the shaft. Tighten the three thumbscrews on thetop of the facebow (Fig 5-3). Place the nasion relator onthe transverse bar of the facebow Extend the shaft whileadjusting the facebow up or down to center the plasticnosepiece on the patients nasion. Tighten the thumb-screw (Fig 5-4)Support the facebow with a firm, forward pressure andslide the toggle lock on the bitefork shaft until it is near,but not touching, the lips. Tighten it firmly with the hexdriver (Model 8600) or T-screw (Model 8645), and thentighten the toggle on the vertical bar in the same manner(Fig 5-5). For extra support and for peace of mind, thepatient can hold the side arms of the facebow. Beextremely careful that the facebow does not tilt out ofposition in any direction during these tightening proce-dures Use your free hand to stabilize the assemblyagainst any torquing while tighteningThe patients approximate intercondylar distance of"small," "medium," or "large" is indicated on the top ofthe front edge of the facebow (Fig 5-6). If you are usinga Model 8500 articulator, this information should berecorded on the patients data record to aid in setting thearticulator later. It is not necessary for the 2200 seriesinstrument shown here, because it has a permanent non-adjustable intercondylar width of 110 mm. This corre-sponds to the "M" width shown on the facebow.Loosen the thumbscrew and remove the plastic nasionrelator. Then loosen the three thumbscrews on the topsurface of the facebow by one-quarter turn. As thepatient slowly opens the mouth, carefully remove theentire assembly from the head. Recheck and securelytighten the toggles. It is sometimes difficult to adequate-ly tighten these toggles while the facebow is on thepatients head.Mounting the Maxillary Caste the articLand lowerator to receive the cast. Separate themembers of the articulator. Set the
    • Fig S-8 The three thumbscre1The incisal guide pin has beencondylar guides at "FB" in preparation for attachment ofthe facebow. If your articulator does not have this setting,adjust the guides to an angulation of 30 degrees. Firmlysecure clean mounting plates to the upper and lowermembers of the articulator. Remove the incisal guide pinThe three thumbscrews on the top of the facebow shouldbe slightly loose for the next step. Hold the facebow inone hand and the upper member of the articulator in theother. Guide first one and then the other pin on the outersurfaces of the condylar guides into the holes on theinner surfaces of the plastic earpieces. Hold the facebowagainst your body while you are doing this (Fig 5-7).Alfow the front end of the member of the articulator to reston the transverse bar of the facebow.An indirect transfer assembly, which can be removedfrom the facebow and attached to a transfer base mount-ed on the articulator base, is available. This permits thefacebow to be used on another patient even if the castsfor this patient have not yet been mounted.Hold the facebow firmly against the upper frame andtighten the three thumbscrews on the facebow. Place theupper frame and attached facebow back onto the lowerframe of the articulator with the fork toggle of the facebowresting on the plastic incisal guide block (Fig 5-8)Soak the maxillary cast, tooth side up, in a plasterbowl. There should not be enough water to cover theteeth. Carefully seat the cast into the bitefork registration.Mix mounting stone (Whip Mix Corp) to a thick, creamyconsistency Lift the upper frame of the articulator andapply a golf-ball-sized mound of stone to the base of thecast. Use one hand for support to prevent any movementof the facebow fork or cast, and close the upper framedown until it touches the transverse bar of the facebow(Fig 5-9). This will force the mounting plate into the softmounting stone.The mounting stone should engage undercuts on thebase of the cast and the mounting plate If necessary,add more mounting stone into these areas to insure ade-quate retention for the mounting. When the stone hascompletely set, remove the facebow from the articulator.Mounting the Mandibular CastReplace the incisal guide pin in the upper frame of thearticulator with the rounded end down and set at a 2 0-mm opening. (Align the second mark above the circum-ferential line of the pin with the top edge of the bushing.)Adjust the plastic incisal guide block slightly so that thepin will rest in the dimple. This compensates for length-ening the straight incisal pin. Snap the centric latchclosed at the rear center of the articulator (Fig 5-10).
    • Whip Mix Facebow and ArliculalorSecure the bilateral elastic straps to the lateral, or outer,aspects of the vertical posts of the base frame, using thethumb holding screws attached to the straps.Place the upper frame of the articulator (with maxillarycast attached) upside down on the laboratory bench withthe incisal guide pin extending over the front edge of thebench. Set the centric relation interocclusal record on themaxillary cast. The teeth should seat completely into thedepressions in the record.Now position the mandibular cast in the interocclusalrecord and confirm that the teeth are fully seated. Themaxillary and mandibular casts should not contact any-where Remove the mandibular cast and soak it, toothside up. in a plaster bowl for approximately 2 minutes.There should not be enough water in the bowl to coverthe teeth. Move the immediate lateral translation guide onthe front of each condylar guide outward to a setting of"0" (Fig 5-11). This will prevent any lateral movement dur-ing mounting of the mandibular castAfter the cast has soaked, reseat it into the record. Mixmounting stone to the consistency of thick cream andplace a golf-ball-sized mound of stone on the bottom ofthe cast. Apply a small portion of stone to the mountingplate on the lower frame, and hinge the lower frame downinto the soft stone until contact is made between theincisal guide pin and the incisal guide block. Hold themandibular cast with your fingers to steady it in the inter-occlusal record until the mounting stone has set (Fig 5-12).
    • Check these features:1. Each condylar element should be against the posteri-or and superior walls of its condylar guide.2. The maxillary and mandibular casts should be com-pletely seated in the interocclusal record.3. The mounting stone should be engaged in the under-cuts on both the base of the cast and on the mountingplate.Allow the mounting stone to set completely. Then con-firm the mounting accuracy by opening the articulator,removing the interocclusal record, and raising the incisalguide pin 2.5 cm (1 inch). Place a 5.0-cm (2-inch) strip ofno. 10 red-inked silk ribbon between the posterior teethon both sides and lightly tap the teeth with the condylesretruded. This will leave red dots at CRCP.Remove the pieces of 28-gauge green wax from thestorage cup and carefully place them over the maxillarycast. If the red dots show through the perforations in thewax, the accuracy of the mounting procedure has beenconfirmed. If they do not show through, recheck the pro-cedure and correct the error.Remove both casts, with their respective mountingplates, from the articulator Mix more mounting stone andfill all voids between the casts and mounting plates. Useyour finger to smooth over the mounting stone to give it aneat appearance. There must be no stone on the surfaceof the mounting plate that contacts the articulator frame.The neatness of the casts (or the absence of same) willbe interpreted by the technician and the patient as indi-cators of how much you care about the work that you aredoing.
    • Whip Mix Facebow and ArticulateFig 5-16 The condylar inincreased until the condyle <superior wall of the guide.Setting Condylar GuidanceLoosen slightly the medial pair of thumb clamp screws onthe lop or back side of the upper frame of the articulator.Set both condylar guides at 0 degrees (Fig 5-13). Nowloosen the lateral translation clamp screws on the for-ward aspect of each condylar guide and set the immedi-ate lateral translation controls at their most open position(Fig 5-14). Raise the incisal guide pin so that it will nottouch the plastic incisal stop in any position.Invert the upper frame, with cast attached, and seatthe right lateral interocclusal record on the teeth of themaxillary cast. Be sure that the teeth seat completely inthe wax indentations. Hold the upper frame in your lefthand and place the right condylar element in the rightcondylar guide. Gently position the teeth ot the mandibu-lar cast in the indentations of the wax record. Be surethey are seated completely. Support the articulator in thisposition with one hand on the right side. Notice that theleft condylar element has moved downward, forward,and inward. It is not touching the condylar guide at anypoint (Fig 5-15).Set the inclination of the left guide by releasing itsclamp screw. Rotate the guide inferiorly until the superiorwall again touches the condylar element (Fig 5-16).Tighten the holding screw. Accommodate mandibularlateral translation by releasing the lateral translationclamp screw and sliding the lateral translation guide lat-erally until it touches the medial surface of the condylarelement (Fig 5-17). Retighten the clamp screw. Set theright condylar guidance by using the record for the leftlateral excursion and repeating these steps.
    • Articulation of CastsFig 5-18 The guidance provided by anterior teethed in acrylic resin on the incisal guide block.Once the lateral interocclusal records have been madefor the diagnostic mounting and the articulator has beenset, the data are recorded on the patients informationcard On the patients casts, mark the correct articulatorsettings for each side. Example: A condylar inclination of40 degrees and a lateral translation of 0 3 mm would berecorded as 40/0.3. When teeth are prepared at somefuture date and working casts are mounted on the artic-utator, it will not be necessary to make new lateral inter-occlusal records. The recorded information from thediagnostic mounting can be used to set the instrument.Anterior GuidanceThe influence of the temporomandibular joint on theocclusal scheme has been noted. The use of lateral inter-occlusal records in the setting of the condylar guidesenables us to transfer some of the influence from the tem-poromandibular joint to the semiadjustable articulator.The influence of the incisors and canines (ie, anteriorguidance) on the occlusion during excursive movementsmust also be taken into account.78The guidance given to mandibular movements by theanterior teeth can be recorded and made part of the set-ting of the articulator (Fig 5-18). Anterior guidance can, ineffect, be transferred from the teeth to the incisal guideblock of the articulator. If crowns restoring the lingualcontours of the anterior teeth are to be placed, it isextremely important that the anterior guidance be regis-tered on the articulator. If this is not done, restorationsmay be made whose lingual contours or length will notprovide anterior guidanceThe mounted casts should be examined on the articu-lator to assess the anterior guidance. If there are non-working interferences on the casts, remove them toenable the articulator to move freely while maintainingcontact between the anterior teeth. Examine the anteriorguidance to determine its adequacy If it is not adequatebecause of wear, fracture, or missing teeth, restore it toan optimum form with inlay wax or denture teeth on thecast.Raise the mcisal guide pin (round end down) so that itwill miss contacting the plastic incisal guide by at least1.0 mm in all excursions (Fig 5-19). Place one or twodrops of monomer on the plastic incisal guide. Mix one-half scoop of tray acrylic resin in a paper cup. While it stillflows freely, place a small amount on the incisal guide. Asthe uncured acrylic resin develops more body, add addi-tional material to the block until there is approximately 6.0mm (1/4 inch) of resin on the plastic incisal guide (Fig 5-20).Lubricate the round end of the incisal guide pin andthe functioning surfaces of the anterior teeth with petro-latum. Close the articulator into full occlusion so that theguide pin penetrates into the soft tray resin (Fig 5-21).Move the articulator repeatedly through all the mandibu-lar movements, making sure that the anterior teethremain in contact at all times (Fig 5-22). The tip of theincisal guide pin molds the acrylic resin to conform to thevarious movements. Continue moving the articulatorthrough all the excursions until the tray resin has poly-merized.Trim off excess resin after it has polymerized. The tip ofthe guide pin has acted as a stylus in forming a registra-tion of the anterior guidance (Fig 5-23). It will now be pos-sible to duplicate the influence of the anterior teeth on themovements of the casts, even if the anterior teeth are pre-pared and the incisal edges shortened.
    • Whip Mix Facebow and Articulator
    • Articulation of CastsFig 5-24 The compobottom): a reference plfacebow with pointer.Slidematic facebow are (top tor, the bitefork assembly, and theDenar Facebow and ArticulatorThe Denar Slidematic facebow (Teledyne Water Pik, FortCollins, CO) is another self-centering ear facebow that iseasy to use (Fig 5-24). The technique for its use isdescribed with the Mark II articulator, an arcon semiad-justable articulator. This articulator also allows inter-changeability of articulated casts with other Mark II artic-ulators without a loss of accuracy.Facebow Armamentarium1. Slidematic facebow (with bitefork, articulator index,reference pin, and reference plane indicator)2. Felt-tip marker3. Denar Mark II articulator4. Plaster bowl5. Spatula6. Laboratory knife with no. 25 blade7. Trimmed maxillary cast8. Pink baseplate wax9. Mounting stoneHeat a sheet of baseplate wax in a bowl of hot wateruntil it can be easily molded. Adapt the wax to the bite-fork to cover all portions of it. Place the wax-covered bite-fork between the teeth, with the bitefork shaft to thepatients right. Center the fork by aligning the index ringon the fork with the patients midline. Instruct the patientto bite lightly into the wax to produce shallow indenta-tions of the cusp tips in the wax. Cool the wax andremove the bitefork from the mouth. Trim any excess waxoff the bitefork.Try the maxillary cast in the wax record to insure that itwill seat without rocking. If the cast fails to seat, checkthe occlusal surfaces of the cast for nodules of stone. Ifnone are evident, there is a distortion in the registrationrthecFasten the reference pin to the underside of the face-bow by tightening the set screw with a hex driver (Fig 5-26). Recent models have finger screws rather than setscrews. The clamp marked "2" should be on the patientsright (your left as you look at the front of the instrument).Place the bitefork in the mouth and have the patienthold it securely between the maxillary and mandibularteeth. The patient should grip both arms of the facebowto guide the plastic earpieces into the external auditorymeati, in the same manner as one would place a stetho-scope into the ears (Fig 5-27). While the patient is insert-ing the earpieces, the operator should slide the clampmarked "2" onto the shaft of the bitefork. The clampshould be positioned above the shaft. Tighten the singlefinger screw on the front of the facebow (Fig 5-28).Extend the anterior reference pointer while moving thefacebow up or down. When the pointer is properlyaligned with the anterior reference point, tighten the fin-ger screw (Fig 5-29). While continuing to support thefacebow, tighten the set screw on clamp " 1 " on the verti-cal reference pin with a hex driver (Fig 5-30). Then tight-en clamp "2" on the horizontal reference pin For addedstability and peace of mind, the patient can continue tosupport the facebow by holding the side arms. Do notallow the facebow to torque or tilt during the tighteningprocedure.Loosen the finger screw on the front of the facebow bya quarter turn. As the patient opens the mouth, removethe assembly from the head. Recheck and tighten theclamps with a hex driver. Remove the bitefork assemblyfrom the underside of the facebow by loosening the setscrew on the clamp by a quarter turn. Only the bitetorkassembly need be used for mounting the maxillary cast.The facebow is ready for use on another patientFacebow RecordUse the reference plane indicator to measure a point 43mm above the incisal edges of the maxillary incisors onthe right side. Mark this point with a felt-tip marker (Fig 5-25). This will form the anterior, or third, reference point forthe icebow transfer.Mounting the Maxillary CastRemove the incisal guide block from the articulator andreplace it with the articulator index (Fig 5-31). Insert thevertical reference pin of the bitefork assembly into thehole on the top of the articulator index. The reference pinhas a flat side, which will match a flat side on the hole.
    • g 5-27 The dentist placehile the patient inserts the i• the bitcfork shaftCheck to be sure that the numbers " 1 " and "2" on theclamps of the bitefork assembly are upright. Use a hexdriver to tighten the set screw in the front of the index.Secure clean mounting plates to the upper and lowermembers of the articulator. Assemble the articulator byplacing the fossae over the condyles. Place the incisalpin at the zero position. The long incisal pin for the dim-pled guide block will rest in the recessed center of theindex. The short pin used for flat guide blocks will con-tact the sliding metal piece in the middle of the index.The incisal pin with the adjustable foot sits on the poste-rior section of the index. Remove the upper member ofthe articulator and set it on the benchtop. with the mount-ing plate up.Soak the maxillary cast, tooth side up, in a plaster bowlcontaining only enough water to wet the sides and bot-tom of the cast. Seat the cast into the wax registration onthe bitefork (Fig 5-32). Mix mounting stone (Whip MixCorp) to the consistency of thick cream. Apply a golf-ball-sized mound of stone to the base of the cast and themounting plate. Assemble the articulator by placing thefossae over the condyles. Close the upper member of thearticulator into the soft mounting stone until the incisalguide pin contacts the appropriate spot on the articulatorindex. Lock the centric latch by pushing it into the downposition.
    • Articulation of CastsFig 5-29 Ihe fatebow hone hand and extend the rtwith the other.Fig 5-30 The clamps iassembly ate tightened.The mounting stone will engage undercuts in themounting plate and cast. Additional stone can be addedif needed to secure the mounting. When the stone hasset completely, remove the transfer jig from the articula-tor. Replace the incisal guide block in the articulator.Mounting the Mandibular CastAdjust the incisal pin for a 2.0-mm opening to accommo-date the thickness of the interocclusal record. Invert thearticulator with the attached maxillary cast, making surethat the centric latch is engaged. Place the centric rela-tion interocclusal wax record on the maxillary cast Checkto insure that the teeth seat completely into the record.Place the mandibular cast into the interocclusal recordand make sure that the teeth are fully seated. Thereshould be no contact between the maxillary andmandibular casts. Remove the mandibular cast and soakthe bottom and sides of it in a partially filled bowl of waterfor about 2 minutes.Reseat the soaked mandibular cast into the interoc-clusal wax record. Mix some mounting stone to a thick,creamy consistency and place a mound of stone on theinverted bottom of the cast. Apply some mounting stone
    • Denar FacebowFig 5-32 The maxillary cast in the biteis positioned by the articulator index.to the mounting plate on the lower member of Ihe ariicu-lator and hinge it down into the soft stone on the cast untilthe incisal guide pin makes firm contact with the incisalguide block. Stabilize the mandibular cast with your fin-gers to keep it securely in the interocclusal record untilthe mounting stone sets (Fig 5-33). Rubber bands orsticky wax can also be used, but they are more likely toslip and produce a mounting error.Examine the casts and articulator for the following:1. The condyle is located against the posterior andsuperior walls of the condylar guide.2. Both casts are completely seated in the interocclusalrecord.3. Mounting stone engages undercuts on both the baseof the cast and the mounting plateWhen the mounting stone has set completely, confirmthe accuracy of the mounting. Open the articulator,remove the interocclusal record, and raise the incisalguide pins 1 inch. Place a 2-inch piece of no. 10 red-inked silk ribbon between the posterior teeth on bothsides. Tap the teeth together lightly with the condylesagainst the posterior wall of the condylar guide, leavingred dots that represent the contacts at centric relationposition.Retrieve the pieces of 28-gauge green wax that havebeen stored in a cup and lightly place them on the teeth
    • of the maxillary cast The accuracy of the mounting willbe confirmed if the red dots are visible through the per-forations in the wax. If they are not visible, the procedureshould be rechecked and the error corrected.Remove the casts and their mounting plates from thearticulator. Mix additional mounting stone to fill any voidsbetween the casts and their mounting plates. Smooth themounting stone with your finger to give it a neat appear-ance. No stone should remain on the surface of themounting plate that will contact the articulator frameBoth the dental technician and the patient will form animpression of you when they see these casts on the artic-ulator Make sure that it is a positive one.Setting Condylar GuidanceWith a hex driver, loosen the set screw on the undersideof each fossa and set the medial side wall to a 6-degreeprogressive lateral translation Release the lock screw oneach end of the posterior aspect of the upper crossbar ofthe articulator using a hex driver and set both condylarguides at 0 degrees. Then loosen the set screw on thetop of each fossa as far as possible to the medial. Lift theincisal guide pin to prevent it from touching the plasticincisal stop in any position. Release the centric latch.Seat the right lateral interocclusal record on the maxil-lary cast attached to the inverted upper member of thearticulator. The teeth should seat completely in the waxindentations. Hold the upper member of the articulator inthe left hand and place the right condylar element in theright condylar guide. Seat the teeth of the mandibularcast gently but completely into the indentations of thewax recordUse one hand on the right side of the articulator to sup-port it in this position. The left condylar element will havemoved downward, forward, and inward. It should not betouching the condylar guide at any point (Fig 5-34).Increase the inclination of the right protrusive condylarpath by rotating the fossa until the superior wall makescontact with the condylar element (Fig 5-35, A). Tightenthe set screw on the back of the upper crossbar with ahex driver. Set the immediate lateral translation by mov-ing the medial wall of the fossa outward or laterally until itcontacts the medial surface of the condylar element (Fig5-35, B). Retighten the set screw. The wax interocclusalrecord for the left lateral excursion is used to set the rightcondylar guidance in the same manner.After setting the articulator, record the data on thepatients information card. Mark the articulator settingsfor each side on the respective side of the patients cast.Example: A condylar inclination of 35 degrees and animmediate lateral translation of 0.6 mm would be record-ed as 35/0.6. When teeth are prepared at some futuretime, working casts can be mounted on the articulatorwithout making new records. The instrument can be resetusing the recorded information from the diagnosticmounting.Anterior GuidanceExamine the mounted casts on the articulator. Removeany nonworking interferences from the casts so that thearticulator can move freely while the anterior teeth remainin contact. If the guidance is inadequate for any reason,restore it to an optimum configuration with a diagnosticwax-up.
    • A1cr1Fig 5-34 The right Iaway from the superkcauses the left conall (B) of the guide.Fig 5-35 To adjust the condylar guide: (A) the condylar inclination is increaseduntil the superior wall contacts the condyle and (B) the medial wall is moved intocontact with the condyle.Raise the mcisal guide pin so that it will be at least 1.0mm off the plastic mcisal guide block in all excursions(Fig 5-36). Moisten the surface of the guide block withmonomer. Mix one-half scoop of tray resin and, while it isstill free-flowing, place a small amount on the incisalguide. As the polymerizing resin becomes stiffen addmore until there is about 1/4 inch of it covering the guideblock (Fig 5-37). Lubricate the end of the incisal guidepin and all contacting surfaces of the anterior teeth withpetrolatum. Close the articulator so that the teeth occludecompletely. The guide pin will penetrate the soft acrylicresin (Fig 5-38). Move the articulator through all excur-sions repeatedly, keeping the teeth contacting at alltimes (Fig 5-39). The tip of the guide pin will mold theacrylic resin to record the pathway of the various move-ments. Continue the movements until the resin is com-pletely polymerized. Trim off the excess. A record of theanterior guidance has now been formed on the incisaltable (Fig 5-40).
    • Fig 5-38 The guide pin is allowed to close into the soft resin. Fig 5-39 The drtitulator is moved through .ill excursiFig 5-40 An anterior guidance record exists on the guide block.
    • Fig 5-41 The components of a Spring-Bofatebow with orbital pointer and the bitefo:Hanau Facebow and ArticulatorThe Hanau Spring-Bow (Teledyne Water Pik, Fort Collins,CO) is an ear facebow that utilizes a one-piece spring-steel bow (Fig 5-41). It is simple in design and can beused either as a direct-mount or an indirect-mount devicewith the removable bitefork assembly and mounting plat-form.9The technique for its use is described with theHanau Series 184 Wide-Vue Articulator, an arcon semi-adjustable instrument.Facebow Armamentarium1. Spring-Bow (with bitefork assembly and mountingguide)2. Hanau Wide-Vue articulator3. Plaster bowl4. Spatula5 Laboratory knife with no. 25 blade6. Trimmed maxillary cast7. Pink baseplate wax8 Mounting stoneFacebow RecordSoften a sheet of baseplate wax in hot water and com-pletely cover the bitefork with it. Position the wax-coveredbitefork against the maxillary teeth and have the patientclose until the mandibular teeth contact the wax on theunderside of the fork. The shaft of the bitefork will be tothe left of the patients midline.Cool the wax in the mouth with an air syringe Removethe fork from the mouth and finish cooling it in a bowl ofcold tap water. Trim off excess and any areas imprintedby soft tissue Seat the maxillary cast in the wax record tobe sure that it is stable If there is any rocking of the cast,check the occlusal surfaces of the cast for nodules ofstone. If there are none, either the cast or the record isdistorted and must be remade.If the bitefork assembly is separate from the facebow,insert the transfer (vertical) rod of the assembly into thebow socket on the underside of the black centerpiece onthe front of the facebow. Make sure the flat surface on thefront of the rod faces you as you place it in the socket.The assembly should be to your right, with the knobs fac-ing you (Fig 5-42). Tighten the thumbscrew on the front ofthe centerpiece.While the patient grips the bitefork between the maxil-lary and mandibular teeth, position the loosened biteforkclamp over the bitefork shaft 4,0 cm (1.5 inches). Thefacebow should be pointed upward during this action(Fig 5-43) Open the bow by pulling outward on the armsand swing it down into position, placing an earpiece gen-tly into each external auditory meatus. Have the patientadjust the earpieces to the most comfortable seatedposition (Fig 5-44).Mark the orbitale (infraorbital notch) on the patientsface with a felt-tip marker to provide an anterior referencepoint (Fig 5-45). Loosen the thumbscrew that holds theorbital pointer and gently swing it in toward the referencemark (Fig 5-46). Elevate the front of the facebow alongthe transfer (vertical) rod of the bitefork assembly untilthe pointer is at the plane of the anterior reference point.Grasp the bow to resist torquing (Fig 5-47) and tightenthe three thumbscrews in order from left to right (Fig 5-48):1. Transfer (vertical) rod/transverse (horizontal) rod
    • Articulation of CastsFig 5-42 The vertical rod of ihe bitefork Fig 5-4assembly is inserted into the bow socket. Theflat side should face you, with the empiy bite-fork clamp to your riBht.Fig 5-44 The patient should adjearpieces should be checked to make2. Transverse rod clamp (upper)3. Bitefork clamp (lower)Be sure that they are tight. Use an Allen wrench if nec-essary.Now rotate the reference pointer back over the righttemple of the bow and tighten the thumbscrew enough tohold it there. Have the patient open while you grasp theends of the bow and remove the earpieces from the audi-tory meati Make sure that you have a firm hold, since thebow is made of spring steel and could snap back. Slidethe bow away from the patientMounting the Maxillary CastPrepare the articulator to accept the casts by setting theinclination of the enclosed condylar track mechanisms at30 degrees on each side (Fig 5-49). The "Bennett angle"ring for the progressive mandibular lateral translationshould be set at 30 degrees (Fig 5-50).Use petrolatum to lubricate the surfaces of the upperand lower members of the articulator around the thread-ed mounting studs Then firmly secure a clean mountingplate to the mounting stud on the upper member of the
    • Hanau Facebow and ArticulatorFig 5-46 The pointer is rotated toward thearticulator. Attach a mounting guide or platform to thelower member of the articulator. Loosen the thumbscrewon the front of the facebow and remove the biteforkassembly. Place the vertical transfer rod of the assemblyinto the hole at the front of the mounting guide andsecure it by tightening the screw. Adjust the cast supportto touch the underside of the wax on the bitefork (Fig 5-51).Soak the maxillary cast in a plaster bowl, but do notcover the teeth with water Carefully seat the maxillarycast into the imprints in the baseplate wax on the bitefork.Raise the upper member of the articulator and place agolf-ball-sized mound of thick, creamy mounting stoneon the base of the cast. Swing the upper member of thecast down until the incisal pin is resting on the mountingguide or the anterior table, depending on the type ofguide used. Be sure that stone is engaging the cutouts inthe top of the mounting plate. Add more stone if neces-sary, and smooth off the top with a spatula. When thestone has set completely, remove the bitefork assemblyand mounting guide from the articulator. Attach a cleanmounting plate to the lower member of the articulator
    • Articulation of CastsFig 5-51 The rarticulator by imounting guidethellary cast isbitefork asisemblyMounting the Mandibular CastExtend the incisal guide pin 1 to 2 mm to compensate forthe thickness of the interocclusal wax record. Tighten thecentric lock on each enclosed condylar track mecha-nism to insure that the articulator is capable of nothingbut a hinge opening.Invert the articulator on the benchtop, resting it on thethree thumbnuts protruding from the upper member ofthe articulator. Place the centric relation interocclusalwax record on the teeth of the maxillary cast. Be sure thatthe teeth seat completely into the wax record.Place the mandibular cast into the interocclusal recordand again confirm complete seating. There should be nocontact between the maxillary and mandibular castsRemove the mandibular cast and soak it for about 2 min-utes. To prevent any erosion of the teeth on the cast,make sure that they are not covered by water. Reseat thesoaked mandibular cast into the record. Swing the lowermember of the articulator up and back. Place a moundof thick, creamy mounting stone on the bottom of thecast. Apply enough to the mounting plate on the lowermember to fill the cutout slots on either side of it Hingethe lower member of the articulator back over into thesoft mounting stone. The incisal guide pin should be rest-ing firmly against the incisal guide table. Use your handto steady the mandibular cast in the retruded positionwax registration until the mounting stone has achievedan initial set (Fig 5-52).
    • Hanau Facebow and Articulate!Inspect the articulated casts;1. The condyle is in the retruded position in its condylartrack mechanism.2. Both casts are seated completely in the interocclusalwax record.3. Mounting stone is securely attached to both casts andmounting plates.After the mounting stone has achieved a final set, cor-roborate the accuracy of the mounting. Open the articu-lator and raise the incisal guide pin so that it will nottouch the incisal table when the teeth are contacting.Remove the interocclusal record and place a 2-inchpiece of no. 10 red-inked silk ribbon between the poste-rior teeth on both sides Tap the teeth together lightly,producing red marks on the teeth where they contact inthe retruded position.Retrieve the pieces of 28-gauge green wax and care-fully position them on the teeth of the maxillary cast. If thecast mounting is correct, the red marks on the teeth willbe visible through the perforations in the wax. If they arenot visible, recheck the procedure step by step and thencorrect the error.Unscrew the mounting plates and remove the castsfrom the articulator. Soak the plates and attached mount-ing stone in water. Add more mounting stone wherever itis needed to fill voids between the casts and the mount-ing plates. Smooth the additional stone as it sets to giveit a neat appearance. Be careful not to leave any stoneon the surface of the mounting plate that will contact thearticulator frame. It has been said that sloppy castmountings are not an indication of a poor operator; theyare absolute proof.Setting Condylar GuidanceWax lateral or protrusive interocclusal records are usedfor setting the condylar inclination of this instrument.Loosen the thumbnut at the rear of each condylar trackmechanism so that it can be easily rotated. At this time,however, leave the condylar inclination at 30 degrees.The incisal guide pin should still be raised out of contactwith the incisal table.Seat the right interocclusal record on the teeth of themandibular cast. Gently lower the upper member of thearticulator until the maxillary teeth engage the waxrecord. Adjust the left condylar guide by changing thecondylar inclination with the thumbnut located at the rearof the guide. The teeth on the right side of the cast willrock in and out of the record. If the condylar path is tooshallow, the anterior teeth will be drawn out of the waxrecord (Fig 5-53, A). When the path becomes too steep,the posterior teeth become unseated (Fig 5-53, B). Thecorrect condylar inclination has been determined whenthe cast is seated completely in the wax record (Fig 5-53,C). Tighten the nut at the rear of the condylar guide.Loosen the thumbnut on the top of each condylarg 5-52 The mandibular cast is held shile the mounting stone sets.guide of the articulator. Slowly rotate the "Bennett angle"ring outward (from 30 degrees toward 0 degrees) untilthe flat side on the outer aspect of the condylar ball con-tacts the inner surface of the sleeve on the condylarshaft, forming a "brass to brass" contact (Fig 5-54).Repeat the process on the right side.If a protrusive interocclusal wax record is used toestablish the condylar inclination, both condylar mecha-nisms are rotated simultaneously in the same mannerdescribed above for setting each condylar inclinationseparately. In this situation, the angle of mandibular lat-eral translation is estimated by use of the "HanauFormula," L = H/8 + 12, where "H" is the condylar protru-sive inclination. Since a change in condylar inclinationfrom 20 to 50 degrees would produce less than a 4-degree change in the "Bennett angle" by this calculation,placing the "Bennett angle" ring at an arbitrary 15-degree angle would produce a minimal error.Enter the condylar inclinations in the patients record.Write the amount of condylar inclination for each condyleon the corresponding side of the cast. When teeth areprepared at some future time, it will not be necessary tomake new interocclusal records to adjust the articulator.The settings developed during the diagnostic mountingcan be reused.Custom Anterior GuidanceA customized anterior guidance jig can be made for thisarticulator by using a round-end incisal pin and a flatanterior table or an incisal cup. Acrylic resin is molded bythe end of the incisal pin in the same manner that theanterior guidance is recorded for the other articulators.Examine the mounted casts on the articulatoki i f Th tiorking interfere . The articulator
    • Articulation ot CastsFig 5-53 To i a prattL;ondy r k d r)ti is rocked up ;rl alcondylar inclinatiidown. When the a „anterior teeth lift out oi th^ record (A).When the inclination is too steep, the pos-terior teeth lift out (Bl. When the cast icompletely seated, the inclination is correct(Q, When lateral interocclusal records areemployed, the left record is used for theright condylar inclination and the rightrecord for the lett condylar inclination
    • Hanau Facebow and ArticulatorFig S-S4 With the casts seated in a lat-eral interocclusal record, there is a gapbetween the condyle and sleeve (A).When the "Bennett angle" ring (andcondylar track mechanisml are rotated,the condyle contacts the sleeve (B). Thenumber on the scale is the angle of themust be able to move freely with the anterior teeth in con-tact. If the guidance is inadequate, rebuild it to an opti-mum configuration with a diagnostic wax-up.Raise the incisal guide pin at least 1.0 mm off the plas-tic incisai guide block in all excursions (Fig 5-55).Moisten the surface of the guide block with monomer, Mixone-half scoop of tray resin and, while it is still free-flow-ing, place a little on the incisal guide. As the polymeriz-ing resin becomes stiffer, add more until there is about6.0 mm (1/4 inch) of it covering the guide block (Fig 5-56). Lubricate the tip of the incisal guide pin and theoccluding surfaces of the anterior teeth with petrolatum.Close the articulator to complete contact between thecasts. The guide pin should sink into the soft acrylic resin(Fig 5-57) Move the articulator through all excursionsrepeatedly, keeping the anterior teeth touching at alltimes (Fig 5-58). The pathways of all the movements willbe imprinted by the tip of the guide pin in the acrylic resinas a permanent record (Fig 5-59). Continue moving thecasts until polymerization is complete. Remove theexcess.
    • •tcutation of CastsFig 5-57 Ihe guide pi.Mechanical Anterior GuidanceThe guidance of mandibular movement imparted by theanterior teeth also can be recorded on this instrumentwith a mechanical incisal guide. Examine the mountedcasts. Remove any interferences from the casts that pre-vent the anterior teeth from remaining in contact in allexcursions. Restore any inadequacies in the guidanceby building up an optimum configuration in a diagnosticwax-up.Loosen the lock nut under the incisal table at the frontend of the lower member of the articulator. The incisal pinshould be in contact with the incisal table.Protect the casts from undue abrasion by lubricatingcontacting surfaces with petrolatum. Gently move theupper member of the articulator back to bring the maxil-lary and mandibular teeth into an end-to-end position.The incisal pin will be lifted off the incisal table. Rotate theincisal guide to raise it posteriorly. Stop when it makescontact with the pin (Fig 5-60, A). Tighten the lock nut tomaintain this inclination of the table.Move the casts into a right lateral excursion. The pinwill move to the left side and will again be lifted off thetable. Loosen the small thumbnut under the left side ofthe table and use the elevating screw to raise the leftwing of the table into contact with the corner of the guidepin (Fig 5-60, B). Repeat the process by moving thecasts into a left lateral excursion. Raise the right wing ofthe incisal table to contact the pin (Fig 5-60, C)
    • Hanau Facebow and AniculatorFig 5-60 To set the mechanical incisalguide, the casts are moved into a protru-sive relationship. The angulation of thetable is increased to contact the pin (A).The casts are moved into a right lateralexcursion and the left wing of the incisaltable is raised (B). The casts are movedinto a left lateral excursion and the rightwing of the table is lifted to completethe recording (C).
    • References1. Pruden WH: The role of study casts in diagnosis and treat-ment planning. JProsthet Dent 1960; 10:707-710. 3. Schuylet CH: The function2. HickeyJC, LundeenHC, Bohannan HM: A new articulate* for ance in oral rehabilitateuse in teaching and general dentistry J Prosthet Dent 1967; 1011-1030.18:425-437. 9. strohaver RA, Ryan JR N.3. Teteruck WR, Lundeen HC: The accuracy of an ear facebow dental laboratory cooperalJ Prosthet Denf96B 16:1039-1045. 638-641.4. Gross MD, Gazit E: Articulators used in North American den-tal schools. JDentEduc 1985; 49:710-711.5. Cowan RD. Sanchez RA, Chappell RP, Glaros AG, HaydenWJ: Verifying the reliability of interchanging casts with semi-adjustable articulators. Int J Prosthodont 1991; 4:258-264.
    • Chapter 6Treatment Planning for Single-Tooth RestorationsBy using cast metal, ceramic, and metal-ceramicrestorations, large areas of missing coronal toothstructure can be replaced while that which remainsis preserved and protected. Function can be restored,and where required, a pleasing esthetic effect can beachieved. The successful use of these restorations isbased on thoughtful treatment planning, which is mani-fested by choosing a restorative material and a restora-tion design that are suited to the needs of the patient. Ina time when production and efficiency are heavilystressed, it should be restated that the needs of thepatient take precedence over the convenience of thedentist.In what circumstances should cemented restorationsmade from cast metal or ceramic be used instead ofamalgam or composite resin restorations? The selectionof the material and design of the restoration is based onseveral factors:1 Destruction of tooth structure2. Esthetics3. Plaque control4. Financial considerations5. RetentionDestruction of tooth structure: If the amount of destruc-tion previously suffered by the tooth to be restored issuch that the remaining tooth structure must gainstrength and protection from the restoration, cast metal orceramic is indicated over amalgam or composite resin.Esthetics: If the tooth to be restored with a cementedrestoration is in a highly visible area, or if the patient ishighly critical, the cosmetic effect of the restoration mustbe considered. Sometimes a partial veneer restorationwill serve this function. Where full veneer coverage isrequired in such an area, the use of ceramic in someform is indicated. Metal-ceramic crowns can be used forsingle-unit anterior or posterior crowns, as well as forfixed partial dentures. All-ceramic crowns are most com-monly used on incisors, although they can be used onposterior teeth when an adequate bulk of tooth structurehas been removed and the patient is willing to accept thepossibility of more frequent replacement.Plaque control: The use of a cemented restorationdemands the institution and maintenance of a goodplaque-control program to increase the chances for suc-cess of the restoration. Many teeth are seemingly primecandidates for cast metal or ceramic restorations, basedsolely on the amount of tooth destruction that has previ-ously occurred. However, when these teeth are evaluat-ed from the standpoint of the oral environment, they may,in fact, be poor risks for cemented restorations. If exten-sive plaque, decalcification, and caries are present in amouth, the use of crowns of any kind should be carefullyweighed. The design of a restoration should take intoaccount those factors that will enable the patient to main-tain adequate hygiene to make the restoration success-ful. The patient must be motivated to follow a regimen ofbrushing, flossing, and dietary regulation to control oreliminate the disease process responsible for destructionof tooth structure It may be desirable to use pin-retainedamalgam "temporary" restorations to save the teeth untilthe conditions responsible for the tooth destruction canbe controlled. This will give the patient the time neces-sary to learn and demonstrate good oral self-care. It willalso permit the dentist and staff to reinforce the skillsrequired of the patient and to evaluate the patients will-ingness and ability to cooperate. If these measures provesuccessful, cast metal, ceramic, or metal-ceramicrestorations can be fabricated. Since these restorationsare used to repair the damage caused by caries and donothing to cure the condition responsible for the caries,they should not be used if the oral environment has notbeen brought under control.Financial considerations: Finances are a factor in alltreatment plans, because someone must pay for thetreatment. That "someone" may be a governmentagency, a branch of the military, an insurance company,and/or the patient. If the patient is to pay, give your bestadvice and then allow the patient to make the choice. Aconscientious dentist must walk a fine ethical line. On theone hand, you should not preempt the choice by select-ing a less than optimum restoration just because youthink that the patient cannot afford the preferred treat-ment. On the other hand, you also should be sensitiveenough to the individual patients situation to offer asound alternative to the preferred treatment plan and notapply pressure.Retention: Full veneer crowns are unquestionably themost retentive12(Fig 6-1). However, maximum retentionis not nearly as important for single-tooth restorations as
    • TreatmentPlanningtorSingle-ToothRestoratioiFig 6-1 A comparisontypes of crowns (P= .05)it is for fixed partial denture retainers It does become aspecial concern for short teeth and removable partialdenture abutments.Twelve restoration types are presented in the followingpages to provide a frame of reference for making a deci-sion whether to use a "plastic restoration" or a "cement-ed restoration." The "plastic restoration" is inserted as asoft, or plastic, mass into the cavity preparation, where itwill harden and be retained by mechanical undercuts oradhesion. The "cemented restoration," made of castmetal, metal and ceramic, or ceramic material alone, isfabricated away from the operatory and is luted in or onthe patients tooth at a subsequent appointment. Onetype can be better suited for a particular application thanthe other, or their suitabilities may overlap.Intracoronal RestorationsWhen sufficient coronal tooth structure exists to retainand protect a restoration under the anticipated stressesof mastication, an intracoronal restoration can beemployed. In this circumstance, the crown of the toothand the restoration itself are dependent upon thestrength of the remaining tooth structure to provide struc-tural integrity.Class lonomerSmall lesions where extensions can be kept minimal andwhere preparation retention will be minimal can berestored with this material. It is useful for restoring class5 lesions caused by erosion or abrasion (Fig 6-2). It alsocan be employed for incipient lesions on the proximalsurfaces of posterior teeth by use of a "tunnel" prepara-tion, which leaves the marginal ridge intact (Fig 6-3).Glass ionomer has found a niche in the restoration ofroot caries in geriatric and periodontal patients (Fig 6-4).An occlusal approach may be precluded by the pres-ence of an otherwise acceptable crown, or a convention-al restoration at such an apical level might require thedestruction of an unacceptable amount of tooth struc-ture. However, handpiece access may be too restrictedto create the needed retention for a small amalgamrestoration. Glass ionomer also lends itself to rapidplacement well enough to serve as an interim treatmentrestoration to assist in the control of a mouth with rampantcaries (Fig 6-5). This is further enhanced by the releaseof fluoride by the material.Composite Resinin esthetically critical areas (Fig 6-6). While it can beused in the restoration of incisal angles assisted by acidetching, a tooth that has received a class 4 resin restora-tion ultimately will require a crown.Composite resin has been used in the restoration ofposterior teeth with mined results. Sufficient abrasionresistance to prevent occlusal wear has b&en a problem.Also, unless the resin is carefully applied in small incre-ments, polymerization shrinkage will lead to leakage andultimately to failure. Its use probably should be restrictedicclusal restorations on firstpremolars.A technique devised to combat the problems of shrink-age and leakage is the fabrication of a composite resin .:inlay (Fig 6-7). This can be accomplished in the dental >office, using a fast-setting gypsum cast, or in a dental )laboratory. The resultant bench-polymerized inlay will •;have greater hardness, and the thin layer of resin used jfor affixing it to tooth structure will be less susceptible to |significant shrinkage at the margin than a restoration that Iis bulk cured in situ ]
    • IIntracoronal Restorationsireparaliun and gla^s ionomer can be used t(in incipient lesion on the proximal surface of a posterio
    • Treatment Planning for Single-Tooth RFig 6-7 Indirect inlays of composite ncan be used for proxtmo-occlusal restitions on posterior teeth.Simple AmalgamThe simple amalgam, without pins or other means of aux-iliary retention, for decades has been the standard one-to three-surface restoration for minor- to moderate-sizedlesions in esthetically noncritical areas (Fig 6-8). It hasreceived a "bum rap" from an ill-informed, sensationaliz-ing press in recent years. Approximately 100 million ormore simple amalgam restorations are placed annually.3They are best used where more than half of the coronaldentin is intact.Tooth preparation size for incipient lesions has dimin-ished in recent years as the concept of "extention for pre-vention" has waned. This move toward less destructivepreparations has been augmented by the developmentof smaller instruments and stronger amalgams.Nonetheless, even a minimal preparation for an amalgamrestoration significantly weakens the structural integrity ofthe tooth."Complex AmalgamAmalgam augmented by pins or other auxiliary means ofretention can be used to restore teeth with moderate tosevere lesions in which less than half of the coronaldentin remains (Fig 6-9) Amalgam used in this mannercan be employed as a final restoration when a crown iscontraindicated because of limited finances or poor oralhygiene. It can be used in the restoration of teeth withmissing cusps, or endodontically treated premolars andmolars—teeth that ordinarily would be restored withmesio-occluso-distal (MOD) onlays or other extracoronalrestorations. In such situations, amalgam is used toreplace or overlay the cusp to provide the protection ofocclusal coverage. It does produce good strength in therestored tooth.5Ideally, however, a crown should be con-structed over the pin-retained amalgam, using it as acore, or foundation restoration
    • Metal InlayMinor io moderate lesions on teeth where the estheticrequirements are low can be restored with this restorationtype (Fig 6-10) While usually made of softer gold alloys,metal inlays can also be fabricated of etchable basemetal alloys if a bonding effect is desired.67The prepa-ration isthmus should be narrow to minimize stress in thesurrounding tooth structure. Premolars should have oneintact marginal ridge to preserve structural integrity andminimize the possibility of coronal fracture.The additional bulk of tooth structure found in a molarpermits the use of this restoration type in an MOD con-figuration. The indications for this type of restoration aremuch the same as those for an amalgam, since thisrestoration only replaces lost tooth structure and will notprotect remaining tooth structure. Because of the amountof destruction of tooth structure required by this restora-tion, it is not recommended for incipient lesions.MOD OnlayThis design can be used for restoring moderately largelesions on premolars and molars with intact facial and lin-gual surfaces (Fig 6-12). It will accommodate a wide isth-mus and up to one missing cusp on a molar. If a castmetal restoration is needed on a premolar with both mar-ginal ridges compromised, it should include occlusalcoverage to protect the remaining tooth structure. Thisrestoration also can be considered an extracoronalrestoration because of the occlusal coverage that over-lays and protects the tooth cusps.The MOD onlay does not have the necessary resis-tance to be used as a fixed partial denture retainer.Although ordinarily fabricated of a gold alloy, this restora-tion design has been used with cast glass and othertypes of ceramics. Ceramic MOD onlays should be usedvery cautiously. Without generous occlusal thickness,these restorations are susceptible to fracture.Ceramic InlayThis restoration is utilized to restore teeth with minor- tomoderate-sized lesions that will permit a narrow prepara-tion isthmus in an area of the mouth where the estheticdemand is high (Fig 6-11). Premolars should have oneintact marginal ridge, but MOD ceramic inlays can beused in molars Because this type of restoration can alsobe etched to enhance bonding, there is some evidencethat the structural integrity of the tooth cusps may be sta-bilized by bonding.8The relatively large size of the cavi-ty preparation required for this restoration mitigates itsuse in the treatment of incipient lesions.Extracoronal RestorationsIf insufficient coronal tooth structure exists to retain therestoration within the crown of the the tooth, an extra-coronal restoration, or crown, is needed. It may also beused where there are extensive areas of defective axialtooth structure, or if there is a need to modify contours torefine occlusion or improve esthetics.
    • Treatment Planning lor Single-Tooth RestoiPartial Veneer CrownThis is a crown that leaves one or more axial surfacesunveneered (Fig 6-13). Therefore, it can be used torestore a tooth with one or more intact axial surfaces withhalf or more of the coronal tooth structure remaining. Itwill provide moderate retention and can be used as aretainer for short-span fixed partial dentures. If toothdestruction is not excessive, a partial veneer crown witha minimally extended preparation and carefully finishedmargins can satisfy moderate esthetic demands in themaxillary arch.Full Metal CrownThe conventional full crown can be used to restore teethwith multiple defective axial surfaces (Fig 6-14). It willprovide the maximum retention possible in any given sit-uation, but its use must be restricted to situations wherethere are no esthetic expectations. This will usually limitit to second molars, some mandibular first molars, andoccasionally mandibular second premolars. Becauseless tooth structure must be removed for its preparationthan for crowns with a ceramic component, and its fabri-cation is the simplest of any crown, this restorationshould remain among those designs considered in plan-ning single-tooth restorations on molars as well as pos-terior fixed partial dentures.Metal-Ceramic CrownThis crown can also be used to restore teeth with multi-ple defective axial surfaces (Fig 6-15). It too is capableof providing maximum retention, but it also will meet highesthetic requirements. It can be used as a fixed partiadenture retainer where full coverage and a good cosmetic result must be combined.All-Ceramic CrownWhen full coverage and maximum esthetics must becombined, this crown is the choice (Fig 6-16). All-ceram-ic crowns are not as resistant to fracture as metal-ceram-ic crowns, so their use must be restricted to situationslikely to produce low to moderate stress. They are usual-ly used for incisors, although cast glass ceramics arealso employed in the restoration of posterior teeth.Preparations for this type of restoration on premolars andmolars do require the removal of large quantities of toothstructure.Ceramic VeneerBecause all-ceramic and metal-ceramic crowns requirethe removal of such large quantities of tooth structure,there has been considerable interest in less destructivealternatives. The ceramic veneer has emerged as ameans of producing a very cosmetic result on otherwiseintact anterior teeth that are marred by severe staining ordevelopmental defects restricted to the facial surface ofthe tooth (Fig 6-17). This restoration also can be used torestore moderate incisal chipping and small proximallesions. The use of a veneer requires only a minimumtooth preparation, so it offers an alternative to crownsthat is attractive to patient and dentist alike.The features and capabilities of the 12 types of single-tooth restorations described in this chapter are shown inTable 6-1.
    • Table 6-1 Attributes of Single-Tooth RestorationsClass 5 Nn JamalgamMetal inlayinlayMOD onlay Moderate tLargeLargeLargeLargeLargePoor toAdequate-Poor toAdequatePoor toAdequate*ClasModerateGoodGoodNo§No§NoNoAdequateClass 2 PoorClass 2 AdequateGood NoGoodGoodAdequatePoorPoorGoodGoodGoodClass 5 NoAll | Yec-tClass 5 NoClass 5 NrNo YesSMayof
    • it Planning for Single-Tooth Restor18—|16-8 14-£ 12-CO 10-Type of RestorationFig 6-18 Comparison of the estimatedlongevity of 12 types of restorations, basedon a survey of 36 dentists. ANOVA was per-formed, with P= .OS. G1R = glass-ionomerrestoration, COM = composite resin restora-tion, VEN = ceramic veneer, CIN = ceramicinlay, ACC = all-ceramic crown, CAM =complex amalgam restoration, MCR =metal-ceramic crown, MIN = metal inlay,PVC = partial veneer crown, SAM = simpleamalgam restoration, MOD = metal MODonly, FMC =fufl metal crown.Restoration LongevityEvery dentist would like to be able to answer the patientsquestion, "How long will my restoration last?" Logicalthough this question may be, unfortunately it is impossi-ble to answer directly. We cannot predict the life span ofa pair of shoes or a television set, and these everydayitems are not custom made, nor do they perform theirservice in a hostile biological environment, submerged inwater.Clinical studies of restoration longevity have producedwidely disparate figures. As a general rule, cast restora-tions will survive in the mouth longer than amalgamrestorations, which in turn will last longer than compositeresin restorations.9A compilation of five studies of 676patients concluded that amalgam restorations exhibit a50% failure rate between 5.5 and 11.5 years, with anextrapolated life expectancy of 10 to 14 years.10Meeuwissen et al11reported a 10-year survival rate of58% for amalgam restorations in Dutch military patients;Arthur et al1?reported an 83% survival rate for the same
    • Restoration Longevitymtime span in a US military population. Qvist et al13foundthat 50% of the amalgam restorations in a group ofDanish patients had failed at 7.0 years. Christensen14estimated a 14-year longevity for amalgam restorations.In selected populations, amalgam restorations ofunspecified types or sizes in one study9have shown 10-year survival rates as high as 72.0%. A 15-year survivalrate of 72 8% was reported for simple amalgams inanother study.15A survey of 571 fixed prosthodontists, nonspecialistrestorative dentists, and dental school faculty projectedan average life span of 11 2 years for simple amalgamsand 6.1 years for complex amalgams.16In fact, onegroup of 125 complex amalgams was reported to have a76% survival rate at 15 years,15while another group of171 complex amalgam restorations exhibited a 50% sur-vival rate at 11.5 years.17Composite resin restorations have not been includedm many longevity studies. A study of dental schoolpatients did incorporate them, reporting a 10-year sur-vival rate of 55.9%.9Another report, done on a generalpatient population, described a shorter life span for com-posite resin restorations, with 50% of them having failedin 6.1 years.18Mount1* disclosed an overall success rate of 93% for1,283 glass-ionomer restorations for up to 7 years, withthe rate varying from 2% to 36% depending on the classof cavity and the brand of cement. In that study, thepatients evaluated had been treated by only two dentists,and not all of the restorations had been in place for thefull 7-year span of the study While promising, these fig-ures must be assessed cautiously until longer studies ofa broader population have been completed.Schwartz et al, after studying a group of 791 failedrestorations, reported mean life spans, at failure, of 10.3years for full crowns, 11.4 years for three-quarter crowns,and 8.5 years for porcelain jacket crowns (anterior all-ceramic crowns). The mean life span for all fixed prostho-dontic restorations was 10.3 years.™ Walton and associ-ates, evaluating a group of 424 restorations, found fullcrowns lasting 7.1 years, partial veneer crowns 14.3years, metal-ceramic crowns 6.3 years, inlays and onlays11.2 years, and porcelain jacket crowns 8.2 years 31The dentists responding to Christensens survey esti-mated the longevity of crowns to be from 21 to 22years.14The estimates supplied by the respondents to asurvey by Maryniuk and Kaplan were 12.7 years formetal-ceramic crowns and 14.7 years for all-gold restora-tions.16Kerschbaum, examining German insurancerecords, found 91.5% of gold crowns still in the mouthafter 8 years.KIn a review of records in 40 Dutch dentaloffices, Leempoel et al told of 10-year survival rates of98% and 95.3% for full crowns and metal-ceramicSeveral of the restorations described in this chapterhave not been in widespread use for a long enough peri-od of time to have been included in longevity studies.Thirty-six restorative dentists and prosthodontists with amean experience of 19.2 years were surveyed to providea basis for estimates of the life expectancies of some ofthe newer restorations discussed in this chapter (Fig 6-18).24The longevities given are only opinions, based onextensive experience with some restoration types andonly limited experience with others. A compilation oflongevities from this survey and from other studies citedin this chapter is presented in Table 6-2.The question of longevity is an important one to con-sider when deciding on treatment for a patient. The moredestructive the preparation required for the restoration,the greater the potential risk tor the tooth, and ultimatelythe greater expense It has been estimated that if a crownwere placed in a patients mouth at age 22, at a fee of$425, attendant sen/ices and replacements of that crownwill have cost the patient nearly $12,000 considering anaverage life expectancy of 75 years.25
    • Table 6-2 Longevity of Single-Tooth RestorationsType of No. ofInvestigatot(s) study respondentsComposite Simple Complex_50%at 6.110 to 14yea58.0%at10yea10 yea s50at 7 0Marymuk andKaplan1Robtains andSummit17Mount96 1ears50%t 11.512.7years_Kersctibaum22ClinicalLeempoel et al?3ClinicalShiilingburg-1Survey
    • References1. Potts RG, Shillmgburg HT, DuncEresistance ol preparations for ca:Oenf1980; 43:303-307.2. Kishimoto M, Shillingbutg HT, Durprepar retentiMOD onlays. J Prosthet Dent 1<3, JW: In defer sofaiinson MG: Influermd resistance F13, 49:35-39.gam. Oper Dent 199o MF, Soars4. Mondelli J, Steagall I, Ishikiriama A, NaviFracture strength of human teeth with cavity preparations JProsthet Dent 1980, 43:419.5. Reagan SE, Scriwandt NW, Duncanson MG: Fracture resis-with and without amalgam cuspal coverage. QuintessenceInf989; 20469-472.6. Kent WA, Shillingburg HT, Duncanson MG, Nelson EL:Fracture resistance of ceramic inlays with three luting mate-rials. J Dent Res 1991; 70:561.7. Livaditis GJ: Etched metal resin-bonded intracoronal castrestorations. Part II: Design criteria for cavity preparation. JProsthet Dent 1986; 56:389-395.8. Bodell RW, Kent WA, Shillingburg HT, Duncanson MG:Fracture resistance of intracoronal metallic restorations andthree luting materials. J Dent Res 1991, 70.562.9. Bentley C, Drake CW: Longevity of restorations in a dentalschool Clinic. J Dent Educ 1985; 50:594-600.10. Maryniuk GA: In search of treatment longevity—A 30-yearperspective. JAm DentAssoc 1984; 109:739-744.11. Meeuwissen R, Elteren P, Eschen S, Mulder J: Durability ofamalgam restorations in premolars and molars in Dutch ser-vicement. Community Dent Health 1985; 2:293-30212. Arthur JS, Cohen ME, Diehl MC: Longevity of restorations ina U.S. military population. J Dent Res 1988; 67:388.i. Qvist V, Thylstrup A, M|oand longevity of amalgarr1986; 44:343-349.k Christensen GJ: The practicability of compacted golds ingeneral practice—A survey. J Colo Dent Assoc 1971; 49:18-22.j Smales RJ. Longevity of cusp-covered amalgams: Survivalsafter 15 years. Oper Den! 1991; 16:17-20.!. Maryniuk GA, Kaplan SH: Longevity of restorations: Surveyresults of dentists estimates and attitudes JAm DentAssoc1986; 112:39-45. Robbins JW, Summit! JB. Longevity of complex amalgamrestorations. Oper Dent 1988; 13:54-57.!. Qvist V, Thylstrup A, Mjorand longevily of resin rt1986; 44:351-356.!. Mount GJ: Longevity of glass ionomer cements. J ProsthetDenM986; 55:682-685.) Schwartz NL, Whitsett LD, Berry TG, Stewart JL:Unserviceable crowns and fixed partial dentures: life spanand causes for loss of serviceability. JAm Dent Assoc 1970;811395-1401. Walton JN, Gardner FM, Agar JR: A survey of crown andfixed partial denture failures: Length of service and reasonsfor replacement. J Prosthet DenM986; 56:416-421.! Kerschbaum T. Uberlebenzeiten von kronen- und bruckenzahneratz heute. Zahnaertzi Mitt 1986; 76:2315-2320.i. Leempoel PJB, de Haan AFJ, Reintjes AGM: The survivalrate of crowns in 40 Dutch practices J Dent Res 1986;65:565.I. Shillingburg HT: Unpublished research>. Cohen BD, Milobsky SA: Monetary damages in dental-miurycases Trial Lawyers Quarterly 1989; 20 80-81.
    • Chapter 7Treatment Planning for theReplacement of Missing TeethThe need for replacing missing teeth is obvious tothe patient when the edentulous space is in theanterior segment of the mouth, but it is equallyimportant in the posterior region. It is tempting to think ofthe dental arch as a static entity, but that is certainly notthe case. It is in a state of dynamic equilibrium, with theteeth supporting each other (Fig 7-1). When a tooth islost, the structural integrity of the dental arch is disrupt-ed, and there is a subsequent realignment of teeth as anew state of equilibrium is achieved. Teeth adjacent to oropposing the edentulous space frequently move into it(Fig 7-2). Adjacent teeth, especially those distal to thespace, may drift bodily, although a tilting movement is afar more common occurrence.If an opposing tooth intrudes severely into the edentu-lous space, it is not enough just to replace the missingtooth (Fig 7-3). To restore the mouth to complete function,free of interferences, it is often necessary to restore thetooth opposing the edentulous space (Fig 7-4). In severecases, this may necessitate the devitalization of thesupererupted opposing tooth to permit enough shorten-ing to correct the plane of occlusion.Selection of the Type of ProsthesisMissing teeth may be replaced by one of three prosthe-sis types: a removable partial denture (RPD), a tooth-supported fixed partial denture (FPD), or an implant-sup-ported fixed partial denture (Table 7-1). Several factorsmust be weighed when choosing the type of prosthesisto be used in any given situation. Biomechanical, peri-odontal, esthetic, and financial factors, as well as thepatients wishes, are some of the more important ones. Itis not uncommon to combine two types in the same arch,such as a removable partial denture and a tooth-sup-ported fixed partial denture, or implant-supported andtooth-supported fixed partial dentures.In treatment planning, there is one principle that shouldbe kept in mind: treatment simplification. There are manytimes when certain treatments are technically possiblebut too complex. Something must be done to cut throughthe possibilities and come up with a recommendationthat will serve the patients needs and still be reasonableto accomplish. At such times, the restorative dentist, orprosthodontist, is the one who should manage thesequencing and referral to other specialists. He or shewill be finishing up the treatment and should act as "thequarterback." Communicate and be open to sugges-tions, but dont allow someone else to dictate the restora-tive phase of the treatment, leaving you with a treatmentplan you do not think will work. You will be doing therestoration and the patient will return to you if it fails, sobe sure you are comfortable with the planned treatment.The following guidelines are not "laws," and they are notabsolute. However, when a preponderance of theseitems is used in the consideration of the planning for onearch or one mouth, a more compelling reason exists forthe selection of the type of prosthesis described.Removable Partial DentureA removable partial denture is generally indicated foredentulous spaces greater than two posterior teeth, ante-rior spaces greater than four incisors, or spaces thatinclude a canine and two other contiguous teeth; ie, cen-tral incisor, lateral incisor, and canine; lateral incisor,canine, and first premolar; or the canine and both pre-molars.An edentulous space with no distal abutment will usu-ally require a removable partial denture. There areexceptions in which a cantilever fixed partial denture canbe used, but this solution should be approached cau-tiously. See the section on cantilevers later in the chapterfor a more detailed description of this type of restoration.Multiple edentulous spaces, each of which may berestorable with a fixed partial denture, nonetheless maycall for the use of a removable partial denture because ofthe expense and technical complexity. Bilateral edentu-lous spaces with more than two teeth missing on oneside also may call for the use of a removable prosthesisinstead of two fixed prostheses.The requirements of an abutment for a removable par-tial denture are not as stringent as those for a fixed par-tial denture abutment. Tipped teeth adjoining edentulousspaces and prospective abutments with divergent align-
    • Treatment Planning for the Replacement of Missing Teethinbetweenteeth(Lments may lend themselves more readily to utilization asRPD rather than FPD abutments. Periodontally weakenedprimary abutments may serve better in retaining a well-designed removable partial denture than in bearing theload of a fixed partial denture. It is also possible todesign the partial denture framework so that retentiveclasps will be placed on teeth other than those adjacentto the edentulous space.Teeth with short clinical crowns or teeth that are justgenerally short usually will not be good FPD abutmentsfor anything other than a single pontic prosthesis. Aninsufficient number of abutments may also be a reason forselecting a removable rather than a fixed partial denture.If there has been a severe loss of tissue in the edentu-lous ridge, a removable partial denture can more easilybe used to restore the space both functionally andesthetically. For successful removable partial denturetreatment, the patient should demonstrate acceptableoral hygiene and show signs of being a reliable recallcandidate.
    • Table 7-1 Replacement of Missing TeethRemovable partial dentilImplant-supported fixed pard l• Posterior spans longer thanteeth• Anterior spans longer thanSpan configurateAbutment alignmeAbutment conditicOcclusionPeriodontal condilRidge formGeneral featuresteethn " N o distal abutment• Multiple or bilateral edentulousspaces;nt • Tipped abutments can betolerated• Widely divergent abutmentalignment>n • Short clinical crowns• Insufficient abutments• More adaptable to irregularities ina healthy opposing natural dentitionion • Can use alternate (secondaryabutments) when primaryabutments are weakened• Gross tissue loss in residual ridge• Dry mouth poor RPD risk• Limited patient finances• Acceptable oral hygiene• Reliable recall candidate• Treatment simplification• Advanced age• Systemic health problems• More adaptable to dentition intransition to edentulous state• Usually has distal abutmentbut can be used with shortcantilever pontic• Less than 25° inclination canbe accommodated bypreparation modification• Good if abutments need crowns• Nonvital teeth can be used if thereis sufficient coronal tooth structure• Favorable loading (magnitude,direction, frequency, duration]• Good alveolar bone support• Crown-root ratio 1:1 or better• No mobility* Favorable root morphology* Provides rigid stabilization• Moderate resorption• No gross soft tissue defects• Dry mouth high caries risk• Muscular discoordination• Mandibular tori• Palatal soft tissue lesions• Large tongue• Exaggerated gag reflex• Unfavorable attitude toward RPD• Patient cant cope with aging,• Favorable opposing occlusion.removable prosthesis orperiodontally weakened naturaldentition may permit FPD in lesstfian optimal situations• Must be within dentists skills• Abutments mesial and distalto pontic• Less than 15° inclinationmesiodistally• Should be in same faciolingual plane• Preparations are not easily modifiedbecause of minimal reduction• Defect-free abutments• Incisor, premolar replacements• Cannot be used for incisorreplacement in presence of deepvertical overlap• No mobility• Periodontal splints (with auxiliaryresistance in tooth preparation)• Moderate resorption• No gross soft tissue defects• Well suited for young patients• Can be used for replacingmolars if masticatory musclesare not too well developed• No distal abutment• Pier in 3 + pontic span• All abutments at ends and aspier(s) of long span• Need for implant/abutmentalignment requires closecoordination between surgeonand restorative dentist• Defect-free abutmentsrequiring no restoration• Occlusal forces must be asnearly vertical as possible toprevent unfavorable lateralloadinq of implants• Dense bone• Broad, flat ridge• Able to survive in dry mouth• May be better choice if teethwill require extensive treatmentand will still be weakquestionable abutments• Unfavorable attitude towardRPD• Must be within dentists skills
    • TreatmentPlanning tor the Repla<Patients oi advanced age who are on fixed incomes orhave systemic health problems may require special treat-ment simplification efforts, either to cut down on theamount of appointment time required to restore themouth or to make the treatment affordable Cajolingpatients of limited means into overinvesting theirresources is not in their best interestA large tongue is a good reason to avoid a removableprosthesis if at all possible, as is muscular discoordina-lion. An unfavorable attitude toward a removable partialdenture also makes it a poor choice.Conventional Tooth-SupportedFixed Partial DentureWhen a missing tooth is to be replaced, a fixed partialdenture is preferred by the majority of patients. The usualconfiguration for a fixed partial denture utilizes an abut-ment tooth on each end of the edentulous space to sup-port the prosthesis. If the abutment teeth are periodon-tally sound, the edentulous span is short and straight,and the retainers are well designed and executed, thefixed partial denture can be expected to provide a longlife of function for the patient. Several factors have aninfluence on the decision whether to fabricate a fixedpartial denture, what teeth to use as abutments, and whatretainer designs to use (see Table 7-1).There should be no gross soft tissue defect in theedentulous ridge. If there is, it may be possible to aug-ment the ridge with grafts to enable the construction of afixed prosthesis This treatment is reserved for patientswho are both highly motivated and able to afford this spe-cial procedure. If this is not the case, a removable partialdenture should be considered.A dry mouth creates a poor environment for a fixedpartial denture. The margins of the retainers will be atgreat risk from recurrent caries, limiting the life span ofthe prosthesis. However, an absence of moisture in themouth also will hinder the successful wearing of a remov-able partial denture. In either case, the patient must bemade aware of the high risk involved. The risk may beminimized through home fluoride application and fre-quent recall, but it cannot be eliminated.Resin-Bonded Tooth-SupportedFixed Partial DentureThe resin-bonded fixed partial denture is a conservativerestoration that is reserved for use on defect-free abut-ments in situations where there is a single missing tooth,usually an incisor or premolar. A single molar can bereplaced by this type of prosthesis if the patients mus-cles of mastication are not too well developed, thusassuring that a minimum load will be placed on theretainers The resin-bonded fixed partial denture requiresan abutment both mesial and distal to the edentulousspace.This prosthesis utilizes a standard pontic form, accom-modating an edentulous ridge with moderate resorptionand no gross soft tissue defects. Because it requires ashallow preparation that is restricted to enamel, the resin-bonded fixed partial denture is especially useful inyounger patients whose immature teeth with large pulpsare poor risks for endodontic-free abutment preparations.Tilted abutments can be accommodated only if there isenough tooth structure to allow a change in the normalalignment of axial reduction. This is limited by the need torestrict most of the reduction to enamel. Rarely can amesiodistal difference in abutment inclination greaterthan 15 degrees be accommodated. There can be littleor no difference in the inclination of the abutments facio-lingually.The resin-bonded prosthesis cannot be used forreplacing missing anterior teeth where there is a deepvertical overlap. Reduction deep into the underlyingdentin of the abutment teeth will be required in this situa-tion, so a conventional fixed partial denture should beemployed.Although this type of prosthesis has been described forperiodontal splints, it should be used with extreme care inthose situations. Preparations will demand additionalresistance features, such as long, well-defined grooves.Abutment mobility has been shown to be a serious haz-ard in the successful use of this type of restoration.Implant-Supported Fixed Partial DentureFixed partial dentures supported by implants are ideallysuited for use where there are insufficient numbers ofabutment teeth or inadequate strength in the abutmentsto support a conventional fixed partial denture, and whenpatient attitude and/or a combination of intraoral factorsmake a removable partial denture a poor choice,Implant-supported fixed partial dentures can beemployed in the replacement of teeth when there is nodistal abutment. Span length is limited only by the avail-ability of alveolar bone with satisfactory density andthickness in a broad, flat ridge configuration that will per-mit implant placement.A single tooth can be replaced by a single implant,saving defect-free adjacent teeth from the destructiveeffects of retainer crown preparations. A span length oftwo to six teeth can be replaced by multiple implants,either as single-unit restorations or as implant-supportedfixed partial dentures. An implant can be used as a pierin an edentulous span three or more teeth long. There issome risk involved in using an immovable implant abut-ment in the same rigid prosthesis with natural teeth. Insuch a situation, it is preferred that implants serve as theabutments at both ends and as the pier(s) of a long span.In fact, an entire arch can be replaced by an implant-supported complete prosthesis, but that type of restora-tion lies outside the realm of this discussion.
    • AbutmentEvstu&tio*The retainers used for most implant systems require agreater degree of abutment alignment precision than dothe retainers for a tooth-supported fixed partial denture.If implants are placed by someone other than the restor-ing dentist, implant/abutment alignment demands closecoordination between surgeon and restorative dentist.The abutments should be positioned so that the occlusalforces will be as nearly vertical to the implants as possi-ble to prevent destructive lateral forces.Implants should be better able than natural teeth tosurvive in a dry mouth Implants may be a better choicefor FPD abutments if prospective tooth abutments willrequire endodontic therapy with or without dowel cores,periodontal surgery, and possibly root resections to sup-port a long-span, complex, and expensive prosthesiswhose success is dependent on "feet of clay."No Prosthetic TreatmentIf a patient presents with a long-standing edentulousspace into which there has been little or no drifting orelongation of the adjacent or opposing teeth, the ques-tion of replacement should be left to the patients wishes.If the patient perceives no functional, occlusal, or esthet-ic impairment, it would be a dubious service to place aprosthesis. This in no way contradicts the recommenda-tion that a missing tooth routinely should be replaced.The teeth adjoining an edentulous space usually move,but they do not always move. When you meet the occa-sional patient who has beaten the odds, recognize it forwhat it is, congratulate the patient for being fortunate,and tend to his or her other needs.Case PresentationIn cases where the choice between a fixed partial den-ture and a removable partial denture is not clear cut, twoor more treatment options should be presented to thepatient along with their advantages and disadvantages.The dentist is in the best position to evaluate the physicaland biological factors present, while the patients feelingsshould carry considerable weight on matters of estheticsand finances.Both dentist and patient must agree on the definitivetreatment plan. If the patient understands and is willing toaccept the risks associated with treatment that is yoursecond choice, it is prudent to make a notation to thateffect and have it signed by the patient. If you are con-vinced that a particular type of treatment is absolutelywrong for a given situation, try to educate the patient tothe reasons for your opinion. If the patient remainsunconvinced, you would do well to refer the patient tosomeone else. Life is too short for the aggravation thatmay follow if you do not.Abutment EvaluationEvery restoration must be able to withstand the constantocclusal forces to which it is subjected. This is of partic-ular significance when designing and fabricating a fixedpartial denture, since the forces that would normally beabsorbed by the missing tooth are transmitted, throughthe pontic, connectors, and retainers, to the abutmentteeth. Abutment teeth are therefore called upon to with-stand the forces normally directed to the missing teeth, inaddition to those usually applied to the abutments.If a tooth adjacent to an edentulous space needs acrown because of damage to the tooth, the restorationusually can double as an FPD retainer. If several abut-ments in one arch require crowns, there is a strong argu-ment for the selection of a fixed partial denture ratherthan a removable partial denture.Whenever possible, an abutment should be a vitaltooth. However, a tooth that has been endodonticallytreated and is asymptomatic, with radiographic evidenceof a good seal and complete obturation of the canal, canbe used as an abutment. However, the tooth must havesome sound, surviving coronal tooth structure to insurelongevity. Even then, some compensation must be madefor the coronal tooth structure that has been lost. This canbe accomplished through the use of a dowel core, or apin-retained amalgam or composite resin core.Teeth that have been pulp capped in the process ofpreparing the tooth should not be used as FPD abut-ments unless they are endodontically treated. There istoo great a risk that they will require endodontic treatmentlater, with the resultant destruction of retentive toothstructure and of the retainer itself. This is a situation thatis better handled before the fixed partial denture is made.The supporting tissues surrounding the abutment teethmust be healthy and free from inflammation before anyprosthesis can be contemplated. Normally, abutmentteeth should not exhibit mobility, since they will be carry-ing an extra load. The roots and their supporting tissuesshould be evaluated for three factors:1. Crown-root ratio3. Periodontal ligament areaCrown-Root RatioThis ratio is a measure of the length of tooth occlusal tothe alveolar crest of bone compared with the length ofroot embedded in the bone. As the level of the alveolarbone moves apically, the lever arm of that portion out ofbone increases, and the chance for harmful lateral forcesis increased. The optimum crown-root ratio for a tooth tobe utilized as a fixed partial denture abutment is 2:3. Aratio of 1 • 1 is the minimum ratio that is acceptable for aprospective abutment under normal circumstances (Fig7-5).
    • Trosttvcnt Planning for the Rept3C6ffl6nt of Missing Tesn fDhAf (7)rBFig 7-6 Although the root surface area of these tethe toot configuration ofthe maxillary premolar (A), faciolingual dimension, makes it a superior abutmei MAVABHowever, there are situations in which a crown-rootratio greater than 1:1 might be considered adequate. Ifthe occlusion opposing a proposed fixed partial dentureis composed of artificial teeth, occlusal force will bediminished, with less stress on the abutment teeth Theocclusal force exerted against prosthetic appliances hasbeen shown to be considerably less than that againstnatural teeth: 26.0 Ib for removable partial dentures and54.5 Ib for fixed partial dentures versus 150 0 Ib for nat-For the saithan desirabl;, an abutment tooth with a lessfully support a fixed partial denture if the opposing occlu-sion is composed of mobile, periodontally involved teeththan if the opposing teeth are periodontally sound. Thecrown-root ratio alone is not an adequate criteria for eval-uating a prospective abutment tooth/Root ConfigurationThis is an important point in the assessment of an abut-ments suitability from a periodontal standpoint. Roots
    • Fig 7-8 Comparative root surfaceareas of maxillary teeth. The figure inparentheses above each tooth is theratio between the root surface area ofthe respective tooth and the root surfacearea of the smallest tooth in the arch, thelateral incisor (based on data by4 5 0 ROOT SURFACE AREAS ^ ^4003503 250g 200S 15010050OF MAXILLARY TEETH273(1.5) ?*i- 20411.1) 179Mu(l.Q)f]hu1 1 111 2 2 0pii^i, (1.2)/IHO1f1^/]/ l HA >•.01nFig 7-9 Comparative root surtaareas of mandibular teeth. The figureparentheses above each toothratio between the root surfacethe respective tooth and the rootarea of the smallest tooth in the acentral incisor (based on dJepsen^).thech, the„ 350i1 150100ROOT SURFACE AREAS „ nl ,1,2oiOF MAND BULAR TEETH268(1.7)168154 n , .(1.0)n11/_:-nli207ISO (1.3)(1.2)1QU0—-—IN——that are broader labiolingually than they are mesiodtstal-ly are preferable to roots that are round in cross section(Fig 7-6). Multirooted posterior teeth with widely separat-ed roots will offer better periodontal support than rootsthat converge, fuse, or generally present a conical con-figuration (Fig 7-7). The tooth with conical roots can beused as an abutment for a short-span fixed partial den-ture if all other factors are optimal. A single-rooted toothwith evidence of irregular configuration or with some cur-vature in the apical third of the root is preferable to thetooth that has a nearly perfect taperPeriodontal Ligament AreaAnother consideration in the evaluation of prospectiveabutment teeth is the root surface area, or the area ofperiodontal ligament attachment of the root to the bone.Larger teeth have a greater surface area and are betterable to bear added stress. The areas of the root surfacesof the various teeth have been reported by Jepsen,3andare shown in Figs 7-8 and 7-9. The actual values are notas significant as the relative values within a given mouthand the ratios between the various teeth in one arch.When supporting bone has been lost because of peri-
    • jfPlanningfortheReplaceFig 7-10 The combined rootand the second molar (fyp+molar being replaced (Aiplj).., ...^ _^cond premolairthan that of the firsiFig 7-11 The combined root sand the second molar aoutmerequal to that of the teeth being n-face area of the first premolar1<A1p+A2m) isapproximatelyFig 7-12 The combined root surface area of the canine and secondmolar {Ac+A2m) isexceeded by that of the teeth being replaced^TD+ J^2D+^1m^Afixedpartialdenturewouldbeapoorriskinthisodontal disease, the involved teeth have a lessenedcapacity to serve as abutments. Millimeter per millimeter,the loss of periodontal support from root resorption isonly one-third to one-half as critical as the loss of alveo-lar crestal bone.4The planned treatment should take thisinto account.The length of the pontic span that can be successfullyrestored is limited, in part, by the abutment teeth andtheir ability to accept the additional load Traditionally,there has been general agreement on the number ofmissing teeth that can be restored successfully. Tylmanstated that two abutment teeth could support two pon-tics.^ In a statement designated as "Antes Law" byJohnston et al,ethe root surface area of the abutmentteeth had to equal or surpass that of the teeth beingreplaced with pontics.7According to this premise, one missing tooth can besuccessfully replaced if the abutment teeth are healthy(Fig 7-10). If two teeth are missing, a fixed partial dentureprobably can replace the missing teeth, but the limit isbeing approached (Fig 7-11). When the root surface areaof the teeth to be replaced by pontics surpasses that ofthe abutment teeth, a generally unacceptable situationexists (Fig 7-12).It is possible for fixed partial dentures to replace morethan two teeth, the most common examples being ante-rior fixed partial dentures replacing the four incisors.Canine to second molar fixed partial dentures also arepossible (if all other conditions are ideal) in the maxillaryarch, but not as often in the mandibular arch. However,any fixed prosthesis replacing more than two teethshould be considered a high risk.As a clinical guideline, there is some validity in theconcept referred to as "Antes Law." Fixed partial den-tures with short pontic spans have a better prognosisthan do those with excessively long spans. It would be anoversimplification to attribute this merely to overstressingof the periodontal ligament, however. Failures fromabnormal stress have been attributed to leverage andtorque rather than overload Biornechamcal factors andmaterial failure play an important role in the potential forfailure of long-span restorations.
    • Biomechanical ConsideratiThere is evidence that teeth with very poor penodontalsupport can serve successfully as fixed partial dentureabutments in carefully selected cases. Teeth with severebone loss and marked mobility have been used as fixedpartial denture and splint abutments.8Elimination ofmobility is not the goal in such cases, but rather the sta-bilization of the teeth in a status quo to prevent anincrease of mobility.9Abutment teeth in these situations can be maintainedIree of inflammation in the face of mobility, if the patientsare well motivated and highly proficient in plaqueremoval.10Crowns that anchor rigid prostheses to mobileteeth do require greater retention than do crownsattached to relatively immobile abutments, however.11Follow-up studies of these patients with "terminal denti-tions" indicate a surprisingly low failure rate—less than8% of 332 fixed partial dentures exhibited technical fail-ure in a time span that averaged slightly more than 6years. 2What is the impact of the success of this type of treat-ment on fixed partial dentures for the average patient?The successful restoration of mouths with severe peri-odontal disease does have significance in everydaypractice. It emphasizes the extreme importance of care-fully evaluating the strengths and weaknesses of theremaining dentition on an individual basis.This should not be a signal for every dentist with ahandpiece to start using severely periodontally involvedteeth as abutments. Bear in mind that the successfultreatments that have been cited are of the work of well-trained and highly skilled clinicians on selected, highlymotivated patients.This type of heroic treatment Cherodontics," if you will)is very demanding technically, and expensive as well.Performed by a well-trained, skilled clinician on aninformed, motivated patient who dreads tooth loss, under-stands the patients role in the success of the treatment,and accepts the risk (and expense) of failure, it can be agood service. "Sold" by a practitioner without specialqualifications to an unmotivated and ill-informed patient,this type of treatment easily could result in a lawsuit.Biomechanical Considerationsin addition to the increased load placed on the peri-odontal ligament by a long-span fixed partial denture,longer spans are less rigid Bending or deflection variesdirectly with the cube of the length and inversely with thecube of the occlusogingival thickness of the pontic.Compared with a fixed partial denture having a single-tooth pontic span (Fig 7-13), a two-tooth pontic span willbend 8 times as much (Fig 7-14). A three-tooth pontic willbend 27 times as much as a single pontic (Fig 7-15).13A pontic with a given occlusogingival dimension willbend (Fig 7-16) eight times as much if the pontic thick-ness is halved (Fig 7-17). A long-span fixed partial den-ture on short rnandibular teeth could have disappointingresults Longer pontic spans also have the potential forproducing more torquing forces on the fixed partial den-ture, especially on the weaker abutment. To minimize flex-ing caused by long and/or thin spans, pontic designs witha greater occlusogingival dimension should be selected.The prosthesis may also be fabricated of an alloy with ahigher yield strength, such as nickel-chromium.All fixed partial dentures, long or short, flex to someextent. Because of the forces being applied through thepontics to the abutment teeth, the forces on castingsserving as retainers for fixed partial dentures are differentin magnitude and direction from those applied to singlerestorations.14The dislodging forces on a fixed partialdenture retainer tend to act in a mesiodistal direction, asopposed to the more common buccolingual direction olforces on a single restoration. Preparations should bemodified accordingly to produce greater resistance andstructural durability. Multiple grooves, including some onthe buccal and lingual surfaces, are commonlyemployed for this purpose (Fig 7-18).Double abutments are sometimes used as a means ofovercoming problems created by unfavorable crown-rootratios and long spans. There are several criteria that mustbe met if a secondary (remote from the edentulousspace) abutment is to strengthen the fixed partial dentureand not become a problem itself. A secondary abutmentmust have at least as much root surface area and asfavorable a crown-root ratio as the primary (adjacent tothe edentulous space) abutment it is intended to bolster.As an example, a canine can be used as a secondaryabutment to a first premolar primary abutment, but itwould be unwise to use a lateral incisor as a secondaryabutment to a canine primary abutment. The retainers onsecondary abutments must be at least as retentive as theretainers on the primary abutments. When the pontic flex-es, tensile forces will be applied to the retainers on thesecondary abutments (Fig 7-19). There also must be suf-ficient crown length and space between adjacent abut-ments to prevent impingement on the gingiva under theArch curvature has its effect on the stresses occurringin a fixed partial denture. When pontics lie outside theinterabutment axis line, the pontics act as a lever arm,which can produce a torquing movement. This is a com-mon problem in replacing all four maxillary incisors witha fixed partial denture, and it is most pronounced in thearch that is pointed in the anterior. Some measure mustbe taken to offset the torque. This can best be accom-plished by gaining additional retention in the oppositedirection from the lever arm and at a distance from theinterabutment axis equal to the length of the lever arm(Fig 7-20).1SThe first premolars sometimes are used assecondary abutments for a maxillary four-pontic canme-to-canine fixed partial denture. Because of the tensileforces that will be applied to the premolar retainers, theymust have excellent retention.
    • Treatment Planning for the Replacement of Missing TeethFig 7-17 There will be 8 times as much deflection (8X1 if thethickness is decreased by one-half (Ml).
    • Fig 7-18 The walls of facial and lingual groovesmesiodiital torque resulting from force applied to the p.Fig 7-19 l"he retainers on secondary abutments will be placed intension when the pontics flex, with the primary abutments acting^nds in the opposite directioSpecial ProblemsSome problem situations occur often enough to deservemention Some of the commonly used solutions to theproblems are also presented.Pier AbutmentsRigid connectors (eg, solder joints) between pontics andretainers are the preferred way of fabricating most fixedpartial dentures. A fixed partial denture with the ponticrigidly fixed to the retainers provides desirable strengthand stability to the prosthesis while minimizing the stress-es associated with the restoration.However, a completely rigid restoration is not indicatedfor all situations requiring a fixed prosthesis An edentu-lous space can occur on both sides of a tooth, creatinga lone, freestanding pier abutment (Fig 7-21).Physiologic tooth movement, arch position of the abut-ments, and a disparity in the retentive capacity of theretainers can make a rigid five-unit fixed partial denture aless than ideal plan of treatment.Studies in periodontometry have shown that the faci-olingual movement ranges from 56 to 108 |im,1flandintrusion is 28 ujn.17Teeth in different segments of thearch move in different directions.16Because of the curva-ture of the arch, the faciolmgual movement of an anteriortooth occurs at a considerable angle to the faciolingualmovement of a molar (Fig 7-22).These movements of measurable magnitude and indivergent directions can create stresses in a long-spanprosthesis that will be transferred to the abutments.
    • nt Planning lor the Replacement of Missing TeethFig 7-21 In this frequently occurring sithe maxillary first premolar and molar aiing, leaving the second premolar as a pi1O897/ 646869ft-"Fig 7-22 The amount of faciolingual movement(in )im) for each tooth in the maxillary arch(based on data by Rudd et allb). The direction ofmovement, indicated by arrows, varies consider-ably from the anterior to the posterior segment ofthe arch.Because of the distance through which movementoccurs, the independent direction and magnitude ofmovements of the abutment teeth, and the tendency ofthe prosthesis to flex, stress can be concentrated aroundthe abutment teeth as well as between retainers andabutment preparations.It has been theorized that forces are transmitted to theterminal retainers as a result of the middle abutment act-ing as a fulcrum, causing failure of the weaker retainer.19However, photoelastic stress analysis and displacementmeasurement indicate that the prosthesis bends ratherthan rocks. Standlee and Caputo suggest that tensionbetween the terminal retainers and their respective abut-ments, rather than a pier fulcrum, is the mechanism offailure.20Intrusion of the abutments under the loadingcould lead to failure between any retainer and its respec-tive abutment.The loosened casting will leak around the margin, andcaries is likely to become extensive before discovery.The retention on a smaller anterior tooth is usually lessihan that of a posterior tooth because of its generallysmaller dimensions. Since there are limits to increasing aretainers capacity to withstand displacing forces, somemeans must be used to neutralize the effects of thoseforces. The use of a nonrigid connector has been recom-mended to reduce this hazard.19In spite of an apparently close fit, the movement in anonrigid connector is enough to prevent the transfer ofstress from the segment being loaded to the rest of thefixed partial denture (Fig 7-23). The nonrigid connector isa broken-stress mechanical union of retainer and pontic,instead of the usual rigid connector The most commonlyused nonrigid design consists of a T-shaped key that isattached to the pontic, and a dovetail keyway placedwithin a retainer.Use of the nonrigid connector is restricted to a short-span fixed partial denture replacing one tooth.21Themagnification of force created by a long span is toodestructive to the abutment tooth under the solderedretainer. Prostheses with nonrigid connectors should notbe used if prospective abutment teeth exhibit significantmobility. There must be equal distribution of occlusalforces on all parts of the fixed partial denture.A nonrigid fixed partial denture transfers shear stressto supporting bone rather than concentrating it in theconnectors. It appears to minimize mesiodistal torquingof the abutments while permitting them to move inde-pendently.22A rigid fixed partial denture distributes theload more evenly than a nonrigid design, making itpreferable for teeth with decreased periodontal attach-ment.33If the posterior abutment and pontic are eitherunopposed or opposed by a removable partial dentureand if the three anterior units are opposed by naturalteeth, the key and the posterior units that are subjectedto little or no occlusal forces may supererupt.The location of the stress-breaking device in the five-unit pier-abutment restoration is important. It usually isplaced on the middle abutment, since placement of it oneither of the terminal abutments could result in the ponticacting as a lever arm.The keyway of the connector should be placed withinthe normal distal contours of the pier abutment, and thekey should be placed on the mesial side of the distalpontic. The long axes of the posterior teeth usually lean
    • Fig 7-23 A nonrigid connector on the middle abutment isolatesforce to thai segment of the fixed partial denture to which it happlied. (From Shillingburg and Fisher.19)AvA i1VSeari nno ActconFig 7-24 If a nonrigid connector is placed on the distal side ofwill seat the key into the keyway. (From Shillingburg and Fisher.")Fig 7-25 If a nonrigid connector is placed okey. (From Shillingburg and Fisher.1)slightly in a mesial direction, and vertically appliedocclusal forces produce further movement in this direc-tion. Nearly 98% of posterior teeth tilt mesially when sub-jected to occlusal forces.24If the keyway of the connec-tor is placed on the distal side of the pier abutment,mesial movement seats the key into the keyway moresolidly (Fig 7-24).19Placement of the keyway on themesial side, however, causes the key to be unseated dur-ing its mesial movements (Fig 7-25).20In time, this couldproduce a pathologic mobility in the canine or failure ofthe canine retainer.Tilted Molar AbutmentsA common problem that occurs with some frequency isthe mandibular second molar abutment that has tiltedmesially into the space formerly occupied by the firstmolar. It is impossible to prepare the abutment teeth for afixed partial denture along the long axes of the respec-tive teeth and achieve a common path of insertion (Fig 7-26).There is further complication if the third molar is pres-ent. It will usually have drifted and tilted with the secondmolar. Because the path of insertion for the fixed partialdenture will be dictated by the smaller premolar abut-
    • Treatwi&nt Planning for the Replacement of Missing TeethFig 7-26 When a mandibul;ctepancy between the long aimolar.iially, there is a dis-and that of the pre-ment, it is probable that the path of insertion will be near-ly parallel to the former long axis of the molar abutmentbefore it tilted mesially. As a result, the mesial surface ofthe tipped third molar will encroach upon the path ofinsertion of the fixed partial denture, thereby preventing itfrom seating completely (Fig 7-27).If the encroachment is slight, the problem can beremedied by restoring or recontouring the mesial surfaceof the third molar. However, the overtapered secondmolar preparation must have its retention bolstered bythe additipn of facial and lingual grooves. If the tilting issevere, more extensive corrective measures are calledfor. The treatment of choice is the uprighting of the molarby orthodontic treatment. In addition to placing the abut-ment tooth in a better position for preparation and for dis-tribution of forces under occlusal loading, uprighting themolar also helps to eliminate bony defects along themesial surface of the root.Uprighting is best accomplished by the use of a fixedappliance.25Both premolars and the canine are bandedand tied to a passive stabilizing wire (Fig 7-28) A helicaluprighting spring is inserted into a tube on the banded
    • V AMli — - .Vmolar and activated by hooking it over the wire on theanterior segment.2526This is frequently followed by theuse of an open coil spring to complete the uprighting andbring the tooth into the best possible alignment for fabri-cation of the fixed restoration. The average treatmenttime required is 3 months.37The third molar, if present, is often removed to facilitatethe distal movement of the second molar. The secondmolar will arc occlusally as it moves distally, so that itmust be watched closely and ground out of occlusion toallow it to continue moving, Immediately upon removal ofthe appliance, the teeth are prepared and a temporaryfixed partial denture is fabricated to prevent postireat-ment relapse.28If orthodontic correction is not possible, or if it is pos-sible to achieve only a partial correction, a fixed partialdenture can still be made. It has been suggested that thelong axis of the prospective abutments should convergeby no more than 25 to 30 degrees.29Photoelastic30andfinite element31stress analyses have shown that a molarwhich has tipped mesially will actually exhibit less stressin the alveolar bone, along the mesial surface of itsmesial root, with a fixed partial denture than without it.There will be an increase in stress along the premolar,A proximal half crown sometimes can be used as aretainer on the distal abutment (Fig 7-29).32This prepa-ration design is simply a three-quarter crown that hasbeen rotated 90 degrees so that the distal surface isuncovered. This retainer can be used only if the distalsurface itself is untouched by caries or decalcificationand if there is a very low incidence of proximal cariesthroughout the mouth. The patient must also demonstratean ability to keep the area exceptionally clean. If there isa severe marginal ridge height discrepancy between thedistal of the second molar and the mesial of the thirdmolar as a result of tipping, the proximal half crown iscontraindicated.A telescope crown and coping can also be used as aretainer on the distal abutment.33A full crown preparationwith heavy reduction is made lo follow the long axis of thetilted molar. An inner coping is made to fit the toothpreparation, and the proximal half crown that will serveas the retainer for the fixed partial denture is fitted overthe coping (Fig 7-30). This restoration allows for total cov-erage of the clinical crown while compensating for thediscrepancy between the paths of insertion of the abut-ments. The marginal adaptation for this restoration isprovided by the coping.The nonrigid connector is another solution to the prob-lem of the tilted fixed partial denture abutment (Fig 7-31).A full crown preparation is done on the molar, with its
    • Trestment Planning (of the RBplscement of Missing Teethg 7-32 A fixed partial denture replacing a maxillarybjected to more damaging stresses because ihe forcesI outward and the pontic lies farther outside the interpath of insertion parallel with the long axis of that tiltedtooth. A box form is placed in the distal surface of thepremolar to accommodate a keyway in the distal of thepremolar crown. It is tempting to place the connector onthe mesial aspect of the tipped molar, but this could leadto even greater tipping of the tooth. A nonrigid connectorfor the tipped molar abutment is most useful when themolar exhibits a marked lingual as well as mesial inclina-tion. Preparing a tooth with a combined mesial and lin-gual inclination as an abutment for a routine fixed partialdenture can lead to a drastically overtapered preparationBecause telescope crowns and nonrigid connectorsboth require tooth preparations that are more destructivethan normal, the selection of one of these would be influ-enced by the nature of previous destruction of theprospective abutment teeth. The presence of a dowelcore or a DO amalgam on the premolar, for example,would favor placement of a nonrigid connector on thattooth, while extensive facial and/or lingual restorations onthe tilted molar would call for the use of a telescopecrown.Canine-Replacement Fixed Partial DenturesFixed partial dentures replacing canines can be difficultbecause the canine often lies outside the interabutmentaxis. The prospective abutments are the lateral incisor.usually the weakest tooth in the entire arch, and the firstpremolar, the weakest posterior tooth. A fixed partial den-ture replacing a maxillary canine is subjected to morestresses than that replacing a mandibular canine, sinceforces are transmitted outward (la.bia.lly) on the maxillaryarch, against the inside of the curve (its weakest point)(Fig 7-32) On the mandibular canine the forces aredirected inward (lingually), against the outside of thecurve (its strongest point) (Fig 7-33). Any fixed partialdenture replacing a canine should be considered a com-plex fixed partial denture. No fixed partial denture replac-ing a canine should replace more than one additionaltooth. An edentulous space created by the loss of acanine and any two contiguous teeth is best restored witha removable partial denture.Cantilever Fixed Partial DenturesA cantilever fixed partial denture is one that has an abut-ment or abutments at one end only, with the other end ofthe pontic remaining unattached. This is a potentiallydestructive design with the lever arm created by the pon-tic, and it is frequently misusedIn the routine three-unit fixed partial denture, force thatis applied to the pontic is distributed equally to the abut-ment teeth (Fig 7-34). If there is only one pontic and it isnear the interabutment axis line, less leverage is appliedto the abutment teeth or to the retainers than with a can-tilever. When a cantilever pontic is employed to replace amissing tooth, forces applied to the pontic have an entire-ly different effect on the abutment tooth. The pontic actsas a lever that tends to be depressed under forces witha strong occlusal vector (Fig 7-35).Prospective abutment teeth for cantilever fixed partialdentures should be evaluated with an eye toward lengthyroots with a favorable configuration, long clinical crowns,
    • SpecialProblemsFig 7-35 Forces on the pontic of a cantilever fixed partial dentutend to tip the fixed partial denture or the abutment looth.Fig 7-36 Cantilever fixed partial denture replary lateral incisor, using the canine as the abigood crown-root ratios, and healthy periodontium.34Generally, cantilever fixed partial dentures shouldreplace only one tooth and have at least two abut-ments.3536A cantilever can be used for replacing a maxillary lat-eral incisor (Fig 7-36). There should be no occlusal con-tact on the pontic in either centric or lateral excursions.^7The canine must be used as an abutment, and it canserve in the role of solo abutment only if it has a long rootand good bone support. There should be a rest on themesial of the pontic against a rest preparation in an inlayor other metallic restoration on the distal of the centralincisor to prevent rotation of the pontic and abutmentThe mesial aspect of the pontic can be slightly "wrappedaround" the distal portion of the uninvolved centralincisor to stabilize the pontic faciolingitally.37The rootconfiguration of a central incisor does not make it a desir-able cantilever abutment.A cantilever pontic can also be used to replace a miss-ing first premolar (Fig 7-37). This scheme will work best ifocclusal contact is limited to the distal fossa. Full veneerretainers are required on both the second premolar andfirst molar. These teeth must exhibit excellent bone sup-port. This design is attractive if the canine is unmarredand if a full veneer restoration is required for the firstmolar in any event.
    • Treatment Planning for the Replacement of Missing TeeFig 7-39 Cantilever fixed partiafirst molar, using both premolarsstress on the abutments, the pontreplacing a mandihularize of a premolar ratherCaniilever fixed partial dentures can also be used toreplace molars when there is no distal abutment present.When used judiciously, it is possible to avoid the insertionof a unilateral removable partial denture.34Most com-monly, this type of fixed partial denture is used to replacea first molar, although occasionally it is used to replace asecond molar to prevent supereruption of opposingteeth.When the pontic is loaded occlusally, the adjacentabutment tends to act as a fulcrum, with a lifting tenden-cy on the farthest retainer (Fig 7-38).3sTo minimize theleverage effect, the pontic should be kept as small aspossible, more nearly representing a premolar than amolar (Fig 7-39). There should be light occlusal contactwith absolutely no contact in any excursion. The ponticshould possess maximum occlusogingival height toensure a rigid prosthesis.A posterior cantilever pontic places maximumdemands on the retentive capacity of the retainer.39Itsuse, therefore, should be reserved for those situations inwhich there is adequate clinical crown length on theabutment teeth to permit preparations of maximumlength and retention. The success of cantilevers in therestoration of the periodontally compromised dentition isprobably due at least in part to the fact that periodontal-ly involved abutments do have extremely long clincialcrowns. While cantilever fixed partial dentures appear tobe a conservative restoration, the potential for damage tothe abutment teeth requires that they be used sparingly.
    • References3. J Am DentAssc 1936;I Penny RE, Kraal JH: Crown-to-root ratio. Its significance inrestorative dentistry. J Prosthet Dent 1979; 42.34-38.i. Jepsen A. Root surface measurement and a method for x-ray determination of root surface area Ada Odontol Scand1963,21-35-46.I. Kalkwarf KL, Kre|ci RF, Pao YO Effect of root resorption onperiodontai support. J Prosthet Denf 1986; 56.317-319.i. Tylman SD: Theory and Practice ot Crown and Fixed PartialProsthodontics (Bridge), ed 6 St Louis CVMosbyCo 1970,p17.i. Johnston JF, Phillips RW, Dykema RW: Modern Practice inCrown and Bridge Prosthodontics. ed 3. Philadelphia, WBSaunders Co, 1971, p 11.. Ante IH: The fundamental principles of abutments MichState Dent Soc Bull 1926; 8:14-23.i. Nyman S, Lindhe J: Prosthetic rehabilitation of patients withadvanced periodontal disease. J Clin Periodontoi 1976;3:135-147.). Nyman S, Lindhe J. Lundgren D: The role of occlusion forthe stability of fixed bridges in patients with reduced peri-odontal tissue support. J Clin Periodontoi 1975; 2:53-66.1 Lindhe J, Nyman S: The role of occlusion in periodontal dis-ease and the biologic rationale for splinting in treatment ofpenodontics. Oral Sci Rev 1977; 10:11-43.1. Jacobi R, Shillingburg HT, Duncanson MG- Effect of mobili-ty, site, and angle of impact on retention of fixed partial den-tures. J Prosthet Dent 1985; 54:178-183.2. Nyman S, Lindhe J: A longitudinal study of combined peri-odontal and prosthetic treatment of patients with advancedperiodontal disease. J Periodontoi 1979, 50:163-169.3. Smyd ES: Mechanics of dental structures: Guide to teachingdental engineering at undergraduate level. J Prosthet Dent1952; 2:668-692.i. Smyd ES: Advanced thought in indirect inlay and fixedbridge fabrication. J Am Dent Assoc 1944; 31.759-768.5. Dykema RW: Fixed partial prosthodontics. J Tenn DentAssoc 1962; 42.309-321.3. Rudd KD, OLeary TJ, Stumpf AJ: Horizontal tooth mobilityin carefully screened subjects. Periodontics 1964; 2:65-68.7 Parfitt GJ: Measurement of the physiological mobility of indi-vidual teeth in an axial direction. J Dent Res 1960;39:608-618.3. Chayes HES, cited in McCall JO, Hugel IM: Movable-remov-able bridgework. Principles and practice as developed byHerman ES Chayes, DDS. Dent Items interest 1949;71:512-525.]. Standlee JP, Caputo AA. Loadtures with three abutments. Quintessence Int 1988;19:403-410.I. Markley MR: Broken-stress principle and design in fixedbridge prosthesis. J Prosthet Dent 1951; 1:416-423I. Sutherland JK, Holland GA, Sluder TB, White JT. A photoe-lastic analysis of the stress distribution in bone supportingfixed partial dentures of rigid and nonrigid designs. JProsthet Dent WBO; 44:616-623J. Landry KE, Johnson PF, Parks VJ, Pelleu GB: A photoelasticstudy to determine the location of the nonrigid connector ina five-unit intermediate abutment prosthesis. J ProsthetDenM987; 57:454-457.1. Picton DCA: Tilting movements of teeth during biting. ArchOral Biol 1962; 7:151-159.>. Khouw FE, Norton LA: The mechanism of fixed molaruprighting appliances. J Prosthet Dent 1972; 27:381-389.i. Norton LA, Profitt WR- Molar uprighting as an adjunct tofixed prostheses. J Am Dent Assoc 1968; 76-312-315.. Simon RL. Rationale and practical technique for uprightingmesially inclined molars. J Prosthet Dent 1984; 52:256-259-i Norton LA, Parker WT: Management of repositioned teeth inpreparation for fixed partial dentures. J Am Dent Assoc1970; 81-916-922.>r fixed prosthodontics J). Hood JA, Farah JW, Craig RG: Modification of stresses inalveolar bone induced by a tilted molar. J Prosthet Dent1975; 34:415-421.I. Yang HS, Thompson VP: A two-dimensional stress analysiscomparing fixed prosthodontic approaches to the tiltedmolar abutment. Int J Prosthodont 1991; 4:416-424.I Smith DE: Fixed bridge restorations with the tilted mandibu-lar second or third molar as an abutment J South Calif DentAssoc 1939; 6:131-138.• tilted abutmen i. NMantilever principle. J,. Wright KWJ, Yettram AL: Reactive force distributions forteeth when loaded singly and when used as fixed partialdenture abutments. J Prosthet Dent 1979, 42411-416.i. Wright WE: Success with the cantilever fixed partial denture.J Prosthet Dent 1986; 55:537-539.. Goldfogel MH, Lambert RL: Cantilever fixed prosthesisreplacing the maxillary lateral incisor: Design considerationJProstfjefDenn985; 54:477-478.!. Schweitzer JM, Schweitzer RD, Schweitzer J: Free-end pon-tics used on fixed partial dentures. J Prosthet Dent 1968,20:120-138.!. Nyman S, Lindhe J: Considerations on the design of occlu-sion in prosthetic rehabilitation of patients with advancedperiodontal disease. J Clin Periodontoi 1977, 4-1-15.
    • Chapter 8Fixed Partial Denture ConfigurationsFixed partial dentures can be categorized as eithersimple or complex, depending on the number ofteeth to be replaced and the position of the edentu-lous space in the arch. The classic simple fixed partialdenture is one that replaces a single tooth Longer spansgenerally place greater demands on the skills of the den-tist, on the resistance of the retainers, and on the abut-ments and their periodontal support.The maximum number of posterior teeth that can besafely replaced with a fixed partial denture is three, andthis should be attempted only under ideal conditions Anedentulous space created by the loss of four adjacentteeth other than four incisors is usually best restored witheither a removable partial denture or an implant-support-ed fixed partial denture. If more than one edentulousspace exists in the same arch, even though each couldbe individually restored with a fixed partial denture, itmay be desirable to use a removable partial denture.This is especially true when the spaces are bilateral andeach involves two or more teeth.Third molars are not shown in any of the examples, andno situation is shown in which a third molar would be aprospective abutment. Rarely can third molars be usedas abutments, since they have been removed from themouths of so many patients. Even when they are present,they frequently display incomplete eruption: short, fusedroots; and a marked mesial inclination in the absence ofa second molar.If a third molar is to be considered as a potential abut-ment, it should be upright, with little or no mesial inclina-tion; have long, distinctly separate roots; and be com-pletely erupted. It must have a healthy cuff of attached,keratinized gingiva that completely surrounds the tooth.The unattached mucosal tissue that frequently surroundsthe distal 30% to 60% of third molars will becomeinflamed adjacent to even a well-fitting crown margin,and the abutment is likely to fail periodontally.The following examples are given as a reference thatwill apply under ideal conditions. The abutment teeth thatnormally would be used are listed, along with the firstchoice of retainer designs based on adequate retention,esthetics, and conservation of tooth structure. Clinical sit-uations vary widely, and less conservative designs will berequired when caries, decalcification, or morphologictraits (such as short clinical crowns) dictate. These con-figurations assume that the prospective abutments arestill in their original positions. If the abutments have drift-ed, the situation could become less demanding, and onoccasion more demanding, depending on the currentposition of the tooth. Fewer or more abutments may benecessitated if there has been drifting, or if there hasbeen bone loss. The ratios shown for root surface areasare intended as a general guideline. An abutment-ponticroot ratio of 1.0 or greater is considered to be favorable.Conventional partial veneer retainers could be used formany of the prostheses described However, the reluc-tance of many patients to accept any display of metaland the lack of dentist familiarity with these preparationsrequire that this design be used only on selected poste-rior abutments. Likewise, resin-bonded fixed partial den-tures ("Maryland bridges") have replaced pin-modifiedthree-quarter crown retainers because the skill levelrequired for the pin-retained restoration, while attainable,lies outside the realm of basic, or "fundamental," fixedprosthodontics.
    • Fixed Partial Denture ConfiguratSimple Fixed Partial Dentures (one tooth)Missing: Maxillary central incisorAbutments: Central incisor and lateral incisorRetainers: Resin-bonded retainersPontic: Metal-ceramicAbutment-pontic root ratio: 1.9Considerations: Abutment discoloration, rotated abutment,improper width of edentulous space, or proximal cariesmay require metal-ceramic retainers. If occlusal contactoccurs on the gingival one-third of the lingual surfaces ofthe abutments, conventional retainers may be neededMissing- Mandibular central incisorAbutments: Central incisor and lateral incisorRetainers: Resin-bonded retainersPontic: Metal-ceramicAbutment-pontic root ratio: 2.1Considerations: Severely rotated, malposed, or mobileabutments will contramdicate the use of resin-bondedretainers. If metal-ceramic retainers are required, thepreparations very easily could encroach on the pulp, andthe patient should be so advised. Endodontic treatmentand a dowel core would then he necessary.Missing: Maxillary lateral incisorAbutments: Central incisor and canineRetainers. Resin-bonded retainersPontic: Metal-ceramicAbutment-pontic root ratio: 2.6Considerations: Caries and/or restorations on the abut-ments would require metal-ceramic retainers. If the canineis long, well-supported periodontally, and in need ofrestoration, and if the pontic will not contact in centric orlateral excursions, a single-abutment cantilever fixed par-tial denture can be used. In that case, a metal-ceramiccrown also should be used as a retainer An untouchedcentral incisor and a first premolar in need of restorationcould call for a pontic cantilevered from metal-ceramiccrowns on the canine and first premolar.
    • Simple Fixed Partial Dentures (one tooth)Missing: Mandibular lateral incisorAbutments: Central incisor and canineRetainers: Resin-bonded retainersPontic: Metal-ceramicAbutment-pontic root ratio: 2.5Considerations: Caries and/or restorations on the abut-ments would require metal-ceramic retainers. The patientshould be warned of the potential for pulpal involvementwith resultant endodontic treatment and dowel core. Evenmoderate bone loss around the central incisor will requirethat the other central incisor be used as a secondary abut-ment. Cantilever fixed partial dentures are not an option forthe replacement of mandibular lateral incisorsMissing: Maxillary first premolarAbutments: Canine and second premolarRetainers- Resin-bonded retainers, if teeth areunblemishedPontic: Metal-ceramicAbutment-pontic root ratio: 2 AConsiderations: Facial caries or any proximal caries otherthan incipient will necessitate metal-ceramic retainers. Ifthe second premolar and first molar are restored or willneed restoration, a cantilever prosthesis using metal-ceramic retainers on the second premolar and first molaris worthy of consideration. A canine-guided occlusalscheme would be necessary to prevent excessive forceson the cantilever pontic. If that is not possible, do not useMissing: Mandibular first premolarAbutments: Canine and second premolarRetainers: Resin-bonded retainers, if teeth are unmarredPontic: Metal-ceramicAbutment-pontic root ratio: 2.5Considerations: Facial caries or any proximal caries otherthan incipient will necessitate metal-ceramic retainers. Ifthe canine is intact and second premolar and first molarare restored or will need restoration, a cantilever fixed par-tial denture can be used, with metal-ceramic retainers onthe second premolar and first molar abutments. If thepatient does not object, an all-metal crown can be substi-tuted on the molar.
    • Fixed Partial Denture Configurat.Missing: Maxillary second premolarAbutments: First premolar and first molarRetainers: Three-quarter crownsPontic: Metal-ceramicAbutment-pontic root ratio: 3.1Considerations: Facial defects or patient request willnecessitate metal-ceramic retainers Resin-bonded retain-ers can be used if the abutments are caries-free or veryminimally affected by caries.Missing: Mandibular second premolarAbutments: First premolar and first molarRetainers: Metal-ceramic crown on premolar and fullcrown on molarPontic: Metal-ceramicAbutment-pontic root ratio: 3.1Considerations: Esthetic requirements of the patient maynecessitate a metal-ceramic retainer on the molar A three-quarter crown can be suggested for the first premolar if ithas an unusually large clinical crown. Patient acceptanceis necessary but may not be forthcoming. Resin-bondedretainers can be used if the premolar is large and if theabutments are caries-free or only minimally affected byMissing: Maxillary first molarAbutments: Second premolar and second molarRetainers: Three-quarter crown on premolar and seven-eighths crown on molarPontic: Metal-ceramicAbutment-pontic root ratio: 1.5Considerations: If the clinical crown of the premolar isshort, an additional set of grooves may be desirable toincrease retention. Patient esthetic requirements canrequire a metal-ceramic crown on the premolar. A seven-eighths crown on the molar will not be objectionable inmost mouths. Heavy occlusal forces and wider edentulousspace of a first molar usually contraindicate resin-bonded
    • Complex Fixed Partial Dentures (one tooth)Missing: Mandibular first molarAbutments: Second premolar and second molarRetainers: Metal-ceramic crown on premolar and fullveneer gold crown on molarPontic: All-metal hygienicAbutment-pontic root ratio: 1.5Considerations: A three-quarter crown is technically feasi-ble on the second premolar if the clinical crown is longerthan average and the patient is agreeable. A tilted molarmay require orthodontic uprighting, a proximal half crown,or a telescope crown.Complex Fixed Partial Dentures (one tooth)Missing: Maxillary canineAbutments: Central incisor, lateral incisor, and firstpremolarRetainers: Metal-ceramicPontic: Metal-ceramicAbutment-pontic root ratio: 2.3Considerations: Restore the occlusion to group function.Use of the two premolars and the lateral incisor as abut-ments is not desirable because it places too heavy a bur-den on the smaller single abutment, the lateral incisor. Asingle implant supported metal-ceramic crown might beconsidered hereMissing: Mandibular canineAbutments: Central incisor, lateral incisor, and firstpremolarRetainers- Metal-ceramicPontic: Metal-ceramicAbutment-pontic root ratio: 1.9Considerations: Use group function to restore the csion. If there has been extensive bone loss around theral incisor, or if it is tilted to produce a line of dravcrepancy, remove the lateral incisor and use both oincisors as abutments. A single implant-supported rceramic crown might be used here. Replacement ctooth is not common.
    • Fixed Partial Denture ConiiguratiorSimple Fixed Partial Dentures (two teeth)Missing: Maxillary central incisor and lateral incisorAbutments: Central incisor and canineRetainers: Metal-ceramicPontic- Metal-ceramicAbutment-pontic root ratio: 1.2Considerations. If the central incisor and canine areunblemished and unusually large, conventional or pm-modified partial veneer crowns can be used. Patient ac-ceptance and dentist skill are strong considerations.Missing. Mandibular central incisorsAbutments: Lateral incisorsRetainers: Resin-bondedPolitics. Metal-ceramicAbutment-pontic root ratio: 1.1Considerations: If there has been any bone loss at allaround the lateral incisors, the canines should be includedas abutments and metal-ceramic retainers used.Malposition of the lateral incisors could dictate theirMissing: Maxillary first and second premolarsAbutments: Canine and first molarRetainers: Metal-ceramic on canine and seven-eighthsPontics: Metal-ceramicAbutment-pontic root ratio: 1.6Considerations: A metal-ceramic crown may be used onthe molar if the mesiofacial cusp is damaged or under-mined, or if the patient requests it. If the canine is largeenough, and the patient will accept a minimal display ofmetal, a three-quarter crown can be used.
    • Simple Fixed Partial Denlu.Missing: Mandibular first and second premolarsAbutments: Canine and first molarRetainers: Metal-ceramic crown on canine and full veneergold crown on molarPontics: Metal-ceramicAbutment-pontic root ratio: 1.8Considerations: If the molar has tilted mesially, orthodonticuprighting or preparation modification may be required.The patients esthetics expectations may require a metal-ceramic crown on the molarMissing: Maxillary second premolar and first molarAbutments: First premolar and second molarRetainers: Metal-ceramic crown on premolar and fullveneer or seven-eighths crown on molarPontics: Metal-ceramicAbutment-pontic root ratio: 1.0Considerations: If the premolar has a long clinical crownand the patient will accept a minimal display of metal, athree-quarter crown with double grooves can be used.Missing: Mandibular second premolar and first molarAbutments: First premolar and second molarRetainers: Metal-ceramic crown on premolar and fullveneer gold crown on molarPontics: Metal-ceramicAbutment-pontic root ratio: 1.0Considerations: If the premolar root is short or thin, or if theclinical crown is very small, the canine should be includedas a secondary abutment.
    • a/ Denture ConfigurationsComplex Fixed Partial Dentures (two teeth)Missing- Mandibular central incisor and lateral incisorAbutments: Central incisor, lateral incisor, and canineRetainers; Resin-bonded retainersPontics: Metal-ceramicAbutment-pontic root ratio: 1.8Considerations: Inadequate bone support around centraland lateral incisors often requires their removal, with aresulting six-unit fixed partial denture with metal-ceramicretainers being required Caries and/or restorations on theabutments would also require metal-ceramic retainers. Thepatient should be warned of the potential for pulpalinvolvement with resultant endodontic treatment and dowelcore. Anterior guidance should be controlled carefully toavoid excessive lingually directed forces.Missing: Maxillary central incisorsAbutments: Canines and lateral incisorsRetainers. Metal-ceramicPontics: Metal-ceramicAbutment-pontic root ratio: 2.3Considerations: When the bony support for the lateralincisors is poor, it is often best to extract them and length-en the fixed partial denture. If the lateral incisors have longroots and crowns, they alone can be used as abutments.If the patient will accept a minimal display of metal, askilled operator can use three-quarter crownsMissing: Maxillary lateral incisor and canineAbutments: Both central incisors and both premolarsRetainers. Metal-ceramicPontics: Metal-ceramicAbutment-pontic root ratio: 1.9Considerations: Span length, abutment position, and rootconfiguration make the use of four abutments desirable.All retainers must have good retention. If the premolarshave drifted mesially, it may not be necessary to includethe second premolar. Use group function to restore theocclusion.
    • Complex Fixed Partial Dentures (twMissing- Mandibular lateral incisor and canineAbutments: Both central incisors and first premolarRetainers: Metal-ceramicPontics: Metal-ceramicAbutment-pontic root ratio: 1.1Considerations: The short edentulous span and the direc-tion of forces on the mandibular canine do not require theuse of the second premolar as an abutment.Missing: Maxillary canine and first premolarAbutments: Central incisor, lateral incisor, second premo-lar, and first molarRetainers: Metal-ceramic on incisors and second premo-lar, and seven-eighths crown on molarPontics. Metal-ceramicAbutment-pontic root ratio- 2.0Considerations: Group funciion should be used. This canbe a difficult restoration.Missing: Mandibular canine and first premolarAbutments: Central incisor, lateral incisor, and second pre-molarRetainers- Metal-ceramicPontics: Metal-ceramicAbutment-pontic root ratio: 1.5Considerations- Use group function in restoring the occlu-sion. This also can be a difficult fixed partial denture, butfortunately it is rarely encountered.
    • Fixed Partial Denture ConfigurationsMissing: Both maxillary lateral incisors and one centralincisorAbutments- Central incisor and both caninesRetainers: Metal-ceramicPontics: Metal-ceramicAbutment-pontic root ratio: 1.3Considerations. There should be a nonrigid connectorbetween the distal of the central incisor retainer and themesial of the lone lateral incisor pontic. If the centralincisor is malposed or periodontally compromised, itshould be extracted. Three-quarter crowns can be usedwhere the teeth are large and the patient will accept somedisplay of metal.Missing- Maxillary lateral incisor and first premolarAbutments- Central incisor, canine, and second premolarRetainers: Metal-ceramic on central incisor and canine,and three-quarter crown on second premolarPontics: Metal-ceramicAbutment-pontic root ratio: 1.7Considerations: Nonrigid connector between canine andfirst premolar. A short clinical crown or esthetic concernwill require a metal-ceramic crown on the second premo-lar. The corresponding mandibular situation would berestored in the same manner.Missing: Maxillary canine and second premolarAbutments: Central and lateral incisors, first premolar, andfirst molarRetainers: Metal-ceramic on incisors and premolar, andseven-eighths crown on molarPontics: Metal-ceramicAbutment-pontic root ratio: 2.1Considerations: Nonrigid connector between first premolarretainer and second premolar pontic. The correspondingmandibular situation would be handled identically with thesubstitution of a full gold crown on the first molar, if thepatient does not object. A metal-ceramic crown could besubstituted.
    • Complex Fixed Partial Dentures (pier abutrrMissing: All maxillary incisors and one first premolarAbutments: Both canines, the first premolar on one side,and the second premolar on the otherRetainers:Metal-ceramicPontics:Metal-ceramicAbutment-pontic root ratio: 1.0Considerations: Nonrigid connector in the distal of theretainer on the canine "pier" abutment. A long second pre-molar or a lack of concern for esthetics by patient wouldpermit the substitution of a three-quarter crown on the sec-ond premolar The mandibular situation is handled similarlyMissing: Maxillary lateral incisor, first and secondpremolarsAbutments: Canine and first molarRetainers:Metal-ceramicPontics:Metal-ceramicAbutment-pontic root ratio: 1.1Considerations: Canine-guided posterior disocclusion.The short lever arm created by the lateral incisor cantilevershould be adequately offset by the long span from firstmolar to canine. The mandibular situation is handled simi-larly.Missing: Maxillary first premolar and first molarAbutments: Canine, second premolar, and second molarRetainers. Metal-ceramic on canine and second premolar,with full veneer gold crown on second molarPontics:Metal-ceramicAbutment-pontic root ratio. 1.4Considerations. Nonrigid connector on distal of premolarretainer. If the canine and/or second premolar have longclinical crowns and the patient is amenable to a small dis-play of metal, three-quarter crowns can be substituted.The corresponding mandibular situation can be treatedsimilarly, with the substitution of an all-metal hygienic pon-tic for the molar.
    • Fixed Partial Denture ConfiguratioiMissing: Both maxillary lateral incisors and one centralAbutments: Central incisor and both caninesRetainers: Metal-ceramicPontics: Metal-ceramicAbutment-pontic root ratio: 1.3Considerations: There should be a nonrigid connectorbetween the distal of the central incisor retainer and themesial of the lone lateral incisor pontic. If the centralincisor is malposed or periodontally compromised, itshould be extracted. Three-quarter crowns can be usedwhere the teeth are large and the patient will accept somedisplay of metal.Missing: Maxillary lateral incisor and first premolarAbutments: Central incisor, canine, and second premolarRetainers: Metal-ceramic on central incisor and canine,and three-quarter crown on second premolarPontics: Metal-ceramicAbutment-pontic root ratio: 1.7Considerations: Nonrigid connector between canine andfirst premolar. A short clinical crown or esthetic concernwill require a metal-ceramic crown on the second premo-lar. The corresponding mandibular situation would berestored in the same manner.Missing: Maxillary canine and second premolarAbutments. Central and lateral incisors, first premolar, andfirst molarRetainers: Metal-ceramic on incisors and premolar. andseven-eighths crown on molarPontics: Metal-ceramicAbutment-pontic root ratio: 2.1Considerations: Nonrigid connector between first premolarretainer and second premolar pontic. The correspondingmandibular situation would be handled identically with thesubstitution of a full gold crown on the first molar, if thepatient does not object. A metal-ceramic crown could besubstituted.
    • Complex Fixed Partial Dentures (pier abutment)Missing: All maxillary incisors and one first premolarAbutments: Both canines, the first premolar on one side.and the second premolar on the otherRetainers: Metal-ceramicPontics: Metal-ceramicAbutment-pontic root ratio: 1.0Considerations: Nonrigid connector in the distal of theretainer on the canine "pier" abutment. A long second pre-molar or a lack of concern for esthetics by patient wouldpermit the substitution of a three-quarter crown on the sec-ond premolar. The mandibular situation is handled similarly.Missing: Maxillary lateral incisor, first and secondpremolarsAbutments: Canine and first molarRetainers- Metal-ceramicPontics: Metal-ceramicAbutment-pontic root ratio: 1.1Considerations- Canine-guided posterior disocclusion.The short lever arm created by the lateral incisor cantilevershould be adequately offset by the long span from firstmolar to canine. The mandibular situation is handled simi-larly.Missing: Maxillary first premolar and first molarAbutments: Canine, second premolar, and second molarRetainers: Metal-ceramic on canine and second premolar,with full veneer gold crown on second molarPontics: Metal-ceramicAbutment-pontic root ratio: 1.4Considerations: Nonrigid connector on distal of premolarretainer. If the canine and/or second premolar have longclinical crowns and the patient is amenable to a small dis-play of metal, three-quarter crowns can be substituted.The corresponding mandibular situation can be treatedsimilarly, with the substitution of an all-metal hygienic pon-tic for the molar.
    • Fixed Partial Denture ConfiguraMissing: Maxillary central and lateral incisors, and first andsecond premolar on one sideAbutments: Central and lateral incisors, canine, and firstRetainersMetal-ceramicPontics:Metal-ceramicAbutment-ponticrootratio:1.3Considerations: This would be an extremely difficult fixedpartial denture to undertake. The span lengths of bothedentulous spaces are too great for nonrigid connectorswith either pontic. The central and lateral incisors musthave excellent retention. A removable partial denture orimplant-supported segments should be considered. Thecorresponding mandibular configuration might use a fullveneer gold crown on the molar.
    • Chapter 9Principles of Tooth PreparationsT"he design of a preparation for a casl restorationand the execution of thai design are governed byprinciples:1. Preservation of tooth structure2 Retention and resistance3. Structural durability4. Marginal integrity5. Preservation of the periodontiurrPreservation of Tooth StructureIn addition to replacing lost tooth structure, a restorationmust preserve remaining tooth structure. Intact surfacesof tooth structure that can be maintained while producinga strong, retentive restoration should be saved if patientacceptance and retention requirements will permit it.Whole surfaces of tooth structure should not be need-lessly sacrificed to the bur in the name of convenience orspeed.Preservation of tooth structure in some cases mayrequire that limited amounts of sound tooth structure beremoved to prevent subsequent uncontrolled loss of larg-er quantities of tooth structure. This is the rationale for theremoval of 1 to 1.5 mm of occlusal tooth structure whenpreparing a tooth for an MOD onlay. The metal on theocclusal surface can protect against dramatic failures,such as fracture of tooth structure, as well as the lessobvious failures that may be occasioned by the flexing oftooth structure.Retention and ResistanceFor a restoration to accomplish its purpose, it must stayin place on the tooth. No cements that are compatiblewith living tooth structure and the biologic environment ofthe oral cavity possess adequate adhesive properties tohold a restoration in place solely through adhesion. Thegeometric configuration of the tooth preparation mustplace the cement in compression to provide the neces-sary retention and resistanceRetention prevents removal of the restoration along thepath of insertion or long axis of the tooth preparation.Resistance prevents dislodgment of the restoration byforces directed in an apical or oblique direction and pre-vents any movement of the restoration under occlusalforces. Retention and resistance are interrelated andoften inseparable qualities.The essential element of retention is two opposing ver-tical surfaces in the same preparation. These may beexternal surfaces, such as the buccal and lingual walls ofa full veneer crown (Fig 9-1, A) An extracoronal restora-tion is an example of veneer, or sleeve, retention {Fig 9-1, B). The opposing surfaces can also be internal, suchas the buccal and lingual walls of the proximal box of aproximo-occlusal inlay (Fig 9-2, A). An intracoronal res-toration resists displacement by wedge retention (Fig 9-2, B). Many restorations are a combination of the twotypes.TaperBecause a cast metal or ceramic restoration is placed onor in the preparation after the restoration has been fabri-cated in its final form, the axial walls of the preparationmust taper slightly to permit the restoration to seat; ie,two opposing external walls must gradually converge ortwo opposing internal surfaces of tooth structure mustdiverge occlusally. The terms angle of convergence andangle of divergence can be used to describe the respec-tive relationships between the two opposing walls of apreparation.The relationship of one wall of a preparation to the longaxis of that preparation is the inclination of that wall. Atapered diamond or bur will impart an inclination of 2 to3 degrees to any surface it cuts if the shank of the instru-ment is held parallel to the intended path of insertion ofthe preparation. Two opposing surfaces, each with a 3-degree inclination, would give the preparation a 6-degree taper.Theoretically, the more nearly parallel the opposingwalls of a preparation, the greater should be the reten-tion. The most retentive preparation should be one with
    • parallel walls. Indeed, parallel walls were advocated bysome early authors.^ However, parallel walls are impos-sible to create in the mouth without producing prepara-tion undercuts. Preparation walls are tapered to visualizepreparation walls, prevent undercuts, compensate forinaccuracies in the fabrication process, and permit morenearly complete seating of restorations during cementa-tion.Ward was one of the first to recommend taper as such,prescribing 5% to 20% per inch (3 to 12 degrees,respectively).3Jorgensen4and Kaufman et al5havedemonstrated experimentally that retention decreases astaper is increased (Fig 9-3). In recent years, recommen-dations for optimum axial wall taper of tooth preparationsfor cast restorations have ranged from 3 to 5 degrees,66degrees,7and 10 to 14 degrees.8To minimize stress inthe cement interface between the preparation andrestoration, a taper of 2.5 to 6.5 degrees has been sug-gested as optimum, but there is only a slight increase instress as taper is increased from 0 to 15 degrees.9However, at 20 degrees, stress concentration was foundto increase sharply.Studies of actual crown preparations have shown aver-age tapers that have been much greater than the valuesrecommended. Ohm and Silness reported mean tapersof 19.2 degrees mesiodistally and 23.0 degrees faciolin-gually on vital teeth, and 12.8 degrees mesiodistally and22.5 degrees faciolingually on nonvital teeth.10Mackfound an average clinical taper of 16.5 degrees." Weedet al found that dental students could produce full veneercrown preparations with a taper of 12 7 degrees ontypodonts, but their clinical preparations had a meantaper of 22.8 degrees.* Noonan and Goldfogel, survey-ing 909 student-prepared full gold crown preparations,reported an overall mean taper of 19.2 degrees.13Onproficiency examinations, preparation tapers weredecreased by 20%. Dies taken at random from commer-cial laboratories by Eames et al were found to have anaverage overall taper of 20 degrees.14Kent and associates evaluated the degree of taper of418 preparations, cut over 12 years by one operator15They found a mean of 15.8 degrees between mesial anddistal walls and 13 4 degrees between facial and lingualwalls for preparations in all areas of the mouth, with anoverall mean of 14.3 degrees. The lowest combinedtaper (9.2 degrees) was seen on 145 anterior metal-ceramic crown preparations, while the greatest (22.2degrees) was measured on 88 mandibular full crowns.Nordlander et al, analyzing 208 preparations done by 10dentists, reported a low of 17.3 degrees for premolarsand a high of 27.3 degrees for molars, with an overallmean of 19 9 degrees.115Tooth preparation taper should be kept minimalbecause of its adverse effect on retention, but Mack esti-mates that a minimum taper of 12 degrees is necessaryjust to insure the absence of undercuts.1The tendencyto overtaper preparations is one that must be guardedagainst constantly in order to produce preparations withthe least possible taper and the greatest possible reten-tion. Consciously attempting to cut a taper can easilyresult in an overtapered and nonretentive preparation. Ataper or total convergence of 16 degrees has been pro-posed as being achievable clinically while still affordingadequate retention.1.^ This is probably an acceptableoverall target. It can be as low as 10 degrees on prepa-rations on anterior teeth and as high as 22 degrees onmolars (Fig 9-4). Recommendations for degree of taperfor specific teeth are given in Table 9-1.Cement creates a weak bond, largely by mechanicalinterlocks, between the inner surface of the restorationand the axial wall of the preparation. Therefore, thegreater the surface area of a preparation, the greater itsretention.^1HSimply stated, preparations on large teethare more retentive than preparations on small teeth (Fig9-5). This is a factor that must be considered when apreparation is done on a small tooth, especially when it isan abutment for a fixed partial denture or a splint.Surface area can be increased somewhat by addingboxes and grooves. However, the benefits derived fromsuch features may relate more to their limiting the free-dom of movement than to the increase in surface area.
    • 200ISO-^ 100-1 -10^ — .20 30Taper (deg *40rees)50 60Fig 9-3 There is a relationship between taper and ntaper increases, retention decreases (after Jorgensen4).Table 9-1 Optimum Degree ofTooth Preparation TaperMolar*BoxtMandlbularAnterior tooth*Premolar*Molar*IsthmustConvergence angle.tDivergence angle.Freedom of DisplacementRetention is improved by geometrically limiting the num-bers of paths along which a restoration can be removedfrom the tooth preparation.20Maximum retention isachieved when there is only one path A full veneerpreparation with long, parallel axial walls and grooveswould produce such retention (Fig 9-6, A) On the oppo-site extreme, a short, overtapered preparation would bewithout retention because the restoration could beremoved along an infinite number of paths (Fig 9-6, B).The best preparation, then, is one that approaches theideal and can be achieved within the limits of operatorskill, accessibility, and laboratory technology.Limiting the freedom of displacement from torquing ortwisting forces in a horizontal plane increases the resis-tance of a restoration. A groove whose walls meet theaxial wall at an oblique angle does not provide the nec-essary resistance (Fig 9-7, A). V-shaped grooves pro-duce roughly one-half as much resistance to lingual dis-placement as do grooves with a definite lingual wall.21Forces that produce rotating movement in the restorationcan produce shear and eventual slippage along the sur-faces oblique to the direction of the force. There must bea definite wall perpendicular to the direction of the forceto sufficiently limit the freedom of displacement and pro-vide adequate resistance (Fig 9-7, B).A proximal box must be treated in a similar manner. If
    • Principles of Preparat.withdrawal, retentionlited freedom of displacFig 9-7 •flie walls of a groove that meet the axial waoblique angle do not provide necessary resistance (A); triea groove must be perpendicular to rotating forces to reFig 9-8 The buccal and lingual walls of a box will nut resist rota-tional displacement if they form oblique angles with the pulpalwall (A); they must meet the pulpal wall at angles near 90 degreesits buccal and lingual walls form oblique angles with itspulpal wall, there will not be adequate resistance to rotat-ing forces (Fig 9-8, A). The buccal and lingual walls mustmeet the pulpal wall at angles near 90 degrees so thatthese walls will be perpendicular to any forces whichwould tend to rotate the restoration (Fig 9-8, B). A flare isthen added to the box so that there can be an acute edgeof gold at the cavosurface margin of the restoration.LengthOcclusogingival length is an important factor in bothretention and resistance. Longer preparations will havemore surface area and will therefore be more retentive.Because the axial wall occlusal to the finish line interfereswith displacement, the length and inclination of that wallbecome factors in resistance to tipping forces.For the restoration to succeed, the length must begreat enough to interfere with the arc of the casting piv-oting about a point on the margin on the opposite side ofthe restoration (Fig 9-9, A).22The shorter wall does notafford this resistance (Fig 9-9, B). The shorter the wall,the more important its inclination The walls of shorterpreparations should have as little taper as possible toincrease the resistance. Even this will no! help if the wallsare too short.It may be possible to successfully restore a tooth withshort walls if the tooth has a small diameter. The prepara-tion on the smaller tooth will have a short rotational radiusfor the arc of displacement, and the incisal portion of theaxial wall will resist displacement (Fig 9-10, A). The longerrotational radius on the larger preparation allows for a
    • Fig 9-9 The preparation wi]tipping displacement ofthe TEs (A) interferes with the;r than the short prepa-Fig 9-10 A preparation on a tooth wresists pivoting movements better thailength on a tooth of larger diameter (B).a smaller diameter (A)a preparation of equalFig 9-11 The resistance of aimproved by adding grooves (B).more gradual arc of displacement, and the axial wall doesnot resist removal (Fig 9-10, B). Parker et al found thatapproximately 95% of anterior preparations analyzed hadresistance form, while only 46% of those on molars did.?3Resistance to displacement for a short-walled prepa-ration on a large tooth can be improved by placinggrooves in the axial walls. In effect, this reduces the rota-tional radius, and that portion of the walls of the groovesnear the occlusal surface of the preparation will interferewith displacement (Fig 9-11).Substitution of Internal Featuresemented restoration isinimal taper. It may notThe basic unit of retention fortwo opposing axial walls withalways be possible to use opposing walls for retention:one may have been destroyed previously, or it may bedesirable to leave a surface uncovered for a partialveneer restoration. It may also be that the walls are pres-ent, but with a greater than desirable inclination.Generally, internal features such as the groove, the boxform, and the pin hole are interchangeable and can besubstituted for an axial wall or for each other (Fig 9-12).Substitution is important, since conditions often precludemaking an ideal preparation.Kent et al reported a marked difference between thedegree of taper of full crown preparations (18.4 to 22.2degrees) and that of boxes and grooves in the axial sur-faces of those preparations (7.3 degrees).15The taper ofthese internal features is nearly the same as the taper ofthe the instruments used to cut them (4 to 6 degrees).Apparently the widely separated axial walls of the prepa-
    • PrinciplesofPreparationsFig 9-12 These preparation featuresate frequently substituted for each other.rations are overinclined because of access, visibility, orbolh. In preparing an internal feature such as a groove ora box, however, the much shorter distance between thewalls allows the dentist to prepare them more precisely.These features offer an excellent means of enhancingIhe overall retention and resistance of an otherwise over-inclined axial wall. Woolsey and Matich found that proxi-mal grooves on short 15-degree dies provide completeresistance to faciolingual horizontal displacement.24Path of InsertionThe path o!insertion is an imaginary line along which therestoration will be placed onto or removed from thepreparation. It is determined mentally by the dentistbefore the preparation is begun, and all features of thepreparation are cut to coincide with that line. The path ofinsertion is not arbitrarily set at the completion of thepreparation by adding some feature, such as grooves. Itis of special importance when preparing teeth to be fixedpartial denture abutments, since the paths of all the abut-ment preparations must parallel each other.The correct technique must be used to survey apreparation visually, since this is the primary means ofinsuring that the preparation is neither undercut nor over-tapered. If the center of the occlusal surface of a prepa-ration is viewed with one eye from a distance of approx-imately 30 cm (12 inches), it is possible to sigh! down theaxial walls of a preparation with a minimum taper (Fig 9-13). However, it is possible to sight down the axial wallsof a preparation with a reverse (ie, undercut) taper of 8degrees when both eyes are open (Fig 9-14). Thisoccurs because of the distance between the eyes, whichis responsible for binocular vision. Therefore, it is impor-tant that preparations be viewed with one eye closed.For a preparation to be surveyed in the mouth, wheredirect vision is rarely possible, a mouth mirror is used(Fig 9-15). It is held at an angle approximately 1/2 inchabove the preparation, and the image is viewed with oneeye. If fixed partial denture abutment preparations arebeing evaluated for a common path of insertion, a firmfinger rest is established and the mirror is maneuvereduntil one preparation is centered. Then, pivoting on thefinger rest, the mirror is moved, without changing itsangulation, until it is centered over the second prepara-tionThe path of insertion must be considered in twodimensions: faciolingualty and mesiodistally. The facio-lingual orientation of the path can affect the esthetics ofmetal-ceramic or partial veneer crowns. For metal-ceramic crowns, the path is roughly parallel with the longaxis of the teeth (Fig 9-16). A facially inclined path ofinsertion on a preparation for a metal-ceramic crown willleave the facio-occlusal angle too prominent, resulting inovercontouring of the restoration, "opaque show-through," or both.Leaning the path to the facial will force the overcuttingof the mesiofacio-occlusal corner of a three-quartercrown preparation, leading to an unnecessary display ofgold. For three-quarter crowns on anterior teeth, the pathof insertion should parallel the incisal one-half of the labi-al surface (Fig 9-17). If it is inclined more facially, shortgrooves and an unnecessary display of gold will result.The mesiodistal inclination of the path must parallel thecontact areas of adjacent teeth. If the path is inclinedmesially or distally, the restoration will be held up at theproximal contact areas and be "locked out" (Fig 9-18).This is a particular problem when restoring a tilted tooth.In this situation, making the path of insertion parallel withthe long axis of the tooth will cause the contacts of theadjacent teeth to encroach on the path of insertion
    • Retention and ResFig 9-15 Preparations in the mouthare viewed through a mouth mirrorusing one eye.
    • Principles of Preparaceramic crown should paralEel the long axis of the tooth (A). If thepath is directed facially, the prominent facioincisal angle may cre-ate esthetic problems of overcontouring or "opaque show-through"(8). However, if the path is directed lingually, the facial surface willintersect the lingual surface, creating a shorter preparation. It alsomay encroach on the pulp (C),>r tooth parallels the kFig 9-18 The path of insertion of apreparation must parallel the adjacentvented from seating (B).Structural DurabilityA restoration must contain a bulk of material that is ade-quate to withstand the forces of occlusion. This bulk mustbe confined to the space created by the tooth prepara-tion. Only in this way can the occlusion on the restorationbe harmonious and the axial contours normal, preventingperiodontal problems around the restoration.Occlusal ReductionOne of the most important features for providing adequatebulk of metal and strength to the restoration is occlusalclearance (Fig 9-19). For gold alloys, there should be 1.5mm of clearance on the functional cusps (lingual of maxil-lary molars and premolars and buccal of mandibularmolars and premolars) Not quite as much is required onthe nonfunctional cusp, where 1.0 mm is sufficient.Metal-ceramic crowns will require 1.5 to 2.0 mm onfunctional cusps that will be veneered with porcelain and1.0 to 1.5 mm on nonfunctional cusps to receive ceram-ic coverage. There should be 2.0 mm of clearance onpreparations for all-ceramic crowns. Malposed teeth mayhave occlusal surfaces that are not parallel with theocclusal table. Therefore, it may not be necessary toreduce the occlusal surface by 1.0 mm to achieve 1.0mm of clearance.The basic inclined plane pattern of the occlusal sur-face should be duplicated to produce adequate clear-ance without overshortening the preparation (Fig 9-20). Aflat occlusal surface may overshorten a preparationwhose length is already minimal to provide adequateretention. Inadequate clearance makes a restorationweaker. In addition, inadequate reduction under theanatomic grooves of the occlusal surface will not provideadequate space to allow good functional morphology.The restoration also will be much more easily perforatedby finishing procedures or by wear in the mouth.
    • Fig 9-19 Inadequate t iction doos not provide the Fig 9-20 Occlusal reduction should reproduce basicr adequate thickness. planes rather than being cut as one Hat plane.Functional Cusp BevelAn integral part of the occlusal reduction is the function-al cusp bevel (Fig 9-21}. A wide bevel on the lingualinclines of the maxillary lingual cusps and the buccalinclines of mandibular buccal cusps provides space foran adequate bulk of metal in an area of heavy occlusalcontact.If a wide bevel is not placed on the functional cusp,several problems may occur. If the crown is waxed andcast to normal contour, the casting will be extremely thinin the area overlying the junction between the occlusaland axial reduction (Fig 9-22). To prevent a thin castingwhen there is no functional cusp bevel, an attempt maybe made to wax the crown io optimal thickness in thisarea. An overcontoured restoration will result and adeflective occlusal contact is likely to occur unless theopposing tooth is reduced (Fig 9-23).If an attempt is made to obtain space for an adequatebulk in a normally contoured casting without a bevel, theresult will be an overcut axial surface (Fig 9-24). In addi-tion iothe unnecessary destruction of tooth structure, thesevere inclination of the surface renders it useless forretention.
    • Principles of PreparationsFig 9-25 Inadequate axial reductioncan cause thin walls and a weak restora-tlon (A) or a bulbous, overcontouredrestoration (Bi.Fig 9-26 The three-quarter crown isreinforced by the bulk of gold that fillsthe offset and grooves (A). The occlusalshoulder strengthens the [ingual margin,and the isthmus and boxes reinforce themain body of an MOD onlay (B).Axial ReductionAxial reduction also plays an important role in securingspace for an adequate thickness of restorative material(Fig 9-25). If restorations are made with normal contoursover preparations with inadequate axial reduction, theywill have thin walls that will be subject to distortion.Frequently laboratory technicians attempt to compensatefor this by overcontouring the axial surfaces. While this"solution" to the problem strengthens the restoration, itcan have a disastrous effect on the periodontium.There are other features that serve to provide space formetal that will improve the rigidity and durability of therestoration: the offset, the occlusal shoulder, the isthmus,the proximal groove, and the box (Fig 9-26). The isthmusconnects the boxes, and the offset ties the groovestogether to enhance the reinforcing "truss effect."^Marginal IntegrityThe restoration can survive in the biological environmentof the oral cavity only if the margins are closely adaptedto the cavosurface finish line of the preparation. The con-figuration of the preparation finish line dictates the shapeand bulk of restorative material in the margin of therestoration It also can affect both marginal adaptationand the degree of seating of the restorationTo Bevel, or . . .metal restorations can be made to fit preparationsa high degree of precision, but even in well-fitting
    • Marginal IntegrityFig 9-27 Any failure of the restorationto seal (D in inset A) is reflected as amarginal opening of the same dimen-sion on a shoulder perpendicular to thepath of insertion (B). As the angle of themargin (|i) approximates 0 degrees (O,the distance between the margin andthe tooth (d) approaches 0, based on theassumption that the gap can be closedcompletely (after Rosner6).castings there is some discrepancy between the marginof the restoration and the preparation. Bevels have beenadvocated as a means of diminishing marginal discrep-ancy,ssIf the vertical discrepancy in fit is designated asD, the distance between the restoration and preparation(Fig 9-27, A) occurs unchanged between the margin, M,and the finish line, P (Fig 9-27, B). However, the closestdistance between the margin and the surface of thepreparation is a line, d, that is perpendicular to the sur-face of the tooth (Fig 9-27, C). It can be stated as a func-tion of D and the sine of angle L, or the cosine of angle ty:d-Dsiord=Dc(1)(2)As angle ji becomes smaller (more acute), the sine ofu. becomes smaller (Table 9-2); or as angle § becomeslarger (more obtuse), the cosine of ij> becomes smaller.By either computation, d diminishes by the sameamount. The more acute the angle of the margin, i, or themore obtuse the angle of the finish line, <|>, the shorter thedistance between the restoration margin and the tooth.This argument is based on the premise that the distancebetween the margin and tooth structure is infinitelycloseable, and as long as there is no cement betweenthe restoration and the preparation, that is true.. . . Not to BevelHowever, as shown so convincingly by Ostlund.^ thepresence of cement changes the scenario completely.The film thickness of the cement will prevent the corn-Table 9-2 Trigonometric Functions of AnglesOto 90 DegreesAngle(degrees)0153045607590Sine00.2590.5000 7070.8660.9661.000Cosinei.ooo -:ggm0.9660.866 •"•^IP0 7070.5000 2590plete seating of a casting with bevels that are nearly par-allel with the path of insertion of the restoration, just asJorgensen,4Kaufman et al,-"1and Eames and associates14found that crowns did not seat completely on dies withminimal taper.The film thickness of the cement imposes a limit on thereduction of the perpendicular distance from the marginto the tooth, d. The distance, d, therefore becomes a con-stant, and the previous equation is solved for D insteadofd:D = d/sin u. (3)D = dice (4)As the angle of the margin bevel becomes more acute,its sine becomes smaller, and as the angle of the finishline becomes more obtuse, its cosine becomes smaller,and D becomes larger The more nearly the bevel paral-lels the path of insertion, the greater the distance bywhich the restoration fails to seat (Fig 9-28)
    • Principles oi PreparatiFig 9-28 Theprevthicknes)l the rvnra bevel of 4addecfto a shoulder, the crown"will beprevented from seating by a factor of1.4. However, as the margin is de-creased to an angle of 30 degrees, [hecrown displaced twice as much a itwould be with a shoulder. Margins of 15and 5 degrees would prevent seating by9 and 11.5, respectively. Ifh m § I gap for the shoulder wereUrn, the ADA specification forn n m thickness, the addition of adegree bevel could keep the castingng by nearly 0.3 mm. Allpa e redrawiMcLean and Wilson have disputed the use of bevelsfor metal-ceramic crowns because the bevel marginmust be 10 to 20 degrees to noticeably improve adapta-tion.28The finish line must also be placed too far subgin-givally to hide the resultant metal collar. Pascoe demon-strated that slightly oversized castings with shouldersexhibit the least marginal discrepancy.29Gavelis et alfound a better marginal seal with acute-edged margins,but they found that shoulders permitted the most com-plete seating of a crown.30Panno and associates report-ed no better adaptability of crowns with highly acute 80-degree bevels than those with less acute 45-degreebevels.31Empirical clinical results dictate that the acute anglemargin should continue to be used on metal restorationsbut that the angle should be in the 30- to 45-degreerange. The tapered edge in a wax pattern margin pro-duced by a bevel is more readily adapted to a die than isa butt joint, and a gold margin can be burnished to slight-ly improve its adaptation after casting.Finish Line ConfigurationsWide, shallow bevels that are nearly parallel with theouter surface of the tooth should be avoided They arelikely to lead to overcontouring. Even if the axial surfacesof the overlying crown are not overcontoured, the resul-tant thin, unsupported wax at the margin potentially willbreak or distort when the wax pattern is withdrawn fromthe die and invested. The optimum margin for a goldalloy casting is an acute edge with a nearby bulk ofThe preferred gingival finish line for veneer metalrestorations is the chamfer (Fig 9-29). This tinish line hasbeen shown experimentally to exhibit the least stress, sothat the cement underlying it will have less likelihood offailure.3^33It can be cut with the tip of a round-end dia-mond, while the axial reduction is being done with theside of that instrument. However, a torpedo diamond isless likely to produce a butt joint. The margin of the castrestoration that fits against it combines an acute edgewith a nearby bulk of metal.A heavy chamfer is used to provide a 90-degree cavo-surface angle with a large-radius rounded internal angle(Fig 9-30) It is created with a round-end tapered diamond.In the hands of an unskilled operator, this instrument cancreate an undesirable fragile "lip" of enamel at the cavo-surface. The heavy chamfer provides better support for aceramic crown than does a conventional chamfer, but it isnot as good as a should&r. A bevel can be added to theheavy chamfer for use with a metal restoration.The shoulderhas long been the finish line of choice forthe all-ceramic crown (Fig 9-31). The wide ledge pro-vides resistance to occlusal forces and minimizes stress-es that might lead to fracture of the porcelain. It producesthe space for healthy restoration contours and maximumesthetics. However, it does require the destruction ofmore tooth structure than any other finish line. The sharp,90-degree internal line angle associated with the classicvariety of this finish line concentrates stress in the toothand is conducive to coronal fracture. The shoulder gen-erally is noi used as a finish line for cast metal restora-tions.The radial shoulder is a modified form of shoulder fin-ish line (Fig 9-3?) The initial instrumentation of the ledgeis accomplished with the same flat-end tapered diamond
    • i support of the ci,1"anSle."used for the classic shoulder A small-radius roundedinternal angle is instrumented by an end-culting parallel-sided carbide finishing bur, and finishing is completedwith a specially modified bin-angle chisel. The cavosur-face angle is 90 degrees, and shoulder width is onlyslightly lessened by the rounded internal angle. Stressconcentration is less in the tooth structure than with aclassic shoulder, and support for ceramic restorationwalls is good. Destruction of tooth structure required forthis configuration is not significantly less than thatrequired for a classic shoulder, however.The shoulder with a bevel is used as a finish line in avariety of situations {Fig 9-33). It is utilized as the gingivalfinish line on the proximal box of inlays and onlays, andfor the occlusal shoulder of onlays and mandibular three-quarter crowns. This design can also be used for thefacial finish line of metal-ceramic restorations where gin-gival esthetics are not critical. It can be used in those sit-uations where a shoulder is already present, eitherbecause of destruction by caries or the presence of pre-vious restorations. It is also a good finish line for prepa-rations with extremely short walls, since it facilitates axialwalls that are nearly parallel.31By adding a bevel to an existing shoulder, it is possibleto create an acute edge of metal at the margin. Theshoulder with a bevel should not be used routinely for full
    • PrinciplesofPreparabFig 9-35 Bucco-occlusal finish lines or a maxillary ihree-quartercrown A flat bevel (A), a contrabevel (B), and, when the cusp isbulky, a knife edge (C), are acceptable finish lines. The knife edges not an acceptable finish line on small, sharp cusps (D). (AfterIngraham et alssand Richter andVeno.51}veneer restorations because the axial reduction requiredto obtain it is unnecessarily destructive of tooth structure.Some variation of a shoulder, with or without a bevel, mayafford some resistance against distortion during porce-lain firing,35The ultimate in finish lines that permit an acute marginof metal is the knife edge (Fig 9-34). Unfortunately, its usecan create problems. Unless it is carefully cut, the axialreduction may fade out instead of terminating in a defi-nite finish line. The thin margin of the restoration that fitsthis finish line may be difficult to accurately wax and cast.It is also more susceptible to distortion in the mouth whenthe casting is subjected to occlusal forces.The use of the knife edge can result in overcontouredrestorations when an attempt is made to obtain adequatebulk by adding to the external axial contours of therestoration. In spite of its drawbacks, it is sometimes nec-essary to use the knife edge. It may have to be used onthe lingual surface of mandibular posterior teeth, on teethwith very convex axial surfaces, and on the surfacetoward which a tooth may have tilted.The finish line used for the bucco-occlusal margin ofmaxillary partial veneer and MOD onlay restorations isworthy of attention. It too must meet the requirement ofproviding an acute edge with a nearby bulk of metal. Theenamel must also be protected by a finishing bevel thatwill leave the tooth structure at the cavosurface anglewith sufficient bulk to resist fracture and chipping.36Themost commonly used form is a narrow (0.3 to 0.5 mm) fin-ishing bevel perpendicular to the path of insertion of therestoration (Fig 9-35, A). A contrabevel may also be usedwhere function is heavy and esthetic requirements areminimal (Fig 9-35, B). There are a few situations in whichno bevel is required (Fig 9-35, C), but this can only beaccomplished on a cusp that is bulky enough to allow theacute edge of metal and still be able to finish the enam-el at the cavosurface angle. A bevel is mandatory if itselimination will create an unsupported edge of enamel(Fig 9-35, D).Preservation of the PeriodontiumThe placement of finish lines has a direct bearing on theease of fabricating a restoration and on the ultimate suc-cess of the restoration. The best results can be expectedfrom margins that are as smooth as possible and are fullyexposed to a cleansing action.37Whenever possible, thefinish line should be placed in an area where the marginsof the restoration can be finished by the dentist and keptclean by the patient. In addition, finish lines must beplaced so that they can be duplicated by the impression,without tearing or deforming the impression when it isremoved past them.
    • Finish lines should be placed in enamel when it is pos-sible to do so. In the past, the traditional concept hasbeen to place margins as far subgingivally as possible,based on the mistaken concept that the subgingival sul-cus is caries-(ree.3aThe practice of routinely placing mar-gins subgingivally is no longer acceptable. Subgingivalrestorations have been described as a major etiologicfactor in periodontitis.39"4* The deeper the restorationmargin resides in the gingival sulcus, the greater theinflammatory response.47"50Although Richter and Ueno reported no differencebetween subgingival and supragingival margins in a 3-year clinical study, they recommended that placement besupragingival whenever possible.51Eissmann et al madea similar recommendation.37Koth also failed to find a linkbetween margin location and gingival health in a select-ed patient population on a strict hygiene regimen.52These studies do not refute the evidence that subgin-gival margins are likely to cause gingival inflammation.They merely demonstrate that margin location is not ascrucial when placed by a highly skilled dentist in themouth of a motivated, cooperative patient. Ego maytempt a dentist to believe that he or she is one of the"good guys" who can handle the "simple" task of achiev-ing well-fitting albeit subgingival margins on a crown.However, subgingival margins can be very difficult toevaluate.Christensen demonstrated that experienced restora-tive dentists can miss marginal defects as great as 120|im when the margins are subgingival.53In a radiograph-ic study, Bjorn et al found that more than half of the prox-imal margins of gold crowns had defects greater than 0.2mm and more than 40% of the proximal margins ofceramic crowns had defects thai exceeded 0.3 mm.54Nonetheless, there will be many situations in whichsubgingival margins are unavoidable. Because prepara-tion length is such an important factor in resistance andretention, preparations are frequently extended subgingi-vally to increase retention.-ts-ss-se The placement of finishlines can also be altered from ideal locations bycaries,4555-58the extensions of previous restora-tions,4555-57trauma,45-57or esthetics.45K"SfiExercise caution if conditions require that the finish linebe placed any closer to the alveolar crest than 2.0 mm,which is the combined dimension of the epithelial andconnective tissue attachments.59Placement of a restora-tion margin in this area probably will result in gingivalinflammation, loss of alveolar crest height, and formationof a periodontal pocket.60"Crown lengthening" may bedone to surgically move the alveolar crest 3.0 mm apicalto the location of the proposed finish line to guarantee thebiologic width and prevent periodontal pathology. Thiswill allow space for the connective and epithelial attach-ments and a healthy gingival sulcus. If the deep finishline is located interproximally and will require extensiveremoval of bone between the tooth being restored andthe adjacent tooth, it may be better to extract the tooth inquestion rather than periodontally compromise itshealthy neighbor.InstrumentationThe preparation of teeth to receive cast metal or ceramicurn (Table 9-3). The excavation of caries should beaccomplished with sharp spoon excavators and roundburs (no. 4 or no. 6) mounted in a contra-angle hand-piece. Hand chisels may be used to accentuate thefacial and lingual walls of proximal boxes. All other pro-cedures usually are accomplished with a high-speed airturbine handpiece.Small diamond points, used with a water-air spray in ahigh-speed handpiece, will remove precisely controlledamounts of tooth structure. The surface that remains canbe easily smoothed. There is no indication for the use oflarge diamond cutting discs in low-speed contra-angle orstraight handpieces. They frequently overextend prepa-rations, and their potential for injury to the patient is great.It is important that the cavosurface finish line besmooth and continuous to facilitate the fabrication ofrestorations with well-adapted margins. Gross reductionis most efficiently accomplished with coarse diamonds.However, they leave irregular cavosurface finishlines.6162and some other instrument should be used toobtain a smooth finish line By using diamonds and car-bide finishing burs of the same size and shape, as devel-oped by Lustig et al,6364it is possible to maintain the fin-ish line configuration developed by the diamond instru-ment Torpedo diamonds are followed by torpedo car-bide burs to produce chamfers; flat-end tapered dia-monds by H158 carbide finishing burs for radial shoul-ders; and flame diamonds by flame burs for gingivalbevels and conservative proximal flares. Acceptable fin-ish lines on vertical flares can be obtained by the use ofabrasive paper discs,6ijbut they should be used with arubber dam to protect soft tissue.Nondentate tapered burs (169L, 170L, and 171L) areused for grooves, boxes, isthmuses, and offsets wherethey are needed. They are also used for smoothing anysurface that will not terminate in a curved finish line,which they would nick, and for creating occlusal andincisal bevels Cross-cut or dentate burs are employedfor removal of old restorations, but the horizontal ridgesthey leave on tooth structure make them unacceptablefor planing tooth surfaces
    • lableShape9-3 Rotary Instruments for Tooth PreparationsUse Brasseler Busch Dtitisco Horico MidwestManufacturerMiltex PremieSSr White Star Union VaiitageRound-end 1. Depth onetapered groovesdiamond 2. Occlusal r199-016 198-016 770 8 854-016 770-8at-end 1. Axial reductioitapered (MCR, PJC)diamond 2 Shoulder(MCR, PJC)172-016 172-018877-010 — 232 130-012 289-012Short needle 1. Initial proximal axireduction(posterior teeth)52-012 — 164-012 16! 016 — 209.6 845-01030006-012 —FlamiSmaldia3 diamond1wheel12.! •(anteProxiGingLingLrior teeth)mal flareival beveljal reduction 909-040 —Tapered 1. Seating groovefissure bur 2. Proximaf groove(posterior teeth)3 Offset4. Occlusal shoulder5. Isthmus6. Proximal box7 Smoothing andfinishing8. Occlusal and mcisbevels216 249-010 249-012 —825 068-040 068-040 —171L-012 — 171L-012 171L 71L-01252-012 260-8 205L 862/012I71L-012 —Tapered 1 Initial groovealignment2. Angles of proxiboxes3. Smoothing and4. Occlusal and inbevels170L-010 170L-010 170L-010169L-009 — 169L-O09170L-010169L-00970L-009 170L69L-008 169L— 170L-010— 169L-009
    • Table 9-3ShapeContinuedUse Bta;sseler Bussch Densco Horico MidwestManMilllufacturer*ex PremieSSr White Star Union Vantage. Conventionalshoulder finishingTorpedo bur 1. Axial wall finishing2. Chamfer finishing— 957-010 —282-010 243-010 —H48L-010 —bur1. Radial shoulderfinishing•Brasseler USA Inc, Savannah, GABusch, Pfingsl 8 Co, Inc. South Plainfield, NJDensco, Teledyne Getz, Elk Grove Village, ILHorico, Pfingst & Co, Inc, South Plainfield, NJMidwest Dental Products Corporation, Des Plaines, ILMiltex Instrument Co, Inc, Lake Success, NYPremier Dental Products Co, Norristown, PASS White Burs, Inc. Lakewood, NJStar Dental Products, Lancaster. PAUnion Broach Division of Moyco Industries, Emigsville,Vantage, Miltex Instrument Co. Inc, Lake Success. NY
    • Principles of PreparationsReferencesI Conzett JV: The gold inlay. DentCosmos 1910; 52.1339.> Ferrier Wl. Cavity preparation tor gold foil, gold inlay, andamalgam operations. J Natl Dent Assoc 1917; 4i441.1. Ward ML: The American Textbook of Operative Dentistry, ed6. New York, Lea & Febiger, 1926, pp 381-395.I. Jorgensen KD: The relationship between retention and con-vergence angle in cemented veneer crowns. Ada OdontoiScand 1955; 13:35-40.i Kaufman EG, Coelho DH, Colin L: Factors influencing theretention of cemented gold castings. J Prosthet Dent 1961;11:487-502.i. Dykema RW, Goodacre CJ, Phillips RW; Johnstons ModemPractice in Crown and Bridge Prosthodontics, ed 4.Philadelphia, WB Saunders Co, 1986, p 24.. Shillingburg HT, Hobo S, Fisher DW. Preparations for CastGold Restorations. Chicago, Quintessence Publ Co. 1974, p16.I. Tylman SD, Malone WFP. Tylmans Theory and Practice ofFixed Prosthodontics. ed 7. St Louis, CVMosbyCo, 1978. p103.) El-Ebrashi MK, Craig RG, Peyton FA: Experimental stressanalysis of dental restorations. Part IV. The concept of par-allelism of axial walls. J Prosthet Dent 1969; 22.346-353.I. Mack PJ; A theoretical and clinical investigation into thetaper achieved on crown and inlay preparations. J OralRehabii 1980; 7:255I Weed RM, Suddick RP, Kleffner JH: Taper of clinical andtypodont crowns prepared by dental students J Dent Res1984; 63:286 (abstr no. 1036).1. Noonan JE, Goldfogel MH: Convergence of the axial wallsof full veneer crown preparations in a dental school environ-ment. J Prosthet Dent 1991; 66:706-708.I. Eames WB, ONeal SJ, Monteiro J, Roan JD, Cohen KS:Techniques to improve the seating of castings J Am DentASSOC1978;96:432.>. KentWA, Shillingburg HT, Dumpreparations for cast restoratic19:339-345.i. Nordlander J, Weir D, Staffer W, Ochi S: The taper of clinicpreparations for fixed prosthodontics. J Prosthet Dent 19860:148-151.J Dodge WW, Weed RM, Baez RJ, Buchanan RN: The effectof convergence angle on retention and resistance form.Quintessence Int 1985; 16.191.). Lorey RE, Myers GE: The retentive qualities of bridge retain-ers. JAm Dent Assoc 1968; 76:569-572.). Rosenstiel E: The retention of inlays and crowns as a func-tion of geometrical form. Sr Dent J 1957; 103:388-394.I. Kishimoto M, Shillingburg HT, Duncanson MG: Influence ofpreparation features on retention and resistance. Part II.Three-quarter crowns. J Prosthet Dent 1983; 49 188-192.!. Smyd ES: Advanced thought in indirect inlay and fixedbridge fabrication. JAm Dent Assoc 1944; 31759-768.!. Parker MH, Malone KH, Trier AC, Striano TS: Evaluation ofresistance form for prepared teeth. J Prosthet Dent 1991;66.730-733.24. Woolsey GD, Matich JA. The effect of axial groovesresistance form of cast restoralions J Am Dent Assoc97.978-980.25. Willey RE: The preparers. JAm Dent Assoc26. Rosner D: Function, placement and reproduction of bevelsfor gold castings. J Prosthet Dent 1963; 13:1160-1166.27. Ostlund LE. Cavity design and mathematics: Their effect ongaps at the margins of cast restorations. Oper Dent 1985;10.122-137.28 McLean JW, Wilson AD: Butt joint versus bevelled gold mar-gin in metal ceramic crowns J Biomed Mater Res 1980;14:239-250.29. Pasc of finis s for full>e DF. Analysis of the geometcrown restorations J Prosthet Dent1978; 40:157-162.30. Gavehs JR, Morency JD, Riley ED, Sozio RB: The effect ofvarious finish line preparations on the marginal seal andocclusal seat of full crown preparations. J Prosthet Dent1981; 45:138-145.31. Panno FV, Vahidi F, Gulker I, Ghalili KM: Evaluation of the 45-degree labial bevel with a shoulder preparation. J ProsthetDent 1986; 56:655-661.32. El-Ebrashi MK, Craig RG, Peyton FA: Experimental stressanalysis of dental restorations. Part III. The concept of thegeometry of proximal margins. J Prosthet Dent 1969;22333-345.33. Farah JW, Craig RG: Finite element stress analysis of arestored axisymmetric first molar. J Dent Res 1974; 53:859-866.34. Gage JP: Rationale for bevelled shoulder veneer crownpreparations Aust Dent J 1977; 22:432-435.35. Shillingburg HT, Hobo S, Fisher DW: Preparation design andmargin distortion in porcelain-fused-to-metal restorations. JProsthet Dent 1973; 29276-284.36. Ingraham R, Bassett RW, Koser JR: An Atlas of Cast GoldProcedures, ed 2. Buena Park, CA, Uni-Tro College Press,1969, p34.37. Eissmann HF, Radke RA, Noble WH. Physiologic design cri-teria for fixed dental restorations. Dent Clin North Am 1971;15:543-568.38 Black GV The management of enamel margins DentCosmos 1891; 3385-100.39. Waerhaug J: Histologic considerations which govern wherethe margins of restorations should be located in relation tothe gingiva. Dent Clin North Am 1960; 4:161-176.40. Mormann W, Regolati B, Renggli HH: Gingival reaction towell-fitted subgingival proximal gold inlays. J ClinPer/odortfo/1974; 1:120-125.41. Janenko C, Smales RJ: Anterior crowns and gtngival health.Aust Dent J 1979; 24:225-230.42. Romanelli JH: Periodontal considerations in tooth prepara-tion for crowns and bridges Dent Clin North Am 1980;24:271-284.43. Wilson RD: Intracrevicular restorative dentistry. Int JPeriodont Rest Dent 1981, 1 (4):35^9.44. Silness J: Periodontal conditions in patients treated withdental bridges. III. The relationship between the location ofthe crown margin and the periodontal condition. J PeriodontRes 1970; 5:225-229.45. Larato DC: Effect of cervical margins on gingiva. J CalifDent Assoc 1969; 45:19-22.46. Reeves WG: Restorative margin placement and periodontalhealth. J Prosthet Dent 1991; 66:733-736.
    • o dental restoration . AdaI. Newcomb GM: The relationship between the location ofsubgingival crown margins and gingival inflammation. JPeriodontal 1974; 45:151-154.). Jameson LM, Malone WFP: Crown contours and gingivalresponse. J Prosthet Deftt-982; 47.620-624.. Richter WA, Ueno H: Relationship of crown margin place-ment to gingival inflammation. J Prosthet Dent 1973"30156-161.. Koth DL: Full cin a contrail48:681-685.stings JL Bjorn AL, Bjorn H, Grkovic B: Marginal fit of restorations andits relation to periodontal bone levet. Part II. Crowns.Odontol Rev 1970; 21:337-346.i. Berman MH: The complete coverage restoration and thegingival sulcus J Prosthet Dent 1973; 29:301-304i. Stein RS, Kuwata M: A dentist and a dental technologistanalyze current ceramo-metal procedures. Dent Clin NorthAm 1977; 21:729-749.57. Behend DA. Ceramometal restorations with supragingivalmargins. J Prosthet Dent 1982; 47:625-632.58. Gardner FM: Margins of complete crowns—Literaturereview J Prosthet Den! 1982; 48:396^100.59. Garguilo AW, Wentz FM, Orban B: Dimensions of the den-togingival junction in humans J Penodontol 1961;32:261-267.60. Ingber JS, Rose LF, Coslet JG1The "biologic width"—A con-cept in penodontics and restorative dentistry. AlphaOmegan 1977; 10:62-65.61. Barnes IE: The production of inlay cavity bevels. Br Dent J1974; 137:379-390.62. Kinzer RL, Morris Q- Instruments and instrumentation to pro-mote conservative operative dentistry. Dent Clin North Am1976; 20:241-257.63. Lustig LP, Perlitsh MJ, Przetak C, Mucko K: A rational con-cept of crown preparation. Quintessence In! 1972; 3:35-44.64 Lustig LP: A rational concept of crown preparation revisedand expanded. Quintessence Int 1976; 7:41-48.65. Tronstad L, Leidal Tl: Scanning electron microscopy of cav-ity margins finished with chisels or rotating instruments atlow speed. J Dent Res 1974; 53:1167-1174.
    • Chapter 10Preparations for Full Veneer CrownsThere are numerous situations that call for the use ofa full veneer restoration. Clinicians have long con-sidered it to be the most retentive of the veneerpreparations.1Controlled laboratory studies have shownthat when compared with partial veneer designs, the fullveneer crown exhibits superior retention23and resis-tance.4This does not mean that a full veneer design mustbe used on every tooth. Instead, it should be used on thoseteeth whose restoration demands maximum retention.A requirement for maximum retention is not commonlyseen in the placement of single restorations. This need islanifested in the design of rifixed partial diplaced on the prepar;of a full veneer crownthe abutment tooth isis longVariations of the fulr the5 additional demands areI and restoration. The selectioniner becomes mandatory whenill or when the edentulous spancrown, the metal-ceramicn, are used in situationsthat require a good cosmetic result. The full veneer crownshould be used when less extensive and less destructivedesigns have been considered and found lacking inretention, resistance, coverage, or esthetics to properlyrestore the tooth.Full coverage in the right circumstances can be excel-lent treatment, but it is overused. A report of dental insur-ance data in 1979 indicated that nearly 93% of the castrestorations done by dentists submitting claims to thatcompany were of a full-coverage design.6Undoubtedlythe percentage would be greater today. The removal ofall morphologic form of the tooth is radical treatment, andrestoring it properly can be difficult.6The dentist shouldbe sure it is necessary.Full Metal Crown PreparationWhen all of the axial surfaces of a posterior tooth havebeen attacked by decalcification or caries, or when thosesurfaces have been previously restored, the tooth is acandidate for a full metal crown. By tying together theremaining tooth structure, a full metal crown canstrengthen and support the tooth.7It should be used judi-ciously, though, because it does require a destructivepreparation. It may weaken rather than strengthen theremaining tooth structure when there has been extensivedestruction previously in the center of the tooth. However,the preparation for a full metal crown is less destructivethan that required for either metal-ceramic or all-ceramicFull coverage should not be used in mouths withuncontrolled caries. The full veneer crown is a restorationthat replaces lost tooth structure and imparts some mea-sure of structural support to the tooth However, it doesnot protect the tooth against the biological causes of thecaries. These processes must be controlled by othermeans before any restoration can be successfulArmamentarium1 Handpiece2. No. 171l_bur3. Round-end tapered diamond4. Short needle diamond5. Torpedo diamond6. Torpedo bur7. Red utility waxThe preparation for a full veneer crown is begun withocclusal reduction, creating about 1.5 mm of clearanceon the functional cusps and 1.0 mm on the nonfunction-al cusps. By accomplishing this step first, the occlu-sogingival length of the preparation can be determined.The potential retention of the preparation can then beassessed, and auxiliary features can be added if neces-sary.Depth-orientation grooves are placed on the occlusalsurface of the tooth to provide an easy reference to deter-mine when reduction is sufficient. If reduction is begunwithout orientation marks, time will be wasted in repeatedchecks for adequate clearance. A round-end tapereddiamond is used to place the grooves on the ridges andthe primary grooves of the occlusal surface. If there isalready some clearance with the opposing tooth because
    • PreparationsforFullVeneerCrov@of malpositioning or fracture of the tooth being prepared,the grooves should not be made as deep.The tooth structure remaining between the orientationgrooves is removed to accomplish the occlusal reduction(Fig 10-1). Any roughness left by the grooves should beremoved, keeping the occlusal surface in the configura-tion of the geometric inclines that make up the occlusalsurface of any posterior tooth.A wide bevel is placed on the functional cusp, againusing the round-end tapered diamond (Fig 10-2) Depth-orientation grooves are also helpful in obtaining thisreduction. The functional cusp bevel, placed on the buc-cal inclines of mandibular buccal cusps and the lingualinclines of maxillary lingual cusps, is an integral part ofthe occlusal reduction. Failure to place this bevel can pro-duce a thin casting or poor morphology in the restoration.Occlusal clearance is checked by having the patientclose on a 2.0-mrn-thick strip of red utility wax held overthe preparation. The wax is then held up to a light todetermine the adequacy of the occlusal clearance. Anypart of the preparation that has insufficient occlusalclearance will be readily detectable as a thin spot in thewax. Additional tooth structure should be removed fromthe indicated areas and rechecked.The occlusal reduction and functional cusp bevel areplaned smooth with a no. 171L bur now or when the buris used to instrument the seating groove. There shouldnot be sharp angles or ridges where the planes or beveljoin. If there are, they should be removed with thetapered fissure bur.The buccal and lingual walls are reduced with a torpe-do diamond, whose sides will produce the desired axial
    • FullMetalCrownPreparationFig 10-6 Scaling groovy: No. 171L bar.Fig 10-7 Features of a mandibuiar fullmetal crown preparation and the func-FunctionalCusp BevelSeating GroovePlanar Occlusal,^ Reduction/ ^ / ^ > ^ structural durability_ _ / 7-^ ^-^X stmc"iralt"irabi""k: sV Chamfer,^VJ» x^ / marginal integrity . Ni^N // ( penodontal preservationreduction while its tapered tip forms a chamfer finish line(Fig 10-3). A definite, even finish line is necessary toenable the fabrication of a well-fitting restoration,8andthe chamfer is the best for providing the bulk needed forstrength while still allowing good adaptation.1The initial proximal cuts are made with a short needlediamond (Fig 10-4). The thin diamond is worked throughthe proximal area in an occlusogingival or buccolingual"sawing" motion, carefully avoiding the adjacent teeth.Once sufficient maneuvering room has been obtained,the torpedo diamond is introduced to plane the wallswhile simultaneously forming a chamfer as the interprox-imal gingival finish line.All of the axial surfaces are smoothed with a torpedocarbide finishing bur whose size and shape enable it tofinish the chamfer finish line as well (Fig 10-5). Specialcare should be taken in rounding the corners from thebuccal or lingual surfaces to the proximal surfaces toinsure that the finish line will be smooth and continuous.The final step in the full veneer preparation is the place-ment of a seating groove (Fig 10-6). It will prevent anyrotational tendencies during cementation, and it will helpguide the casting to place. The groove is formed with ano. 171L bur and is placed in the axial surface with thegreatest bulk. This usually will be on the buccal surfaceof mandibuiar preparations and on the lingual surface ofmaxillary preparations. On preparations for long-spanfixed partial dentures, there should be a buccal and a lin-gual groove io increase the resistance to mesiodistalmovement. The features of a preparation for a full veneermetal crown and the function served by each are shownin Fig 10-7
    • ^ Preparations lor Full Veneer CrownsMetal-Ceramic CrownsThe metal-ceramic restoration, also called a porcelain-fused-to-metal restoration, consists of a ceramic layerbonded to a thin cast metal coping that fits over the toothpreparation. Such a restoration combines the strengthand accurate fit of a cast metal crown with the cosmeticeffect of a ceramic crown. With a metal understructure,metal-ceramic restorations have greater strength thanrestorations made of the ceramic alone. Friedlander et alfound the metal-ceramic restoration to be 2.8 times asstrong.9As a result, the longevity of metal-ceramicrestorations is greater, and it can be used in a wider vari-ety of situations, including the replacement of missingteeth with fixed partial dentures.Since the restoration is a combination of metal andceramic, it is not surprising that the tooth preparation forit is likewise a combination. There is deep reduction onthe facial surface to provide space for the coping and aceramic layer thick enough to achieve the desired cos-metic result. On the lingual surface and the lingualaspects of the proximal surfaces, there is shallowerreduction similar to that used for a full metal crown. Theremay be a wing on each proximal surface where the deepfacial reduction ends and the shallower proximal reduc-tion begins.10Adequate reduction is essential to achieving a goodcosmetic result. Without the space for a sufficient thick-ness of ceramic material, two things can happen. (1) therestoration will be poorly contoured, adversely affectingboth the cosmetic effect of the crown and the health ofthe surrounding gingiva, and (2) the shade and translu-cency of ihe restoration will not match adjacent naturalteeth.Anterior Metal-Ceramic CrownsA uniform reduction of approximately 1.2 mm is neededover the entire facial surface. To achieve adequatereduction without encroaching upon the pulp, the facialsurface must be prepared in two planes that correspondroughly to the two geometric planes present on the facialsurface of an uncut tooth (Fig 10-8). If the facial surfaceis reduced in one plane that is an extension of the gingi-val plane, the incisal edge will protrude, resulting in abad shade match or an overcontoured "block." If thefacial surface is prepared in one plane that has adequatefacial reduction in the incisal aspect, the facial surfacewill be overtapered and too close to the pulp.Armamentarium1. Laboratory knife with no. 25 blade2. Silicone putty and accelerator3. Handpiece4. Flat-end tapered diamond5. Small wheel diamond6. Long needle diamond7. Torpedo diamond8. Torpedo bur9. H158-012 radial fissure bur10. RS-1 binangle chiselIf an index is made before the preparation is begun, itwill be possible to have a positive check on reductionproduced by the preparation. If the contours of the exist-ing tooth are correct, the index can be made mtraorallywhile waiting for the anesthetic to take effect. However, ifthe tooth is badly broken down, or if contours are to bechanged in the finished restoration, the index should bemade from a preoperative wax-up on the diagnostic cast.One-half scoop of putty is mixed with the appropriateamount of accelerator and kneaded in the palm of thehand until all streaks of the accelerator have disap-peared. The putty is then adapted with a thumb and fore-finger over the tooth to be prepared (Fig 10-9). It shouldbe allowed to polymerize on the tooth, which should takeabout 2 minutes. The index should cover the entire labialand lingual surface of the tooth to be prepared, plus thecorresponding surfaces of at least one adjacent tooth(Fig 10-10).The index is then removed from the teeth. A laboratoryknife with a no. 25 blade is used to cut along the incisaledges of the tooth imprints to separate the index into alabial and a lingual half (Fig 10-11). The lingual half is setaside for the time being. The labial portion of the index iscut from mesial to distal across the imprints of the labialsurfaces of the teeth to produce an incisal and a gingivalhalf (Fig 10-12).The gingival half of the labial portion is positioned onthe teeth to insure that it is closely adapted to the labialsurfaces (Fig 10-13). After removing the labial index, thelingual index is put in position and its adaptation to theincisal edges of the teeth is checked (Fig 10-14).The labial and lingual indices are set aside until thepreparation is completed. Then the gingival half of thelabial index is positioned and checked for adequate labi-al clearance for a metal coping and porcelain (Fig 10-15). If the reduction is inadequate, the index is removedfrom the mouth and more tooth structure must beremoved. The incisal clearance is checked by putting thelingual index in place and evaluating the distancebetween the incisal edge of the prepared tooth and theincisal edge of the tooth imprint on the index (Fig 10-16).The initial step in the preparation for a metal-ceramiccrown is the placement of depth-orientation grooves onthe labial and incisal surfaces with a flat-end tapered dia-mond. These orientation cuts, recommended byPreston10and Miller,1are a means of judging the amount
    • Metal-Ceramic CroiFig 10-8 li is important to reduce themetal-cearmic restoration (A). If onlyone plane is produced, opaque porce-lain may show through (B), ibe labialsurface may be overcontoured (C), orthe pulp may be encroached upon (D).Fig 10-9 Mold silicone putty on ihe labial and lingual surfaces of Fig 10-10 The index should contact the labial and linguathe tooth to be prepared and the teeth adjacent to it. faces of the tooth on either side of the tooth to be prepared.labial and a lingual hal
    • Preparations lor Full Veneer Crownsof tooth structure to be removed. The full diameter of aninstrument of known dimension is sunk into the tooth. Thedepth of reduction can be measured using the uncutouter surface o( the remaining tooth structure as a refer-ence point.11If reduction is done without grooves, timewill be wasted in repeatedly rechecking reduction withthe index.The labial grooves should be cut in two sets: one setparallel with the gingival half of the labial surface andone set parallel with the incisal half of the labial surface(Fig 10-17). These grooves should be 1.2 mm deep. Theincisal grooves should be cut all the way through theincisal edge and should extend 2.0 mm gingivally.Incisal reduction is done with the flat-end iapered dia-mond so that it parallels the inclination of the unpreparedincisal edge (Fig 10-18). This is done first to allow easyinstrument access to the axial surfaces and the gingivalfinish line. Inadequate incisal reduction results in poorincisal translucency in the finished restoration.Reduction of the incisal portion of the labial surface isdone with the same flat-end tapered diamond. All toothstructure is planed off to the depth of the orientationgrooves (Fig 10-19). The gingival portion of the labialsurface is likewise reduced to the depth of the grooveswith the flat-end tapered diamond. The reduction is car-ried around the labioproximal line angles to a point 1.0
    • Fig 10-17 Depth-orientalFlat-end tapered diamond.Fig 10-18 Flat-end Fig 10-19 Labial reduction (incisal half):Flat-end tapered diamond.Fig 10-20 Labial reduction (gingivFlat-end tapered diamond.I half): Fig 10-21 Lin; Fig 10-22 Initial pr<Long needle diamond.mm lingual to the proximal contacts (Fig 10-20). Althoughthe resulting wings of tooth structure can provide someresistance to rotation, that is not the primary reason fortheir existence. They conserve tooth structure, if in factthere is still sound tooth structure left on the proximal sur-faces. It is important that the portion of each wing thatfaces labially has the same inclination as the gingivalportion of the labial surface.The lingual surface is reduced with a small wheel dia-mond to obtain a minimum of 0.7 mm of clearance withthe opposing teeth (Fig 10-21). Those portions of the lin-gual surface that will have a ceramic veneer should have1.0 mm of clearance. The junction between the cingulumand the lingual wall must not be overreduced.Overshortening the lingual wall will reduce retention.A long needle diamond is used to complete accessthrough the proximal areas to minimize the chances ofnicking the adjacent teeth (Fig 10-22). Much of the axialreduction in the region of the proximal contact will havebeen accomplished already by the flat-end tapered dia-mond. The lingual aspect of the proximal axial walls, aswell as the lingual surface, are reduced with the torpedodiamond (Fig 10-23). The lingual and proximal axial sur-faces are smoothed with the torpedo bur, accentuatingthe chamfer on the lingual and proximal surfaces at thesame time (Fig 10-24).
    • i finishing: Torpedo bur.An H158-012 radial fissure bur is used to smooth thelabial surface (Fig 10-25) All angles and edges on thepreparation are rounded with the sides of the bur to facil-itate seating of the restoration later At the same time thatthe labial surface is being planed by the side of the bur,the end is forming a radial shoulder finish line.Shoulders have been advocated for gingivofacial finishlines of metal-ceramic preparations alone?-18or with nar-row bevels.1017"20Some investigators have reported thatmetal-ceramic crowns with metal gingivofacial marginsmade over shoulder finish lines distort less during porce-lain firing.2122A possible explanation is that the shoulderconfiguration provides space for an internal rib of metalto buttress the margin.">.23 Other investigators havereported not finding a difference in marginal fit. Theyhypothesize that marginal gaps following ceramic firingmay be caused either by technical difficulties in forminga knife edge of metal and ceramic24or by differences inmetal/ceramic combinations.?5However, there is a compelling reason for not using ametal margin at all. The metal collar that accompanies abevel on a shoulder26often requires the finish line to beplaced deep in the gingival sulcus to hide the metal.27Ifsome form of shoulder without a bevel is used, an all-ceramic margin can be fabricated. This eliminates ametal collar at the faciogingival margin of the finishedmetal-ceramic restoration, and there is no need to burythe margin beneath the gingivaQuanlitative evaluations of the marginal fit of all-ceram-ic shoulders on metal-ceramic crowns have found satis-factory adaptation of the ceramic to the preparation fin-ish line. Belser et al reported in vivo marginal discrepan-cies of 46 jim on cemented metal-ceramic crowns withall-ceramic facial margins.23They found no significantdifferences among crowns with all-ceramic margins andthose with metal collar margins over shoulder andbeveled shoulder finish lines. In vitro studies by West andassociates29and Hunt et al30found minimal marginal dis-crepancies in all-ceramic shoulder margins on metal-ceramic crowns. Of course, a dentist can use all-ceram-ic margins on metal-ceramic crowns only if the technicianis capable of producing restorations with accurateceramic margins.Zena et al demonstrated that all-ceramic marginsmade over hand-planed shoulders fit significantly betterthan margins made over finish lines cut solely with rotaryinstruments.31However, if a conventional enamel chisel isused for planing a radial shoulder, the sharp angles atthe ends of the cutting blade will destroy the roundedinternal angle of the finish line (Fig 10-26).A modified 15-8-8 binangle chisel, the RS-1 (SuterDental Mfg, Chico, CA), is recommended to avoid thisproblem (Fig 10-27). This instrument has a hoe (pullstroke) blade at both ends, unlike a conventional 15-8-8binangle chisel, which has a hoe (pull stroke) blade atone end and a chisel (push stroke) blade at the other (Fig10-28). One corner of one RS-1 blade is rounded with amounted Arkansas stone (Fig 10-29, A), and the oppositecorner is rounded on the other end (Fig 10-29, B).One end, with the rounded corner against the gin-givoaxial "angle," is used to instrument the radial shoul-der on one-half of the preparation (Fig 10-30). The otherend, with its modified corner also against the roundedgingivoaxial junction, is used to smooth the finish line onthe other half of the preparation. The 1,5-mm-wide bladewill extend over the actual finish line, which is 1.2 to 1.5mm wide. This will remove any lip of enamel that mightextend occlusally from the cavosurface angle.The features of a preparation for an anterior metal-ceramic restoration and the function served by each areshown in Fig 10-31.
    • Fig 10-26 The sharp corners of a conventional chisel will gougethe gingivoaxial angle (inset) of a radial shoulder.Fig 10-29 Round an angle at one endof the RS-1 (A} and the opposite angleon the other end (B).
    • Preparations for Full Veneer Cro— M r i*DFig 10-30 The rounded corner of onendoftheRS-1 is placed against the gingivoaxial angle while planing the mesialhalf of the shoulder IM). The other end iused to instrument the distal half of thfinish line (D).Radial Shoulder ^penodontal ^p^e rvatrai nsWing ^~"^preservation of tooth structureL / s Chamfer~ X A/ TKrtTT^rvation. j "/-—- Axial Reduction -if ^ Incisal Notch^S structural durabilityFig 10-31 Features of an anteriormetal-ceramic preparation and thePosterior Metal-Ceramic CrownsThe use of metal-ceramic crowns on posterior teethallows the creation of an esthetic restoration on a poste-rior tooth needing a full crown in the appearance zone.Maxillary premolars, maxillary first molars, and mandibu-lar first premolars are almost always in the appearancezone. Mandibular second premolars also can fall into thiscategory. Maxillary second molars and mandibularmolars may require metal-ceramic crowns if a patient willnot accept all-metal crowns on those teeth.Routinely placing metal-ceramic crowns on all premo-lars and molars is overtreatment because of the addi-tional tooth structure that must be destroyed to accom-modate the combined thickness of metal and ceramic.Often there is added expense for the patient because ofhigher laboratory fees, as well as an increased risk of fail-ure from ceramic veneer fracture.The routine use of all-ceramic occlusal surfaces hasbeen criticized.32This restoration design offers maximumcosmetic effect when required by location in a highly vis-ible area or by patient preference. Patients who demandceramic occlusai surfaces should know of the potentialproblems. The use of all-ceramic occlusal surfacesrequires the removal of more tooth structure, and thecompleted restorations pose a threat to the structuralintegrity of opposing occlusal surfaces. Conventionalglazed dental porcelain is approximately 40 times as
    • abrasive as gold to tooth enamel33Preparations formetal-ceramic crowns should be done with a plan for theextent of ceramic coverage in mind, since the areas to beveneered with ceramic require deeper reduction thanthose portions of the tooth that will be overlaid with metalalone.Armamentarium1. Laboratory knife with no. 25 blade2. Silicone putty and accelerator3. Handpiece4. Flat-end tapered diamond5. Short needle diamond6. Torpedo diamond7. Torpedo bur8. H158-012 radial fissure bur9. RS-1 bmangle chiselBefore the preparation is begun, silicone putty is adapt-ed (o the facial, lingual, and occlusal surfaces of thetooth to be prepared as well as to one tooth on each side.After polymerization, a midsagittal index can be formedby cutting the silicone in half along the faciolingual mid-line of the tooth to be prepared. The putty is placed backon the tooth to insure good adaptation. If the clinicalcrown of the tooth being restored is severely damaged,the index should be made from a diagnostic wax-up.A facial index is made by cutting through the siliconealong the facial cusps of the teeth The facial piece isdivided along a line midway between the cervical lines ofthe teeth and the facial cusp tips. The occlusal portion isdiscarded and the gmgival portion is used as an index.The occlusal reduction is begun by making depth-orien-tation grooves with a round-end tapered diamond. In theareas where there will be ceramic coverage, reductionshould be 1.5 mm34to 2.0 min.1 0 1"5The occlusal reduc-tion is completed by removing the strips of intact enamelbetween the depth-orientation grooves with the samediamond. The reduction should take the form of definiteplanes reproducing the general occlusal morphology36orthe basic geometric shape of the occlusal surface (Fig10-32).The functional cusp bevel, which allows a uniform bulkof restorative material on the lingual inclines of maxillarylingual cusps and the facial inclines of mandibular facialcusps, is also begun with depth-orientation grooves (Fig10-33). The depth required will be 1.5 mm if the coveragewill be metal only, and 2.0 mm if the metal will beveneered with ceramic. The functional cusp bevel iscompleted by removing the tooth structure between thedepth-orientation grooves. The angulation of the bevelapproximates the inclination of the opposing cusps,A no. 171L bur is used to smooth the planes of theocclusal reduction to remove any roughness or pits thatmight interfere with the complete seating of the finishedrestoration. Any sharp corners or edges on the prepara-tion that might cause problems in impression pouring,investing, casting, and ultimately in the seating of thecompleted crown should be rounded over.The flat-end tapered diamond is aligned with theocclusai segment of the facial surface and three verticalgrooves are cut in the occlusal portion of the facial sur-face. These are nearly the full diameter of the instrument,fading out gmgivally (Fig 10-34). The same diamond isaligned with the gingival component of the facial surface,and the side of the instrument is used to cut into the toothsurface. The full diameter of the instrument must cut intothe tooth. The instrument tip should be slightly supragin-gival at this point, even if the intended location of the fin-ish line is flush with or slightly below the gingival crest. Atleast two more orientation grooves should be placednear the line angles of the tooth.All tooth structure remaining between the depth-orien-tation grooves in the occlusal segment of the facial sur-face is removed with the flat-end tapered diamond (Fig10-35). The gingival portion of the facial surface is thenreduced, extending it well into the proximal surface (Fig10-36), If facial reduction of less than 1.2 mm is done fora base metal-ceramic crown or 1.4 mm for a noblemetal-ceramic crown, the restoration will be eitheropaque or overcontoured.The proximal axial reduction is begun with a short nee-dle diamond (Fig 10-37). Its narrow diameter allows inter-proximal reduction without nicking adjacent teeth. Theinstrument can be used with an up-and-down motion onthe facial aspect of the interproximal tooth structure, or itcan be used on the occlusal portion with a faciolingualmovement. Initially, the objective is to achieve separationbetween the teeth without overtapering the preparedwalls or mutilating the adjacent tooth. The proximal axialsurfaces are then planed with the needle diamond.The lingual axial wall is reduced with a torpedo diamond(Fig 10-38). Enough tooth structure is removed on boththe lingual and proximal axial walls to create a distinctchamfer finish line wherever there will not be a ceramicveneer. The chamfer finish line and the axial surfacesadjacent to it are smoothed with a torpedo carbide fin-ishing bur. All axial surfaces that will be veneered onlywith metal are finished in this way.The facial surface and those parts of the proximal sur-faces to be veneered with ceramic are smoothed with anH158-012 radial fissure bur (Fig 10-39). At the lingual-most extension of the facial reduction, lingual to the prox-imal contact, the transition from the deeper facial reduc-tion to the relatively shallower lingual axial reductionresults in a vertical wall or "wing" of tooth structure. Thewings must not be undercut with the facial or lingual axialwalls of the preparation.If the shoulder and wings are not lingual to the proxi-mal contact, the proximal area of the ceramic veneer willlack translucence. If there was an amalgam restoration inthe tooth prior to this preparation, the wing is made tocoincide with the lingual wall of the amalgams proximalbox. If the entire proximal surface is to be veneered withceramic, the shoulder is extended across the proximalsurface with no wing.
    • is for Full Veneer CrowiFig 10-32 Planar occlusal reductioRound-end tapered diamond and no. 17Fig 10-34 Depth-orientalFlat-end tapered diamond.Fig 10-38 Lingual axial redifinishing: Torpedo diamond and
    • lir Tooth and the fuf a preparationwn on a posteri-ction served byGingival Bevel(Optional) i_marginal inte ,ty ^Radial Shoulder 1W i n -^preserva ion o toot stru t rePlanaRedu" "/yiyr Occlusaal durabilityChamferpenoaontal preservationAxial Reduction£ ^ l AiraMV " "FunctionalCusp BevelThe radial shoulder, started with the flat-end tapereddiamond at the time the facial reduction was accom-plished, is finished now with the radial fissure bur. Onhighly visible posterior teeth, such as the maxillary pre-molars, an all-ceramic margin is frequently used toachieve a good esthetic result without intruding into thegingival sulcus. The 1.0-mm-wide shoulder is smoothedby planing it with the RS-1 modified binangle chisel,which will preserve the rounded internal angle created bythe radial fissure bur. Any "lip" or reverse bevel of enam-el at the cavosurface angle should be removed. Small,sharp edges in this area may not be reproduced whenthe impression is poured, and they are susceptible tofracture on the cast or on the tooth in the mouth.There are occasions when a shoulder with a bevel isthe finish line of choice: when esthetic needs are not ascritical or the dental technician is unable to consistentlyproduce a precise all-ceramic margin. A narrow bevel,no wider than 0.3 mm, can be placed on the shoulderwith the tip of a flame-shaped diamond (Fig 10-40). Thebevel should be kept narrow, since the metal collar onthe resulting crown must be as wide as the bevel. Thebevel is easier to wax and cast to if the diamond isleaned toward the center of the tooth as much as possi-ble. The bevel is finished with an H48L-010 flame-shaped carbide finishing bur to create a finish line that isas clear as possible. The features of a preparation for aposterior metal-ceramic restoration and the functionserved by each are shown in Fig 10-41.AM-Ceramic CrownsThe all-ceramic crown differs from other cementedveneer restorations because it is not cast in gold or someother metal. It is capable of producing the best cosmeticeffect of all dental restorations. However, since it is madeentirely of ceramic, a brittle substance, it is more sus-ceptible to fracture The development of dental porcelainreinforced with alumina in the 1960s created renewedinterest in the restoration.37Dicor cast glass ceramic, Hi-ceram, In-ceram, and IPS Empress restorations havemaintained the interest of the profession over the pastdecade.Preparations for this type of crown should be left aslong as possible to give maximum support to the porce-lain. An overshortened preparation will create stress con-centrations in the labiogingival area of the crown,3* whichcan produce a characteristic "half-moon" fracture in thelabiogingival area of the restoration.38-40A shoulder ofuniform width (approximately 1 mm) is used as a gingivalfinish line to provide a flat seat to resist forces directedfrom the incisal.3841The incisal edge is flat and placed ata slight inclination toward the linguogingival to meetforces on the incisal edge and prevent shearing.4243Finally, all sharp angles of the preparation should beslightly rounded to reduce the danger of fracture causedby points of stress concentration.38^43The position of the tooth in the arch, factors relating toocclusion, and morphologic features of the tooth allshould be weighed when an all-ceramic crown is consid-ered for a restoration. All-ceramic crowns are best suitedfor use on incisors. If they are used on other teeth,patients should know that there is an increased risk offracture.Use of the all-ceramic crown should be avoided onteeth with an edge-to-edge occlusion that will produce
    • x Full Veneer Crownsshould not be used when the opposing teeth occlude onthe cervical fifth of the lingual surface. Tension will beproduced, and a "half-moon" fracture is likely to occur.Teeth with short cervical crowns also are poor risks forall-ceramic crowns because they do not have enoughpreparation length to support the lingual and incisal sur-faces of the restoration.Armamentarium1. Handpiece2. Flat-end tapered diamond3. Small wheel diamond4. H158-012 radial fissure bur5. RS-1 binangle chiselDepth-orientation grooves are placed on the labial andincisal surfaces with the flat-end tapered diamond beforeany reduction is done (Fig 10-42). Without grooves it isimpossible to accurately gauge the depth of reductiondone on the labial surface. The grooves are 1.2 to 1.4mm deep on the labial and 2.0 mm deep on the incisal.Three labial grooves are cut with the diamond held par-allel to the gingival one-third of the labial surface. A sec-ond set of two grooves is made parallel to the incisal two-thirds of the uncut labial surface. The labial surface of anall-ceramic preparation is done in two planes to achieveadequate clearance for good esthetics without en-croaching on the pulp.*2Incisal reduction is done with the flat-end tapered dia-mond so that it will be possible lor instruments to reachthe finish line area of the preparation in subsequent(Fig 10-43).The tooth structure remaining between the depth-ori-entation grooves on the incisal portion of the labial sur-face is planed away (Fig 10-44). The gingival portion ofthe labial surface is reduced with the flat-end tapereddiamond to a depth of 1.2 to 1.4 mm. This reductionextends around the labioproximal line angles and fadesout on the lingual aspects of the proximal surfaces (Fig10-45). The end of the flat-end tapered diamond bur willform the shoulder finish line, while the axial reduction isdone with the sides of the diamond. The shoulder shouldbe a minimum of 1.0 mm wide. Lingual reduction is donewith the small wheel diamond, being careful not tooverreduce the junction between the cingulum and thelingual wall (Fig 10-46). Overshortening the lingual wallwill reduce the retention of the preparation.Reduction of the lingual axial surface is done with theflat-end tapered diamond (Fig 10-47) The wall shouldform a minimum taper with the gingival portion of the labi-al wall. The radial shoulder is at least 1.0 mm wide andshould be a smooth continuation of the labial and proxi-mal radial shoulders. All-ceramic crowns made overshoulder finish lines exhibit greater strength than thosemade over chamfers.944All of the axial walls should besmoothed with an H158-012 radial fissure bur, accentu-ating the shoulder at the same time (Fig 10-48). All sharpangles should be rounded over at this time. The RS-1modified binangle chisel is used to smooth the shoulder,removing any loose enamel rods at the cavosurfaceangle. Care must be taken not to create undercuts in theaxial walls where they join the shoulder. The features of apreparation for an all-ceramic crown and the purposeserved by each are shown in Fig 10-49.
    • Fig 10-42 Depth-orientation grooves: Fig 10-43 IncisaFlat-end tapered diamond. tapered diamond.Fig 10-44 Labial reductiol:Jat-end tapered diamond.jnd tapered diamond.Fig 10-48 Axial wall and radial shoulder Fig 10-49 Features of an afinishing: Radial fissure bur.reparation and the funrlion served by each.
    • is lor Full Veneer CroiReferencesI Thom LW: Principles of cavity preparation in crown andbridge prostheses: I. The full ctown. J Am Dent Assoc 1950;41 284-289I Lorey RE, Myers GE The retentive qualities of bridge retain-ers. JAm DentAssoc 1968; 76.568-572.J. Reisbick MH, Shillingburg HT: Effect of preparation geome-Calif Dent Assoc 1975; 3:50-59.. Potts RG, Shillingburg HT, Duncanson MG: Retention andresistance of preparations for cast restorations J ProsthetDenM980; 43:303-308.j. Howard WW: Full coverage restorations Panacea or epi-demic? Gen Dent 1979; 27:6-7.i. Wheeler RC. The implications of full coverage restorativeprocedures. J Prosthet DenM955; 5:848-851.. Smith GP: What is the place of the full crown in restorativedentistry? Am J Orth Oral Surg 1947; 33:471-478.J. Smith GP: The marginal fit of the full cast shoulderlesscrown. J Prosthet Dent 1957; 7:231-243.i. Friedlander LD, Munoz CA, Goodacre CJ, Doyle MG, MooreBK: The effect of tooth preparation design on the breakingstrength of Dicor crowns. Part 1. Int J Prosthodont 1990,3:159-168.). Preston JD: Rational approach to tooth preparation for cer-amo-metal restorations. Dent Ciin North Am 1977;21:683-698.I. Miller L- A clinicians interpretation of tooth preparations andthe design of metal substructures for metal-ceramic restora-tions, in McLean JW (ed): Dental Ceramics; Proceedings ofthe First International Symposium on Ceramics. Chicago,Quintessence Publ Co, 1983, pp 173-206.I Johnston JF, Mumford G, Dykema RW: The porcelainveneered gold crown. Dent Ciin North Am 1963; 7:853-864.i. Shelby DS. Practical considerations and design of porcelainfused to metal. J Prosthet Dent 1962; 12:542-548.1. Romanelli JH: Periodontal considerations in tooth prepara-tion for crown and bridge. Dent Ciin North Am 1977;21:683-698.>. Grundy JR: Color Atlas of Conservative Dentistry. Chicago,Year Book Medical Publishers, 1980, pp 68-75.i. Behrend DA: Ceramometal restorations with supragingivalmargins J Prosthet Dent 1982; 47:625-632.. Brecker SC: Porcelain baked to gold—A new medium inprosthodontics. J Prosthet Dent 1956, 6801-810.t. Silver M, Howard MC, Klein G: Porcelain bonded to a castmetal understructure. J Prosthet Dent 1961, 11:132-145.). Hobo S, Shillingburg HT: Porcelain fused to metal. Toothpreparation and coping design. J Prosthet Dent 1973,30 28-36) Goldstein RE: Esthetic principles for ceramo-mctal restora-tions. Dent Ciin North Am 1977; 21:803-822.. Shillingburg HT, Hobo S. Fisher DW: Preparation design andmargin distortion in porcelain fused to metal restorations. JProsthet Dent 1973; 29:276-284.;. Faucher RR, Nicholls Jl: Distortion related to margin designin porcelain-fused-to-metal restorations. J Prosthet Dent1980; 43:149-15524. Hamaguchi H, Cacciatcre A, Tueller VM: Marginal distortionof the porcelain-bonded-tc-metal complete Crown An SEMstudy. J Prosthet Dent 1982; 47:146-153.25 DeHoff PH. Anusavice KJ: Effect of metal design on mar-ginal distortion of metal-ceramic crowns. J Dent Res 1984,63:1327-1331.26. Stating H, Pameijer CH, Gildenhuys RR: Evaluation of themarginal integrity of ceramo-metal restorations. Part I. JProsthet Dent 1981; 46:59-65.27 Wilson RD: Intracrevicular restorative dentistry. Int JPeriodont Rest Dent 1981; 1:35-49.28. Belser UC, MacEntee Ml, Richter WA: Fit of three porcelain-fused-to-metal marginal designs in vivo1A scanning elec-tron microscope study J Prosthet Dent 1985; 53.24-29.29. West AJ, Goodacre CJ, Moore BK, Dykema RW. A compar-ison of four techniques for fabricating collarless metal-ceramic crowns. J Prosthet Dent 1985; 54:636-642.30 Hunt JL, Cruickshanks-Boyd DW, Davies EH: The marginalcharacteristics of collarless bonded porcelain crowns pro-duced using a separating medium technique Quint DentTechnol-978; 2:21-25.31. Zena RB, Khan Z, von Fraunhofer JA: Shoulder preparationsfor collarless metal ceramic crowns: Hand planing asopposed to rotary instrumentation. J Prosthet Dent 1989;62:273-277.32. Nabers CL, Christensen GJ, Markely MR, Miller EF PankeyLD, Potts JW, Pugh CE: Porcelain occlusals-To cover or notto cover? Tex Dent J 1983; 1006-10.son MG. A comparison ofsurfaces and gold. Ji. Jacobi R, Shillingburg HT, Duncanthe abrasiveness of six ceramiProsthet Dent 1991, 66:303-309.I Johnston JF, Dykema RW, Mumford G, Phillips RW:Construction and assembly of porcelain veneer gold crownsand pontics J Prosthet Dent 1962, 12:1125-1137.j. Goldstein RE1Esthetics in Dentistry. Philadelphia, JBLippincott, 1976, pp 65-85, 332-341.i. Tjan AH: Common errors in tooth preparation. Gen Dent1980; 28:20-25. McLean JW, Hughes TH: The reinforcement of dental porce-lain with ceramic oxides. Br Dent J 1965; 119:251-267.S Pettrow JN. Practical factors in building and firming charac-teristics of dental porcelain. J Prosthet Dent 1961"11:334-344.>. Nuttal EB: Factors influencing success of porcelain jacketrestorations. J Prosthet Dent 1961; 11:743-748.). Bartels JC: Preparation of the anterior teeth for porcelainjacket crowns. J South Calif Dent Assoc 1962; 30:199-205.. BastianCC: The porcelain |acket crown. Dent Ciin North Am1959; 3:133-146.. Bartels JC: Full porcelain veneer crowns. J Prosthet Dent1957; 7:533-540.i. Fairley JM, Deubert LW: Preparation of a maxillary centralincisor for a porcelain jacket restoration Br Dent J 1958;104:208-212k Sjogren G, Bergman ML Relationship between compressivestrength and cervical shaping of the all-ceramic Cerestorecrown Swed Dent J 1987; 11:147-152.
    • Chapter 11Preparations for Partial Veneer CrownsThe partial veneer crown is a conservative restora-tion that requires less destruction of tooth structurethan does a full veneer crown. Its use is based onthe premise that an intact surface of tooth structureshould not be covered by a crown if its inclusion is notessential to the retention, strength, or cosmetic result ofthe final restoration. No technician can exactly duplicatethe texture and appearance of untouched enamel.Gingival health near a partial veneer crown is protectedby the supragingival margin,|Jtand a tooth with a fullveneer crown is about 2.5 times as likely to have a pulpalproblem as one with a partial veneer crown 5A partial veneer restoration should be considered firstwhen a cast restoration is needed A full veneer crownshould be chosen only when the coverage or retentionafforded by a partial veneer crown is found wanting.Reluctance to use a three-quarter crown because it hasmore margin than a full crown is unfounded; the addi-tional margin is vertical, which fits better than a horizon-tal margin.3There are many advantages to the use of partialveneer restorations:1. Tooth structure is spared2. Much of the margin is accessible to the dentist for fin-ishing and to the patient for cleaning.3. Less restoration margin is in proximity to the gingivalcrevice, lowering the possibility of periodontal irritation.4. An open-faced partial veneer crown is more easilyseated completely during cementation, while a fullveneer crown tends to act like a hydraulic cylindercontaining a highly viscous fluid.5 With some of the margin visible, complete seating of apartial veneer crown is more easily verified.6. If an electric pulp test ever needs to be conducted onthe tooth, a portion of enamel is unveneered andaccessible.8A partial veneer crown is not as retentive as a fullveneer crown,9- but it has adequate retention for singlerestorations and retainers for short-span fixed partialdentures. Some preparation feature must be substitutedto compensate for the retention and resistance lost whenan axial surface is not covered The most commonlyused feature is a grooveTo achieve maximum effectiveness, grooves must havedefinite lingual walls.1 Resistance to torqumg is pro-duced by achieving a "lingual hook"8or a "lock effect"13by directing the bur (and groove) slightly to the oppositecorner of the tooth (Fig 11-1, A). A V-shaped groove,without a definite lingual wall, provides only 68% of theretention and 57% of the resistance of a concave groovewith a lingual wall (Fig 11-1, B).1Maxillary PosteriorThree-quarter CrownsThe standard three-quarter crown is a partial veneercrown in which the buccal surface is left uncovered. It isthe most commonly used partial veneer crown. Theocclusal finish line on a maxillary tooth terminates nearthe bucco-occlusal angle. If designed skillfully, the three-quarter crown can be very esthetic.15It can be used suc-cessfully on maxillary posterior teeth, where estheticdemands are moderate and reasonable Metal will not beinvisible, but it will not be seen in normal conversationArmamentarium1. Handpiece2. Round-end tapered diamond3. Short needle diamond4. Torpedo diamond5. Torpedo bur6 No. 169Lbur7. No. 171Lbur8. Flame diamond9 Flame bur10 Enamel hatchetOcclusal reduction is the first step in preparing a toothfor a three-quarter crown. Depth-orientation grooves arecut on the anatomic ridges and grooves of the occlusalsurface with a round-end tapered diamond. Clearanceshould be 1 5 mm on the functional cusp (lingual on max-illary teeth) and 1.0 mm on the nonfunctional cusp
    • Preparations lor Partial Veneer Croundei11-1 A: Definite lingual wallsdisplacement. B: An oblique I i n-wall offers poor resistance. C: Anjcmiined buccal enamel plate may;ture. D: A groove that is too far lin-il does not provide bulk of metal to(facial). The depth-orientation grooves should be madethat deep on the respective cusps. The grooves doextend through the occlusobuccal line angle, but theywill be only 0 5 mm deep there.Occlusal reduction is completed by removing the toothstructure between the grooves (Fig 11-2), reproducingthe geometric inclined plane pattern of the cusps. Thedepth decreases at the occlusobuccal line angle to min-imize the display of metal.15ieNext the functional cusp bevel is made. Holding theround-end tapered diamond at a 45-degree angle to thelong axis of the preparation, three to five depth-orienta-tion grooves are placed on the lingual or outer incline ofthe lingual cusp. The grooves are 1.5 mm deep at thecusp tip and fade out at their apical end.The functional cusp bevel is completed by removingthe tooth structure between the grooves with the samediamond (Fig 11-3). The bevet extends from the centralgroove on the mesial to the central groove on the distal.It makes space for metal on the lingual-facing incline ofthe lingual cusp to match the space on the buccal-facingincline created by the occlusal reduction. The occlusalreduction and functional cusp bevel are smoothed with ano. 171Lbur.Axial reduction is begun by reducing the lingual sur-face with a torpedo diamond, taking care not to overin-cline the lingual wall. The cut is extended interproximallyon each side as far as possible without nicking the adja-cent teeth (Fig 11-4). As the axial reduction is done, achamfer finish line is formed. A smooth, continuous tran-sition should be made from the lingual to the proximalsurface with no sharp angles in the axial reduction or inthe chamfer.Proximal access is gained by using a short needle dia-mond in an up and down sawing" motion. This is con-tinued facially until contact with the adjacent tooth is bro-ken and maneuvering space is produced for largerinstruments. Final extension to the buccal is achievedwith the short needle diamond or, in esthetically criticalareas, with an enamel hatchet. The gingivofacial angleshould not be underextended; it is the most likely area ofa three-quarter crown to fail "A flame diamond, with its long, thin tip, can be used asan intermediate instrument where there is minimal proxi-mal clearance. It is followed by the torpedo diamond tocomplete the axial reduction and form a chamfer (Fig 11-5). The axial wall and chamfer are finished with the torpe-do bur of the same size and configuration (Fig 11-6).Proximal grooves are approximately the size of a no.171L bur (Fig 11-7), but an inexperienced student mayfind it easier to begin the groove with a no. 169L bur,leaving room for minor adjustment. A groove must be cutinto the tooth to the full diameter of the bur to create adefinite lingual wall.The outline form of the finished groove is drawn on theocclusal surface with a sharp pencil (Fig 11-8). The pen-cil outline is followed to cut a "template" approximately 1.0mm deep (Fig 11-9, A). This template is used as a guideto extend the groove to half its length, keeping the buraligned with the path of insertion (Fig 11-9, B). If exami-nation of the groove shows it to be properly aligned anddirected, it should be extended to its full length, ending it
    • Maxillary Posterior Three-quarter CrownsI.zusp bevel: Round-end taperedFig 11-4 Lingual axiaf reduction: Torpedo diamond. Short needle jnd torpedoFig 11-b Axial finishing: Torpedo b Fig 11-7 Proximal grooves: No. 171L but.
    • Preparations lor Partial Veneer CmFig 11-9 The groove is prepared in stages: A, shalbvextension to half length; C, completion to full length.?mplatn; B, Fig 11-10 To help align the second groove, zmay be held in the first groove with utility wax.about 0,5 mm occlusal to the chamfer13(Fig 11-9, C).Grooves should be placed as far facially as possiblewithout undermining the facial surface, paralleling thelong axis of a posterior tooth. Grooves are done first onIhe more inaccessible proximal surface of molars (thedistal) and the more esthetically critical surface of pre-molars (the mesial). If a problem is encountered in plac-ing the first groove, alignment of the second can bealtered in a more accessible area or without adverselyaffecting the cosmetic result. The first few times thatgrooves are prepared, it may help to place a bur in thefirst groove as an alignment guide while the secondgroove is made (Fig 11-10).A flare is a flat plane that removes equal amounts ofthe facial wait of the groove and the outer surface of thetooth. It is cut from the groove outward with the tip of aflame diamond to prevent overextension (Fig 11-11). Theflare is reachable by explorer and toothbrush, but thereshould not be a noticeable display of metal. The flareshould be smoothed with a carbide bur matching the
    • Maxillary Posterior Three-quarter Croconfiguration of the flame diamond. Short, crisp strokesof the bur in one direction prevent rounding of the finishline. Where facial extension is critical, the flare can beformed with a wide enamel chisel.The occlusal offset, a 1.0-mm-wide ledge on the lin-gual incline of the facial cusp, is made with a no. 171Lbur (Fig 11-12). It forms an inverted "V" that lies a uniformdistance from the finish line. It provides space for a trussof metal that ties the grooves together to form a reinforc-ing staple 15"22The angle between the upright wall of trieoffset and the lingual slope of the facial cusp is rounded.Any sharp corners between the lingual inclines of thefacial cusp and the flares are removed.A flame diamond and a no. 170 bur are used to placea 0.5-mm bevel along the bucco-occlusal finish line, per-pendicular to the path of insertion (Fig 11-13). It roundsover the mesial and distal corners and blends into theproximal flares. The function served by each of the fea-tures of the maxillary posterior three-quarter crownpreparation is shown in Fig 11-14.
    • Preparations tor Partial VetChamferpenodontal preservation N . I . ^ ^ ^ _Axial Reduction f.Vr VFunctional { I J-L-.Cusp Bevel --^Jg^jjUL.Planar Occlusal /Reductionstructural durability1 Proximal Groove^*-~~7rQ/^ structural durabilityI ••» Proximal Flaremarginal integrityBuccal Bevel Occlusal OffsetPosterior Partial Veneer VariationsThere are several modifications of posterior partialveneer crowns that can be used. A three-quarter crownpreparation with proximal boxes (Fig 11-15) is moreretentive than a standard preparation with grooves,10?3but boxes are very destructive. They can be justified onlyif there has been proximal caries or previous restora-tions. A less destructive way to augment retention andresistance uses four grooves,24which is not significantlyless retentive than two boxes.23A three-quarter crown preparation on a mandibularmolar or premolar has many features found in the prepa-ration of a maxillary tooth (Fig 11-16). The biggest differ-ence is the location of the occlusal finish line on the facialsurface, gingival to occlusal contacts. The occlusalshoulder on the buccal aspect of the buccal cusp(s)serves the same purpose as the offset on the maxillarypreparation, tying the grooves together and strengthen-ing the nearby bucco-occlusal margin. There is no needfor an offset on the lingual inclines of the buccal cusps.The seven-eighths crown is a three-quarter crownwhose vertical distobuccal margin is positioned slightlymesial to the middle of the buccai surface (Fig 11-17).Esthetics are good because the veneered distobuccalcusp is obscured by the mesiobuccal cusp With more ofthe tooth encompassed, resistance is better than that ofthe three-quarter crown.11The accessible location of thedistobuccal finish line makes the preparation easy to do.Margin finishing by the dentist and cleaning by thepatient are also facilitated.The seven-eighths crown can be used on any posteri-or tooih needing a partial veneer restoration where thedistal cusp must be covered.^^ It is most commonlyused on maxillary molars, but it also can be placed onmandibular premolars and molars 27It is good for restor-ing teeth with caries or decalcification on the distalaspect of the buccal surface, and it is an excellent fixedpartial denture retainer.The reverse three-quarter crown is used on mandibu-iar molars22to preserve an intact lingual surface. It isuseful on fixed partial denture abutments with severe lin-gual inclinations, preventing the destruction of largequantities of tooth structure that would occur if a fullveneer crown were used. The grooves at the linguoprox-imal line angles are joined by an occlusal offset on thebuccal siope of the lingual cusps. This preparationclosely resembles a maxillary three-quarter crown prepa-ration because the axial surface of the nonfunctionalcusp is uncovered (Fig 11-18).The proximal half crown is a three-quarter crown that isrotated 90 degrees, with the distal rather than the buccalsurface left intact (Fig 11-19). It can be a retainer on a tilt-ed mandibular molar fixed partial denture abutment.2629This design can be used only in mouths with excellenthygiene and a low incidence of interproximal caries It iscontraindicated if there is a blemish on the distal surface.The mesial surface parallels the path of insertion of themesial abutment preparation. Clearance of 1.5 mm isobtained from occlusal reduction that terminates at thedistal marginal ridge, with little or no reduction of themesial cusps. Grooves paralleling the mesial surface areplaced in the buccal and lingual axial walls. A heavychannel or occlusal offset connects the grooves tostrengthen the disto-occlusal margin. An occlusal isth-mus augments retention and rigidity. A countersink in thedistal channel helps resist mesial displacement.
    • Anterior Three-quarter CmAnterior Three-quarterCrownsDemands for the avoidance of any display of metal, cou-pled with the ease of preparing a tooth for a metal-ceramic crown, have led to the near total demise of theanlerior three-quarter crown. Unsightly, unnecessary dis-plays of metal in poor examples of this restoration madeit unpopular with both the public and the profession.When a partial veneer is used, it is usually a pin-modifiedthree-quarter crown in which metal coverage is mini-mized by using pins.However, a well-executed standard three-quartercrown on a maxillary incisor or canine need not showmuch metal. II can be used as a retainer for short-spanfixed partial dentures on restoration- and caries-freeabutments.3031Well-aligned, thick, square anterior teethwith a large faciolingual bulk of tooth structure are thebest candidates for three-quarter crowns.13Two factors must be controlled successfully to producea restoration with a minimal display of metal: (1) path ofinsertion and groove placement, and (2) placement and
    • Preparations for Partial Vetinstrumentation of extensions. The path of insertion of ananterior three-quarter crown parallels the incisal one-halfto two-thirds of the labial surface, not the long axis of thetooth.13This gives the grooves a slight lingual inclination,placing their bases more apically and labially, and mak-ing the grooves longer. If the grooves incline labially, thelabioincisal corners are overcut, displaying metal. Thebases of the grooves then move lingually, becomingshorter and less retentive.32Proximal extensions are done with thin diamonds orhand instruments with a lingual approach to minimize thedisplay of metal. Use of a large instrument or a labialapproach will result in overextension and an unsightlydisplay of metalArmamentarium1. Handpiece2. Small round diamond3. Small wheel diamond4. Long needle diamond5. Torpedo diamond6. Torpedo bur7. No. 169L bur8. No. 170L bur9. Flame diamond10. Flame bur11. Enamel hatchetA small wheel diamond is used to create a concave lin-gual reduction incisal to the cingulum (Fig 11-20). It isnecessary to create 0.7 mm or more clearance withopposing teeth. To ensure adequate reduction, depth-ori-entation cuts are made on the lingual surface with a smallround diamond whose head has a diameter 1.4 mm larg-er than its shaft. Buried in enamel to the shaft, the dia-mond penetrates 0.7 mm. Reduction is done to the depthof the orientation cuts. The lingual reduction of a canineis done in two planes, with a slight ridge extendingincisogingivally down the middle of the lingual surface.On incisors, the entire surface is smoothly concave. Thejunction between the cingulum and the lingual wall mustnot be overreduced. If excessive tooth structure isremoved, the lingual wall will be too short to provideIncisal reduction is done with the small wheel diamond(Fig 11-21). It parallels the inclination of the uncut incisaledge and barely breaks through the labioincisal lineangle. Near the junction between the incisal edge andthe lingual surface, it is about 0.7 mm deep. On a canine,the natural mesial and distal inclines of the incisal edgeare followed. On an incisor, a flat plane is cut from mesialto distal.The lingual axial wall is reduced with a torpedo dia-mond, creating a chamfer finish line at the same time (Fig11-22). The diamond is kept parallel with the incisal two-thirds of the labial surface to initiate the path of insertionof the preparation.The vertical lingual wall is essential to retention. If thecingulum is short, wall length can be increased with a lin-gual beveled shoulder that moves the wall farther into thetooth. A 3.0-mm-deep pin hole can be placed in the cin-gulum to compensate for a very short lingual wall. Thiscommon variation of the anterior three-quarter crown isfrequently used on abutments for fixed partial dentures.Proximal reduction is started with a long needle dia-mond (Fig 11-23). The instrument comes from the lingual,to minimize the display of metal later. An up and downmotion is used, with care not to nick the adjacent tooth orlean the diamond too far into the center of the preparedtooth. The labial proximal extensions are completed, andcontact with the adjacent tooth should be barely brokenwith an enamel hatchet, not with the diamond.The axial reduction is completed and the finish line isaccentuated with a torpedo diamond To prevent bindingbetween the prepared proximal axial wall and the adja-cent tooth, it may be necessary to use a flame diamondbefore the torpedo diamond. The axial surface andchamfer are then planed with the torpedo carbide bur(Fig 11-24).The grooves are placed as far labially as possible with-out undermining the labial enamel plate. To implementgroove placement, outlines of the grooves are drawn onthe lingual incisa! area of the preparation The first grooveis begun by cutting a 1.0-mm-deep "template" within thepenciled outline using a no. 170L bur. The groove isextended gingivally in increments to its full length. Anovice may want to use a no. 169L bur initially to allowadjustment of the groove without overcutting it.The second groove is cut parallel with the first, endingboth just short of the chamfer (Fig 11-25) Remember thatgrooves in an anterior three-quarter crown preparationparallel the incisal one-half to two-thirds of the facial sur-face, unlike those in a posterior tooth, which parallel thelong axis of the tooth. Boxes may be substituted forgrooves if there are existing proximal restorations orcaries Boxes must be narrow to be resistant, becausethe lingual wall of a box shortens as it moves lingually.On the facial aspect of each groove, a flare is startedat the gingival end with the thin tip of a flame diamond(Fig 11-26). It is finished with the flame bur to make asmooth flare and a sharp, definite finish line If a very min-imal extension is desired, a wide enamel chisel should beused instead.Using a no. 170L bur, the grooves are connected withan incisal offset, staying a uniform distance from theincisal edge (Fig 11-27). The offset is a definite step onthe sloping lingual surface, placed near the opposingocclusal contact. The metal that occupies the space rein-forces the margin. 1s.25.33.34 Qn a canine it forms a V, buton an incisor it is a straight line.The angles between the incisal edge and the uprightwall of the offset and between the incisal reduction andeach flare are rounded. A 0.5-mm-wide bevel is placedon the labioincisal finish line using a no. 170Lbur(Fig 11-28). This can also be done with a flame diamond and bur,but finishing is still done with a bur to create the sharpest
    • r Thr&e-qusrt&r Crowns*9T* V JFig 11-23 Pioximal axial reduclion: [.cng Fig 11-24needle and toipedo diamonds.L I
    • Preparations for Partia,Proxirrretention^maral Groove /mnal integrityV—Chamfer/ / STtaSrvalior==¥1— Axial Reduction/ ^ ~ / j per.odor.tal preservationy_/^~^ Lingual ReductionIncisal OffsetFig 11-29 Features of an anteriorthree-quarter crown preparation and thefunction served by each.finish line. The bevel is perpendicular to the path of inser-tion along the mesial incline A contrabevel can beplaced on the distal incline, where esthetic considera-tions are not as critical. A contrabevel should never beused on an incisor.Conservative extension and careful finishing of thegold incisal margin will cause light to be reflected down-ward, making the incisal edges appear dark rather thanmetallic to the viewer.15As a result, it will blend in with thedark background of the oral cavity. The functions servedby each of the features of the anterior three-quartercrown preparation are shown in Fig 11-29.Pin-modified Three-quarterCrownsThere are situations calling for a partial veneer crown thatwill not permit the use of a "classic" preparation design.The pin-modified three-quarter crown is an esthetic mod-ification that has long been considered the retainer ofchoice on unblemished teeth used as fixed partial den-ture abutments in esthetically critical areas.35Althoughresin-bonded retainers gained popularity in such situa-tions in the 1980s, the pin-modified three-quarter crownis still an excellent retainer for short-span fixed partialdentures.The pin-modified three-quarter crown preserves thefacial surface and one proximal surface. With minimalsubgingival margins, it is periodontally preferable to a fullcrown. An unsightly display of metal is avoided withoutresorting to a destructive full veneer metal-ceramicrestoration. The pin-modified three-quarter crown is goodfor repairing incisors and canines with severe lingualabrasion.^ 37It should not be used on teeth with cariesrations urfat ered, oin mouths with extensive caries.Although this restoration design is conservative in theamount of enamel that is untouched, a variety of factorscould place the pin holes near or even in the pulp.Therefore, pin-modified three-quarter crowns should notbe used on teeth that are small,33thin,39i4° possessed oflarge pulps,41or malpositioned. They should not be usedby unskilled dentists.Pins are likely to produce less retention, and pm-retained castings are less retentive than standard three-quarter crowns.9However, the greater the number,depth, or diameter of pins, the greater the retention.^Thepin-modified three-quarter crown is an old restorationthat was revived in the 1960s by the development ofsmall twist drills to make pin holes and nylon bristles toaccurately reproduce them.43Pin holes are usually made with a 0.6-mm drill.3"843 4-sNylon bristles, 25 to 50 microns smaller in diameter thanthe drill, are placed in the pin holes4344because the pinholes are too small to be reproduced by impressionmaterial. Impression material surrounds the pin andincorporates it into the impression. When the impressionis poured, the nylon bristles protruding from it reproducethe pin holes.Serrated pins produce more retention than smoothpinSj42.46.47 so serrated iridioplatinum pins 25 to 50microns smaller than the pin holes in the stone cast43areused in the wax pattern (Fig 11-30). The resulting pins inthe casting are 50 to 100 microns smaller than the origi-nal pin holes in the preparation.Pins should be 2.0 to 3.0 mm long.38-43.4448Adequatepin length is essential to retention, and short pins willcause the failure of a conservative fixed partia! denture.These are very destructive failures, because the pinholes become channels for oral fluids and microorgan-isms to penetrate deep into the tooth. Considerable dam-age may occur before a loose retainer is detected. If ade-
    • Pin-modified Throe-quarter CrownsFig 11-30 Retentive pins are rr(A), a smaller diameter nylon breven smaller diameter iridioplat n pin as part of the restoraquate pin hole depth is not possible, a differdesign should be usedArmamentarium1 Handpieces2. Small round diamond3. Small wheel diamond4. Long needle diamond5. Torpedo diamond6. Torpedo bur7. No. 169Lbur8. No. 170Lbur9. Flame diamond10. Flame bur11. Enamel hatchet12. No. 1/2 round bur13. 0.6-mm drill14. Nylon bristleConcave reduction of the the lingual aspect of thetooth is done with a small wheel diamond to produce aminimum clearance of 0.7 mm with adjacent teeth (Fig11-31). Depth-orientation cuts can be made using asmall round diamond with a head diameter 1.4 mmgreater than its shaft diameter. It is sunk into enameldown to the shaft to make a cut approximately 0.7 mmdeep. Excessive shortening of the vertical wall of the cin-gulum should be avoided.A lingual incisal bevel paralleling the uncut surface ofthe incisal edge is also prepared with the wheel dia-mond This bevel is approximately 1.5 mm wide, but itmay vary on teeth with unusually thick or thin incisaledges. It should stop lingual to the labioincisal line angleto prevent a display of metalUsing a torpedo diamond, the lingual axial wall isreduced to parallel the incisal two-thirds of the labial sur-face (Fig 11-32), simultaneously forming a chamfer finishline. Care should be taken not to extend too far labiallyinto the lingual proximal embrasure on the proximal sur-face opposite the retentive feature The finish line mustbe far enough lingual to the proximal contact so that therestoration margin can be finished by the dentist andcleaned by the patient. If the cingulum is short, a beveledshoulder should be used to move the lingual wall towardthe center of the tooth, making it longer.The torpedo diamond is used to continue the axialreduction to its most facial extension near the labioproxi-mal line angle (Fig 11-33). The reduction is diminished atthe finish line. The location of this finish line is critical. If itis not far enough facial, it can cause an undersized, weakconnector,37and a margin that would be impossible tofinish properly. The axial reduction and the chamfer finishline should be smoothed with a torpedo carbide bur (Fig11-34).The primary axial retention/resistance features, twogrooves, are placed next to the edentulous space (Fig11-35). If the proximal surface is carious or has beenrestored previously, a box form is used. The box is toodestructive to use routinely on unblemished proximal sur-faces. Kishimoto et al demonstrated that two grooves areequal to a box on a premolar.14On an anterior tooth, theyare probably superior. Since the lingual surface slopeslinguogingivally, moving the lingual wall a slight distancelingually shortens it and decreases res i stan ce."9By usingtwo grooves, there will be two lingual walls. The wall of themore facially positioned groove will be longer and moreresistant than the single, shorter lingual wall of a box.The facial groove is placed with a no. 170L bur. Aninexperienced dentist may want to start the grooves witha no. 169L bur to avoid overcuttmg. Shallow pilot groovesare made and checked for location and direction. Then ano. 170L bur is sunk into the track of the trial groove tothe full diameter of the bur.The lingual groove is placed next, paralleling it with the
    • islorPartialVeneerCrovFig 11-31 Lingual reductfirst. A third, much shorter groove is placed on the oppo-site side of the cingulum near the vertical finish line onthat surface This groove enhances the restoration resis-tance slightly, and it accommodates a bulk of metal toreinforce the margin.Proximal flares are formed with a flame diamond (Fig11-36). For the flare to draw, it must be wider incisallythan it is gingivally. It nearly eliminates the facial wall ofthe groove at its incisal end. A slight flare is placed on themesial groove. The distal and mesial flares are reinstru-mented with a matching flame carbide bur. Care shouldbe taken not to round over the finish line.A flat ledge or countersink is cut in the incisal corneropposite the site of the proximal grooves using a no170L bur. It must be gingival to the incisal edge, indentin, and lingual to the finish line. A ledge is alsoplaced in the middle of the cingulum. These flat areas onthe sloping lingual surface provide easy starts for precisepin hole placement (Fig 11-37), and they create spacefor a reinforcing bulk of metal at the base of the pins.50The no. 170L bur is used to connect the incisal ledgeand the facialmost proximal groove with an incisal offset.A V-shaped trough is cut along the side of the lingual sur-face from the incisal ledge to the short cingulum groove.The metal in the trough will reinforce the linguoproximalmargin of the restoration (Fig 11 -38).A shallow depression to begin a pin hole in the centerof each ledge is made using a no. 1/2 round bur. To initi-ate the first pin hole, a low-speed contra-angle 0.6-mm(0.024-inch) drill is carefully aligned with the grooves.
    • •e-quarter Crowns -ggting pin holes: Form the ledge with itapered fissure bur (A); start the pin holewith a small round bur (B); and finish thepin hole with a twist drill (C),The handpiece is started before touching the tooth andshould not be stopped while the drill is in the pin hole, asit will snap off. When the first pin hole is approximately3.0 mm deep, the handpiece is withdrawn and a nylonbristle is placed in the pin hole. Using the bristle andgrooves as guides, a 3.0-mm-deep pin hole is made inthe other ledge (Fig 11-39).The angle between the facial wall of the offset and theincisal edge of uncut tooth structure is beveled. Careshould be taken not to extend this bevel too far facially,as metal will show. A finishing bevel is placed on thefunctional area of the incisal edge using a flame diamond(Fig 11-40). Care is taken to prevent an unnecessary dis-play of metal, but it may be necessary to extend thebevel on the distal incline of the incisal edge of a canineonto the labial surface. This is not likely to be unaccept-able cosmetically. since it is usually hidden from view.This should not be done on an incisor. The incisal bevelis blended into the flare and the bevel is redefined on themarginal ridge next to the incisocingulum trough.The areas just described are smoothed with a flamebur. Acute angles between the lingual and proximal sur-faces are blunted, and any sharp corners at the incisalends of the grooves are eliminated. The functions servedby each of the features of a pin-modified three-quartercrown preparation on a maxillary canine are shown in Fig11-41
    • Axial Reductionstructural durability >Proximal Groove - ^ j retention and resistance ^ ^ V/Lingual Reduction AMstructural durability U II jTrough ~ ~ ~ — " y ^Pin Hole/ LedgeChamfer^ ^ ^ periodontal preservation^ L j ^ l L — — Pin Hole / Ledge— • ^ " " " " " " " ^ Proximal Grooves^ ^ ^ y ^ - v Proximal Flare ^ Incisal Offset^ Incisal Bevelmarginal IntegrityReferencese. J Prosthet Dent 1960;. Kahn AE: Partial versus fu10:167-178.I. Maxwell EL, WasserVE: Debate: Full vs partial coverage asthe abutment of choice in fixed bridgework. J DC Dent Soc1961; 36:9-11.1. Miller LL: Partial coverage in crown and bridge prosthesiswith the use of elastic impression materials. J Prosthet Dent1963; 13:905-910.I. Silness J: Periodontal conditions in patients treated withdental bridges. II. The influence of full and partial crowns onplaque accumulation, development of gingivitis and pocketformation. J Penodont Res 1970; 5219-224.>. Felton D, Madison S, Kanoy E, Kantor M, Maryniuk G: Long-term effects of crown preparation on pulp vitality. J Dent Res1989; 68:1008, abstr no. 1139.i. Kishimoto M, Hobo S, Duncanson MG, Shillingburg HT:Effectiveness of margin finishing techniques on cast goldrestorations. Int J Pehodont Rest Dent 1981, 1(5):21-29.. Jorgensen KD. Structure of the film of zinc phosphatecements crowns. Acta Odontol Scand 1960; 18:491-501.!. Ho G1Lecture notes, School of Dentistry, University ofSouthern California, 1959.retain-). Reisbick MH, Shillingburg HT: Effect of preparation geome-try on retention and resistance of cast gold restorations. JCall! Dent Assoc 1975; 3:50-59.i. Potts RG, Shillingburg HT, Duncanson MG: Retention andresistance of preparations for cast restorations. J ProsthetDen! 1980, 43:303-308Cowger GT: Rerior three-qu;62:167-171.rtenticrown. J3, and esthiAm DentI. Kishimoto M, Shillingburg HT, Duncanson MG: Influence ofpreparation features on retention and resistance. Part II:Three-quarter crowns. J Prosthet Deni 1983; 49:188-192., Ingraham R, Bassett RW, Koser JR: An Atlas of Cast GoldProcedures, ed 2. Buena Park, CA, Uni-Tro College Press,1969, pp 161-165.i. Racowsky LP, Wolinsky LE- Restoring the badly broken-down tooth with esthetic partial coverage restorations.Compend Contin Educ Dent 1981; 11 322-335. Tinker HA: The three-quarter crown in fixed bridgework JCan Dent Assoc 1950, 16.125-129.;. Tjan AHL, Miller GD: Biometric guide to groove placementon three-quarter crown preparations J Prosthet Den! 1979;42:405-410ations. J Am Dent Assoc 1931;!. Rhoads JE: Preparation of the teeth for cast restorations. InHollenback GM1Science and Technic of the CastRestoration. St Louis, CV Mosby Co, 1964, p 66.;. Kishimoto M, Shillingburg HT, Duncanson MG: Influence ofpreparation features on retention and resistance. Part IMOD onlays. J Prosthet Dent 1983; 4935-39.-. Tanner H Ideal and modified inlay and veneer crown prepa-rations. Ill Dent J 1957; 26:240-244
    • Pin-modified Three-quarter Crcn25. Willey RE: The preparation of abutments for veneer retain-ers. J Am Dent Assoc 1956; 53: 141-15426. Ingraham R, Basset! RW, Koser JR. An Atlas of Cast GoldProcedures, ed 2. Buena Park, CA, Uni-Tro College Press,1969, p 34.27. KesslerJC, Shillingburg HT: The seven-eighths crown GenDent 1983; 31:132-133.28. Smith DE: Fixed bridge restorations with the tilted mandibu-lar second or third molar as an abutment J South Calif DentAssoc 1939: 6:131-138.29. Shiilingburg HT: Bridge retainers for tilted abutments. NewMexico Dent J 1972; 22:16-18, 32.30. Hughes HJ: Are there alternatives to the porcelain fused togold bridge? AustDentJ 1970; 15:281-287.31. Leander CT: Preparation of abutments for fixed partial den-tures. Dent Clin North Am 1959; 3:59-72.32. Tinker ET: Fixed bridgework. JNatlDA 1920; 7:579-595.33. Smith DE: Abutment preparations. J Am Dent Assoc 1931;18:2063-2075.34. Tjan AHL, Miller GD: Biometric guide to groove placementon three-quarter crown preparations. J Prosthet Dent 1979-42:405^110.35. Baum L: New cast gold restorations for anterior teeth. J AmDent Assoc 1960; 61:15-22.36. Arbo MA: A simple technique for castings with pin retention.Dent Clin North Am 1970; 14:19-29.n. Are-apprai). Hughes HJ: Are there alternatives to the porcelain fused togold bridge? AustDentJ 1970, 15.281-287). Crispin BJ. Conservative alternatives to full crowns. JProsthet Dent 1979; 42:392-397.I. Bruce RW: Parallel pin splints for periodontally involvedteeth. J Prosthet Dent 1964; 14:738-745.> Moffa JP, Phillips RW: Retentive properrestorations J Prosthet Dent K ~i. Shooshan ED: A pin-ledge casting technique—its applica-tion in periodontal splinting. Dent Clin North Am 1960;4:189-206.1. Mosteller JH: Parallel pin castings Practical DentalMonographs. Chicago, Year Book Medical Publishers, Inc.1963, pp5-29.j Burns BB: Pin retention of cast gold restorations. J ProsthetDent1965, 15:1101-1108i. Lorey RE, Embrell KA, Myers GE: Retentive factors in pin-retained castings. J Prosthet Dent 1967; 17:271-276.. Courtade GL, Timmermans JJ: Pins in Restorative Dentistry.St Louis, CV Mosby Co, 1971, p 6.i. Mann AW, Courtade GL, Sanell C: The use of pins in restora-tive dentistry. Part I. Parallel pin retention obtained withoutusing paralleling devices. J Prosthet Dent 1965;15:502-516.). Welk DA: Personal communication.). Pruden WH1Partial coverage retainers: A critical evaluation.J Prosthet Dent 1966; 16:545-548
    • Chapter 12Preparations for Intracoronal RestorationsT•oronal inlay is the simplest of the castrestorations and has been used for the restorationgingiv ind prc lalIntracoronal restorations utilize "wedge" retention, whichexerts some outward pressure on the tooth. This pressureis exerted first during try-in and cementation, but itoccurs again when occlusal force is applied. For therestoration to be successful, there must be some form ofcounteraction. When an inlay is placed in a tooth withample bulk of looth structure, the tooth structure itselfresists the force.The use of cast metal inlays, at one time consideredthe mark of quality restorative care, has declined inrecent years. A group of US dental educators concludedin 1979 that: Cast gold restorations should be limited tothose teeth which need cusp coverage for protection andreinforcement of the tooth. The true cast gold inlay is nolonger a reasonable consideration in the conservativetreatment of unrestored teeth.1A survey of NorthAmerican dental faculty in the early 1980s indicated thatnearly one-third of their schools taught limited use ofinlays, or none at all.2The indications for an inlay are virtually the same as foran amalgam restoration. The inlay simply replaces miss-ing tooth structure without doing anything to reinforcethat which remains.3If the tooth requires protection fromocclusal forces, the protection must be gained by the useof some other type of restoration that incorporates aveneer of casting alloy over the occlusal surface.4Inlaystend to wedge cusps apart,5and a lone-standing unsup-ported cusp is at risk of fracture.6Mechanical cusp height is normally equal to anatomiccusp height, measured from cusp tip to the bottom of thecentral groove. An occlusal intracoronal preparationincreases mechanical cusp height to a hazardousextent,7as it becomes the distance from the cusp tip tothe gingival extension of the preparation. In premolars,this elongation of the lever arm can increase stress.Stress concentrations can manifest themselves in vari-ous forms of clinical failure. The most dramatic and themost evident is the loss of a whole cusp because of frac-ture. Failure also may occur in less obvious ways. Thewhen tooth structure flexes in weakened cusps andpreparation walls bend without actually fracturing8orspring away from the restoration.7This may not becomeapparent for some period of time, but it would eventuallysurface as an open margin, possibly with recurrentcaries This type of failure may escape being identifiedas an ill-designed restoration that did not protect thetooth from destructive, occlusally generated stresses.Analysis has detected greater stress when intracoronalpreparations are wide.910Because a wider isthmus canlead to failure,^"•12and an inlay that is one-third the facio-lingual width of the occlusal surface can wedge thecusps apart,13the recommended isthmus width hasbeen reduced to one-fourth the intercuspal distance.14Vale5found a 35% decrease in the fracture resistanceof a maxillary premolar when the isthmus of a proximo-occlusal preparation was widened from one-fourth toone-third the intercuspal distance. Mondelli et al16report-ed decreases of 42%, 39%, and 29% with similar isthmuswidening of proximo-occlusal. occlusal, and MOD prepa-rations, respectively.Depth, combined with width, decreased the fracturestrength of teeth in studies by Blaser and associates11and Re et al.17This corroborates clinical observations ofinlays acting as wedges between the facial and lingualcusps of teeth.57Deepening an isthmus to increaseresistance, or inlay strength, is not a good practice.Proximo-occlusal InlaysA proximo-occlusal inlay is indicated for premolars ormolars, with minimal caries or previous restoration, thatneed a mesio-occlusal or disto-occlusal restoration. Itoffers a superior material and margins that will not dete-riorate with time. The restoration will be visible on premo-lars, although careful extensions on mesiobuccal flaresshould keep the display minimal. MOD inlays that can bekept narrow are acceptable for molars. If a premolar isdamaged badly enough to warrant even a conservativeMOD cast restoration, that restoration should be an onlay.Class 2 inlays should be used in mouths that have showna low caries rate for some time preceding the placementof the restoration. It is a dubious service to place a two-surface restoration in a tooth that has a high likelihood ofrequiring that the third surface be restored in the not-too-
    • distant future. Patients with accumulations of plaque or arecent history of caries, or those who are still in adoles-cence, are poor candidates for inlays.Armamentarium1. Handpiece2. No. 170L bur3. No. 169L bur5. Flame bur6. Enamel hatchet7. Binangle chisel8. Gingival margin trimmerUse a no. 170L bur to make the occlusal outline (Fig12-1). Initial penetration is made in a fossa with the edgeof the bur tip. The isthmus is then cut to its final extensionby following the central groove and any deep or faultygrooves leading to it The extension should be conserva-tive because an occlusal bevel will widen it later.A distinct dovetail extends facially, enhancing resis-tance and retention. The pulpal floor should be flat, at aneven depth of approximately 1.5 mm, and perpendicularto the path of insertion for maximum resistance.7The out-line should avoid occlusal contacts marked with articu-lating paper. The initial cut extends far enough to under-mine the marginal ridge, which will be removed shortly.The walls of the isthmus will be slightly inclined by the burused to cut them. Check the walls to make sure there areno undercuts. Do not err in the opposite direction byovertapering the walls.If the tooth being prepared has not been previouslyrestored, complete the undermining of the marginal ridgewith a no. 169L bur. Do not cut all the way through theenamel to the outer surface at this time. Penetrate in anapical direction with the bur, with the tip apical to the con-tact (Fig 12-2). Do not be too conservative with the gin-gival extension, since box length is an important factor ininlay retention.14Cut buccally and lingually to the approx-imate width of the proposed box, just inside the cemen-toenamel junction.Break through the undermined enamel to rough out theproximal box, using either the no. 169L bur or an enamelchisel. Use the 169L bur to finish smoothing the box.Extend it buccally and lingually just far enough to barelybreak contact with the adjacent tooth (Fig 12-3). The finalextension will be achieved when the facial and lingualflares are placed. Widen the isthmus where it joins thebox, rounding any angle in the area where they meet.The buccoaxial and linguoaxial line angles of the boxare accentuated with a no. 169L bur. The same bur isalso used to form the facial and lingual walls of the box,and they are smoothed with an enamel chisel. The boxwalls, not the angles, resist displacement.14Those wallsshould have a minimum degree of divergence of thefacial and lingual walls to promote optimum retention andresistance. As taper increases, stress rises and retentiondecreases.The pulpal floor of the isthmus and the gingival floor ofthe box should be flat. A gingival margin trimmer is usedto form a V-shaped groove at the junction of the axial walland the gingival floor of the box (Fig 12-4). This groove,sometimes referred to as the "Minnesota ditch,"1Sisplaced to enhance resistance to displacement byocclusal forces.19Flares are flat planes added to the buccal and lingualwalls of the box using a flame diamond or an enamelhatchet (Fig 12-5). The hatchet is reserved for use inthose areas where esthetics is an important considera-tion. The flares provide for the acute angle of gold tomeet the finish line on the preparation. Check the flaresto make sure that they "draw." The buccal flare leansslightly to the buccal; the lingual flare, slightly to the lin-gual: and both flares, slightly to the center of the tooth A
    • Fig 12-6 Clingivdil bcvcflare is cut equally at the expense of the wall of the boxand of the outer enamel surface of the tooth. As a result,a flare is narrow at its gingival end and much wider at itsocclusal end.To start the flare, place the flame diamond in the prox-i box ethe jt thesurface angle of the box from the gingival floor up.Continue the occlusally directed sweep of the diamondtip without changing the angle or direction of the instru-ment. The diamond should be cutting only when it ismoving in the occlusal direction. If it is moved back andforth, the finish line may be rounded over.The flame diamond is carried across the gingival cavo-surface angle of the box, forming a gingival bevel on thebox that is a smooth continuation of the buccal and lin-gual flares (Fig 12-6). Avoid creating undercuts wherethe gingival bevel joins the flares. Lean the flame dia-mond against the pulpal axial line angle. The bevelshould lay between 30 and 45 degrees to provide anoptimum blend of strength and marginal fit.?DA gingivalmargin trimmer is unacceptable because it will producea ragged finish line.The inlay preparation is finished by placing a bevel onthe occlusal isthmus with a flame diamond [Fig 12-7). Ifa shallow bevel is used in this location, the result will bea thin flash of gold that will probably extend into areas ofocclusal contact. The bevel on the isthmus begins at thejunction of the occlusal one-third and the gingival two-thirds of the isthmus walls, and should extend outward atan angle of 15 to 20 degrees.31The bevel must be minimal, because compressivestress increases as the inclination of the bevel increas-es.10The bevel is likely to produce some stress, but it isa necessary risk to produce a finishable casting. Blendthe occlusal bevel into the proximal flares to produce asmooth, continuous finish line. Use a flame carbide bur
    • Preparations for Intracoronal RestorationsGingivmarginaProxstructurestr1 Bevel n^==^Sintegrity Y /f?--^malBox<?^Kl"S3 .—£xiyfrDovetail V s ^ctural durability^^. Proximaf Ftaremarginal integrity— Isthmusstructural durabilityIsthmus Bevelmarginal integrityFig 12-9 Futures of .ipi-oxito go over the flares and the bevels (Fig 12-8). The flamebur produces the most consistent bevel,32and carbidefinishing burs will produce the smoothest finish lines.23A torpedo diamond can be used to create the bevel; itwill produce one that is slightly concave, as suggestedby Tucker24The finish line is much more easily read. Thefeatures of the class 2 inlay preparation and the functionserved by each feature are shown in Fig 12-9.Metal Inlay VariationsOther (ypes of metal inlays are used even less frequent-ly than the class 2 restoration. A class 1 inlay can beused to restore a moderately sized occlusal lesion in themouth of a patient with predominantly gold restorations inother teeth. The 1.0-mm-wide isthmus follows the centralgroove, ending short of the marginal ridges or transverseridge, if there is one on the tooth.The outline extends moderately into the facial and lin-gual grooves, with small "barbell" dovetails at each end(Fig 12-10). Besides increasing retention and resistance,these extensions place the finish line on the slopes of thetriangular and marginal ridges, where the inlay marginscan be finished more easily. A 15- to 20-degree bevelextends a third of the way down the sides of the isthmuswall. Overextending the bevel will make the restorationtoo wide, and the finish line will form such an obtuseangle with the enamel surface that it will be difficult toidentify during margin finishing .The class 3 inlay shows metal, making it unacceptablefor incisors However, it is useful for restoring the distalsurface of canines if a slight display of metal is accept-able to the patient.25A well-done inlay in a canine willlook better than an amalgam restoration, last longer thana composite resin restoration, and be much less destruc-tive than a porcelain crown. It is not commonly used, butthe restoration does have a place.The class 3 inlay preparation has a 1.0-mm-deep lin-gual dovetail at the incisal end of the cingulum that resistsdisplacement (Fig 12-11).S6The proximal box is preparedwith a lingual approach to minimize the display of metal21An incisal approach will destroy excessive tooth structureas well as create an unesthetic restoration.The class 5 inlay is used to restore severe abrasion?6or erosion as well as large caries on the gingivofacialaspect of molars (Fig 12-12). It cannot tie into otherrestorations without producing a poor marginal seal. Thepreparation should be 1.0 mm deep axially and extend tothe line angles. The gingival finish line is supragingival, ifdamage permits, and approximately 0.5 mm above thejaw of the cervical rubber dam clamp placed for prepar-ing the tooth.2!!The height of contour is the occlusal limitof the preparation.To enhance retention and resistance,3031drill 0,6-mm-diameter pin holes to a depth of 3.0 mm at the proximaledges of the outline form. Place a 0.5-mm-wide. 45-degree bevel around the periphery of the preparation. Forthe impression, use a custom tray that draws buccally.
    • MOD OnlaysThi of ir eslore mesio-occluso-distal lesionsin premolars is questionable. Occlusal force on an inlayproduces stress along the sides of the restoration and atits base, as the inlay pushes against the tooth structuresurrounding it. This could fracture the tooth,32so the inlaymust be modified to distribute the load evenly over awide surface. Stress analysis has shown that coveringthe occlusal surface with metal will do much to minimizethe potentially damaging effects of stress in an intracoro-nal restoration (Fig 12-13).1°.33The MOD onlay is indicated for a variety of situations3.1. Broken down teeth with intact buccal and lingualcusps.2 MOD restorations with wide isthmuses3. Endodontically treated posterior teeth with sound buc-cal and lingual tooth structure. (Access for root canaltherapy weakens a tooth structurally, and the crown ofthe tooth must be protected after treatment is com-plete.)There has been a renewed interest in the MOD onlay,based on an occiusion-centered approach to restorativedentistry rather than one that is solely tooth oriented.MOD onlays are significantly less retentive and resistantthan three-quarter crowns34and should not be used asfixed partial denture retainers. They lack sufficient reten-tion to successfully resist the additional forces placed onan abutment tooth by a fixed partial denture.Fisher et al31showed that onlays protect teeth from thehigh stress concentrations at the walls and line angles ofthe isthmus that are found under inlays. Studies by Craiget al3* and Farah and associates10also showed the supe-riority of MOD onlays in protecting teeth from stress.Armamentarium1. Handpiece2. Round-end tapered diamond3. No. 171Lbur4. No 170L bur5 No 169Lbur6 Flame diamond7. Flame bur8 Enamel hatchetThe previous restoration should be removed at thispoint. The occlusal reduction is done with a round-endtapered diamond to establish preparation length. About1.5 mm of clearance is gained on the functional cusp and1.0 mm on the nonfunctional cusp (Fig 12-14).Orientation grooves are used to gauge the depth ofreduction. There should be one on the crest of each tri-angular ridge and one in each major developmentalOn a maxillary tooth where the nonfunctional facialcusp will be highly visible, do not overreduce the facio-occlusal angle or the restoration will show metal unnec-essarily. The depth of the orientation grooves and theocclusal reduction should be about 0.5 mm at the lineangle.Occlusal reduction is accomplished by removing thetooth structure left between the depth-orientation grooveswith the round-end tapered diamond. The reduction fol-lows the original contours of the cusp,315reproducing thegeometric inclined planes of the occlusal surface.37Ithas been hypothesized that this corrugated multiplanardesign enhances restoration strength.38A wide bevel is placed on the outer-facing inclines ofthe functional cusp with the round-end tapered diamondto insure an adequate bulk of metal on the functional
    • Preparations for Inlrail fore. , applied toibaiFig 12-13an MOD inlay proditend to separate the cusps (A), while thisame force applied to an MOD onlay idissipated over a wide area in lesFig 12-14 Plana, o,Round-end tapered dial ond and no. 171L end tapered diamond and no. 171L bur.cusp (Fig 12-15). The functional cusp bevel approxi-mates the inclination of the cusps in the opposing arch,extending from the central groove on the mesial to thecentral groove on the distal surface.Begin with depth-orientation cuts that are 1.5 mm deepat the cusp tip. They fade out along a line that will later bethe occlusal shoulder, 1.0 mm apical to the lowestocclusal contact. Remove the tooth structure left betweenthe orientation grooves. Smooth the occlusal reductionand funtional cusp bevel with the no. 171L bur. Theinclined planes should be well defined, but there shouldbe no sharp angles where they meet. Check the occlusalreduction visually in the facial half of the occlusal surfaceand with red utility wax on the lingual cusp.Cut an occlusal shoulder on the nonfunctional cuspwith a no. 171L bur at the level of the axial termination ofthe functional cusp bevel (Fig 12-16). The shoulder is 1.0mm wide and extends from the central groove on themesial to the central groove on the distal surface It pro-vides space for metal to reinforce the occlusal margin onthe funtional cusp.There are two acceptable occlusal finish lines for thefunctional cusp of an MOD onlay: an occlusal shoulderor a heavy chamfer (Fig 12-17).3aBoth configurationsprovide an acute edge of gold at the cavosurface angle,with a nearby bulk of metal for strength. The shoulderwith a bevel is easier to prepare properly and should beused by the novice.
    • Fig 12-17 Functional cusp finish lines for MOD onlay: Ocishoulder (top) and chamfer (bottom). (After Ingraham.7)The isthmus is made next with the no. 171L bur (Fig 12-18). If an old restoralion was removed earlier, the isthmusis retouched to smooth the walls and impart a minimumtaper. Besides removing caries and old restorations, theisthmus reinforces the restoration. It provides someretention and a great deal of resistance.40Because theocclusal surface already has been reduced, the isthmusof an onlay is shallower than that of an inlay.The no. 170L bur is used to begin the proximal boxes(Fig 12-19). If the proximal surface is intact, it is easier tostart with a no. 169L bur. The walls of the boxes are car-ried far enough buccally and lingually to barely breakcontact with the adjacent teeth. The facial extension ofthe mesial box is usually more conservative than that ofthe distal box. Extensions will be finalized with a flamediamond on the flares later.Redefine the buccoaxial and iinguoaxial line angles ofeach box with the no. 169L bur. Then use an enamelchisel to plane the facial and lingual walls. Flat walls per-pendicular to the direction of rotating forces, not boxangles, give a restoration resistance. Be sure the boxeshave a common path of insertion. Smooth the pulpal floorof the isthmus, the 1,0-mm-wide occlusal shoulder on thefunctional cusp bevel, and the gingival floors of the prox-imal boxes, which are also 1.0 mm wide.Proximal flares are added after the boxes have beenformed (Fig 12-20). If the flares were cut first, facial andlingual box walls will be poorly defined, and retention willsuffer. Flares are usually cut with the tip of the flame dia-mond, starting from within the box. A wide enamel hatch-et can be used for mesiobuccal flares in areas where thecosmetic result is important.Use a flame diamond to add a bevel 0.5 to 0.7 mmwide to the gingival cavosurface angle of each box (Fig12-21). It provides for an acute edge of metal in theseareas. The instrument is leaned against the pulpal-axialFie 12-19 Piline angle to prevent the bevel from being too long andhaving too sharp an angle. This may round the proxtmo-occlusal line angle, which is acceptable. Blend the bevelinto the facial and lingual flares without creating an under-cut. Smooth the flares and gingival bevel with a flame car-bide bur. This produces a sharp, distinct finish line thatwill facilitate marginal adaptation of the restoration.Occlusal finishing bevels 0.5 to 0.7 mm wide areplaced at the buccal and lingual occlusal finish lines witha flame diamond followed by a no. 170L carbide bur (Fig12-22). The buccal bevel is perpendicular to the path ofinsertion where esthetics are important, and forms aheavier contrabevel where they are not. The bevels areblended into the respective flares. If the bevel on the
    • IGingival Bevel — _ _ _ _ / ;margmahntegrity /Lingual Bevel - /marginal integrity ^ JOcclusal Shoulder — WFunctional Cusp Bevel. . Proximal Box* -"•-<____-4 y ^ retention and resmtanceI P~~>^^ -^ Proximal Flare// 1 -^ marginal integrity^i^JLiL-—I8*mu8~^ y^ y-—Buccal Bevel" ^ A _ / marginal integrityOcclusal ReductionFig 12-24 MOD onlay prep.nocclusal shoulder is too wide, a thin, unsupported marginwill result in the wax pattern and the casting. Figure 12-23 identifies the features of an MOD onlay preparation ona maxillary premolar and the function served by eachfeature.The preparation on a mandibular molar differs fromthat on a maxillary tooth in that the functional cusp beveland occlusal shoulder are located on the buccal cusp{Fig 12-24). In addition, the lingual bevel is wider and itcan be a definite contrabevel, since esthetics is not aconsideration on the lingual cusp of a mandibular toothand structural durability is. These bevels should blendinto the proximal flares, with the cavosurface line of thebevel continuous with the cavosurface line of the flare.There should not be a sharp occlusoproximal cornerwhere the bevel and flare meet
    • References ilay cavity bevels Br Dent Ji amalgam n ; S C Dent JI Clark NP, Smith GE1Teaching gold castings in NorthAmerican dental schools. OperDenM984; 9:26-313. Shillingburg HT, Fisher DW: The MOD onlay—A rationalapproach to a restorative problem. N M Dent J 1970: 21.12-14.1. Tanner H: Ideal and modified inlay and veneer crown prepa-rations. Ill Dent J 1957, 26:240-244.5 Smith DE1Twenty-five years of fixed bridgework J SouthCalif Dent Assoc 1936; 7:794-799.3 McCollum BB: Tooth preparation and its relation to oralphysiology. JAm DentAssoc 1940; 27:701-707.7. Ingraham R: The application of sound biomechanical prin-ciples, in the design of inlay, amalgam, and gold foil restora-tions. J Am Dent Assoc 1950; 40:402-413.i. Mahler DB, Terkla LG: Relationship of cavity design torestorative materials. Dent Clin North Am 1965; 9:149-157.i. Granath LE: Photoelastic studies on certain factors influ-encing the relation between cavity and restoration. Odontolfleiy1963, 14.278-293.). Farah JW, Dennison JB, Powers JM: Effects of design onstress distribution in intracoronal gold restorations J AmDentAssoc 1977; 94:1151-1154.I. Blaser PK, Lund MR, Cochran MA, Potter RH. Effects ofdesigns of class 2 preparations on resistance of teeth tofracture. OperDenM983; 8:6-10.>. Larson TD. Douglas WH, Gustfeld RE: Effect of preparedcavities on the strength of teeth. OperDenM98i; 6:2-5.I Werrin SR, Jubach TS, Johnson BW: Inlays and onlays:Making the right decision. Quintessence Int 1980; 11:13-181. Smith GE, Grainger DA: Biomechanical design of extensivecavity preparations for cast gold. J Am Dent Assoc 1974;89: 1152-1157.5. Vale WA: Cavity preparation. Ir Dent Rev 1956, 2.33-41.3. Mondelh J, Steagall L, Ishikiriama A, Navarro MF, Soares FB.Fracture strength of human teeth with cavity preparations. JProsthet Dent 1980; 43:419-422.7. Re GJ, Norling BK, Draheim RN: Fracture resistance oflower molars with varying faciocclusolingual amalgamrestorations. J Prosthet Dent 1982; 47:518-5213. Frates FE: Inlays. Dent Clin North Am 1967; 11:163-173). Gabel AB: Present-day concepts of cavity preparation. DentClin North Am 1957; 1:3-17.1 Rosenstiel E. To bevel or not to bevel Br Dent J 1975138:389-392.1. Ingraham R, Bassett RW, Koser JR. An Atlas of Cast GoldProcedures ed 2 Buena Park CA Uni-Tro CollegePress.1969. p 12inlay cavity design. J Am DentAssocI inlay. Oper Dent 1983;!. Christensercast-gold itI Tucker RV: Variation o1972; 84:616-620.j Redfern ML: The dovetail8:67-72.i. Thorn LW. Principles of cavity preparation in crown andbridge prosthesis. III. The inlay abutment. JAm DentAssoc1950; 41:541-544.. Gerson IV: Invisible gold restorations for anterior teeth. JProsthet Dent 1961; 11:749-764.J. Mack AO, Allan DN: Reconstruction of a severe case of attri-tion and abrasion. Br Dent J 1974; 137:379-390.). Ingraham R, Bassett RW, Koser JR: An Atlas of Cast GoldProcedures, ed 2. Buena Park, CA, Uni-Tro CollegePress,1969, p 209.). Finger, EM: Restorations for class V cavities. J Prosthet Dent1960; 10:775-778.I. Howard WW: Atlas of Operative Dentistry, ed 2. SI Louis, CVMosby Co, 1973. p 73!. Maxwell EH, Braly BV- Incomplete tooth fracture Predictionand prevention. J Calif Dent Assoc 1977, 5:51-55.(. Fisher DW. Caputo M, Shillingburg HT, Duncanson MG:Photoelastic analysis of inlay and onlay preparations. JProsthet Dent 1975; 33:47-53.L Kishimoto M, Shillingburg HT, Duncanson MG1Influence ofpreparation features on retention and resistance. Part II:Three-quarter crowns. J Prosthet Dent 1983; 49 188-192.>. Craig RG, El-Ebrashi MK, LePeak PJ, Peyton FA:Experimental stress analysis of dental restorations. Part I.Two-dimensional photoelastic stress analysis of inlays. JProsthet Dent 1967, 17:277-291.i. Draheim RN: Current concepts in intracoronal castingpreparations. A new look at the gold casting preparation.Compend Contm Educ Dent 1985; 6:373-379.. Shillingburg HT: Conservative preparations for cast restora-tions. Dent Clin North Am 1976; 20259-271.1. Racowsky LP, Wolinsky LE: Restoring the badly broken-down tooth with esthetic partial coverage restorations.Compend Contin Educ Dent 1981; 2:322-333.I Ingraham R, Bassett RW. Koser JR: An Atlas of Cast GoldProcedures, ed 2. Buena Park, CA, Uni-Tro CollegePress.1969, p 35.I. Kishimoto M, Shillingburg HT, Duncanson MG: Influence ofpreparation features on retention and resistance. Part I:M O D onlays J Pro&thet Dent 983; 49-35-39
    • Chapter 13Preparations for Extensively Damaged TeethOne of the criteria for the use of a cast metal, metal-ceramic, or all-ceramic restoration is a tooth thathas been damaged lo the extent that it must bereinforced and protected It should not be surprising thatunmodified classic preparation designs are used infre-quently. They are applicable only on intact fixed partialdenture abutments and on severely damaged teeth fol-lowing the replacement of coronal bulk with an amalgamMost individual teeth requiring cemented restorations,as well as many fixed partial denture abutments, havebeen damaged enough to require modification of a clas-sic preparation design. The amount of tooth structuredestroyed is only one factor to consider in selecting arestorative material and designing a preparation. Equallyimportant is the location of the destruction and theamount of tooth surface involved. Location can be clas-sified as peripheral, occurring on the axial surfaces of thetooth; central, in the center of the tooth; or combined,with destruction in both sites.1Peripheral destruction, even when it does not threatenthe pulp, may require an extensive restoration such as afull crown because of the wide expanses of enamel thathave been affected (Fig 13-1). A large central lesion thathas undermined much of the enamel may require theplacement of an amalgam core followed by a crown (Fig13-2). However, less extensive damage in the centralregion, with or without proximal involvement, may be bet-ter restored with a less destructive MOD onlay that gainsretention from peripheral tooth structure rather thandestroying it (Fig 13-3). Combined destruction of severedimensions may also require the placement of a core orfoundation restoration followed by a crown (Fig 13-4)Principle of SubstitutionWhen it is necessary to compensate for mutilated ormissing cusps, inadequate length, and in extreme caseseven a missing clinical crown, the principle o! substitu-tion is used. For those teeth with moderate to severedamage that test a dentists ingenuity, a preparation maybe modified by squaring the walls of defects left bycaries and old restorations, and by adding features toenhance retention and resistance. Boxes may be substi-tuted where grooves might ordinarily be utilized. Groovesmay be used to augment retention and resistance whereaxial walls have been shortened. Pins may be employedwhere much of the supragingival tooth structure hasbeen destroyed. More than one of these auxiliary fea-tures may be employed where damage is severeTwo rules should be observed to avoid excessive toothdestruction while creating retention in an already weak-ened tooth:1. The central "core" (the pulp and the 1,0-mm-thick sur-rounding layer of dentin) must not be invaded in vitalteeth.2No retentive features should extend farther intothe tooth than 1.5 mm at the cervical line or down 1.5mm from the central fossa (Fig 13-5). If caries removalresults in a deeper cavity, any part lying within the vitalcore should be filled with glass ionomer cement. Anypreparation feature added for mechanical retention iskept in the safe area of the tooth, peripheral to the vitalcore.2. No wall of dentin should be reduced to a thicknessless than its height for the sake of retention. This maypreclude the use of a full veneer crown, or if one mustbe used, it might first require the placement of a coreor foundation restoration.Box FormsSmall to moderate interproxirnal carious lesions or priorrestorations can be incorporated into a preparation as abox form. This substitute for grooves serves the dual pur-pose of caries removal and retention form3"5(Fig 13-6).Because large quantities of tooth structure must beremoved for it, the box is not usually used on an intactOpposing upright surfaces of tooth structure adjacentto a damaged area can be used to create a box form ifat least half the circumference (180 degrees) remains inthe area outside the lingual walls of the boxes. The wallsof the box, and not the line angles, will resist displace-ments If the mesial and distal surfaces are extensively
    • Preparations tor Extensively Damaged TeethFig 13-1 Teeth with large areas of enamel involverequire full-coverage restorations regardless of the identin that has been destroyed.Fig 13-2 A large central lesion may require a full-crestoration, but only after the tooth is built up with a coreFig 13-3 Moderate central darestoration that preserves and userather than destroying it.involved, another means must be used to compensatefor the diminished lingual tooth structure (Fig 13-7). Thissituation may require a crown placed over a pin-retainedThis is particularly helpful when the facial and lingualwalls of a box are a considerable distance apart.However, too many grooves in a crown preparation canadversely affect the seating of a full veneer crown.sGroovesGrooves placed in vertical walls of bulk tooth structuremust be well formed, at least 1.0 mm wide and deep, andas long as possible to improve retention and resistance.Multiple grooves are as effective as box forms in provid-ing resistance,7and they can be placed in axial wallswithout excessive destruction of tooth structure. Theymay also be added to the angles of oversized box formsto augment the resistance provided by the box walls.PinsPins effectively increase retention9" by generating addi-tional length internally and apically rather than external-l y " They do not require vertical, supragingival toothstructure for their placement, and they can be usedwhere there is insufficient axial wall length. They canextend apically beyond the gingival attachment withoutharming it.Pins are commonly used in two ways: (1) Pin holes par-allel the path of insertion of the preparation, receiving
    • Principle of Substitutionarics may preempt the use of a groove {dotted line)imodates caries removal and provides retention IB).Fig 13-7 If significantly less than 18degrees of the tooths circumferencremains between two boxes, the lingu.cusp is susceptible to fracture during funition, upon removal of the provision;restoration, or at try-in of the permanerrestoration {A!. A core with a differerpreparation design will minimize the risof fracture and provide better longevity kpins that are an integral part of the cast restoration (Fig13-8, A), or (2) nonparallel pins are placed in the tooth toretain an amalgam or composite resin core in which aclassic preparation for a cast restoration can be formed(Fig 13-8, B).Careful pin hole placement is critical for restorationsuccess. Four guidelines should be followed in drillingpin holes12:1. Place them in sound dentin.2. Do not undermine enamel.3. Avoid perforation into the periodontal membrane.4. Do not encroach upon the pulp.Pin holes should be placed vertically in shoulders orledges halfway between the outer surface of the toothand the pulp, surrounded by at least 0.5 mm of dentin.13The safest locations for pin holes are the line angles orcorners of the teeth (Fig 13-9). "> The least desirable areafor placing pin holes is midway between the corners,ldespecially in regions overlying the furcations.1STo avoid problems, the location and direction of thedrill must be carefully controlled. After studying a radi-ograph, gently place a probe,14or the drill itself,16intothe gingival sulcus, against the side of the tooth, to get aclear picture of the direction of the outer tooth surface inthe area of the pin hole. This limits the use of parallel pinsthat are part of the casting, because the preparationpath of insertion may dictate a pin direction that couldcause pulpal or periodontal complications.If bleeding occurs while drilling a pin hole, determinewhether the misdirected drill has gone into the pulp orthe periodontal membrane. If it is in the pulp, performendodontic therapy before proceeding. If the hole exitsthe root surface, measure the pin before insertion so that
    • Preparations lor Extensively Damaged Teethurn will help toFig 13-9 Areas for the placetretentive pin holes in posterk(after Fisher).it neither overfills nor underfills the hole. Healing is thenpossible, although not guaranteed. A pin that extendsinto the periodontium coronal to the alveolar crest shouldbe exposed with a surgical flap and trimmed flush withthe root surface.The technique used for placing the pin holes andreproducing them in the impression is that described byShooshan.17It uses a 0.6-mm (0.024-inch) drill to cut thepin hole, a nylon bristle to reproduce the pin hole in theimpression, and a nylon bristle or indioplatinum pin toproduce a pin in the restoration. The pin hole is counter-sunk slightly to form a funnel-shaped opening. Thisstrengthens the pin where it joins the casting18andguides the pin into the hole during seating.Although retention increases as the number, depth,and diameter ol pins increases,1930a point of diminishingreturns occurs after four or five pins are placed.21Thisexperimental finding confirms the clinical recommenda-tions that one pin should be used for each missingcusp,22line angle,23or axial wall.24Self-thread ing pinsare nearly five times more retentive than cemented pinsand need be placed to a depth of only 2 0 mm. However,cemented pins that are an integral part of the restorationneed to extend 4.0 mm into the tooth.25
    • Bases and CoresWhen Ihe destruction of tooth structure is more extensive,a decision must be made whether to augment the reten-tion and resistance by adding auxiliary features or tobuild up the tooth preparation with a pin-retained core(Fig 13-10).BasesCement bases are used only to protect the pulp and toeliminate undercuts in defects in tooth structure pro-duced by the removal of caries or old restorations. Theyare used if there is adequate bulk of tooth structure toresist occlusal forces and enough axial wall surface toprovide retention for the final restoration.Glass ionomer and polycarboxylate cements areexcellent materials for this purpose. They are nonirritatingto the pulp and have some adhesive properties thatmake them less likely to become dislodged during sub-sequent preparation of the tooth. Deep areas of thepreparation near the pulp may be covered with calciumhydroxide. Cement bases do not have sufficient strengthto effectively replace weakened dentinal walls, unlessthere are two walls of tooth structure remaining.26Amalgam or composite resin should be used for that pur-pose.An undercut left by caries removal often can be elimi-nated by creating a box, if the additional retention isneeded. However, if creation of a box will destory exces-sive sound tooth structure, it is better to fill the defect withcement. If the defect is very close to a finish line, amal-gam should be used because it is strong and insoluble.CoresIf half or more of the clinical crown has been destroyed,an amalgam or composite resin core should be placed inthe tooth. The core is then treated as though it were toothstructure, and a classic full veneer preparation is used. Ifless than half of a clinical crown has been destroyed, apreparation design that will empioy auxiliary features foradded retention in the area of missing cusps can beused.All cusps thinner than half their height should be short-ened or removed. Cavity floors and walls are flattened forincreased resistance, taking care not to traumatize thepulp or weaken the remaining walls. A core must beanchored firmly to the tooth and not just placed to fill thevoid. Otherwise, it offers no advantage over allowing thebulk of the casting to occupy the space.Pin-retained cores have been utilized to retain castrestorations on severely damaged teeth for nearly 40years,16S7MBoth amalgam and composite resin havebeen used for this purpose Composite resins arefavored by some because they are easily molded intolarge cavities and they polymerize quickly, allowing thecrown preparation to be done at the same appointment.However, composite resin cores exhibit greatermicroleakage than do amalgam cores,29and they are notcrowns made for teeth with composite resin cores failedto seat by 226 urn more than crowns made for teeth withamalgam cores after immersion in body-temperature nor-mal saline solution for 1 week.30The surface of a com-posite resin core is affected adversely by exposure tozinc oxide-eugenol temporary cement,31although thatdoes not seem to have a negative effect on the tensilestrength of the final crown.32Single-phase, copper-rich amalgams attain sufficienthardness to allow a crown preparation to be made afteronly 10 minutes.33Retention devices other than pins canbe used for amalgam cores. Slots that are the width anddepth of a no. 337a bur can be placed around the periph-ery of the preparation.34"Dentin chambers," or pot holes,2 to 3 mm deep can be placed with no. 1156, 1157, or1158 burs. When amalgam is condensed into theseholes, they become "amalgapins."35Retentive features for the core must be deep enoughnot to be removed by the axial reduction done in thecrown preparation. A properly contoured amalgam corecan serve as a temporary restoration for several weeks,giving the tissue an opportunity to recover while moreurgent treatment is being performed.The preparation finish line for the cast restorationshould extend beyond the core into tooth structure.30Thefarther the core extends subgingivally, the more likely it isto have voids and overhangs that will make it unsuitableto remain exposed beyond the margin of the final restora-tion. If the core is amalgam, dissimilar metals in contactwith it are more prone to corrosion when exposed to theoral environment. If the core is composite resin, it is sus-ceptible to leakage.
    • Preparations lor Extensively Damaged TeethFig 13-10 If the tooth to be preparedfor a cast restoration has been onlymoderately damaged (eg, an old MODamaigam), a standard MOD onlaypreparation or a three-quarter crownpreparation with boxes can be used (A).If one cusp has been destroyed, awidened box with groove augmentationcan be used (B). When half of the crownhas been destroyed, grooves may pro-vide sufficient retention if the supragin-gival tooth structure in which they areplaced has sufficient length. Pin holesmay be added to the preparation (Q. Ifthree or more cusps have beendestroyed, a pin-retained core should befabricated before proceeding to a full-coverage cast restoration (D). Extensiveperipheral destruction often requif l lppfull-c erage cghas been controlled (E).qon if c
    • Modifications toi Damaged Vital TeethModifications forDamaged Vital TeethIn preparing a damaged tooth (Fig 13-11, A), follow anorderly sequence to lake full advantage of remainingtooth structure to attain the most retentive preparationpossible.1. Evaluate pulpai health. If it is questionable, or if thereis an exposure, however small, endodontic therapyshould be done before placing a cast restoration.37Otherwise, the restoration later may be compromisedby the endodontic access. Nonetheless, make everyeffort to maintain the vitality of the pulp. Endodontictreatment is usually successful, but nothing is perfect.Even if it is successful, it weakens the tooth andincreases the cost of restoring it.2. Assess the periodontal condition. Examine penodon-tal tissues for deep subgingival extensions of caries,fractures, or previous restorations. Finish line exten-sions that violate the "biologic width" of 2.0 mm of tis-sue attachment may require periodontal surgerybefore a restoration is made.38363. Make a preliminary preparation design. A generalconcept can be formulated beforehand, but the spe-cific features to be used and their location cannot beascertained until the initial phases of the preparationhave been completed.4. Remove previous restorations and bases, all caries,and any unsupported enamel (Fig 13-11, B). Even ifan existing restoration appears sound, it may concealcaries or a pulp exposure. Remove it. Concave,roughened areas from which caries and previousrestorations have been removed, or sloping surfacesremaining after cuspal fracture, must be oriented toenhance resistance and retention. They should beformed into vertical and horizontal components, orsteps, with essentially vertical surfaces made parallelwith the path of insertion (Fig 13-11, C). They must bekept at the periphery of the preparation, with gmgivalshoulders and floors no wider than 1.5 mm. Horizontalsurfaces are made perpendicular to the path of inser-tion to increase resistance to occlusal forces (Fig 13-11, D). No flat horizontal surface in the central portionof the tooth should be any deeper than the level of thepulpai floor of a classic isthmus.5. Evaluate the strength of the remaining walls. Decidewhether to incorporate remaining defects into thepreparation or to fill them in. If more than 50% of thecoronal tooth structure of a posterior tooth is sound,and the tooth will not be an abutment, sufficient reten-tion can be achieved by adding supplemental fea-tures to the preparation. Internal features such as isth-muses or box forms must have surrounding walls ofdentin that are at least as wide as they are high. If thethickness-to-height ratio of a wall lies between 1 • 1 and1:2. it should be supported Any wall with a thickness-to-height ratio of less than 1:2 is subject to fractureand should be shortened.6. Finalize the preparation design. Begin with occlusalreduction (Fig 13-11, D) and then proceed with axialreduction (Fig 13-11, E). With abase, fill in the centralareas of the tooth that were too deep to be included inthe orientation of horizontal and vertical surfaces. Donot bother to mold a large bulk of base to a classicpreparation configuration, since no retention is gainedfrom a cement base.The preparation is ready for the placement of its reten-tion features. Only after all other portions of the prepara-tion are complete can a decision be made about thetype, number, and location of retentive features that willbe used. The preparation is completed by their addition(Fig 13-11, F).Placement of grooves, pin holes, and box walls in abase is the same as not using them at all (Fig 13-12, A).Retention and resistance forms must be placed in solidtooth structure, not in base, if they are to provide anyresistance to dislodgment (Fig 13-12, B). Since retentivefeatures can be formed no more than 1.5 mm from theouter surface of the tooth, deep destruction of toothstructure requires that the axial wall of a box be placed ina nonretentive base rather than in dentin If the buccaland lingual walls are in dentin, the box will provide sig-nificant retention. The danger to the pulp from extendingthe box closer to the pulp would be an unacceptable riskfor the little retention that might be added.An important aspect of restoring damaged teeth is theprotection of remaining tooth structure. Teeth alreadyweakened by the loss of large amounts of tooth structureare ill-equipped to withstand occlusal forces unassistedProtection can be provided by capping cusps with thecast restoration.4041The occlusal thickness in metalshould be 1.0 mm over the nonfunctional cusps and 1.5mm over the functional cusps.The choices for anterior teeth are more limitedbecause of esthetic requirements and the smaller bulk ofdentin in which supplemental features can be placed.Modifications of classic anterior preparations are limitedto substitution of a box for a groove to encompass a car-ious lesion, or addition of extra grooves or pin holes. Ifmore than one-third of the coronal structure is lost, place-ment of a pin-retained core followed by a metal-ceramicThere will be times when it is necessary to devitalize atooth to obtain retention. If a crown is to be placed on anarrow, single-rooted tooth with little or no coronal toothstructure, a core may not have sufficient resistance todislodgment without a dowel that extends into the root
    • Preparations for Extensively Damaged TeethFig 13-11 MaxAll caries, previoin sloping areasfaces perpendicuremaining toothpreparation (F).algamfary molar with a missing distohuccal cusp and a defectiv grestorations, bases, and undermined enamel are removed {B). Steps are formedh vertical surfaces made parallel with the path of insertion and horizontalr to it (C). Occlusal reduction (D) and axial reduction (E) are done onructure. Addition or refinement of auxiliary retention features completesFig 13-12 A box placed in cement (A) will not provide retentiowidened buccolingually and lengthened gingivafly so that the facitooth structure, retention will be improved (B).
    • Orthodontic Adjuncts to Restoring Damaged TeethOrthodontic Adjuncts toRestoring Damaged TeethCanes or irauma may produce tooth destruction of amagnitude or in a location that makes it difficult or impos-sible to restore the tooth without serious esthetic or peri-odontal compromise. Simple orthodontic procedures canbe employed in some of these situations to make it pos-sible to restore the teeth in a manner that will improve theprognosis for long-term success and provide a morepleasing esthetic result where required.Regaining Interproximal SpaceA long-standing carious lesion on the proximal surface ofa molar often will result in migration of the adjacent molarinto the void created by the caries (Fig 13-13). It is notenough just to excavate the caries and place a restora-tion in such a situation. The teeth frequently contact at, orapical to, the cementoenamel junction. Simply placing arestoration in these circumstances would result in a con-cave proximal contour and a closed embrasure spacethat would wreak havoc on the periodontium. Instead, thespace should be regained by separating the teeth withthe brass wire technique described by Reagan.42A core or foundation restoration is placed in the toothrequiring restoration (Fig 13-14) and then it is preparedfor a full crown (Fig 13-15) An acrylic resin provisionalcrown is fabricated using the technique described in
    • Preparations lor Extensively Damaged Teeth 1Y i , t [ »• /Fig 13-17 Brass wire is wrappedto further separate the teeth.led Fig 13-18 Hie contact is closed by adding resin to the dislaspect of the provisional restoration (arrow).Fig 13-19 The occltinue moving distallyChapter 15. After adjusting and polishing the provisionalcrown, it is cemented. An elastic orthodontic separator isinserted into the proximal surface to initiate the move-ment of the adjacent tooth (Fig 13-16).At a subsequent appointment, the elastic is removedand a piece of 0.6-mm (0.025-inch) brass wire is thread-ed between the teeth from the facial side, apical to thecontact. The wire is wrapped around the contact, bring-ing the two ends together on the facial side. There thewire is twisted together until the patient feels pressure.The twisted end of the wire is cut off, leaving a 5- to 6-mmtail. The cut end is bent over so that it will not stab thepatients cheek (Fig 13-17),At approximately 1-week intervals, the wire is tightenedby twisting until the tooth shows no movement from theprevious appointment. At this point the provisionalrestoration is removed and the crown is built back intocontact with the adjacent tooth by adding acrylic resin(Fig 13-18). The crown is repolished and recemented,and the brass wire is reapplied. As the adjacent tooth istipped distally, it may move upward into the occlusalplane. If it does, adjust it occlusally to permit it to contin-ue to move distally (Fig 13-19).Caries extensive enough to require orthodontic move-ment often extends far enough apically that some type ofsurgical crown-lengthening procedure will be required.This will not only facilitate successful completion of thecrown, but it will also prevent subsequent periodontalinflammation around the crown margin. Then the fullcrown that will serve as the final restoration is fabricatedand cemented (Fig 13-20).
    • Orthodontic Adjuncts to Restoring Damaged Teethtured to the level of the alveolar <Fig 13-22ig. Theo for aanatorincisor is 11:14 (A). In this example, thetooth is fractured 3.0 mm beyond thecementoenamel junction (B). Surgicalcrown lengthening alone would pro-duce an unstable and unesthetic crown-root ratio of 14:11 (C). Extrusion fol-lowed by crown lengthening produces amore stable crown-root ratio of 11:11with a more esthetic, normal crownlength (D).Extrusion of TeethWhen all tooth structure has been lost to the level of thealveolar crest or beyond, because of either fracture orcaries, the tooth cannot be satisfactorily restored withoutsome extraordinary measure (Fig 13-21). Even if a dowelcore is placed in the tooth, the root will remain suscepti-ble to fracture without the crown encircling the tooth api-cal to the core. This ferrule effect around the tooth pro-tects it from fracture by the dowel from within.36In fact, iftooth structure is lost "only" to the level of the epithelialattachment, minor extrusion may be desirable to permitaccess to enough tooth structure apical to the finish lineto produce a ferrule effect.Burying the finish line subgingivally will not solve theproblem. Rather, it will create new ones: the increasedpossibility of an ill-fitting crown and placement of themargin in an area that would violate the biologic width"of soft tissue attachment. This particular problem can beovercome by surgical crown lengthening alone, but theresult will be most unesthetic Surgery shortens the rootand also increases the crown-root ratio (Fig 13-22).Orthodontic extrusion has been used to move solidroot structure into an accessible area.43The use of ortho-dontic brackets has been described for this purpose.44"47However, they are bulky and unesthetic, and they may bedifficult to place far enough apically to permit sufficientspace for extrusion Furthermore, their use may causeunwanted movement of the abutment teeth.48Removableappliances also can be used to extrude teeth,49but theyrequire a high degree of patient compliance. The tech-nique presented below utilizes an anchorage wire bond-ed to adjacent teeth as described by Oesterle andWood.48
    • Preparations lor Extensively Damaged Teethofthe pro to he extruded. There is a loop in the wire over both terminamerits, to aid retention by resin, and a loop in the middle o- bw (2.0 mm)t 1.0 mmExtrusion distance = x + bw + 1Fig 13-25 The amount of extrusion needed is determined byadding the distance the destruction extends beyond the alveolarcrest, the biologic width of 2.0 mm, and 1.0 mm between the bot-tom of the sulcus and the crown margin. If the destruction extends1.0 mm beyond the alveolar crest, 4.0 mm of extrusion would benecessary, ac = alveolar crest, bw - biologic width, dd = deepestuxtent of destruction, fern = final crown margin, and fsb = final hot-The tooth first must be endodontically treated. Theextrusion can be done with either a permanent or a tem-porary dowel core in the tooth. In either case, place aprovisional crown on the tooth to be extruded This main-tains space and provides an esthetic appearance duringtreatment. If the permanent dowel core is fabricatedbefore extrusion, make it at least 3.0 mm short of its nor-mal incisal length to allow space for extrusion.Embed a TMS pin (Coltene-Whaledent, New York, NY )in the mesiodistal center of the facial surface of the pro-visional crown, as near the gingiva as possible. The pinis either directed slightly gingivally or bent to facilitateretention of the elastic that will be placed on it later (Fig13-23).Bend a facial 0.018 x 0.025-inch stainless steel ortho-dontic arch wire, with a small loop opposite the middle ofthe tooth to be extruded. The loop, an attachment for theelastic, is bent in an incisal direction to prevent the elas-tic from slipping off. The base of the loop should touchthe facial surface of the tooth to prevent the tooth frommoving lingually as it erupts. The arch wire should extendfor two teeth on either side of the tooth to be extrudedwith a loop in each end of the wire for retention (Fig 13-24). The use of this number of abutments minimizes thepossibility of moving them rather than the intended tooth.Place the arch wire at the incisogingival level to whichthe TMS pin will be moved, equaling the amount of extru-sion to be accomplished. The distance that the tooth is tobe extruded is calculated by adding (1) the distancefrom the most apical point of fracture or caries to thealveolar crest (if the damage extends subcrestally): (2)2.0 mm for the biologic width^; and (3) at feast 1.0 mmto prevent placement of the crown margin too far subgin-givally (Fig 13-25). If the damage is flush with the alveo-lar crest, a minimum of 3.0 mm of extrusion would berequired.48Affix the arch wire to each of the four abutment teeth,using a light-activated resin. Create an occlusal clear-ance of 1 0 mm on the provisional crown, and attach anelastic to the pin on the crown and the loop on the wire(Fig 13-26) Check the patient weekly.15The tooth willelongate at a rate of 1.0 to 1.5 mm per week.4411849Relieve the occlusion again and replace the elastic.When the TMS anchorage pin in the facial surface ofthe provisional crown is even with the arch wire, theextrusion is completed. Remove the elastic and replaceit with a ligature wire, tying the pin on the crown to theloop in the arch wire (Fig 13-27). Check the occlusion to
    • Orthodontic Adjuncts to Restoring Damaged TeethFig 13-27 When ibe tooth has been extruded so that the pin onthe crown contacts the loop in the arch wire, it should be stabi-lized with ligature wire. The descended level of the gingiva makesinsure that there are no interferences. Traumatic occlusalcontacts will interfere with healing and stabilization of thetooth. The teeth should remain ligated for at least 1 monthbefore proceeding lo the next phase of the treatment ^The alveoiar bone and gingival attachment frequentlywill descend with the tooth (Fig 13-28). If there was a pre-existing periodontal defect, it may be lessened or elimi-nated.f.50-52 However, if the periodontium was normalbefore the extrusion was undertaken, surgery may benecessary to bring the levels of the bone and the gingi-val crest into line with those of the adjacent t e e t h . 4 8^ ^ Aflap is reflected over the extruded tooth, and bone isremoved to match the osseous level of the adjacent teeth(Fig 13-29). The final restoration can be started approxi-mately 4 weeks after the surgery (Fig 13-30).48Fig 13-30 Final restoration on a tooth withwhose length is similar to that of the adjacent te
    • Preparations for Extensively Damaged TeethFig 13-31 A t<quately restoredunnecessary "rei(Bt. (From Shillin)othwinforsbuith"S icomposite resinnent" that may md Kessler.")ikal crown can be .ide-(A). A dowel providesveaken the tooth insteadRestoration of EndodonticallyTreated TeethThe restoration to be used on an endodontically treatedtooth is dictated by the extent of coronal destruction andby the type of tooth. Traditionally, a pulpless toothreceived a dowel to "reinforce" it and a crown to "protect"it. Retrospective clinical surveys in recent years havecaused a reappraisal of this thinking. In a study of 220endodontically treated teeth, Ross55found that nearly61% of the teeth that had been in service for 5 years orlonger had not been restored with dowels. Sorensen andMartinoff56reported almost identical success rates forendodontically treated anterior teeth restored with andwithout dowels.RationaleIn that same study by Sorensen and Martinoff,5Stherealso was no significant difference between the successachieved with anterior pulpless teeth that had receivedcrowns and those that had not. It is then obvious thatendodontically treated anterior teeth do not automatical-ly require crowns 57-s9If a mode rate-si zed anterior toothis intact except for the endodontic access and one or twosmall proximal lesions, composite resin restorations willsuffice. Placement of a dowel in such a tooth is more like-ly to weaken it than to strengthen it (Fig 13-31).Lovdahl and Nicholls60found that intact endodontical-ly treated central incisors were three times as resistant tofracture as teeth that had been restored with dowel cores.Fig 13-32 A single-rooted pulpless tooth with a severely danaged crown (A) usually will require a dowel core before placemeof a crown (B|. (From Shillingburg and Kessler.58)For a tooth that has become discolored following devital-ization, bleaching is preferable to crown placement if thetooth is relatively intact.67A laminate veneer offers a lessdestructive alternative if the facial surface of a reasonablyintact tooth must be masked by a restoration.However, the axial reduction for a crown preparation(peripheral destruction) combined with an endodonticaccess preparation (central destruction) frequentlyleaves insufficient sound dentin to support a crownunaided. If a metal-ceramic crown is required because ofextensive coronal destruction, a dowel core probably isneeded (Fig 13-32). A dowel is placed to provide theretention for a crown that ordinarily would have beengained from coronal tooth structure.61 KThe use of adowel requires that the canal be obturated with gutta-percha. It is difficult to ream out a canal filled with a silverpoint or other hard material. Lateral perforation of the rootbecomes a distinct possibility. If a dowef is used, itsextension into the root must at least equal the length ofthe crown for optimum stress distribution63and maximumretention, or the dowel should be two-thirds the length ofthe root, whichever is greater (Fig 13-33). A minimumlength of 4.0 mm of gutta-percha, and more if possible,should remain at the apex to prevent dislodgment andsubsequent leakage. If it is not possible to meet thesecriteria, the prognosis for the restoration will be compro-mised and some alternative should be explored.The longer a dowel, the greater its retention.64-67Atooth with a dowel that is three-quarters the length of thecrown or shorter has less chance for success than atooth that has no dowel at all.65However, the successrate of dowel-treated teeth can increase to more than97.5% when dowel length equals or exceeds the lengthf
    • Restoration of Endodonticalty TretFig 13-33 The length of the dowel (DU should equal the clength (C!_) or two-thirds the length of the root, whichever is griThe length of the remaining apical fill IAF) should be at leasPosterior teeth must be treated differently. Because oftheir naturally divided occlusal surface, even caries-freeteeth can fracture vertically under occlusal forces. Theminimum treatment indicated for an endodontically treat-ed molar or premolar is the placement of a cast restora-tion with occlusal coverage, such as an MOD onlay.69Sorensen and Martinoff68found that 94% of endodonti-cally treated molars and premolars that subsequentlyreceived coronal coverage were successful, while only56% of occlusally unprotected endodontically treatedposterior teeth survived.Those endodontically treated posterior teeth with suffi-cient sound tooth structure to be restored with an MODonlay are in a distinct minority. Many teeth that requireendodontic therapy have been so damaged by caries,previous restorations, and the endodontic access, thatlimited coronal tooth structure remains to be used forretaining the final restoration.Frequently a core must be substituted for the supragin-gival axial walls and auxiliary features that are customar-ily used. Maxillary premolars often have drastically taper-ing roots, thin root walls, and proximal root concavities orinvaginations, all of which are predisposing factors toperforation or fracture.70In a study of 468 teeth that hadfractured in vivo, 78% were premolars, with 62% beingmaxillary premolars.71A dowel core should be utilized onpremolars only if the roots are adequately long, bulky,and straight (Fig 13-34)Care must be exercised in the selection of restorationsfor teeth that have no remaining coronal tooth structureThe encirclement of 1.0 to 2.0 mm of vertical axial toothstructure within the walls of a crown creates a ferruleeffect around the tooth to protect it from fracture (Fig 13-35).^ If the crown margin is not placed onto solid toothstructure, the risk of root fracture is greatly increased (Fig13-36). Orthodontic extrusion and crown lengtheningsurgery may be needed to prevent encroachment onperiodontal tissues (Fig 13-37).Rosen72advocated a subgingival collar to act as anextracoronal brace. Hoag and Dwyer73determined thatthe type of dowel core was not as important as the pres-ence of a full crown with margins that extended beyondthe core Having 1 0 mm of vertical tooth wall betweenthe margin of the core and the shoulder of the prepara-tion was found by Sorensen and Engleman74to provide aferrule effect, enhancing fracture resistance by 80% to139%. Milot and Steins demonstrated that a steep,1.0-mm-wide bevel that is nearly parallel with the long axis ofthe preparation also strengthens the tooth against frac-ture.If a minimum of 1.0 mm of vertical axial wall cannot becovered by a crown on a premolar that is to serve as anabutment, the tooth should be extracted. Endodonticallytreated teeth should not be used as abutments for distalextension removable partial dentures.76They are morethan four times as likely to fail than pulpless teeth notserving as abutments.77Pulpless fixed partial dentureabutment teeth fail nearly twice as often as single teeth.Even with a ferrule effect, it is questionable whether apulpless tooth should be used as an abutment for a fixedpartial denture with a span longer than one pontic. Thetooth is structurally compromised and susceptible tofracture if overloaded. The more extensive the restorationrequired for an endodontically treated tooth, the moretime-consuming and technique-sensitive the restorationwill be.79If a fixed partial denture must be used in suchcircumstances, strong consideration should be given tothe use of an implant-supported prosthesis
    • isively Damaged TeethFig 13-34 Roots of a premolar requibulk and length for the successful use fdowel core. Both canals of a two-ctooth are used if possible.Fig 13-35 The preparation for a dowel core should preserve solid tooth structure (A). Thef a crown preparation finish line should be apical to the dowel-core margin (B), enabling thecrown to girdle the tooth (arrow) and brace it externally (C). (From Shillingburg andKessler.58)Fig 13-36 If a tooth is flush with the gin-giva (A), fabrication of a dowel core and acrown without encirclement of toothstructure by the cShillingburg and Kessler.5B|(FroFig 13-37 A tooth without coronal toothstructure (A) can be protected by movingthe crown preparation finish line apically
    • Restoration of Endodontically Treated TeethFig 13-38 A core teiained by pinsslots, amalgapins, or extension into thepulp chamber is used to build up amolar with some coronal tooth structure(A). However, if there is insufficientcoronal tooth structure to support thecore, two dowels are added for re Itante (B).A pulpless molar with a moderately damaged clinicalcrown can be built up with an amalgam or compositeresin core prior to placement of an artificial crown (Fig13-38, A). If there is one sound cusp, the core may beretained by gross extension of the amalgam into the pul-pal chamber alone,79or in conjunction with pins,80peripheral slots,34or dentinal wells (amaigapins).35Avariation, usually employing two dowels, is used formotars that have little or no remaining coronal tooth struc-ture (Fig 13-38, B).The core and its attachment(s) are made separatelyfrom the final restoration. The crown is then fabricatedand cemented over the core just as a restoration wouldbe placed over a preparation done in tooth structure.This two-unit system offers several advantages over aone-piece dowel crown. The marginal adaptation and fitof the restoration are independent of any dowel that mustbe used The restoration can be replaced at some futuretime, if necessary, without disturbing the dowel core. If adowel is necessary, the choice is not limited to a customcast device Prefabricated systems can be used if thedowel does not have to be incorporated into the crown. Ifthe endodontically treated tooth must serve as a fixedpartial denture abutment, it is not necessary to make theroot canal preparation parallel with the path of insertionof other preparations.Prefabricated Dowel WithAmalgam or Resin CoreNumerous techniques have been described for the fabri-cation of dowel cores. Prefabricated dowels with amal-used dowel cores today, and there is a wide variety ofdowel systems available. Kits for prefabricated dowelsutilize special reamers or drills for canal preparations thatare the same size and configuration as the dowels.Through the use of one of these systems, it is possible tocomplete the entire procedure in a single appointment.81Amalgam provides greater strength. Kovarik et al62found that 67% of the amalgam cores tested in an in vitrostudy survived 1,000,000 cycles of 75-lb loading, whileonly 17% of the composite resin cores survived. In thatsame study, all of the glass lonomer cores had failedwithin the first 220,000 cycles. Composite resin remainspopular because it is easily placed, polymerizing in min-utes and allowing work on the core preparation toprogress almost immediately. Resin requires less bulk ofmaterial than does amalgam, which makes it useful onsmall teeth.A dowel increases resistance to lateral forces appliedto the crown from 15%83to 48%.84Dowels can be madeof stainless steel, titanium, brass, or a chromium-contain-ing alloy. The preferred materials in light of current knowl-edge of galvanism and corrosion are titanium, high plat-inum, and cobalt-chromium-molybdenum alloys86Theleast desirable are brass and chromium-nickel steel.95Prefabricated dowels are made in both parallel-sidedand tapered configurations.Dowel systems can be classified by their mechanismof retention: passive (cemented) or active (threaded).The threaded dowels are more retentive than the cement-ed, but they also produce more stress in the tooth.67-8687The techniques for all of these systems are similar,except for the final dowel space (canal) preparationinstrumentation, which is usually specific for the particu-lar dowel system being used.
    • •• Preparations for Extensively Damaged TeethI 13-39 The initial step intion for the crown preparation.Armamentarium1. Handpiece2. Flat-end tapered diamond3. Small wheel diamond4. Flame diamond5. No. 171Lbur6. No. 4 round bur7. Endodontic condenser8. Set of six Peeso reamers9. Dowel kit, including dowel, special rand drill10. Cement spatula and glass slab11. Amalgama. Copper band and wedgesb. Capsule(s) and amalgamatorc. Carrierd. Condensere. Carver(s)12. Composite resina. Crown form (clear or polycarbonateb. Re: i kitc. Plastic fillin lentThe preparation for a dowel core is begun by prepar-ing the coronal tooth structure for the crown that will bethe final restoration for the tooth (Fig 13-39). Removeexisting restorations, caries, bases, and thin or unsup-ported walls of tooth structure (Fig 13-40). Preserve asmuch coronal tooth structure as possible, to enable theaxial walls of the crown to externally brace the tooth.Measure a Peeso reamer (Union Broach Div of MoycoIndustries, Philadelphia, PA) against a radiograph of thetooth being restored to determine the length to which theinstrument (and later, the dowel) will be inserted into thecanal (Fig 13-41). Slide a silicone rubber endodonticstop onto the shank of the reamer, aligning it with a land-mark such as the incisal edge of the adjacent tooth toinsure insertion of the instrument to the proper depth inthe tooth. Place a rubber dam to prevent contaminationof the canal and to protect nearby tissues. Begin thedowel space preparation by first removing gutta-perchain the canal with a hot endodontic condenser.1*0Startenlarging the canal with the largest Peeso reamer orGates Glidden drill (Union Broach) that will fit into thecanal (Fig 13-42).Even if a specific reamer or drill is prescribed for a par-ticular dowel system, begin with safety-tipped instru-ments that will follow the path of least resistance, thegutta-percha in the canal (Fig 13-43). With a series ofsuccessively larger reamers, enlarge the canal to a diam-eter slightly smaller than that of the specific instrumentrequired for the system being used. Enlarging a previ-ously instrumented canal in 0.2-mm increments diminish-es the possibility of the instrument straying from thecanal. Conventional drills used without any prior enlarge-ment of the canal are more prone to stray from the origi-nal canal pathway than either Peeso reamers98or GatesGlidden drills.89Complete the preparation of the dowelspace with the prescribed drill or reamer for the systembeing used (Fig 13-44). General guidelines for the finaldowel diameter are shown in Fig 13-45, but individualteeth may require smaller dowels.In the area of greatest bulk between the canal and theperiphery of the tooth, drill one or two 0.6-mm pin holes toa depth of 2.0 mm. Place the pins in these holes to pro-
    • Restoration of Endodontically Treated Teeth1IB i-aas^IFig 13-41 The depth of insertion of the Peeso reamer is deter- Fig 13-42 The canal is prepared with Keeso rrmined by superimposing it over a radiograph of the iooih beingrestored.Fig 13-43 A Peeso reamer withpath of least resistance, staying witroot canal. A bur (B) or a drill (C)pushed.safety tip (A) will follo1 the previously instrumi cut in any direction th;lowel space preparation is finished Var for the dowel system being used.vide antirotational resistance against forces transmittedfrom the incisal edge of the crown to the core under it. Tryin the dowel to confirm fit and length (Fig 13-46). When itis necessary to shorten the dowel, do it at the apical endif the dowel has a special shape to the head, such as theParapost fColtene/Wh ale dent, Brooklyn, NY). On the otherhand, if the dowel has a specially shaped tip, such as theBCH, do any needed shortening at the coronal end.Make a thin mix of cement, and coat the dowel with it.Introduce cemenl into the dowel space with a plasticinstrument. Use a lentulo spiral (LD Caulk, Milford, DE) toinsure that the walls of the canal are completely coated
    • Preparations for Extensively Damaged TeethFig 13-45 The outlines of the roots (pictured atmidroot) and the dowels are shown superim-posed on the occlusal surfaces of the right teeth(on the readers left). The recommended doweldiameters are shown on the left teeth (the read-ersright).Fig 13-46 The prefabricated dowelpin(s) will give it resistance to
    • istoratiori of EndodoriSically Treated Teeth1/ y ly- 1 Fig 13-48 The gingival portion of ais cut io follow the contours of therounding the tooth.wn form Fig 13-49 Excr the the prefabricated dowel andwith cement (Fig 13-47). Retention can be increased byas much as 90% if a lentulo spiral is used.90Push thedowel slowly to place, allowing the excess cement toescape. Hold the dowel in place with finger pressure untilinitial set occurs. Then remove excess cement fromaround the dowel head and pins.If amalgam will be used for the core, select a copperband of correct diameter to fit the tooth and festoon thegingival end to follow ihe gingival contours If the core isto be composite resin, a copper band can be used, butit is easier and faster to use a crown form. A clear crownform permits the use of a light-activated resin, while apolycarbonate form can be used with autopolymenzingresins (Fig 13-48).If a polycarbonate crown form is used, place a sepa-rating medium in it. Fill it with light-bodied impressionmaterial and blow out the excess with an air syringe,leaving a thin film lining the wails of the crown (Fig 13-49). Then fill the crown form with resin and hold it in posi-tion over the protruding dowel until the resin core mater-ial has polymerized (Fig 13-50). Remove the matrix andshape the core with diamonds and burs to the form of acrown preparation (Fig 13-51). Be sure that the gingivalfinish line is on tooth structure.
    • Preparations lor Extensively Damaged TeethFabricate a provisional restoration and make theimpression for the crown. If a polycarbonate crown wasused as a matrix, it can be used as the provisional crownafter the elastomeric material is peeled out and the mar-gins are refined. The final restoration will be cemented atthe return appointment (Fig 13-52).Gates GhddeInstrument i0.6 0.7sr — 1Dia0.923meter fin1.13mm)1.3451.551.76Custom Cast Dowel CoresPrefabricated noble-metal dowels have been combinedwith wax cores.9192Direct wax patterns have been fabri-cated using either a fissure bur72or a paper clip93as rein-forcement. A direct technique can be used to fabricate adowel-core pattern from acrylic resin.94-96The direct acrylic dowel-core technique can be usedfor teeth with single or multiple roots. When a dowel coreis made for a premolar with two canals, a dowel of opti-mal length is made for the most desirable canal, and thesecond canal accommodates a short key that serves asan antirotational device. It adds little or no retention.The direct method for fabrication of a dowel core isaccomplished in three steps:1. Canal preparation2. Resin pattern fabrication3. Finishing and cementation of the dowel coreArmamentarium1. Handpiece2 Flat-end tapered diamond3. Small wheel diamond5. No. 170 bur6. No. 4 round bur7. Endodontic condenser8. Set of six Peeso reamers9. Straight handpiece10. Coarse garnet disc on a Moore mandrel11. Fine sandpaper disc on a Moore mandrel12. Large green stone13. Burlew wheel on mandrel14. 14-gauge solid plastic sprue15. Dappen dish16. Cement spatula17. Cotton pellets18. Petrolatum19. Resin monomer and polymer20. Medicine dropper21. IPPA plastic filling instrumentCanal PreparationThe preparation for the final restoration is roughly approimated. For an anterior tooth, the final restoration wprobably be a metal-ceramic crown. Axial reduction arincisal reduction of 2.0 mm are accomplished with a flat-end tapered diamond (Fig 13-53). Labial reductionshould be 1.0 to 1.2 mm deep axially. Lingual reductionis done with a small wheel diamond.All caries, bases, and previous restorations areremoved, and the remaining tooth structure is evaluatedto determine that which is sound enough to be incorpo-rated into the final preparation. Thin walls of unsupportedtooth structure should be removed at this time (Fig 13-54). It is neither necessary nor desirable to remove allsupragingival coronal tooth structure unless it is weakand undermined.The tooth is now ready for preparation of the canal. Theinstruments of choice for removing the gutta-percha andenlarging the canal are Peeso reamers. They are availablein sets of six graduated sizes ranging from 0.7 to 1.7 mmin diameter (Table 13-1). with noncutting tips that followthe path of least resistance, the gutta-percha in the canal.Begin the removal of gutta-percha in the canal with ahot endodontic condenser. Measure as large a Peesoreamer as will fit in the obturated canal against a radi-ograph of the tooth being restored to determine thelength to which the reamer will be inserted into the canal(Fig 13-55). Use a landmark, such as the incisal edge ofan adjacent tooth, to locate a stop on the shank of thereamer. Slide a small square of rubber dam material tothe place on the reamer that will correspond with thelandmark when the reamer is inserted to the properdepth in the canalPlace the reamer in the tooth to the predetermineddepth and expose a radiograph to check the accuracy ofthe length. Use this radiograph to establish the finallength. Continue enlarging the canal with the graduatedsizes of reamers until reaching the size that has beendecided upon for that tooth. The size of reamer used willdepend upon the diameter of the tooth As a general rule,it will be no greater than one-third the diameter of the rootat the cementoenamel junction, and there should be aminimum thickness of 1.0 mm of tooth structure aroundthe dowel at midroot and beyond (Fig 13-56).After the canal has been prepared for the dowel, use ano. 170 bur to make a keyway, or groove, in the orifice ofthe canal. Place it in the area of the tooth where there isthe greatest bulk (Fig 13-57). The keyway should be cutto the depth of the diameter of the bur (approximately 0.6mm) and up the canal to the length of the cutting bladesof the bur (approximately 4 mm). On a premolar, the sec-ond canal serves the same antirotational function.
    • Restoration of Endodontically Treated TeeFig 13-55 A Peeso reamerthe tooth being restored to d
    • Preparations lor Extensively Damaged TeethIf there is supragingival tooth structure, use a flamediamond to place a contrabevel around the externalperiphery of the preparation (Fig 13-58). This featureprovides a metal collar around the occlusal circumfer-ence of the preparation to aid in bracing the tooth againstfracture of the remaining tooth structure.Resin Pattern FabricationTrim a 14-gauge solid plastic sprue (Williams Dental,Buffalo, NY) so that it will slide easily into the canal to theapical end of the dowel preparation. It must not bind inthe canal. Cut a small notch on the facial portion of theocclusal end of the plastic sprue to aid in orienting thedowel-core pattern when it is reseated in subsequentsteps (Fig 13-59).In a dappen dish, mix acrylic resin monomer and poly-mer to a runny consistency. Lubricate the canal withpetrolatum on a small piece of cotton on a Peeso ream-er. Fill the orifice of the canal as full as possible withacrylic resin (Duralay, Reliance Dental, Worth, IL) appliedwith" an IPPA plastic filling instrument Coat the sprue withmonomer and seat it completely in the canal. Make surethat the external bevel is covered at this time (Fig 13-60).Trying to cover the bevel later may disturb the fit of thedowel in the canal.When the acrylic resin has become tough and doughy,pump the pattern in and out to insure that it will not lockinto any undercuts in the canal. As the resin polymerizes,remove the dowel from the canal and make sure that itextends to the apical end of the prepared canal. If thereare any voids, they can be filled with a soft, dead wax.such as utility wax. Reinsert the dowel into the canal andmove it up and down to insure that it can be withdrawneasily at a later time.After the resin in the dowel portion has polymerized.relubricate the canal and reseat the dowel. Make a sec-ond mix of acrylic resin and place it around the exposedsprus to provide the bulk from which to fashion a prepa-ration for the final restoration (Fig 13-61). While the resinis polymerizing, the coronal portion can be roughly mold-ed on the facial and lingual aspects by holding itbetween the thumb and forefingerThe core can be roughly shaped in the hand withgreen stones and coarse garnet discs. The preparationfor the final restoration is completed with the dowel-corepattern in place (Fig 13-62). It is desirable to completereduction and contouring in resin, because it is both dif-ficult and time-consuming to shape the metal after thedowel core has been cast. The finished pattern shouldbe smoothed with fine sandpaper discs and a Burlewwheel (JF Jelenko, Armonk, NY). There should be noroughness or undercuts.Wipe the dowel-core pattern with an alcohol sponge toremove any residual lubricant that could displace invest-ment or promote bubble formation. Either could result inmetal projections that would interfere with complete seat-ing of the cast metal dowel core.Finishing and Cementation of the Dowel CoreThe dowel-core pattern is sprued on the incisal orocclusal end (Fig 13-63). Add 1 0 to 2.0 cc of extra water
    • Restoration of Endodontically Treated TeethFig 13-59loosely in thFig 13-61 A second mis is added to buildup the coronal portion of the dowel core.Fig 13-62 Coronal portiopattern is prepared to reito 50 g of investment, and do not use a liner in the ring.These measures will result in a slightly smaller dowelcore that should have less tendency to bind in the canal.The invested pattern should remain in the burnout ovenfor 30 minutes longer to insure complete elimination oithe resin. After the casting is removed from the invest-ment, it is pickled and the sprue is cut off.Check the fit of the dowel core in the tooth by seatingit with light pressure If it binds in the canal or will not seatcompletely, air abrade the dowel and reinsert it in thecanal. Relieve any shiny spots. The core portion of thecasting should be polished to a satin finish with a Burlewwheel. Cut a groove on the side of the dowel from apicalend to contrabevel to provide an escape vent for cement(Fig 13-64).Mix the cement and insert some of it in the canal witha lentulo spiral. Slowly insert the dowel core into thecanal so that the excess cement may escape, allowingthe dowel core to seat completely Touch up the prepa-ration for the final restoration, if necessary, and make theimpression for it. The crown will be cemented at a sub-sequent appointment (Fig 13-65)
    • Preparations for Extensively Damaged TeethCast dowel cores can be used on premolarsMandibular premolars with a single root require no varia-tions in procedure from dowel cores for anterior teeth. Onmaxillary premolars with two canals, one canal isemployed for the dowel preparation, and a stabilizingkeyway is placed in the other. Cast dowel-cores are veryrarely done on molars, because they have divergentcanals that require elaborate, interlocking multipiececastings.A parallel pin may be added to a prefabricated resinpost for antirotational stabilization and some minimaladditional retention (Parapost). The canal is preparedwith aspecial drill that is the same diameter as the dowel,and 0.6- or 0.7-mm pin holes are drilled parallel with thecanal.9 A resin core is fabricated over the parallel-sided.serrated, preformed resin post in the canal, with iridio-platinum pins or nyloitern is invested, cast, and cas a custom pattern.If endodontic therapy mihas received a crown, thecrown retention by approxibristles in the pin holes. The pat-nd cemented in the same mannerit be done on a tooth after it.ccess opening will diminishlately 61%.9SPlacement of adowel inlay has been described for stabilizing thecrown.*3A cast dowel is fabricated on a cast of the pre-pared tooth, with a slightly flared segment at the coronalend seating into the beveled orifice of the canal (Fig 13-66). If a tooth preparation fractures under a crown, aretrofitdowelcorecan befabricated under the dislodgedcrown. Thecrown iscleaned out, lubricated, and used asa matrix for forming the core portion after the dowel seg-ment of the pattern has been completed in the usual
    • Restoration of Endodontically Treated TeethftReferences1. Shillingbutg HT, Jacobi R, Brackett SE: Preparation modifi-cations for damaged vital posterior teeth. Dent Clm NorthAm 1985; 29:305-326.1. Shillingburg HT, Jacobi R, Dilts WE: Preparing severelydamaged teeth. J Calif Dent Assoc 1983; 11:85-91.3. Rhoads JE: Preparation of the teeth for cast restorations. InHolienback GM: Science and Technic of the CastRestoration. St Louis, CV Mosby Co, 1964, pp 34-671. Ingraham R, Bassett RW, Koser JR: An Atlas of Cast GoldProcedures, ed 2. Buena Park, CA, Uni-Tro College Press,1969. pp 161-165.j. Guyer SE: Multiple preparations for fixed prosthodontics. JProsthet Dent 1970; 23:529-553.6. Smith GE, Grainger DA: Biomechanical design of excavity preparations for cast gold. J Am Dent Assoi89:1152-1157.7. Kishimoto M, Shillingburg HT, Dur1974;canson MG: Influence ofThree-quarter crowns. J Prosthet Dent 1983; 49:188-192.i. 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Simon JHS, Kelly WH. Gordon DG, Ericksen GW. Extrusionof endodontically treated teeth. J Am Dent Assoc 1978;97.17-23.i. Ivey DW, Calhoun RL, Kemp WB, Dorfman HS, Wheless JE:Orthodontic extrusion: Its use in restorative dentistry JProsthet Dent 1980; 43: 401-407.
    • Preparations for Extensively Damaged Teethm GK, Nieberg LG: Vertical extrusioinodontic appliance. J Am DentAsso. Ross S. Dorfman HS. Palcams KG: Orthodontic extrusion: Amultidisciplinary treatment approach. J Am Dent Assoc1981; 102-189-191.i. Oesterle LJ, Wood LW: Raising the root—A look at ortho-dontic extrusion. J Am Dent Assoc 1991; 122.193-198.). Beis BJ, Johns*a removable ort116:521-523.). Ingber JS: Forced eruption. Part II. A method of treating iso-lated one or two wall infrabony osseous defects—Rationaleand case report. J Periodontol 1974; 45:199-206.I. Garrett GB: Forced eruption in the treatment of transverseroot fractures. JAmDentAssoc 1985; 111:270-272.I Biggerstaff RH, Sinks JH, Carazola JL: Orthodontic extru-sion and biologic width realignment procedures: Methodsfor reclaiming nonrestorable teeth. J Am Dent Assoc 1986-112:345-348.i. Johnson GK, Sivers JE: Forced eruption in crown lengthen-ing procedures. J Prosthet Dent 1986, 56: 424-427.I. Molina DG, Miller CS: An esthetic extrusion device. GenDent 1987; 35:43^15.». Ross IF: Fracture susceptibility of endodontically treatedteeth. J Endod 1980; 6:560-565.5. Sorensen JA, Martinoff JT; Clinically significant factors indowel design. J Prosthet Dent 1984; 52:28-35.. Goerig AC, Mueninghoff LA: Management of the endodonti-cally treated tooth. Part I. Concept for restorative designs. JProsthet Dent 1983; 49:340-345.3. Shillingburg HT, Kessler JC: After the root canal—Principlesof restoring endodontically treated teeth. Okla Dent Assoc J1984, 74.19-24.). Halpern BG: Restoration of endodontically treated teeth—Aconservative approach. Dent Clin North Am 1985-29:293-303.). Lovdahl PE, Nicholls Jl. Pin-retained amalgam cores vs.cast-gold dowel-cores. J Prosthet Dent 1977; 38:507-514.I. Gelfand M, Goldman M, Sunderman EJ. Effect of completeveneer crowns on the compressive strength of endodonti-cally treated teeth. J Prosthet Dent 1984; 52:635-638.>. Nathanson D, Ashayeri N: New aspects of restoring theendodontically treated tooth. Alpha Omegan 1990;83:76-80.t. Standlee JP, Caputo AA, Collard EW, Pollack MH: Analysisof stress distribution by endodontic posts. Oral Surg 1972,33:952-960.I. Colley IT, Hampson EL, Lehman ML: Retention of postcrowns: An assessment of the relative efficiency of posts indifferent shapes and sizes. Br DenrJ1968; 124:63-69.i. Krupp JD, Caputo AA, Trabert KC, Standlee JP: Dowelretention with giass ionomer cement. J Prosthet Dent 1979141:163-166i. Johnson JK, Sakumura JS1Dowel form and tensile force. JProsthet Dent 1978; 40:645-649.. Standlee JP. Caputo AA, Hanson EC1Retention of endodon-tic dowels. Effects of cement, dowel length, diameter anddesign. J Prosthet Dent 1978; 39:401^105.i. Sorensen JA, Martinoff JT: Intracoronal reinforcement andcoronal coverage: A study of endodontically treated teeth. JProsthet Dent 1984; 51:780-784.s tooth.Rud J Omnell K-A. Root fractures due to corrosion-Diagnostic aspects. Scand J Dent Res 1970; 78:397-403.. Rosen H: Operative procedures on mutilated endodontical-ly treated teeth. J Prosthet Dent 1961; 11:973-986.i. Hoag EP, Dwyer TG: A comparative evaluation of three postand core techniques. J Prosthet Dent 1982; 47:177-181.-. Sorensen JA, Engelman MJ: Ferrule design and fractureresistance of endodontically treated teeth. J Prosthet Dent1990; 63:529-536.i. Milot P. Stein RS. Root fracture in endodontically treatedteeth related to post selection and crown design. J ProsthetDenf 992; 68:428-435.i. Kratochvil FJ: Partial Removable Prosthodontics.Philadelphia, WB Saunders Co, 1988, p 101.. Sorensen JA, Martinoff JT: Endodontically treated teeth asabutments. J Prosthet Dent 1985; 53:631-636.! Colman HL: Restoration of endodontically treated teethDent Clin North Am 1979, 23:647-662.i. Nayyar A, Walton RE, Leonard LA. An amalgam coronal-radicular dowel and core technique for endodontically treat-ed posterior teeth. J Prosthet Dent W&O; 43:511-515.i Goerig AC. Mueninghoff LA; Management of the endodonti-cally treated tooth. Part II. Technique. J Prosthet Dent 9B3:-497.lent in thei. Frank AL: Protective coronal coverage of the pulpleJAm Dent Assoc 1959; 59:895-900.1. Gutmann JL: The dentin-root complex: Anatomic and bio-logic considerations in restoring endodontically treatedteeth J Prosthet Dent 1992; 67458-467.tooth. J Conn State Dent Assoc 1979;53:116-117.I Kovarik RE, Breeding LC, Caughman WF: Fatigue life ofthree core materials under simulated chewing conditions. JProsthet Dent 1992; 68:584-590.I Christian GW, Button GL, Moon PC, England MC, DouglasHB Post core restoration in endodontically treated posteriorteeth. J Endod 1981; 7:182-1851. Kern SB, von Fraunhofer JA, Mueninghoff LA: An in vitrocomparison of two dowel and core techniques for endodon-tically treated molars. J Prosthet Dent 1984; 51:509-514>. Wirz J, Graber G, Widmer W: MetallischeVerankerungselemente in der Restaurativen Zahnmedizm.Berlin, Quintessenz Verlag, 1987, pp41, 51, 66, 105.5. Standlee JP, Caputo AA, Holcomb J, Trabert KC: The reten-tive and stress-distributing properties of a threadedendodontic dowel J Prosthet Dent 1980; 44:398-404.. Standlee JP, Caputo AA: The retentive and stress-distribut-ing properties of split threaded endodontic dowels. JProsthet Dent 1992; 68:436-442.i. Fisher DW, Jeannet DJ, Kwan SK: An evaluation of methodsfor preparing teeth to receive retentiveposts [abstract 532]J Dent Res 1982; 61237.I. Gegauff AG, Kerby RE, Rosenstiel SF: A comparative studyof post preparation diameters and deviations usingParapost and Gates Glidden drills. J Endod 1988,14:377-380.I. Goldman M, DeVitre R, Tenca J. Cement distribution andbond strength in cemented posts. J Dent Res 1984:63:1392-1395.I. Gerstein J. Burnell SC1Prefabricated precision dowels. JAm Dent Assoc 1964; 68:787-791I Taylor AG1Dowel abutment crown. Royal Canad Dent CorpsQuart 1963; 4:1-4I. Bartlett SO: Construction of detached core crowns for pulp-less teeth in only two sittings. J Am Dent Assoc 196877 843-845.
    • e fabri-4-449.96. Shillingburg HT, Fisher DW, Dewhirst RB: Restoration ofendodontically treated posterior teeth. JProstfiefDenf1970:24:401^10997. Baraban DJ: A simplified method for making posts andcores. J Prosthet Dent 1970; 24:287-297.98. McMullen AF, Himel VT, Sarkar NK: An in vitro study of theeffect endodontic access preparation has upon the reten-tion of porcelain fused to metal crowns of maxillary centralincisors. J Endod 1989; 15:154-156.i. Shillingburg HT, Kessatment. Quintes100. Shillingburg HT, Jacobi R Two-piece retrofit dowel-concase report. Int J Periodont Rest Dent 1987; 7:31-41.
    • Chapter 14Preparations for Periodontally Weakened TeethTeetn that have been saved by periodontal therapyoften need cast restorations. This may occurbecause of caries or previous damage, or ihe teethmay need to be splinted together to improve their stabil-ity. These teeth also may be needed as abutments forprostheses replacing missing teeth.Preparation Finish LineRestoration of a tooth around which there has been a lossof gingival height or other change in gingival architecturefrequently requires modification of the tooth preparation.The type and location of the finish line may have a signif-icant impact on the success of the restoration. Animproperly designed preparation can unnecessarilydamage the tooth and potentially compromise thelongevity of the restoration and of the tooth itself. Theproximity of the preparation finish line to the furcationscan necessitate even further modification of the toothpreparation.LocationThe optimum location for the gingival finish line of a crownpreparation is on enamel, away from the gingival sulcus.However, it is frequently necessary for the restorationmargin to extend apically to cover an expanse of root sur-face that may have been affected by caries or erosion.If an all-ceramic shoulder is used as the gingivofacialmargin for a metal-ceramic crown, a 1,0-mm-wide shoul-der will be required as the gingival finish line. This con-figuration is destructive under the best of circumstanceswhen it is placed in the enamel of the clinical crown (Fig14-1). Nevertheless, it is generally well-tolerated inmature teeth.A shoulder is a poor choice when the margin must beplaced on the root surface, The constricted, smallerdiameter of the root will require that the axial reduction beextended into the tooth to a pulp-threatening depth toachieve the same 1.0-mm-wide shoulder {Fig 14-2),Aside from possible pulpal encroachment, this grossdestruction of axial tooth structure weakens the naturalstructural durability of the tooth. Additionally, the shoul-der has a greater potential for concentrating stresses thatcould ultimately lead to fracture of the tooth.shoulder in the*_H_IWI p ui i {i nidnMllsry premolar with a 1.0-rnmshoulder apical io the CEJ. Notice the additionaldestruction of axial tooth structure required toproduce the shoulder at this level.
    • is for Peridontally Weakened TeethFig 14-3 Preparation for a metal-ceramiccrown on a maxillary premolar wiln a chamferapical 10 the CEJ. The amount of axial reductionis similar to that required for a shoulder at theusual position.Fig 14-4 Wide gingival collar is used to blendthe root contour with thai required for a ceramicveneer of adequate thickness.A chamfer finish line on the facial surface in this apicalposition will result in approximately the same depth ofaxial reduction as would a shoulder at the usual level (Fig14-3). A metal-ceramic crown fabricated in such circum-stances should have a wide metal gingival collar (Fig 14-4). Extension of the ceramic veneer to the gingival mar-gin will create overcontouring or will require use of themore destructive shoulder.Furcation FlutesSometimes the crown margins on a molar must extend farenough apically that the preparation finish line approach-es the furcation, where the common root trunk dividesinto two or three roots (Fig 14-5). The designs of both thetooth preparations and the crowns for these teeth mustbe different from those customarily used. This is causedby the intersection of the preparation finish line with thevertical flutes or concavities in the common root trunk,extending from the actual furcation in the direction of thecementoenamel junction. When that occurs, the axial sur-faced) of the tooth preparation occlusal to the inversionof the gingival finish line must also have vertical concav-ities or flutes1(Fig 14-6).Examples can be seen in the mandibular furcation,which is frequently encountered by crown preparationsthat do not extend very far apically. The entrances to thefacial and lingual furcations are 3 and 4 mm apical to thecementoenamel junction on mandibular first molars.2Onthe mesial, facial, and distal surfaces of maxillary firstmolars the furcation entrances are 3.6, 4.2, and 4.8 mmfrom the cementoenamel junction, respectively.3Theflutes on a maxillary molar are seen less frequently, andtheir presence often is an indication of greater gingivalrecession and vertical bone loss.The axial contours of crowns placed on teeth whosefurcation flutes are intercepted by preparation finish linesmust likewise reflect the concavity rising from the furca-tion flute (Fig 14-7). The artificial crown should recreatethe contours of the furcation flute and not follow the orig-inal crown contours.4The facial surface should be invagi-nated into a concavity above the bifurcation that extendsocclusally until it meets the facial groove in the occlusalone-third of the facial surface 5The concavities usuallymerge with features originating on the occlusal surface.There must be no interruption in the vertical concavity ris-ing at the margin of the restoration. Any horizontal ridgeon the facial or lingual surface of the tooth that intersectswith this concavity and blocks it will result in a plaque-retaining area (Fig 14-8).There also will be concavities on the mesial and distalaspects of a maxillary molar arising from their respectivefurcations. They should be "softened" or blended into thesurrounding axial surfaces of the crown. This will mini-mize the difficulty of cleaning those areas in the lessaccessible lingual embrasures of the posterior segmentsof the maxillary arch.Root ResectionRoot resection is a procedure m which the root isremoved, irrespective of what is done with the crown.1Theresection of a root also may be called a radectomy.6Rootamputation is removal of a root without touching thecrown.1A hemisection is a procedure in which the tooth isseparated through the crown and the furcation,1.rproduc-ing two essentially equal-sized teeth. Although the wide-spread use of these procedures is fairly recent, similarprocedures were described in the literature more than 100years ago by Farrar,8Black,9and Tomes and Tomes.10
    • Fig 14-5 Facia! furcations for a maxillary (A) anda mandibular (B) first molar. The portion of the fur-cation fating apically or toward the bone is thevault (vt), or roof. The vertical concavity on thecommon root trunk is the flute (fl).g 14-6 Vertical concavities in •£ tooth preparations (arrows) e>m the Paginations where the
    • Preparations for Peridontally Weakened TeethIndicationsOne or more roots of a molar may be removed to eradi-cate areas of the tooth that create problems in the main-tenance of good hygiene and plaque control. A root orroots can be eliminated because of an invasion or uncov-ering of the furcation by severe vertical bone loss.711-13The severe loss of bone or attachment around one rootmay also necessitate the removal of a root.14"16The con-cept of "periodontal strategic extraction" may simplify theperiodontal treatment of an entire quadrant.17It alsoreduces the risk of extension of the lesion to the survivingroots of that tooth or to neighboring teeth.In 58% of the maxillary and mandibular first molarsexamined by Bower,18furcation entrances were narrowerthan the width of the smallest curettes available. Whenthe furcation entrance is that narrow, maintenance maybe compromised by instrument inaccessibility, andresection may be the only way to create an area that cartbe adequately cleaned. Root removal can aid in reestab-lishing furcation control5by changing furcation anatomyto facilitate cleaning.19Nevertheless, involvement of a furcation does not auto-matically require resection of a root. Hamp et alsoreport-ed a clinical study of 100 patients with 175 multirootedteeth afflicted with varying degrees of salvageable furca-tion involvement. About half were treated with root resec-tion, while the others received scaling and root planing,furcation operations, or other procedures. Both groupsretained all of their teeth during the 5-year period of thestudy. The actual percentages will vary among practi-tioners based on individual philosophies, patient accep-tance, and a number of other factors.Resection may be performed to salvage teeth withendodontic problems..sn-iais.ie These encompass awide variety of situations including perforations, irretriev-able broken instruments, anatomic anomalies that wouldprevent successful instrumentation or obturation of acanal, and other nonspecific failures.A tooth that has other sound roots can be saved byremoving a root that has fractured,11•1316or one afflictedwith untreatable caries14"16that extends into it Rootresection is also done where roots of two adjacent teethare in such close proximity that embrasure space is oblit-erated.1 11131SResection of a root on one tooth may facil-itate retention of both teeth. Indeed, the removal of a par-ticular root may be accomplished as much to improve theprognosis of an adjacent tooth as that of the tooth beingsectionedContraindicationsFused roots,11or those that approximate other roots ofthe same tooth15are contraindicated for resections. If thefurcation is too far apical, roots cannot be resectedbecause there will be too little bone left to support theremaining roots.11The furcation must be in the coronalone-third to do a hemisection on a mandibular molar, andresections cannot be done on maxillary first premolars.19If excessive alveolar support has been lost uniformlyaround all of the roots, nothing is gained by removing aroot. The remaining roots will have no better support thanthe one removed. A root resection also may not be usedif the root that is to be kept cannot be successfully treat-ed endodontically.Capacity of Resected RootsTeeth that have been resected can be used as abutmentteeth for fixed partial dentures, splints, or vertical stopsfor cantilever fixed partial dentures.31The retention of astrategic tooth by root resection may preclude the needfor a removable partial denture.22Keep in mind, howev-er, that their load-bearing ability has been lessened bytheir diminished attachment area. As the level of bone islowered by periodontal disease, the surface area of peri-odontal attachment diminishes (Fig 14-9).The mesial root of a mandibular first molar provides37% of the attachment surface area and the distal pro-vides 32%.23If the furcation is uncovered, 31% of theattachment area, which is imparted by the root trunk, hasbeen lost. The mesiofacial, distofacial, and palatal rootsof a maxillary first molar furnish 25%, 19%, and 24% ofthe attachment area, respectively.24The root trunk sup-plies 32% of the attachment for the tooth.Removal of a corresponding root on a second molar willprobably result in a similar percentage loss of support.However, the length of the root trunks of second molarstends to be both more variable and somewhat greaterthan that of first molars.?The total root surface areas offirst and second molars differ by only 0 5% to 1.2% 25Resection TechniqueIt is usually desirable to complete endodontic treatmentbefore removing the root,61113"1519since a root canal willbe transected during the surgery. However, often it is notpossible to adequately evaluate the extent of furcationinvolvement until the flap has been reflected to permit adirect visual examination.20To avoid possible misunder-standings over the time, discomfort, and expense of a"needless" endodontic procedure on a tooth that cannotbe saved because of the inability to separate the target-ed root from the others, it is often necessary to do theresection first. The pulp should be protected by a provi-sional restoration, and endodontic therapy should bescheduled as soon as possible.Begin the resection with a long, thin diamond to cutthrough the vault of the furcation.15Remove all traces ofthe resected root at the time of surgery. Do not leave anyvestigial remnants of the furcation vault. They will actmuch as overhanging crown margins would, interfering1
    • Fig 14-9 Relationship between vertical boneloss and the root surface area of maxillary3andmandibular" first molars.Bone Loss and Root Surface Area in First Molars100-T.2 3 4 5 6 7 8 9 10 11 12 13 H 15 16istance from CEJ to alveolar crest (in mm)Fig 14-10 Any rewill impede plaqueFig 14-11 Crown preparation finish line extends beyond thepulp chamber (small shadedarea), but it need not encompass theentirerootremovalsite(cross-hatchedarea).Shownisaprepara-with plaque removal and increasing tissue inflammation(Fig 14-10).If any ridges are discovered at the time the tooth is pre-pared for a crown, they should be smoothed over. Anintermediate bifurcations! ridge is present in 73% ofmandibular first molars,26and there is a "bridge" of toothstructure connecting the distofacial and palatal roots ofmaxillary molars.15The finish line of the crown prepara-tion should extend apically beyond the obturated pulpchamber (Fig 14-11). It is neither necessary nor desir-able to extend the preparation finish line far enough api-cally to cover all areas of the root whose configurationhas been altered by root removal.If the root of a maxillary molar is being resected forperiodontal reasons, there is usually enough coronaltooth structure so that the pulp chamber need only befilled with amalgam. A dowel is frequently not needed inthis situation and might actually weaken a thin, isolatedroot rather than strengthen it.If a dowel core is required because of coronal dam-age, a custom cast dowel core is preterable to a prefab-ricated dowel.27The minimal diameter of a periodontallyweakened, root-resected segment does not permit a suf-ficient bulk of core material to remain around the dowelwhen the crown preparation is done
    • Preparations for Pertdontalty Weakened TeethFig 14-12 Proper contours for a distofaci,resection on a maxillary molar after the suning area has been smoothed (A). A metal-cicrown is fabricated for the preparation afteris placed (B). The preparation does not covetheo surfaceTooth Preparation and Crown ConfigurationWhen a root has been removed from a tooth, both thetooth preparation and the contours of the crown will bedifferent because of the altered tooth shape.Maxillary Dlstofacial Root. The distal furcation of themaxillary first molar is susceptible to frequent periodon-tal involvement because of the proximity of the divergentdistofacial root to the nearby second molar2and its inac-cessibility to the patient. The distofacial root of a maxil-lary molar is the one that is most frequently removed28(Fig 14-12) Because the distofacial root is a relativelysmall one, the occlusal outline of the resulting prepara-tion commonly resembles a lamb chop when viewedfrom the occlusal direction (Fig 14-13).The completed restoration placed in this situation usu-ally will not restore the complete occlusal outline of the
    • Root Resectionig 14ttachrerami-16 Mesiofacial rootlolar afterrent hasic crown iplaced (Bthe area <been cont).surrounding the roaured (A). A mekstore the tooth after)! has been removed.inlact tooth. The distofacial embrasure is larger thanusual, enabling the patient to keep the area clean (Fig14-14). Making the distofacial cusp smaller generallydoes not create an esthetics problem, because the dis-tofacial cusp is hidden by the mesiofacial cusp in normaltooth alignment.The proximal contact is restored to its normal faciolin-gual size. In the finished restoration, it is important thatthe contours of the distofacial cusp apical to the contactarea have a definite concave shape1 5(Fig 14-15). Thisinsures that crown contours will be aligned with the rootconfiguration in that critical area, preventing impinge-ment on the gingiva.Maxillary Mesiofacial Root. Loss of the mesiofacialroot (Fig 14-16) represents a greater loss of support forthe remaining tooth than does the loss of the distofacialroot. The mesiofacial root accounts for 25% to 36% of thefirst molar root area, depending upon the amount of lossof bone around the root trunk.23If the mesiofacial rootmust be removed, the resulting occlusal outline tends tobe more triangular in configuration because of thegreater faciolingual dimension of the root that has beenremoved (Fig 14-17). Again, the finish line will extend api-cally past the pulp chamber, but it will not include all ofthe area where the mesiofacial root was removed. Therewill be a concavity gingivofacial to the proximal contacton the mesial surface of the crown (Fig 14-18).Maxillary Palatal Root. In those situations where thepalatal root has been removed from a maxillary molar, thepalatal surface of the preparation will be flat, reflectingthe general configuration of the remaining root stump(Fig 14-19). The tooth preparation will have an abbreviat-ed faciolingual dimension The central groove of thepreparation is aligned with those of the occlusal surfaces
    • Preparations for Peridonlally Weakened TeethFig 14-19 Area surrounding the root titof the palatal root of a maxillary m( d smoothing (A). The tooth isFig 14-21 The lingualmolar without a palat Fig 14-22 The presence of lingual cusps on a maxillary molardeprived of the support of its palatal root would subject the toothto torquing forces (arrow) that could tip the tooth lingually.
    • Fig 14-23 Correct contours for the attachmentsites of the facial roots of a maxillary molar afteraothing (A). A crown is placedover the preparation after core fabrication (B).of adjacent teeth (Fig 14-20) The facial cusps of thepreparation will be near normal faciolingually. The lingualcusps will be quite small, possibly little more than a nar-row ledge lingual to the central groove.The preparation and resulting restoration usually willhave a distinct concave flute on the facial surface arisingfrom the facial bifurcation. Essentially there will be no lin-gual cusp15(Fig 14-21). The presence of lingual cuspswould produce an area inaccessible to hygiene mainte-nance in the linguogingival segment of the crown. Itwould also create a severe torquing momenl on the tooth,which could either tip the tooth lingually or fracture thetooth preparation under the crown (Fig 14-22)Maxillary Facial Roots. When both of the maxillaryfacial roots are removed, only the palatal root remains(Fig 14-23). Preparation of the tooth overlying this root willresult in either an oval or a circular configuration depend-ing upon the shape of the root itself (Fig 14-24). Theresulting crown should occlude with its mandibular coun-terpart in such a way that occlusal forces cannot bedirected facially. This will place it in a near reverseocclusal or cross-bite relationship16(Fig 14-25].Mandibular Hemlsection. When separating the rootsof mandibular molars, the possibilities are fewer sincethere are only two roots Frequently one root is removedwhile the other remains. Saving the mesial segment
    • rations for Perldontally Weakened TeethVJtB 14-26 The mesial root of a mandibular second molar car"lively extend the occluding segment of the mandibular arch tce as a stop for the opposing occlusion.Fig 14-27 The distal root of a mandibular muiabutment for a short-span prosthesis replacing tlFig 14-28the abutmeroffers less thThe mit for a molar replaceinandibularsecnent fixed par;-third of the support of an untial deiolflrcanbe•nture, but itwould be desirable if the molar in question were the lasttooth in the arch (Fig 14-26) and the opposing teeth didnot extend very far distal to the mandibular first molar.The distal root could be used as an abutment for a short-span fixed partial denture replacing the mesial root (Fig14-27). Occasionally the one root may be used as thedistal abutment for a longer-span fixed partial denture,replacing an entire molar (Fig 14-28). This must beviewed as a high-risk prosthesis, since the remaining dis-tal root has slightly less than one-third of the alveolar sup-port of the intact tooth with normal bone.33If an effort is made to save both roots of the molar fol-lowing the resection, the process is described as "bicus-pidization."13If both roots are maintained, it is importantthat they be separated from each other to allow normalgmgival embrasure spaces. Sometimes the roots are dis-tinctly separate, angling out from the furcation and pro-viding the separation naturally. However, if they are notnaturally separated, some measure must be taken toaccomplish it, or the crowns placed over those roots willhave no embrasure space. The result will be a proximalcontact that extends subgingivally to the marginal ridge.
    • Root ResectionFig 14-29 If theresection, there wiOrthodoniare not separated afterio gingival embrasure (A).Fig 14-30 The contact that obliterates the gival embrasures of restorations placed on a hipcted molar (A) can be alleviated in some cU placing shoulders on the interradiculariflpnt of the preparation that face each c11row the former furcation (B).The prognosis lor teelh restored in such a manner isextremely poor Separation may be accomplished bymoving the roots apart orthodontically (Fig 14-29), or itmay be accomplished with interradicular shoulders on thecrown preparations on the separated roots15(Fig 14-30)."Skyfurcation." Occasionally it may be desirable toseparate the roots of a maxillary molar without removinga root This is possible only if the roots are long, well-sup-ported by bone, and distinctly separate. The roots are cutapart (Fig 14-31) and then rejoined by a "crown" that inreality is a very short interradicular splint with concaveconnectors from one root to the other. The occlusal con-figuration of the splint, or "crown," is pretty much that ofan ordinary molar. This procedure, in effect, makes thefurcation metal and moves it occlusally while separatingthe roots (Fig 14-32). This improves access to the furca-tion and protects a caries-prone area.1420
    • rs for Peridontally Weakened TeethSuccess and FailureRoot resection does not guarantee success (Table 14-1).Ehrlich et al29reported an 87% success rate in furcation-involved teeth treated by root resection after 10 to 18years. Ross and Thompson,30on the other hand, pub-lished a similar success rate (88%) for furcation-involvedmolars that were treated conservatively without rootresection (Table 14-2) Hamp and associates20reportedbeing able to maintain all 87 of the resected teeth in theirstudy over a 5-year period, but they claimed equal suc-cess with 88 furcation-involved teeth that were kept intactLanger et al31found that failures usually occurred 5 to10 years after treatment, with 55% of the failures occur-ring in 5 to 7 years The failure is more likely to beendodontic or restorative than periodontal in nature. Thisusually means that a root will fracture.Mandibuiar roots are more likely to fail than maxillaryroots. This probably is explained by the fact that resec-tion of mandibuiar teeth always creates single-rootedsegments. In the maxillary arch, a root resection will usu-ally leave a tooth with two roots, providing it with addi-tional support as well as stability.Successful restoration of periodontally weakened teethis aided by creating an occlusal scheme with canine-pro-tected articulation, decreased vertical overlap, and flat-tened posterior cusps.32e 14-1 Success Rates ofRoot ResectionTable 14-2 Success Rates ofNonresection MethodsYears5-2455-24Numberof teeth34188429Percentsuccess8810090InvestigatorRoss and Thompson30Hamp ct al)(!OVERALL
    • Root ResectionReferencesacted teeth J Prosthct> Ghet ME. Vernino AB. Root morphology-Clinical signifi-cance in pathogenesis and treatment of periodontal dis-ease. JAm DentAssoc 1980; 101:627-633.i. Gtier ME, Dunlap RW Linear variation of the root surfacearea of the maxillary first molar J Periodontol 1985,56:39-43.I. Yuodelis RA, Weaver JD, Sapkos S: Facial and lingual con-tours of artificial complete crown restorations and theireffect on the periodontium. J Prosthet Dent 1973; 29:61-66.). Eissman HF, Radke RA, Noble WH: Physiologic design cri-teria for fixed dental restorations Dent Clin North Am 1971;15:543-568.> Bergenholtz A: Radectomy oAssoc 1972; 85:870-875.multirooted teeth. J Am Dentmputation. J Periodontol!. Farrar JN: Radical and heroiiby amputation of roots of26:79-81.i. Black GV. In LitchWF The An1. Philadelphia, Lea Brothersyp 997.m ot Dentistry, vol). Tomes J, Tomes CS: Dental Surgery, ed 3. Philadelphia, P.Blakeston & Son, 1887, p 526Basaraba N: Root amputation and tooth hemisection. DentClin North Am 1969; 13:121-132.i. Marin C, Carnevale G, De Febo G, Fuzziendodontically treated teeth with mterbefore roof removal and/or root separatioRest Dent 1989; 9:43-57.s. J ClinInt J Periodont. Amsterdam M, Rossman SR: Technique of hemultirooted teeth Alpha Omegan 1960; 53:4 1I. Bower RC: Furcationtreatment—Furcation1979; 50:23-27.I. Staffileno HJ: Surgical management of the furca invasion.Dent Clin North Am 1969; 13:103-119.I. Hamp S-E, Nyman S, Lindhe J: Periodontal treatment of mul-tirooted teeth. J Clin Periodontol-975; 2:126-135.. Reinhardt RA, Sivers JE: Management of class III furcallyinvolved abutments for fixed prosthodontic restorations JProsthet Dent 1988, 60:23-28.i Dunlap RW, Gher ME: Root surface measurements of themandibular first molar. J Periodontol 1985; 56:39-43I. Hermann DW, Gher ME, Dunlap RM, Pelleu GB: The poten-tial attachment area of the maxillary first molar J Periodontol1983; 54:431-434.>. Jepsen A: Root surface measurement and a method for x-ray determination of root surface area. Ada Odontol Scand1963; 21:35-46.i. Everett FG, Jump EB, Holder TD, Williams GC: The interme-diate bifurcational ridge: A sludy of the morphology of thebifurcation of the lower first molar J Den! Res 1958137:162-169.. Klavan B: Clinical observations following root amputation inmaxillary molar teeth. J Periodontol 1975, 46:1-5.I Ehrlich J, Hochman N, Yaffe A. Root resection and separa-tion o( multirooted teeth. A 10-year follow-up study.Quintessence /nf19S9; 20:561-564.). Ross IF, Thompson RH: A long term study of root retentionin the treatment of maxillary molars with furcation involve-ment. J Periodontol1978; 49:238-244.I. Langer B, Stein SD, Wagenberg B An evaluation of rootresections—A 10-year study J Periodontol 198V52:719-722.I Kois JC, Spear FM: Periodontal prosthesis: Creating suc-cessful restorations. JAm Dent Assoc 1992; 123:108-113.i. Grant DA, Stern IB, Listgarten MA. Penodontics.Louis. CV Mosby Co, 1988, pp 921-949.
    • Chapter 15Provisional RestorationsIt is important that the prepared tooth or teeth be pro-tected and that the patient be kept comfortable while acast restoration is being fabricated. By successfulmanagement of this phase of the treatment, the dentistcan gain the patients confidence and favorably influencethe ultimate success of the final restoration. During thetime between the preparation of the tooth and the place-ment of the final restoration, the tooth is protected by aprovisional restoration. This type of restoration has alsobeen known for many years as a temporary restoration. Agood provisional restoration should satisfy the followingrequirements:1. Puipal protection. The restoration must be fabricatedof a material that will prevent the conduction of tem-perature extremes. The margins should be adaptedwell enough to prevent leakage of saliva.2. Positional stabiiity The tooth should not be allowed toextrude or drift in any way. Any such movement willrequire adjustments or a remake of the final restorationat the time of cementation.3. Occlusa! function. Being able to function occlusally onthe provisional restoration will aid patient comfort,ward off tooth migration, and possibly prevent joint orneuromuscular imbalance.4. Easily cleaned. The restoration must be made of amaterial and contour that will permit the patient tokeep it clean during the time it is worn. If the gingivaltissues remain healthy during the wearing of the pro-visional crown, there is less likelihood of a problemarising after cementation of the final restoration.5. Nonimpinging margins. It is of utmost importance thatthe margins of a provisional restoration not impingeupon the gingival tissue.MThe resulting inflammationcould cause gingival proliferation, recession, or at thevery least, hemorrhage during the impression orcementation. A damaging overhang can result from apreformed metal or resin provisional restoration thathas not been contoured properly, while a custom resinprovisional crown can produce a horizontal overhangif it is incorrectly trimmed. A restoration with drastical-ly underextended margins also may result in a prolif-eration of gingival tissue.56. Strength and retention. The restoration must stand upto the forces to which it is subjected without breakingor coming off the tooth. Having to replace a provision-al restoration is time-consuming and does not aidpatient rapport. A broken provisional fixed partial den-ture can accelerate tooth movement. The restorationshould also remain intact during removal so that it canbe reused if necessary.. Esthetics. In some cases, the restoration must providea good cosmetic result, particularly on anterior teethand premolars.Types of Provisional RestorationsThere are numerous ways of providing protective cover-age for teeth while permanent restorations are being fab-ricated. These range from zinc oxide-eugenol cement forsmall intracoronal inlay preparations, to provisionaland provisional fixed partial dentures.Prefabricated vs Custom RestorationsProvisional restorations can be classified by whether theyare prefabricated or custom made Prefabricated formsinclude stock aluminum cylinders ("tin cans"), anatomicmetal crown forms, clear celluloid shells, and tooth-col-ored polycarbonate crown forms. They can be used onlyfor single-tooth restorations. Custom crowns and fixedpartial dentures can be fabricated of several differentkinds of resins by a variety of methods, direct or indirect.Direct vs Indirect TechniquesProvisional restorations also can be classified by themethod used for adapting the restoration to the teeth: thedirect technique is done on the actual prepared teeth inthe mouth, and the indirect technique is accomplishedoutside of the mouth on a cast made of quick-set plaster.The direct technique is inviting to novices, because iteliminates the alginate impression and the plaster cast.
    • However, the direct reline is very technique-sensitive. Intodays computer terminology, it is decidedly "userunfriendly." If the direct technique has any place inrestorative dentistry, it is in the hands of experiencedoperators using a resin other than polyfmethyl methacry-late).The indirect technique is preferred over the direct tech-nique for its accuracy.6To avoid locking into undercuts, adirectly fabricated resin provisional restoration must beremoved from the tooth before it has completely poly-merized. Since polyfmethyl methacrylate) shrinksapproximately 8% when it polymerizes,7polymerizationoutside the mouth without a supporting form results indistortion and a less than optimal fit.^9In a study of themarginal adaptation of provisional restorations, Crispin etal10showed that the marginal fit of poly(methyl methacry-late) provisional restorations could be improved nearly70% by fabricating them indirectly.The fit of provisional restorations made from almost allresins can be improved by using the indirect technique.For some materials, the improvement in fit obtained byusing the indirect technique is as much or more than theimprovement seen with poly(methyl methacrylate).10Monday and Blais11found better margins onpoly(vinylethyl methacrylate) crowns made indirectlythan those made either directly or by relining.The indirect technique also is preferred for the protec-tion that it provides the pulp,6particularly if poly(methylmethacrylate) is used. The placement of polymerizingpolyfmethyl methacrylate) on freshly cut dentin couldlead to thermal irritation from the exothermic reaction orchemical irritation from the free monomer.17 rAIt has beenreported that this produces an acute pulpal inflammation,as evidenced by an accumulation of neutrophilic leuko-cytes in the pulp horns.14This is another irritant added toa tooth that in most cases has already been subjected tocaries, previous restorations, and high-speed cutting inthe preparation of the tooth. It is an additional insult thatshould be avoided whenever possible. A further advan-tage of the indirect technique is that much of the workcan be delegated to auxiliary personnel.Techniques for CustomProvisional RestorationsThe requirements for a good provisional restoration aremost easily and completely met by a custom indirectrestoration. There are a variety of techniques for makinga mold to form the outer surface of a custom provisionalrestoration that provides the appearance of a tooth whereneeded, physiologic axial contours adjacent to the gingi-va, occlusion with opposing teeth, proximal contact, andmarginal fit. The inner surfaces will be shaped by a castof the preparation(s).Both elastomeric1286^^23and alginate56-24ovenm-pressions have been used to shape the provisionalrestoration. An overimpression is made on the diagnosticcast, or in the mouth, before the tooth preparation isbegun. An elastomenc impression provides excellentstability, but it is more expensive than alginate.A template formed from clear thermoplastic resin alsocan be used for this purpose.325"37It is shaped on a diag-nostic cast, using a vacuum forming machine or animpression tray filled with silicone putty. The template isfilled with resin and applied to the prepared teeth or to afast-setting plaster cast of the prepared teeth. Templatesare very stable, and they can be adapted well enough tobe used for checking preparation reduction or startingwax patterns.27A thin shell crown or fixed partial denture can be madeof autopolymerizing resin in an impression prior to thepreparation appointment by alternately dripping mon-omer and gently blowing polymer with an atomizer.28-30The resulting form is relined. after the tooth or teeth areprepared.1628A second shell can be made from thesame impression as a spare.28The shell also can be heatprocessed in a laboratory.18Selected techniques are discussed in detail in the fol-lowing pages. Although an overimpression is shown formaking a provisional crown, and a clear resin templatefor a provisional fixed partial denture, they are inter-changeable.Resins for Provisional RestorationsThere are several types of resins that can be used formaking custom provisional restorations. Polyfmethylmethacrylate) has been in use the longest. Poly(ethylmethacrylate). polyfvinylethyl methacrylate), bis-acrylcomposite resin, and visible light-cured (VLC) urethanedimethacrylate have come into common usage in recentyears. Epimine resin, which for a decade also was usedfor this purpose, is no longer available. No one resin issuperior in all respects,15and the restorative dentist mustassess the advantages and disadvantages of each inselecting which to use (Table 15-1).Overimpression-Fabricated Provisional CrownThe use of an alginate overimpression remains a populartechnique, because it is always readily available in thedental operatory. It is easily adapted to mtraoral use in theevent that the proposed restoration of a tooth with amal-gam is unexpectedly replanned as a cast restoration.
    • Table 15-1 Characteristics of Resins Used for Provisional RestorationsPoly(vinylethylVLC uerthanedimethacrylateCr & Br R,DuralayGC AmericaLD CaulkReliance DenLang DentalGood marginal fit16Good transverse strength6Good polishability15Durability^Gooct polishability15Minimal exothei " "GoodsLow shrinkage3Good polishability16Minimal exothermic heat incriGood abrasion resistance15Flexibility!*Good marginal (it16Low exothermic heat increasiGood abrasion resistance15Good transverse strength15Low shrinkage8High surface hardness16Good transverse strength16Good abrasion resistance15Controllable working time20Color stability16Surface hardness16Transverse strength15Durability16Fracture toughness19urface hardness15ess stain resistance16imited shade selection6imited polishabilitye
    • ProvisionalRestorationsFie 15-1 Defects, such as a missing cusp (arrow), should be Fig 15-2 Utility wax is placed in the defecOverimpression Armamentarium1. Diagnostic cast2. Utility wax3. No 7 wax spatula4. Quadrant impression trays (two, sam5. Alginate6. Rubber bowl7. Spatula8. Quick-set plaster9. Laboratory knife with no. 25 blade0. Heavy-duty laboratory knife1. Large camel-hair brush2. Cement spatula3 Dappen dish4 Separating medium5 Monomer and polymer6. Medicine dropper7. Heavy rubber band8. Straight handpiece9. Acrylic burs20. Abrasive discs and Moore rrn
    • Techniques for CusThe overimpression frequently is made in the patientsmouth while waiting for the anesthetic to take effect.However, if the tooth to be restored has any obviousdefects, the overimpression should be made from thediagnostic cast (Fig 15-1). After any defects are filled andsmoothed over with red utility wax, the diagnostic cast isimmersed in a plaster bowl of water for 5 minutes (Fig 15-2). Wetting the cast in this manner will keep the alginatefrom adhering to it.When the alginate has set, the overimpression isremoved from the diagnostic cast and checked for com-pleteness (Fig 15-3). A laboratory knife with a no. 25blade is used to trim off all excess alginate. Thin flashesof impression material that replicate the gingival creviceare removed to insure that there will be no impedimentsto the complete seating of the cast into the overimpres-sion later (Fig 15-4). The impression is wrapped in a wetpaper towel and placed in a ziplock plastic bag for laterWhen the tooth preparation is completed, anotherquadrant impression is made in alginate (Fig 15-5). Thisimpression is poured up with a thin mix of quick-settingplaster (Snow White Impression Plaster No. 2, KerrManufacturing Co, Romulus, Ml) (Fig 15-6). Excessmaterial should be trimmed off on a model trimmer whenthe plaster has set. The trimmed cast should have atleast one tooth on either side of the prepared tooth, ifpossible. Areas of the cast that duplicate the soft tissuesshould be reduced as much as possible (Fig 15-7).Check the occlusal surfaces and gingival crevices forany plaster nodules that will prevent complete seating.Then try the trimmed quick-set plaster cast in the over-impression to make sure that it will seat completely (Fig15-8). Coat the prepared tooth and adjacent areas of thecast liberally with a "tin foil substitute" separating medi-um (Alcote, LD Caulk Div, Dentsply International, Milford,DE) (Fig 15-9). Allow the material to dry before mixing theacrylic resin. Drying can be accelerated by the use of anair syringe.Mix tooth-colored acrylic resin in a dappen dish with acement spatula (Fig 15-10). Use 12 drops of monomer foreach tooth being restored. Place the resin in the overim-pression so that it completely fills the crown area of thetooth for which the provisional restoration is being made(Fig 15-11).
    • Fig 15-8 The cast is tried in the overim press ion before proceeding. Fig 15-9 Separating medium is painted on the pla1Seat the cast into the overimpression, making sure thatthe teeth on the cast are accurately aligned with the toothimpressions (Fig 15-12). The force used to seat the castinto the alginate impression is critical.31Excessive forcecan overseat the cast and uneven force can torque thecast, either of which will affect trie restoration.Once the cast has been firmly seated and the excessresin has been expressed, hold the cast in place with alarge rubber band (Fig 15-13). It is important that thecast be oriented securely in an upright position so thatthe space between the cast and the impression that isfilled with the resin forming the provisional restoration willnot be distorted (Fig 15-14, A). If the cast is torqued toone side by the rubber band, the cast may be forcedthrough the soft resin in some areas, resulting in a provi-sional restoration that may be thin in those areas andthicker than desirable in others (Fig 15-14, B). if the castis seated with too much force, or if the rubber band iswrapped around the assembly too many times, the castmay be forced through the resin occlusally, resulting in aprovisional restoration with an occlusal surface that is toothin (Fig 15-14, C).Place the overimpression-plaster cast assembly in aplaster bowl full of hot tap water for approximately 5 min-utes, or into a pressure pot if one is available. Allowing apoly(methyl methacrylate) provisional restoration to poly-merize in a pressure pot (Sure-Cure Pressure Unit.Howmedica Dental Div, Chicago, IL) under 20 psi willdecrease porosity and increase the transverse strengthof the restoration by 28%.32
    • Techniques for Custom Provisional ResFig 15-12 The cast is seated firmly inthe overimpression.Fig 15-14 Cross secthnscast is pushed to one side, the provisional restoration will be deficient (B); overseatingof the cast will produce a provisional restoration with a thin occiusal surface (C).
    • ProvisionalRestoratiotWhen the resin has polymerized, remove the rubberband to disassemble [he quick-set plaster cast from theoverimpression. ff the restoration is not easily removedfrom the cast, break the tooth off the plaster cast with aheavy-bladed laboratory knife (Fig 15-15). Use the sharpend of a thin-bladed knife or some other small, pointedinstrument to remove any plaster that remains in the pro-visional restoration (Fig 15-16). Ease of removal is one ofthe advantages of using the weak, quick-set plaster.Acrylic burs or coarse Moore discs are used to trim theexcess resin from the provisional restoration (Fig 15-17).Before attempting to seat the restoration on the tooth, besure to remove all resin extending beyond the prepara-tion finish line into undercut areas. Smooth the axial sur-faces near the margins of the restoration with a fine sand-paper disc (Fig 15-18).
    • Techniques for Custom Provisional RestiFig 15-19 Occlusion on the restoration is checked in the mouth. Fig 15-20 Occlusion is adjusted outside the mouth.Cementation Armamentarium1. Articulating paper2. Miller forceps3. Straight handpiece4. High-speed handpiece5. No. 171L FG bur6. Muslin rag wheel7. Pur nee8. Cement spatula9. Paper pad10. Zinc oxide-eugenol cement11. Petrolatum12. Explorer13. Mouth mirror14. Dental flossSeat the provisional restoration on the tooth in themouth. Check the occlusion with thin articulating paper(Fig 15-19). Remove the restoration from the tooth andadjust the occlusal prematurities with a nondentate bur(Fig 15-20). When the occlusion has been adjusted tomake the patient comfortable, polish the restoration firstwith pumice and then polishing compound (YellowDiamond Polishing Compound, Matchless Metal PolishCo, Chicago IL) on a muslin rag wheel (Fig 15-21).Besides making the provisional restoration easier toclean and more comfortable for the patient, polishedmaterials are much less likely to discolor.33To fit a provisional crown under an existing removablepartial denture, undercontour the crown so it does nottouch any rests or clasps on that tooth. Add resin to theoutside of the crown, and while the resin is still soft, seatthe crown on the tooth. To form the rest seat and guideplanes on the crown, lubricate the partial denture withpetrolatum and seat it over the provisional crown. Pumpthe partial denture up and down several times to insurethat it is not locked into any undercuts. Remove thecrown from the tooth, smooth any rough areas, and pol-ish the crown.The restoration should be cemented with a temporarycement of moderate strength. After the zincoxide-eugenol cement has been mixed to a thick,creamy consistency, an amount of petrolatum equal to5% to 10% of the cement volume is incorporated toslightly reduce the strength of the cement (Fig 15-22).This will facilitate removal of the provisional restoration ata subsequent appointment. If the preparation is short orotherwise lacking in retention, the petrolatum should notbe added.It is not necessary to keep zinc oxide-eugenol cementdry while it is setting. In fact, moisture will accelerate thehardening Coating the outside of the restoration with athin film of petrolatum prior to cementation will aid in the
    • removal of excess cement. After the cement has hard-ened, all excess must be removed from the gingivalcrevice. Use an explorer in accessible areas and dentalfloss interproximally (Fig 15-23).Template-Fabricated ProvisionalFixed Partial DentureWhen a fixed partial denture is to be made for a patient,the provisional restoration should also be in the form of afixed partial denture rather than individual crowns. In theanterior region it will provide a better cosmetic result.However, even in the posterior region, a provisional fixedpartial denture will better stabilize the teeth and will affordthe patient the opportunity to become accustomed tohaving a tooth in the edentulous space again.Template Armamentarium1. Diagnostic cast2. Mor-Tight3. No. 7 wax spatula4. Denture tooth5. Crown form6. Vacuum forming machine7. Coping material or temporary splint material8. Quadrant impression trays9. Silly Putty10. Wire frame11. Bunsen burner12. Scissors13. Laboratory knife with no. 25 blade14. Heavy-duty laboratory knife15. Large camel-hair brush16. Cement spatula17. Dappen dish18. Separating medium19. Monomer and polymer20. Medicine dropper21. Heavy rubber band22. Straight handpiece23. Acrylic burs24. Abrasive discs and Moore mandrelTo make a template, place a metal crown form or a den-ture tooth in the edentulous space on the diagnostic cast(Fig 15-24). All of the embrasures should be filled withputty (Mor-Tight, TP Orthodontics, LaPorte, IN) to elimi-nate undercuts during adaptation of the resin template.To facilitate removal of the template, a thin strand ofputty can be placed around the periphery of the cast andon the lingual surface of the cast, apical to the teeth (Fig15-25). Use a large acrylic bur to cut a hole through themiddle of the cast (midpalatal or midlingual). Place a 5 x5-inch sheet of 0.020-inch-thick resin (translucentCoping Material or transparent Temporary Splint Material,Buffalo Dental Manufacturing Co, Syosset, MY) in theframe of the vacuum forming machine (Sta-Vac, BuffaloDental Manufacturing Co) with the shiny surface down(Fig 15-26). If temporary splint material is used, bothsides will be shiny. Turn on the heating element of themachine and swing it into position over the plastic sheet.As the resin sheet is heated to the proper temperature,it will droop or sag about 1.0 inch in the frame. If you areusing coping material, it will lose its cloudy appearanceand become completely clear (Fig 15-27). The castshould be in position in the center of the perforated stageof the vacuum forming machine. Turn on the vacuum.Grasping the handles on the frame that holds the heat-ed coping material, forcefully lower the frame over theperforated stage (Fig 15-28). Turn off the heating elementand swing it off to the side. After approximately 30 sec-onds, turn off the vacuum and release the resin sheetfrom the holding frame. After removing the resin sheetfrom the frame, use a laboratory knife with a sharp no. 25blade to cut through the resin over the Mor-Tight strand(Fig 15-29).
    • Techniques for Custom Provisional ffesftFig 15-24 A crown form or a denture tooth is placed in the eden- Fig 15-25 A rope ot Mor-Tight is placed around the periphery of
    • II a vacuum forming machine is not available, it is stillpossible to fabricate a template for a provisional restora-tion. Fill a quadrant impression tray with a soft siliconeputty available in most variety or toy stores (Silly Putty,Binney & Smith, Easton, PA). Cut a sheet of coping mate-rial in half and insert it, shiny side down, into a wire framebent from a coat hanger. Heat the resin sheet over aBunsen burner flame until it sags and becomes clear,which usually occurs in about 10 seconds (Fig 15-30).Place the softened sheet over the cast (Fig 15-31).Forcefully seat the tray of silicone putty over the copingmaterial (Fig 15-32). To accelerate cooling, blow com-pressed air on the plastic sheet and the impression tray.After about a minute, snap the tray off the cast (Fig 15-33). If the silicone putty sticks to the resin sheet, the puttycan be easily removed by pulling it off in quick jerks.Rapid separation causes the silicone putty to exhibit brit-tleness that will result in easy removal. Replace the puttyin its original container for later reuse. Separate the tem-plate from the diagnostic cast.Trim the template, however it was fabricated, with apair of scissors (Fig 15-34). It should extend at least onetooth on either side of the prepared teeth. Save thoseportions not needed for possible later use.Upon completion of the preparations, make an alginateimpression of them and pour it in fast-setting plaster. Theplaster cast will include replicas of soft tissue and teeththat are not needed (Fig 15-35). Trim the cast so that itincludes only one tooth on either side of the preparedteeth. Try on the template to verify its fit (Fig 15-36).Coat the cast with Alcote separating medium and allowit to dry. Mix the acrylic resin in a dappen dish and placesome on protected areas of the cast, such as interproxi-mal spaces and in grooves and boxes (Fig 15-37). As theresin begins to lose its surface gloss and becomesslightly dull, fill the area for which the provisional fixedpartial denture is being made (Fig 15-38). Place someextra bulk in the portion that will serve as the pontic.Wrap rubber bands around the template and cast,being careful not to place them over the abutment prepa-
    • Techniques for Custom Provisional RestoraFig 15-38 Resin is plated in the Icmpl.i!
    • Fig 15-39 Thelemplai vith rubber hands.Fig 1S-40 The lingual ridge of the saddopen the lingual embrasure of the pontic.rations, lest they cause the template to collapse in thatarea (Fig 15-39) Place the cast in a pressure pot if one isavailable. Otherwise, place it in warm (not hot) tap waterto hasten polymerization. Hot water causes the monomerto boil, increasing porosity. Wait for about 5 minutes. Pryoff the template and save it in case it is needed again.Before removing the provisional restoration from the cast,add resin to any voids or thin spots and place the castback in warm water Do not replace the template for thiscorrection. Placing the unpolymerized resin back intowater will prevent evaporation of monomer and the for-mation of a granulated, "frosted" surface.Remove the fixed partial denture from the cast. Do nothesitate to break the cast if necessary. Trim off the excessacrylic resin. Use discs to trim the axial surfaces down tothe margins. The pontic should be trimmed with discsand burs to open up the proximal embrasures (Fig 15-40). Remove the saddle configuration that was createdby the crown form in the edentulous space (Fig 15-41).The pontic should have the same general shape that thepontic on the permanent prosthesis will have. This willinsure that the patient will be comfortable and satisfiedwith the pontic form before the completed fixed partialdenture is inserted.
    • Techniques foi Custom Provision^ Restor3tion&Template-Fabricated VLCProvisional RestorationA transparent template is essential to the use of a visiblelight-cured (VLC) resin (Triad, Dentsply International,York, PA}, because the clear matrix allows the lightaccess to the resin to initiate polymerization.Template-VLC Armamentarium1. Items in template armamentarium2. Silicone impression putty3. Triad resin4. Model release agent (MRA)5. Air barrier coating material (ABC)6. Triad curing unit7. Straight handpiece8. Acrylic burs9. Abrasive discs and Moore mandrel10. Items in cementation armamentariumFabricate a template on the diagnostic cast. If therestoration is to be a fixed partial denture, set a metalcrown form or denture tooth in Mor-Tight putty in the eden-tulous space. If a diagnostic wax-up has been made,soak the cast for 5 minutes and duplicate it with an algi-nate impression. Pour the impression in quick-set plaster.Produce a template from a resin sheet on the vacuumforming machine. Trim the template and replace it on thecast. Mix a scoop of silicone impression putty with accel-erator (Citricon, Kerr Manufacturing Co) and mold itaround the template on the cast (Fig 15-42). This is need-ed to reinforce the unsupported template and preventdisplacement by the highly viscous resin later.20Quick-set plaster also can be used to make this reinforcingFig 15-44 The resin-lquick-set plaster ctie teethindex. Set the template and the index aside uhave been prepared.Make an alginate impression of the prepared abutmentteeth and pour a cast of quick-set plaster. Coat the castwith a layer of model release agent (MRA, DentsplyInternational), which is part of the resin system. Thenplace some of the Triad resin around the finish lines of theabutment preparations. Lay a strand of resin inside theclear template (Fig 15-43). "Enamel" resin can be placedin the incisal or occlusal portion of the template first toenhance esthetics.Use firm pressure to seat the loaded template on thequick-set plaster cast of the prepared abutments (Fig 15-44). Compress the silicone putty index over the template
    • to insure complete seating of the template and an eventhickness of resin in the provisional restoration (Fig 15-45). In an alternative technique, the template can be seat-ed into the silicone putty index before the resin is loadedinto the template.20Remove the putty index from the cast,leaving the resin and template in position on the cast.Place the cast in the Triad curing unit to polymerize theresin in the template for 4 minutes (Fig 15-46). Carefullyremove the template and then the provisional restorationfrom the cast. Paint all surfaces of the restoration with airbarrier coating material (ABC, Dentsply International).Place the provisional restoration back in the curing unit,tissue side up, for an additional 6 minules. Retrieve therestoration from the curing unit and remove all of the ABCwith a brush and water.Trim as much excess material as possible with a pair ofcurved scissors (Fig 15-47). Finish trimming the axial sur-faces to the margins with discs. Open the embrasuresaround the pontic with discs and burs. Be sure to removethe saddle form produced by the template. Polish therestoration with pumice and a high-shine polishing mate-rial (Yellow Diamond Polishing Compound, MatchlessMetal Polish Co).Another technique has been described in which therestoration is started in a template on the prepared teethin the mouth.21Polymerization of the restoration is initiat-ed by a 10-second application of a hand-held curingfight. After the restoration is "frozen" in this manner, it isremoved from the mouth and further exposed to the high-intensity curing light in the laboratory.
    • Techniques lor Custom Provisional RestorationsFig 15-48 Monoroverimpression wiliquid applicator.is applied lo thea needle-tippedFig 15-49 Enough polymer is appliedto turn the surface of the impressionShell-Fabricated Provisional RestorationA thin shell crown or fixed partial denture can be madefrom any of the acrylic resins, and then that shell can berelined indirectly on a quick-set plaster cast. It also canbe relined directly in the mouth. 16,26,34,35 if the reline isdone directly, a methacrylate other than poly(methyl)should be used. This technique can save chair timebecause the restoration is partially fabricated prior to thepreparation appointment.Care must be taken not to make the shell too thick. IItoo thick, the shell will not seat completely over the pre-pared teeth and it will need to be trimmed internally. Thiscan be time-consuming and defeats any advantagegained by making it before the preparation appointment.Shell Fabrication Armamentarium1. Items in overimpression armamentarium2. Items in cementation armamentarium3. Liquid applicator4. Powder blowerAn overimpression is made irom a diagnostic wax-upbefore the preparation appointment. Check it for com-pleteness. Trim off thin flashes of impression material cre-ated by the gingival crevice to produce an extra bulk ofresin near the margins. Use a plastic squeeze bottle witha fine tip (Liquid Applicator, Prairie Village Prosthetics,Prairie Village, KS) to deposit one drop of monomer onthe Facial and one drop on the lingual surface of theimprint of each tooth to be restored (Fig 15-48).30Keep
    • Fig 15-50 Girtgival flash is removed and gingiv.opened vvilh a fine sandpaper disc.the monomer near the gingival portion of the impressionto prevent excess from accumulating in the incisal orocclusal area. Extend the coverage by the resin to onetooth imprint on either side of the teeth being restored.2ISWith an insufflator (Powder Blower, Prairie VillageProsthetics), gently spray enough polymer onto the sur-face of the impression to absorb the monomer (Fig 15-49).30Repeat the process four times, inverting theimpression frequently to allow the material to run down tothe margins rather than puddling in the incisal or occlusalareas of the impression. Gently remove the shell from theimpression after 4 minutes. Trim the flash from the gingi-val area and open the gingival embrasures with an abra-sive disc (Fig 15-50).When the teeth have been prepared, make a quadrantalginate impression and pour it with a thin mix of quick-setting plaster. Trim off excess plaster on a model trim-mer. Save one tooth on either side of the prepared tooth,if possible. Remove areas of the cast that duplicate softtissues. Examine the cast for nodules that would preventcomplete seating.Try the shell gently on the cast to make sure it seatscompletely without binding. If it does bind, relieve theinner surfaces of the shells until the restoration seatscompletely and passively. Liberally coat the tooth prepa-rations on the cast with separating medium and makesure it is dry before mixing the acrylic resin.Monomer and polymer can be added directly to theshell and mixed there. The resin also can be mixed in adappen dish and then transferred to the shell, complete-
    • T? Provisional RestoraFig 15-53 Impression mailoaded into a quadrant tray forly filling each tooth. Seat the shell onto the prepared teethon the cast (Fig 15-51). Wrap a rubber band around theshell and cast, and place them in a plaster bowl Full of hottap water for approximately 5 minutes, preferably in apressure pot. The use of a pressure pot will significantlyincrease the strength of the restoration.32If the direct technique is employed, seat the shell onthe prepared teeth in the mouth (Fig 15-52). When theresin becomes rubbery, elevate the restoration 2.0 mmand flush theteeth under it with water.34Pump therestoration up and down several times to eliminate under-cuts. Then remove the restoration from the mouth andWhen the resin has polymerized, remove the rubberband and disassemble the shell from the plaster cast. Ifthe restoration resists removal from the plaster cast,break the teeth off with a heavy-bladed laboratory knife.Use a small, pointed instrument to remove any plaster leftin the provisional restoration. Trim excess resin from theprovisional restoration with acrylic burs or coarse Moorediscs. Smooth the axial surfaces of the restoration with afine sandpaper disc, followed by pumice and polishingcompound on a muslin rag wheel.Overimpression-FabricatedBis-acryl Composite CrownBis-acryl composite resin (Protemp II, ESPE-Premier,Norristown, PA) can be used to fabricate a provisionalrestoration on a quick-set plaster cast. Its polymerizationproduces very little heat, and it has minimal toxic effecton soft tissues and the pulp. It probably is as well suitedas any resin for use in a direct technique, based on thestudy of materials by Wang et al.15Its use in making adirect provisional restoration is presented here, althoughit bears repeating that the direct technique is not a desir-able o 3 for [Alginate makes a satisfactory overimpression, but thisdiscussion will focus on the use of an elastomeric impres-sion material, polyvinyl siloxane (Extrude Extra, KerrManufacturing Co), for the sake of presenting as manytechniques as possible in this chapter. A heavy-bodiedelastomeric material has the advantages of being verystable and difficult to distort. Its disadvantages includegreater expense and extra time required for the impres-sion material to polymerize.Load a disposable aluminum sextant tray with impres-sion material and make the overimpression while waitingfor anesthesia (Fig 15-53). Trim the excess from the bor-ders of the impression to facilitate accurate placementback in the mouth (Fig 15-54). Remove the webs of mate-rial between the imprints of individual teeth in the impres-sion (Fig 15-55). These could interfere with completereseating of the overimpression.The margins of a provisional restoration may be thin ordeficient because the overimpression was not seatedstraight, or because the thickness required for a resinrestoration is greater than that needed for a metalrestoration. To avoid this problem, use a no. 8 round burto cut a trough in the gingival area of the facial and lin-gual surfaces of the tooth imprint(s) in which the restora-tion will be fabricated (Fig 15-56). This will produce abead of material parallel with the margin of the resultingrestoration (Fig 15-57). This insures adequate material inthe margin, and the excess can be trimmed off during fin-ishing.After the tooth preparation has been completed, beginthe provisional restoration. Check to be sure that theplastic catch is engaged in the vertical groove on thethreaded plunger in the ratchet at the back end of thelarge blue syringe containing the Protemp II base mater-ial (Fig 15-58). To extrude one full measure of base pasteonto a mixing pad, give the thumbscrew at the end of thethreaded plunger one complete turn clockwise until itclicks (Fig 15-59) Check the simple ratchet on thetal
    • Fig 15-56 A gingival trough is cut with a no. 8 bur in the facialand lingual surfaces of the imprint of the tooth being restored.threaded center plunger of the smaller white, double-bar-reled catalyst paste syringe to see that it is in place (Fig15-60). Express an equal amount of each of the two cat-alyst pastes onto the same pad by twisting the singlethreaded shaft one full revolution or "dick" (Fig 15-61).Mix the catalyst pastes and the base material with acement spatula for approximately 30 seconds (Fig 15-62). Use the spatula to load the back end of a frostedplastic syringe (Fig 15-63). Place the resin in the overim-pression with the syringe, as suggested by vonKrammer36(Fig 15-64). Keep the syringe tip buried inresin and fill the cusp tip or incisal edge areas from thebottom up to prevent voids in the completed provisionalrestoration. The use of an application syringe will fre-quently require a second unit of resin, but it greatlyreduces the possibility of creating bothersome voids inthe restoration.Lubricate the prepared teeth with petrolatum and posi-tion the impression tray on them no later than 2 minutesfrom the start of mixing. Allow the resin to polymerize inthe mouth for approximately 2 minutes. Check excessresin around the border of the tray for consistency. Do notrely on material left on the mixing pad as an indication ofpolymerization, because the reaction in the oral cavity at
    • Techniques for Custom Provisional Resto,Fig 15-5H The catch should be engaged in the slot in the thread-ed plunger at the back of the base syringe.Fig 15-59 The plunger of the baseto produce one measure of base resi5 15-60 The catch must be engaged in the slot in the thread-i middle plunger at the back of the catalyst syringe.Fig 15-61 The threaded middle plunrotated one click to produce enough Cisure of base paste.body temperature and 100% humidity will proceed morerapidly than on a mixing pad at room temperature. Whenthe resin becomes elastic, it is ready for removal. Thatshould occur no later than 6 minutes from the start of theTease the restoration from the tooth (Fig 15-65] or fromthe impression (Fig 15-66). Remove as much excess aspossible with scissors. Replace the provisional restora-tion on the tooth and ask the patient to close down on itseveral times. Then pump it several times to insureremovability. Remove the restoration no later than 7 min-utes from the start of mixing. Wipe off the air-inhibited,unset resin with an alcohol sponge. If there are voids orother defects, they can be repaired by mixing anotherbatch of resin and applying it to the affected area with aninstrument. Repairs also can be effected by using VLCcomposite resins and a light.Remove excess near the margins (including the inten-tional bead, if used) with fine abrasive discs. Place therestoration back on the tooth in the mouth. Test andadjust the occlusion if necessary. Polish the outer sur-faces of the restoration with pumice and polishing com-pound. Seat the restoration with a temporary cement.
    • ProvisionalRestorationsFig 15-64 Mixed resin is expressed into thimprint of the tooth for which the provision*restoration is being fabricated.eased from the Fig 15-66 The partially polymerized provisional restorat
    • Techniques for Prefabricated Provisional RestoratTechniques for PrefabricatedProvisional RestorationsClinical situations will arise in which it may not be possi-ble or desirable to make a custom acrylic resin provi-sional crown. Prefabricated polycarbonate crowns areeasily adapted to produce esthetic provisional crowns inan expeditious manner on prepared single anterior teethin most patients.37A patient may present with an emer-gency situation in which a posterior tooth has fractured,and there is not time available for a definitive tooth prepa-ration and a custom provisional crown. In those cases, apreformed anatomic metal crown form can be employedto protect the tooth and the patient made comfortableuntil sufficient time can be arranged for completing thetreatmentAnterior Polycarbonate CrownA suitable provisional restoration can be made for singleanterior teeth by the use of polycarbonate crowns.However, they frequently will require extensive alterationto correct morphologic discrepancies and improper con-tours.31If they are not carefully contoured, they will havehorizontal overhangs that will be damaging to the gingi-va.5To accomplish the recontouring that is required andto provide the necessary retention, the tooth-coloredcrown form must be relined with a resin. This can beaccomplished with the greatest accuracy by doing thereline on a quick-set plaster cast of the prepared tooth.Armamentariummpression tray (one only)2.3.4.5.6.7.8.9.10.11.12.13.14.15.1617.18,19.20.21.AlginateRubber bowlSpatulaQuick-set plasterPolycarbonate crown kitPencilStraight handpieceAcrylic burCoarse garnet disc on Moore mandreBurlew disc on mandrelLarge camel-hair brushCement spatulaDappen dishIPPA plastic instrumentSeparating mediumMonomer and polymerMedicine dropperMuslin rag wheelWhite polishing compoundMiller forceps22. Articulating paper23. Paper pad24. Zinc oxide-eugenol cement25. Petrolatum26. Explorer27. Mouth mirror28. Dental flossWhen the tooth preparation has been completed,make an alginate impression of the prepared tooth, usingan anterior sextant tray (Fig 15-67). Apply alginatearound the prepared tooth with the tip of the index finger.After the impression has been removed from the mouth,pour it up with a thin mix of fast-setting plaster (KerrsSnow White Impression Plaster No. 2). Separate the castfrom the impression as soon as a fingernail cannot scorethe cast (Fig 15-68).Use the mold guide provided with the kit being utilizedto determine the proper mesiodistal size for the crownform (Fig 15-69). Remove the corresponding size ofcrown from its compartment in the kit and place it on theprepared tooth on the cast or in the mouth. With a pencil,make a mark on the gingival portion of the labial surface(Fig 15-70). The distance from the pencil mark to themargin should equal the length discrepancy between theincisal edge of the crown form and the incisal edges ofthe adiacent teeth.The excess gingival length is trimmed away with alarge carborundum stone or an acrylic bur, using thepencil line as a reference mark (Fig 15-71). Try the short-ened crown back onto the prepared tooth (Fig 15-72). Ifit is too tight interproximally, adjust it.Paint the cast of the prepared tooth and the surround-ing area with liberal amounts of a "tin foil substitute" sep-arating medium (Alcote) (Fig 15-73). Accelerate the dry-ing with an air syringe, and make sure that the cast is drybefore starting to mix the resin.Place four drops of monomer into a dappen dish andadd tooth-colored polymer While polycarbonate crownsare available in only one shade, it is possible to modifythat shade somewhat by the shade of acrylic resin usedto reline it. Fill the crown form with resin applied with anIPPA plastic instrument. When the acrylic resin justbegins to lose its gloss, seat the crown form on the plas-ter cast, slowly expressing all the excess resin aroundthe margins (Fig 15-74). Make sure that it is seated com-pletely, and place it in a bowl of hot tap water to acceler-ate polymerization.When the resin has polymerized completely, removethe provisional crown from the cast, breaking the cast ifnecessary. A coarse garnet disc on the straight hand-piece is used to trim away the excess at the margins (Fig15-75). In many cases this will mean that part of the orig-inal polycarbonate crown will be cut into and recon-toured. Do not leave any sharp ledges or abrupt contourchanges near the margin. If necessary, recontour the gin-gival half of the axial contours. Only in this way will it bepossible to obtain a satisfactory provisional restorationby this technique.
    • Provisional RestorationsFig 15-67 ATI anterior sectional tray is used to maktimpression of the prepared tooth.Fig 15-68 Quick-set plaster cast and the impression in which itFig 15-70 With the crown on the preparation, aa distance from the labial margin that is equal towhich the crown exceeds the height of adjacent ttIf the tooth is nonvital. or if a resin other thanpoly(methyl methacrylate) is used, the crown can berelined on trie prepared tooth in the mouth. The prepara-tion is coated with petrolatum, and the crown must beremoved before the resin has polymerized to a stiffnessthat locks it into interproximal undercuts. Cut off as muchof the rubbery excess as possible with a pair of curvedscissors. Keep reseating and removing the crown untilthe relining resin has completely polymerized.Place the crown on the prepared tooth in the mouthand check the occlusion with articulating paper (Fig 15-76). Adjust any high spots with a nondentate bur afterremoving the crown from the tooth. Smooth out the roughabraded areas in the lingual and incisal areas, as well asthose surfaces recontoured near the margin, with aBurlew wheel in the straight handpiece (Fig 15-77).Polish all surfaces of the provisional restoration withpolishing compound (Yellow Diamond PolishingCompound, Matchless Metal Polish Co) on a muslin ragwheel (Fig 15-78). It is possible to return the crown to itsoriginal luster by this means. Coat the outer surface ofthe crown with petrolatum to prevent the cement fromsticking to it. Cement the restoration with zincoxide-eugenol cement. Make certain that all cement hasbeen removed from the gingival crevice by using anexplorer (Fig 15-79). Use dental floss interproximally toremove any cement left there.
    • Techniques for Prefabricated Provisional RestorstionsFig 15-72 Polycarbonate crown after removal of thelenRih. The tab is left on at this point to facilitate handling.of the plaster Fig 15-74 The crown filled with resin is placed onto the pre-Fig 15-73 The preparation and adjacent porticast H^G painted with separdting medium.Fig 15-75 Gingival excess created by theexpressed acrylic is trimmed back with agarnet disc until the margin coincides withthe imprint of the finish line (arrow).
    • ProvisionalRestoratioiProvisional Crown for anEndodontically Treated ToothIt is often difficult to fabricate a provisional restoration fora tooth that has been prepared for a dowel core becausethere is so little intact supragingival tooth structure Thiscan be accommodated for in the use of a standard poly-carbonate crown by placing a piece of paper clip orother stiff wire into the canal and placing the resin-filledcrown down over that (Fig 15-80)1-2-5Preformed Anatomic Metal CrownEmergency cases involving fractured molars are one ofthe best indications for the use of preformed metalcrowns. Zinc oxide and eugenol alone will not adhere tothe tooth, and there is rarely enough time at the emer-gency appointment to fabricate a custom acrylic resinprovisional crown. By using the preformed anatomicmetal crown, it is possible to provide the patient with tem-porary coverage to protect the fractured tooth and pre-vent irritation of the tongue and mucosa.
    • Techniques lor Prefabricated Provisional RestoraticFig 13-80 A pin is incorporated inio a polycbonate crown for use as a provisional restoraton a tooth prepared for a dowel core.There are several systems available for this purpose,utilizing the same general principles. The procedureconsists of:1. Minimal tooth preparation2. Measurement and selection of crown3. Trimming and adaptation of gingival margin4. Occlusal adjustment5. CementationArmamentarium1. High-speed handpiece2. No. 170 bur3. Measuring gauge5. Stretching block6. Crown and bridge scissors7. Contouring pliers8. Straight handpiece9. Sandpaper disc on Moore mandrel0. Articulating paper1. Miller forceps2. Cement spatula3. Paper pad4. Zinc oxide-eugenol cement5. Petrolatum6. LL 6-7 curved burnisher7. Explorer8. Mouth mirror9. Dental flossThe maxillary molar with a lingual cusp fractured off inot an uncommon dental emergency (Fig 15-81). It ismost easily protected on a short-term basis with a pre-formed metal crown (Iso-Form Temporary Crown, 3MDental Products, St Paul, MN).The tooth must be prepared minimally to create spacefor the restoration. The initial step is occlusal reduction,which follows the inclined planes of the occlusal surface(Fig 15-82). The depth will be 1.0 mm on the nonfunc-tional cusps and 1.5 mm on the functional cusps. A func-tional cusp bevel (on the lingual incline of the maxillarylingual cusp) is placed to a depth of 1.5 mm to completethe occlusal reduction (Fig 15-83).Only enough proximal reduction is done to permit theseating of the crown. If an MOD amalgam restoration ispresent in the tooth, the proximal reduction is most easi-ly accomplished by removing the amalgam in the boxes(Fig 15-84) The boxes are cut with a no. 170L or 171Lbur. All caries is removed at this time. No effort is madeto remove all of the existing restoration, nor to providepermanent bases or a completed preparation.Each of the three measuring heads in the metal crownform kit has converging blades that measure a 1.0-mmrange: 9 to 10 mm, 10 to 11 mm, and 11 to 12 mm (Fig15-85) Hold the gauge in line with the contact points,resting it on the occlusal surfaces of the other teeth inthe arch. Slide the blades until they wedge between thecontacts of the teeth on either side of the preparation (Fig15-86). The point at which the blades wedge indicatesthe dimension to be used for selection of the propercrown form.The crown is tried on the tooth. If the gingival collar istoo tight, the crown is placed on the appropriate post ofthe stretching block (Fig 15-87). There is a tapered postcorresponding to each of the maxillary and mandibularmolars, left and right. Flaring the margins is also requiredwhen there is a shoulder finish line. The crown is pushed
    • ProvisionalRestoratidown on the post until an adequate amount oi gingivalflare is obtained.The crown is placed on the tooth to evaluate its occiu-sogingival length. Compare the height of each marginalridge ol the crown with that of the adjacent tooth (Fig 15-88). Use crown and bridge scissors to remove an amountat the gingival margin equal to the marginal ridge heightdiscrepancy (Fig 15-89). Festoon the margin to follow thecontours of the gingival tissue.Smooth rough spots and any irregularities in the gingi-val margin with a sandpaper disc (Fig 15-90). Use no.114 contouring pliers to produce a slightly convex con-tour occlusal to the margins (Fig 15-91). The margin willbe slightly constricted as a result.Place the crown on the tooth and check the occlusionwith articulating paper (Fig 15-92). Remove the crown andburnish areas on the occlusal surface that are in hyper-occlusion. Open proximal contacts can be corrected byburnishing the proximal area from the inside of the crown.Coat the outside of the crown with petrolatum to facili-tate the removal of excess cement later Mix zinc oxideand eugenol to a thick creamy consistency on a paperpad. Fill the crown with the cement and seat it on the pre-pared tooth with finger pressure (Fig 15-93).Burnish the margins of the crown with an LL 6-7 curvedburnisher before the cement hardens (Fig 15-94) Rundental floss through the proximal contacts to removehardened cement from the interproximal areas (Fig 15-95). Use an explorer to remove all remaining subgingivalcement (Fig 15-96). Make a final check of the margins toinsure that they are not impinging on the gingiva.
    • Techniques for Prefabricated Provisional RestorationsFig 15-85 Measuring gauge for selecting a preformed metal Fig 15-86 Mesiodistal measurement of the space is obtained.tFig 15-88 Marginal ridge height discrep-ancy between the restoration and the adja-cent tooth is estimated.
    • ProvisionalRestorationsFig 15-91 Axial surfaces are contoured with pliers. Fig 15-92 Occlusion is checked with articulating paper.
    • Techniques for Prefabricated Provisional ReshFig 15-93 Crown filled with zinc oxide-eugenol cement is seated. Fig 15-94 Margin is burnished. V ^ /•• 7Fig 15-95 Excess cement is removed from the interpmxiin.il Fig 15-9tregion with dental floss. explorer.
    • isional RestorationsReferences. Mumford JM, Ferguson HW. Temporary restorations anddressings. Dent Pract Dent Rec 1959; 9:121-124.!. Segat L: Protection of prepared abutments betweenappointments in crown and bridge prosthodontics. J MichDentAssoc 1962; 44:32-35.restorative dentistry. Jt Rose HP: A simplified technique for temporary crowns DentDig 1967; 73:449-450.j. Behrend DA: Temporary protective restorations in crownand bridgework. Aust Dent J 1967, 12.411-416.j. Fisher DW, Shillingburg HT, Dewhirst RB: Indirect temporaryrestorations. J Am Dent Assoc 1971; 82:160-163.. Phillips RW: Skinners Science of Dental Materials, ed 9.Philadelphia, WB Saunders Co, 1991, p 193.i. Lui JL, Setcos JC, Phillips RW: Temporary restorations: Areview. Oper DenM986; 11:103-110.). Lockard MW, Wackerly J: Excellence in dentistry: Acrylicprovisional crowns. Dent Manage 1987, 27:60-62.). Crispin BJ, Watson JF, Caputo AA: The marginal accuracyof treatment restorations: A comparative analysis. J ProsthetDent 1980; 44:283-290.I. MondaacrylicI. Grossman LI: Pulp reaction to the insertion of self-curingacrylic resin filling materials. J Am Dent Assoc 1953;46:265-269.3. Kramer IRH, McLean JW Response of the human pulp toself-polymerizing acrylic restorations Br Dent J 1952,92:255-261, 281-297, 311-315.1. Langeland K, Langelend L: Pulp reactions to crown prepa-ration, impression, temporary crown fixation and permanentcementation. JProstfief DenM965; 5:129-1435. Wang RL. Moore BK, Goodacre CJ, Swartz ML, Andres CJ:A comparison of resins for fabricating provisional fixedrestorations. Int J Prosthodont 989; 2:173-184.1. Vahidi F: The provisional restoration. Dent Clin North Am1987: 31:363-381.. Driscoll CF, Woolsey G. Ferguson WM: Comparison ofexothermic release during polymerization o! four materialsused to fabricate interim restorations J Prosthet Dent 1991"65.504-506.i. Moulding MB, Teplitsky PE. Intrapulpal t3Ct of proProsthodont 1990; 3:299-304.i Gegauff AG, Pryor HG: Fracturresins for fixed prosthodontici58:23-29.Int JI Goldfogel M: Direct technique for the fabrication of a •light-curing resin lor provisional restorations. Quintes/nM990; 21:699-703.I. Freese AS: Impressions for temporary acrylic resincrowns. J Prosthet Dent 1957; 7:99-101.Leff A. An improved temporary acrylic fixed bridge. JProsthet Dent 1953; 3:245-249.i. Fiasconaro JE, Sherman H: Vacuum-formed prostheses. I. Atemporary fixed bridge or splint. J Am Dent Assoc 1968;76:74-78.i. Sotera AJ: A direct technique for fabricating acrylic resintemporary crowns using the Omnivac. J Prosthet Dent 197329.577-580.1Preston JD. Ceramometai Restorations and Fixed Prostho-dontic Esthetics. Continuing education program presentedby the University of Oklahoma College of Dentistry.Oklahoma City, OK, September 12, 1975.i. Ferencz JL1Fabrication of provisional crowns and fixed par-tial dentures utilizing a "shell" technique. N Y J Dent 1981"51:201-206.I. Elledge DA, Hart JK, Schorr BL: A provisional restorationtechnique for laminate veneer preparations. J Prosthet Dent1989:62:139-142.). Elledge DA, Schorr BL: A provisional and new crown to fitinto a clasp of an existing removable partial denture. JProsthet Dent 1990; 63.541-544.. Fritts KW, Thayer KE: Fabrication of temporary crowns andfixed partial dentures. J Prosthet Dent973; 30:151-155.!. Donovan TE, Hurst RG, Campagni WV: Physical propertiesof acrylic resin polymerized by four different techniques. JProsthet Dent 1985; 54:522-524.I. Yuodelis RA. Faucher R: Provisional restorations: An inte-grated approach to periodontics and restorative dentistryDent din North Am 1980; 24:285-303.i. Chiche GJ, Avila R: Fabrication of a preformed shell for aprovisional fixed partial denture. Quint Dent Techno! 1986;10:579-581.i. von Krammer R: fiautocuring acrylic ret1Nayyar A, Edwards WS. Fabrication of a single anteriorintermediate restoration. J Prosthet Dent 1978; 39.574-577.
    • Chapter 16Fluid Control and Soft Tissue ManagementComplete control of the environment of the opera-tive site is essential during restorative dental pro-cedures. For the patients comfort and safety, andfor the operators access and clear visibility, saliva, aswell as water introduced during instrumentation, must beremoved from the mouth.Control of the oral environment extends to the gingivasurrounding the teeth being restored. The gingiva mustbe displaced to make a complete impression and some-times even to permit completion of the preparation andcementation of the restoration. Occasionally it is neces-sary to permanently alter the contours of the gingival tis-sues around the teeth or of the edentulous ridge to insurea better, longer-lasting result for the fixed restoration.Fluid ControlThe need for removal of fluids varies depending upon thetask being performed. During the preparation of teeth, itis necessary to remove large volumes of water producedby a handpiece spray and to control the tongue to pre-vent accidental injury. When an impression is made or arestoration is cemented, there is a much smaller volumeof fluid to be removed, but a much greater degree of dry-ness is required. Several types of attachments can beused with low-volume (saliva ejector) or high-volume vac-uum outlets to remove fluids (Fig 16-1). Some combinethe functions of fluid removal with isolation.Rubber DamThe rubber dam is the most effective of all isolationdevices utilized in restorative dentistry. Its use is valuablein the removal of old restorations or excavation of carieswhen exposure of the pulp is a possibility. It also providesexcellent isolation and access when a pin-retained amal-gam or composite resin core is required before a castrestoration can be fabricated Teeth with old or question-able endodontic treatments should be isolated in thismanner for dowel-core preparation, pattern fabrication,and cementation.If the premise is accepted that the rubber dam ismeant to be an instrument of convenience, it has only lim-ited direct application in the area of cast restorations. Itcan be used during tooth preparation for inlays andonlays (if the occlusal reduction is done before the damis placed), and it can be readily used for making impres-sions and cementing the same types of restorations.When used with elastomeric impression materials, thedam must be lubricated and the clamp must be removedor avoided. It should not be used with polyvmyl siloxaneimpression material, because the rubber dam will inhibitits polymerization.1The occlusion must be adjusted on onlays before theactual cementation. Some would argue that the rubberdam can be used for preparation, impression, andcementation of all cast restorations. However, it is likely toproduce more aggravation than assistance for the major-ity of dentists when its use is attempted with most full orpartial veneer crowns.Fig 16-1 Three commonly usedejector: B, Svedoptet; C, vacuum ti
    • Fluid Control and Soft Tissue Managementnillary atch is being treated.High-Volume VacuumA high-volume suction tip is extremely useful during thepreparation phase and is most effectively utilized with anassistant. When wielded by a knowledgeable assistant, itmakes an excellent lip retractor while the operator uses amirror to retract and protect the tongue (Fig 16-2). Its useis not practical during the impression or cementationSaliva EjectorThe simple saliva ejector can be utilized effectively insome situations by the lone dentist. It is most useful as anadjunct to high-volume evacuation, but it can be usedalone for the maxillary arch. The saliva ejector is placedin the corner of the mouth opposite the quadrant beingoperated, and the patients head is turned toward it (Fig16-3). It can also be used very effectively on the maxillaryarch for impressions and cementation simply by addingcotton rolls in the vestibule facial to the teeth being iso-lated It can be used on the mandibular arch while a cot-ton roll holder positions cotton rolls facial and lingual tothe teeth. Tongue control and fluid removal in this appli-cation may be less than ideal, however.excellent tongue control and isolation is provided forimpression making or cementation (Fig 16-5).The Svedopter is most effective when it is used with thepatient in a nearly upright position. In this position, waterand other fluids collect on the floor of the mouth, wherethey are pulled off by the vacuum (Fig 16-6). If the patientis in a supine position, the throat and back of the mouthmust fill with fluid before it reaches the level of the evac-Although this is an excellent device for the lone opera-tor or one with only intermittent chairside assistance, it isnot without its drawbacks. Access to the lingual surfacesof the mandibular teeth is limited. Because the device ismade of metal, care must be exercised to avoid bruisingthe tender tissue in the floor of the mouth by overzeal-ously cinching down the clamp that fits under the chin.The presence of mandibular tori usually precludes itsuse. Selection of an oversized reflector should be avoid-ed, since it could cut into the palate above or trigger thegag reflex. The medium size seems to work best in mostmouths.For better positioning, the anterior part of theSvedopter should be placed in the incisor region, withthe tubing under the patients arm (Fig 16-7). This pro-vides the security of having the tubing firmly under thepatients control. This is especially important if the salivaejector tubing originates from a movable assistants cart,a common design feature of many dental units today.SvedopterFor isolation and evacuation of the mandibular teeth, themetal saliva ejector with attached tongue deflector isexcellent. It can be used without cotton rolls during thepreparation phase, with a mouth mirror as a lip retractor(Fig 16-4). By adding facial and lingual cotton rolls,AntisialagoguesThere are some patients for whom no mechanicaldevice is effective in producing a dry enough field forimpression making or cementation. For the patient whosalivates excessively, some other measure may be nee-
    • Fig 16-4 The Svedopter can be used on the mandibular arch diing ihe preparation phase. undibuUr quadrant durirFig 16-6 If the patients head is upright, fluids collect on the floorof the mouth, where they are easily picked up by the SvedopterFig 16-7 The fubing for the Svedopter is placed under thepatients arm to prevent any jerking on the attachment while it is inthe mouth.essary. Drugs can be used to control salivary flow.Methantheline bromide (Banthine) and propanthelinebromide (Pro-Banthine), both manufactured by Schiap-parelli Searle (Chicago, IL), have been used for this pur-pose.2They are gastrointestinal anticholinergics that acton the smooth muscles of the gastrointestinal, urinary,and biliary tracts, producing a dry mouth as a side effect.Usually one 50-mg tablet of Banthine or 15-mg tabletof Pro-Banthine taken 1 hour before the appointment willprovide the necessary control. If previous experiencehas shown this amount to be inadequate for a particularpatient, the dosage can be doubled on subsequentappointments. The patient may experience drowsinessand blurred vision Unfortunately, these substances alsoproduce an unpleasant, bitter aftertaste.Methantheline and propantheline are contraindicatedin any patient with a history of hypersensitivity to thedrugs, eye problems such as glaucoma, asthma,obstructive conditions of the gastrointestinal or urinarytracts, or congestive heart failure. They should not beused by lactating females. They may be potentiated byantihistamines, tranquilizers, and narcotic analgesics,and in the presence of corticosteroids they may increaseocular pressure.Propantheline can be made tasteless by injecting 2.0to 6.0 mg in solution intraorally. Onset of action occurs in5 to 10 minutes, and the duration of a dry working envi-ronment is approximately 1.5 hours.3The drying effectcan be prolonged after 1.5 hours by injecting an addi-tional 2.0 to 3.0 mg of propantheline. Administration of
    • Fluid Control and Soft Tilarger doses at one time may result in bladder discomfort.Another drug that has been shown to be effective asan antisialagogue is clonidine hydrochloride (Catapres,Boehringer Ingelheim Pharmaceuticals, Ridgefield, CT).Wilson et al4demonstrated that a 0.2-mg dose of thisdrug is as effective as 50 mg of Banthine in diminishingsalivary flow. Clonidine hydrochloride is an antihyperten-sive agent, and it should be used cautiously in patientswho are receiving other antihypertensive medication, itsprincipal side effect, besides a dry mouth, is drowsiness,which is not altogether undesirable in a patient undergo-ing a lengthy restorative dental appointment. The dose of0.2 mg should be administered an hour before theappointment, and because of the sedative effect of thedrug, someone should accompany the patient to do anydriving.Finish Line ExposureIt is essential that gingival tissue be healthy and free ofinflammation before cast restorations are begun. To starttooth preparations in the face of untreated gingivitismakes the task more difficult and seriously compromisesthe chances for success. Because the marginal fit of arestoration is essential in preventing recurrent caries andgingival irritation, the finish line of the tooth preparationmust be reproduced in the impression.Obtaining a complete impression is complicated whensome or all of the preparation finish line lies at or apicalto the crest of the free gingiva. In these situations, thepreparation finish line must be temporarily exposed toinsure reproduction of the entire preparation. Control offluids in the sulcus, particularly when a liydrophobicimpression material is used, is also necessary, becauseliquids can cause an incomplete impression of the criti-cal finish line area. These measures are accomplishedby one or more of three techniques: mechanical, chemi-comechanical. and surgical.5The surgical techniquescan be further broken down into rotary curettage andelectrosurgery.8MechanicalPhysically displacing the gingiva was one of the firstmethods used for insuring adequate reproduction of thepreparation finish line. A copper band or tube can serveas a means of carrying the impression material as well asa mechanism for displacing the gingiva to insure that thegingival finish line is captured in the impression.One end of the tube is festooned, or trimmed, to followthe profile of the gingival finish line, which, in turn, oftenfollows the contours of the free gingival margin (Fig 16-8). The tube is filled with modeling compound, and thenit is seated carefully in place along the path of insertionof the tooth preparation (Fig 16-9). The technique hasbeen utilized in restorative dentistry for many years.7Ithas been used with impression compound710and elas-tomeric materials.11Several types of die material can beused, depending on the material used for the impression.If the impression is made with an elastomeric material,the die can be formed of stone or electroplated metal11;if the impression is compound, the die can be made ofamalgam711or electroplated metal.89The use of copper bands can cause incisional injuriesof gingival tissues,12but recession following their use isminimal, ranging from 0.1 mm in healthy adolescents12to0.3 mm in a general clinic population.13Copper bandsare especially useful for situations in which several teethhave been prepared. The likelihood of capturing all of thefinish lines in one impression decreases as the number ofprepared teeth increases. The use of a copper bandcould negate the necessity of remaking an entire full-archimpression just to capture one or two preparations.A rubber dam also can accomplish the exposure of thefinish line needed.14Generally it is used when a limitednumber of teeth in one quadrant are being restored andin situations in which preparations do not have to beextended very far subgingivally. It can be used with mod-ified trays if the bow and wings of the clamp are blockedout. As mentioned previously, a rubber dam should notbe used with polyvinyl siloxane impression material,because the rubber inhibits its polymerization.1With the introduction of elastic impression materials,new means had to be used for displacing the gingiva.Plain cotton cord was used for sulcus enlargement,16physically pushing away the gingiva from the finish line.Unfortunately, its effectiveness is limited because the useof pressure alone often will not control sulcular hemor-rhage. One group of investigators found that over half ofthe impressions preceded by the use of plain cotton cordhad to be remade16; however, this may have been exag-gerated by the fact that the cord was used dry.Chemicomechanical (retraction cord)By combining chemical action with pressure packing,enlargement of the gingival sulcus as well as control offluids seeping from the walls of the gingival sulcus ismore readily accomplished. Caustic chemicals such assulfuric acid,5trichloracetic acid,517negatol (a 45% con-densation product of meta cresol sulfonic acid andformaldehyde),6and zinc chloride18have been tried inthe search for an effective chemical for gingival retrac-tion, but their undesirable effects on the gingiva led totheir abandonment.Over the years, racemic epmephrine has emerged asthe most popular chemical for gingival retraction.Surveys published in the 1980s document that cordimpregnated with 8% racemic epinephrine is the mostcommonly used means of producing gingival retraction(Table 16-1). w
    • Finish Line ExposureillIuGM— i —Fig 16-8 The end of a copper band is trimmed ttfollow the preparation finish line.Fig 16-9displaces tltopper tnnd imprusion, the band:c gingivaTable 16-1 Results of Surveys of Material PreferemInvestigatorsShillingburg et al19Shaw and Krejci^1Yearpublished198019851986Number ofrespondents373?495814;es for GinglvaEpinephrinecord73%79%/ Retractioni Astringentcord19%33%Electro-surgery11%2%Misc orNone7%10%The three criteria for a gingival retraction material are("^effectiveness in gingival displacement and hemosta-sis, (2) absence of irreversible damage to the gingiva,and (3) paucity of untoward systemic effects.20 22Epinephrine produces hemostasis, and it causes localvasoconstriction, which in turn results in transitory gingi-val shrinkage. In research conducted on dogs, epineph-rine produced slight tissue injury that healed in 6 days23to 10 days.18A study using human subjects showed thatepinephrine cord did not produce significantly greatergingival inflammation than potassium aluminum sulfate oraluminum chloride.34However, there is controversy surrounding the use ofepinephrine for gingival retraction,25and its use is declin-ing, particularly among dentists who have graduatedsince 1980.21Epinephrine causes an elevation of bloodpressure and increased heart rate. Some investigatorshave fpund that the physiologic changes that occur whenepinephrine-impregnated cord is placed in an intact gin-gival sulcus are minimal.2a~2aHowever, the heart rateincrease and blood pressure elevation are more dramat-ic when the cord is applied to a severely lacerated gingi-val sulcus, or when cotton pellets soaked in epinephrineare applied.a9The use of liquid, epinephrine-containinghemostatic agents is therefore not warranted in this situ-ation; there are effective hemostatic agents without epi-nephrine available for such use.For those patients with cardiovascular disease, hyper-tension, diabetes, hyperthyroidism, or a known hyper-sensitivity to epinephrine, a cord impregnated with someother agent must be substituted. Epinephrine also shouldnot be used on patients taking Rauwolfia compounds,ganglionic blockers, or epinephrine-potentiatmg drugs.30Neither should patients taking monoamine oxidaseinhibitors for depression receive epinephrine.20Patients without the aforementioned contraindicationscan also exhibit "epinephrine syndrome" (tachycardia,rapid respiration, elevated blood pressure, anxiety, andpostoperative depression).6The amount of epinephrineabsorbed is highly variable, depending on the degree ofexposure of the vascular bed,31as well as the time ofcontact and the amount of medication in the cord.2 9 KThe amount of epinephrine lost (and presumedabsorbed) from 2.5 cm of typical retraction cord during 5to 15 minutes in the gingival sulcus is 71 u,g.MThisamount is slightly less than that obtained from receivingthe injection of four carpules of local anesthetic contain-ing a 1:100,000 concentration of epinephrine.33It also isapproximately one-third the maximum dose of 0.2 mg(200 ug) for a healthy adult and nearly twice the recom-
    • Fluid Control and Soil Tissue Managementmended amount of 0.04 mg (40 ±g) for a cardiacpatient.3*Although the absorbed amounts reported by Kellam etal33are lower than estimates by some authors,20thepatient nonetheless is receiving a large dose from thecord around one tooth. If cord is placed around morethan one tooth, if more than one impression is made of asingle tooth (not an uncommon occurrence in a teachinginstitution), and/or if an epinephrine-containing anesthet-ic is used, a patient couid easily exceed the recom-mended maximum dosage of epinephrine.Donovan and associates20report that only 3% of thedentists they surveyed recorded the patients pulse, andfewer than 10% recorded blood pressures routinely.Given this, it is likeiy that few patients would receive evena rudimentary cardiovascular evaluation. The routine useof epinephrine in dentistry, even on healthy patients, hasbeen questioned.34Because epinephrine has been used successfully fornearly half a century, there is reluctance to abandon itsuse. However, the fact that many dentists manage with-out it proves that it is not indispensable. Its proper nicheprobably lies in utilization as an adjunct method in diffi-cult situations where other agents have been ineffective.Even then it must be used only on healthy patients withno history of cardiovascular problems.Aluminum chloride [AfCI3], alum (aluminum potassiumsulfate) [AlKfSCMa], aluminum sulfate [A!2(S04)3], andferric sulfate [Fe2(SO4)3] are also used for gingivalretraction35(Table 16-2). Investigators have comparedseveral of these agents with epinephrine for displace-ment effectiveness, hemostasis, and tissue irritation.No significant difference was found in sulcular widtharound teeth treated with alum- and epinephrine-impreg-nated cord before impressions (0.49 mm vs 0.51 mm,respectively).36In an in vivo study of 120 human teeth,Weir and Williams37found no significant differencebetween the hemorrhage control offered by cordsimpregnated with aluminum sulfate and those impreg-nated with epinephrine.In a study conducted on dogs. Shaw et al38found noadditional inflammation in gingival crevices in whichdilute aluminum chloride (0.033%) was placed, but thosereceiving concentrated solutions (60%) demonstratedsevere inflammation and necrosis. Another study onhuman subjects found no significant difference in gingivalinflammation produced by alum-, aluminum chloride-, orepinephrine-impregnated cords.24Over-the-counter drugs commonly used as nasal andophthalmic decongestants show promise as gingivalretraction agents.3* Phenylephrine hydrochloride 0.25%(Neosynephrine, Winthrop Consumer Products Div,Sterling Drug, New York, NY) was found to be as effec-tive as epinephrine and alum in widening the gingivalsulcus, while oxymetazoline hydrochloride 0.05% (Afrin,Schering-Plough Health Care Products, Memphis, TN)and tetrahydrozoline hydrochloride 0.05% (Visine,Consumer Health Care Div, Pfizer, New York. NY) were57% more effective.36There is evidence to suggest that tissue hemorrhagecan also be controlled indirectly by the adjunctive use ofantimicrobial rinses. Sorensen et al39report loweredplaque, bleeding, and gingivitis indices with the admin-istration of 0.12% chlorhexidine gluconate fPeridex,Proctor & Gamble, Cincinnati, OH) 2 weeks before toothpreparation, 3 weeks during provisional restorations, and2 weeks after final restoration cementation.Retraction Cord Armamentarium1. Evacuator (saliva ejector, Svedopter)2. Scissors3. Cotton pliers4. Mouth mirror5. Explorer6. Fischer Ultrapak Packer (small)7. DE plastic filling instrument IPPA8. Cotton rolls9. Retraction cord10. Hemodent liquid11. Dappen dish12. Cotton pellets13. 2 x 2 gauze spongesThe operating area must be dry. An evacuating deviceis placed in the mouth, and the quadrant containing theprepared tooth is isolated with cotton rolls. The retractioncord is drawn from the dispenser bottle with sterile cot-ton pliers, and a piece approximately 5.0 cm (2.0 inches)long is cut off (Fig 16-10). If a twisted or wound cord isused, grasp the ends between the thumb and forefingerof each hand. Hold the cord taut and twist the ends toproduce a tightly wound cord of small diameter (Fig 16-11). If a braided or woven cord is used, twisting is notnecessary.Be careful not to touch any of the cord other than theends, which will be cut off later, with your gloved fingers.It has been postulated that handling the cord with latexgloves may indirectly inhibit polymerization of a polyvinylsiloxane impression.41If that happens, it will occur in thatsegment of the impression replicating the gingivalcrevice and the gingival finish line of the preparation.The retraction cord should be moistened by dipping itin buffered 25% aluminum chloride solution (Hemodent,Premier Dental Products Co, Norristown, PA) in a dappendish. Cords impregnated with either epinephrine or alu-minum sulfate are twice as effective when saturated withaluminum chloride solution prior to insertion into the gin-gival crevice.37If there is slight hemorrhage in the gingi-val crevice, it can be controlled by the use of a hemo-static agent, such as Hemodent liquid (aluminum chlo-ride). In any event, the cord must be slightly moist beforeit is removed from the sulcus.41Removing dry cord fromthe gingival crevice can cause injury to delicate epithe-lial lining that is not unlike the "cotton roll burn" produced
    • Table 16-2 Principal Chemical in Brands of Gingival Retraction CordGingi-Aid (T,W)Sulpak K-AlumAstringentR-24, 25, 26 (T)Sulpak Epinephnne Astringent PlusVasoconstrictor VasoconstrictorR-34. 35, 36, (T) R-44, 45-46 (T)fepinephrine + alum)Gingi-Pak(T.W)scord (T)ix A.S. (W)Racord II (T.W)(epmephrine + zincphenolsulfonate)Retrax (T)Siltrax (W)Sultan Dental ProdEnglewood, NJGingiGel (W) FlexiBraid (W)GingiYarn (T)Astringedent (W)Suipak fT)UHrax (W)(4% epinephrine +GingiBraid (W)FlexiBraid (W)GingtCord (T)GingiBraid (W)GingiYarn (T)T = twisted; W = w in (braided o< knitted)
    • FluidControlandSoftTissueManagementFig 16-10 A 2-inch piece of retraction cord is cut off.Fig 16-12 A loop of. retraction cord is formed aand held tautly with the thumb and forefinger.by prying an adhering cotton roll off the desiccatedmucous membrane of the mouth.Form the cord into a "U" and loop it around the pre-pared tooth (Fig 16-12). Hold the cord between thethumb and forefinger, and apply slight tension in an api-cal direction. Gently slip the cord between the tooth andthe gingiva in the mesial interproximal area with a Fischerpacking instrument or a DE plastic instrument IPPA (Fig16-13, A). Cord placement is a finesse move, not a powerplay. Once the cord has been tucked in on the mesial,use the instrument to lightly secure it in the distal inter-proximal area (Fig 16-13, B).Proceed to the lingual surface and begin working fromthe mesiolingual corner around to the distolingual comer.The tip of the instrument should be inclined slightlytoward the area where the cord has already been placed;ie, the mesial (Fig 16-14, A). If the tip of the instrument isinclined away from the area in which the cord has beenplaced, the cord may be displaced and pulled out (Fig16-14, B).In some instances where there is a shallow sulcus or afinish line with drastically changing contours, it may benecessary to hold the cord already placed in positionwith a Gregg 4-5 instrument held in the left hand.Placement of the cord can then proceed with the pack-ing instrument held in the right hand (Fig 16-15). Gentlypress apicaily on the cord with the instrument, directingthe tip slightly toward the tooth (Fig 16-16). Slide the cordgingivally along the preparation until the finish line is felt.Then push the cord into the crevice.If the instrument is directed totally in an apical direc-tion, the cord will rebound off the gingiva and roll out ofthe sulcus (Fig 16-17). If cord persists in rebounding froma particularly tight area of the sulcus, do not applygreater force. Instead, maintain gentle force for a longertime If it still rebounds, change to a smaller or more pli-able cord (ie, twisted rather than braided)Continue on around to the mesial, firmly securing thecord where it was lightly tacked before. Cut off the lengthof cord protruding from the mesial sulcus as closely aspossible to the interdental papilla (Fig 16-18). Continuepacking the cord around the facial surface, overlappingthe cord in the mesial interproximal area. The overlapmust always occur in the proximal area, where the bulk oftissue will tolerate the extra bulk of cord. If the overlapoccurs on the facial or lingual surface where the gingivais tight, there will be a gap apical to the crossover, andthe finish line in that area may not be replicated in theimpression.Pack all but the last 2.0 or 3.0 mm of cord (Fig 16-19).This tag is left protruding so that it can be grasped foreasy removal. Tissue retraction should be done firmly butgently, so that the cord will rest at the finish line {Fig 16-20, A). Heavy-handed operators can traumatize the tis-sue, create gingival problems, and jeopardize thelongevity of the restorations that they place. Do not over-pack! (Fig 16-20, B),Pface a large bulk of gauze in the patients mouth. Thiswill make the patient more comfortable by having some-thing to close on and, at the same time, it will keep thearea dry (Fig 16-21). After 10 minutes, remove the cordslowly to avoid bleeding. Inject impression material only
    • F Finish Line ExposureFig 16-13 Placement of the retractioncord is begun by pushing it into the sul-cus on the mesial surface of the tooth(A). It should also be tacked lightly intothe distal crevice (B| to hold the cord inposition while it is being placed.Fig 16-14 As the cord is being placedsubgingivally, the instrument must bepushed slightly toward the area alreadytucked into place (A). If the force of theinstrument is directed away from thearea previously packed, the cordalready packed will be pulled out (B).
    • Fluid Control and Soft Tissue Management*>ent while packing with the second. root to facilitate the subgingrval placFig 16-17 If the instrument is held paitooth, the retraction cord will be pushed against the waif of thegival crevice, and it will rebound.Fig 16-19 Placement of the distal end of the cord is continueduntil it overlaps the mesial. The force of the instrument must bedirected toward the cord previously packed (to the distal in this
    • Finish Line Exposurif the sulcus remains clean and dry. It may be necessaryto gently rinse away any coagulum. then lightly blow airon it. If active bleeding persists, abort the impressionattempt. Electrocoagulation and ferric sulfate are some-times effective in stopping persistent bleeding.If ferric sulfate (Astingedent, Ultradent Products, SaltLake City, UT) is used as the chemical, soak a plain knit-ted cord in it and place the cord in the gingival sulcus asjust described. After 3 minutes, remove the cord. Loadthe 1.0-cc special syringe (Dento-lnfusor) with the astrin-gent chemical, and place a tip on the syringe. Use thefibrous syringe tip to rub or burnish cut sulcular tissueuntil all bleeding stops (Fig 16-22). Using the tip in thismanner will wipe off excess coagulum.Keep the sulcus moist so that the coagulum will beeasy to remove. Keep circling the preparation untilbleeding has stopped completely. The solution usuallywill puddle in the sulcus when hemostasis is complete.Verify this by thoroughly rinsing the preparation with awater/air spray. The coagulum is black, and traces maylinger in the sulcus for a few days.
    • Fluid Control and Soft Tissue ManagementFig 16-23 Prior to rotary curettage, ashoulder is formed at the level of the gingi-l tFig 16-24 A torpedo-tipped diamond Fig 16-25 A cord issimultaneously forms a chamfer finish line "troughed" sulcus for hemand removes the epithelial lining of the sul-Rotary CurettageRotary curettage is a "troughing" technique, the purposeof which is to produce limited removal of epithelial tissuein the sulcus while a chamfer finish line is being createdin tooth structure.42The technique, which also has beencalled "gingettage,"4344is used with the subgingivalplacement of restoration margins, It has been comparedwith periodontal curettage, but the rationale for its use isdecidedly different.42Periodontal curettage is used todebride diseased tissue from the sulcus to allow re-epithelialization and healing.The removal of epithelium from the sulcus by rotarycurettage is accomplished with little detectable trauma tosoft tissue, although there is a lessened tactile sense forthe dentist.15Rotary curettage, however, must be doneonly on healthy, inflammation-free tissue4244to avoid thetissue shrinkage that occurs when diseased tissueheals.«The concept of using rotary curettage was describedby Amsterdam in 1954.46The technique described herewas developed by Hansing and subsequently enlargedupon by Ingraham.4448Suitability of gingiva for the use ofthis method is determined by three factors: absence ofbleeding upon probing, sulcus depth less than 3.0 mm,and presence of adequate keratinized gingiva.44The lat-ter is determined by inserting a periodontal probe intothe sulcus. If the segment of the probe in the sulcus can-not be seen, there is sufficient keratinized tissue toemploy rotary curettage. Kamansky et al47found thatthick palatal tissues responded better to the techniquethan did the thinner tissues on the facial aspect of maxil-lary anterior teeth.In conjunction with axial reduction, a shoulder finishline is prepared at the level of the gingival crest with aflat-end tapered diamond (Fig 16-23). Then a torpedo-nosed diamond of 150 to 180 grit is used to extend thefinish line apically, one-half to two-thirds the depth of thesulcus, converting the finish line to a chamfer (Fig 16-24).« A generous water spray is used while preparingthe finish line and curetting the adjacent gingiva. Cordimpregnated with aluminum chloride4247or alum4344isgently placed to control hemorrhage (Fig 16-25). Thecord is removed after 4 to 8 minutes, and the sulcus isthoroughly irrigated with water. This technique is wellsuited for use with reversible hydrocolloid.44Several studies have been done to compare both theefficacy and the wound healing of rotary curettage withthose of conventional techniques. Kamansky and hisassociates reported less change in gingival height withrotary curettage than with lateral gingival displacementusing retraction cord.47With curettage there was anapparent disruption of the apical sulcular and attachmentepithelium, resulting in apical repositioning and anincrease in sulcus depth. The changes were quite small,however, and they were not regarded as clinically signif-icant.Tupac and Neacy43found no significant histologic dif-ferences between retraction cord and rotary curettage.Ingraham et al42reported slight differences in healingamong rotary curettage, pressure packing, and electro-surgery at different time intervals after the tooth prepara-tion and impression. However, complete healing hadoccurred by 3 weeks with all techniques.There is poor tactile sensation when using diamondson sulcular walls, which can produce deepening of thesulcus.47The technique also has the potential fordestruction of periodontium if used incorrectly,44makingthis a method that is probably best used only by experi-enced dentistsI,
    • Finish Line ExposureFig 16-26 Electrosurgical electrode enlarges the gin;ElectrosurgeryThere are situations in which it may not be feasible ordesirable to manage the gingiva with retraction cordalone. Even if the general condition of the gingiva in amouth is healthy, areas of inflammation and granulationtissue may be encountered around a given tooth. Thiscan be caused by overhangs on previous restorations orby the caries itself. It may have been necessary to placethe finish line of the preparation so near the epithelialattachment that it is impossible to retract the gingiva suf-ficiently to get an adequate impression. In these cases, itmay be necessary to use some means other than cordimpregnated with chemicals to gain access and stopminor bleedingThe use of electrosurgery has been recommended forenlargement of the gingival sulcus and control of hemor-rhage to facilitate impression making (Fig ^6-26).4B•••0Strictly speaking, electrosurgery cannot stop bleedingonce it starts. If hemorrhage occurs, it first must be con-trolled with pressure and/or chemicals, and then the ves-sels can be sealed with a coagulating ball electrode.51Electrosurgery has been described for the removal ofirritated tissue that has proliferated over preparation fin-ish lines,52and it is commonly used for that purpose.There has been concern expressed about the use ofelectrosurgery on inflamed tissue, based on an exagger-ated response to an electrosurgical procedure.53Proximity to bone and lateral heat production may havebeen responsible for the response. Bone is very sensitiveto heat.54Electrosurgery is unquestionably capable of tissuedamage Most surgical instruments are dangerous ifused improperly. Tremendous iatrogenic damage hasbeen done over the years by the rotary handpiece, butno one has suggested that it not be used. Kalkwarf et a:Areported that wounds created by a fully rectified, filteredcurrent in the healthy gingiva of adult males demonstrat-ed epithelial bridging at 48 hours and complete clinicalhealing at 72 hours. In a double-blind study on 27patients, Aremband and Wade56detected no differencein healing in gingivectomies done by scalpel or electro-surgery. When variables are properly controlled in elec-trosurgery, untoward events in wound healing are rare.57An electrosurgery unit is a high-frequency oscillator orradio transmitter that uses either a vacuum tube or a tran-sistor to deliver a high-frequency electrical current of atleast 1.0 MHz (one million cycles per second) (Fig 16-27). It generates heat in a way that is similar to amicrowave oven heating food, or a diathermy machineproducing heat in muscle tissue for physical therapy.Electrosurgery has been called surgical diathermy.51Credit for being the direct progenitor of elecirosurgeryis generally given to dArsonval.5859His experiments in1891 demonstrated that electricity at high frequency willpass through a body without producing a shock (pain ormuscle spasm), producing instead an increase in theinternal temperature of the tissue. This discovery wasused as the basis for the eventual development of elec-trosurgery.Electrosurgery produces controlled tissue destructionto achieve a surgical result. Current flows from a smallcutting electrode that produces a high current densityand a rapid temperature rise at its point of contact withtrie tissue. The cells directly adjacent to the electrode aredestroyed by this temperature increase. The current con-centrates at points and sharp bends. Cutting electrodesare designed to take advantage of this property so theywill have maximum effectiveness (Fig 16-28). The circuitis completed by contact between the patient and aground electrode that will not generate heat in the tissuebecause its large surface area produces a low currentdensity, even though the same amount of current passesthrough it.eoThe cutting electrode remains cold; this dif-
    • FluidControlandSoftTisiFig 16-27 Typical electrosurgical unitwith active electrode (A) and groundelectrode (B).Fig 16-28 Five commonly used electrosurgical electrodes: A,coagulating; B, diamond loop; C, round loop; D, small straight; E,small loop.fers from electrocautery, in which a hot electrode isapplied to the tissue.Types of Current. There are different forms of currentthat can be generated for electrosurgical use, dependingon the type of machine [and circuitry) used or the settingon any given machine. These currents exhibit differentwave forms when viewed on an oscilloscope. They aresignificant because each produces a different tissueresponse.The unrectified, damped current is characterized byrecurring peaks of power that rapidly diminish (Fig 16-29,A). It is the current produced by the old hyfurcator orspark gap generator, and it gives rise to intense dehy-dration and necrosis It causes considerable coagula-tion, and healing is slow and painful. Sometimes referredto as the Oudin or Telsa current, it is not used routinely indental electrosurgery today.A partially rectified, damped (half-wave modulated)current produces a wave form with a damping in the sec-ond half of each cycle {Fig 16-29, B). There is lateral pen-etration of heat, with slow healing occurring in deep tis-sues. The damping effect produces good coagulationand hemostasis. but tissue destruction is considerableand healing is slow.A better current for enlargement of the gingival sulcusis found in the fullyrectified(full-wave modulated) currentthat produces a continuous flow of energy (Fig 16-29, C).Cutting characteristics are good and there is somehemostasis.The fully rectified, filtered (filtered) is a continuouswave that produces excellent cutting (Fig 16-29, D).Healing of tissues cut by a continuous wave current willbe better initially than tissues cut by a modulated wave.The continuous wave produces less injury to the tissuethan does a modulated wave.61However, a controlledhistologic study62found that after 2 weeks, healing ofwounds produced by filtered current was not remarkablybetter than healing of wounds produced by nonfilteredfull-wave modulated current.Filtered current probably produces better healing insituations requiring an incision and healing by primaryintention, because there is less coagulation of the tissuesin the walls of the wound. This is not critical in those pro-cedures done in conjunction with restorative dentistry,when either the inner wall of the gingival sulcus isremoved, or modified gingivoplasty is accomplished byplaning the surface of the tissue. In these cases, hemo-stasis is required, and moderate tissue coagulation is notonly tolerated but desired.Grounding. For the patients safety, it is important thatthe circuit be completed by the use of the ground elec-
    • Finish Line ExposureElectrosurgical Wave Formsfig 16-29 Four forms of electrosurgery current: A, unrectified, damped; B, partial-ly reciified, damped (half-wave modulated); C, fully reciified (full-wave modulated);and D, fully rectified, filtered (filtered).trode,63which is also known as a ground plate, indifferentplate, indifferent electrode, neutral electrode, dispersiveelectrode, passive electrode, or patient return (Fig 16-30). Some dentists, prompted by the unfortunate adver-tising of a few electrosurgical manufacturers, have cho-sen to dispense with the use of this vital piece of equip-ment. An electrosurgery unit will work without one, but itis neither as efficient nor as safe.Grounding the chair is not an acceptable alternative.Current will be dissipated through the path of least resis-tance, and patient contact with a piece of equipment,including metal parts of the chair, could cause a burn.64It is acceptable, however, to permanently attach a metal-lic mesh grounding antenna to the chain underlbe uphol-stery and msultated from all metal chain parts. This cando much to reduce patient anxietyThe safe use of electrosurgery dictates that currentflow be facilitated along the proper circuit from the gen-erator to the active electrode, the patient, and back to thegenerator.65Because patient burns have been attributedto faulty grounding in many cases,3466-67the propergrounding of a patient is considered to be the single mostimportant safety factor when electrosurgery is used.68Oringer69recommends that the ground be placedunder the thigh rather than behind the back, as is oftendone. Contact with a small, bony protuberance, such asa vertebra or shoulder blade, could produce a highenough current density to cause a burn The only pre-
    • Fluid Control and Soft TiSicaution to be observed in placing ihe ground under thelegs is that the patient does not have keys in a pantspocket or is not wearing metal garters {the latter is unlike-ly in this day].Contraindications. For reasons of safety, electro-surgery should not be used in some circumstances. Itshould not be employed on patients with cardiac pace-makers. The demand (synchronous) type of pacemaker,which is the most common, is designed to sense cardiacimpulses (the R wave).70When bradycardia occursbecause the heart does noi emit an impulse, the pace-maker fires at an appropriate rate to keep the heart beat-ing. External electromagnetic interference hinders thepacemakers sensing function.71Incorrectly sensing theinterference as an intrinsic myocardial impulse, the gen-erator shuts down until the interference ceases, with con-sequences that could be quite serious for the patientElectrosurgery will alter the normal function of a pace-maker/3and it presents a hazard to the patient whowears one.7- Shielding in recent pacemaker modelsdiminishes the risks from extraneous electromagneticinterferences, but the use of electrosurgery is still con-traindicated for those patients who wear pacemakers.7JBecause it can produce sparks in use, electrosurgeryshould not be used in the presence of flammable agents.This does not present the risk in dentistry that it does inmedicine, because flammable gases are not routinelyemployed as dental anesthetic agents. However, the useof topical anesthetics such as ethylchioride and otherflammable aerosols should be avoided when electro-surgery is to be used.Many fires in hospital operating rooms do not involveflammable anesthetics. Instead they occur when ordinarycombustible materials are ignited in an oxygenatedatmosphere that will support a fire.6365There is a slightdanger attached to the use of nitrous oxide with electro-surgery because of the enriched oxygen atmospherethat will be present in the oral cavity and nasopharynx.
    • Finish Line Exposure5 16-31 A small drop of a sirongly scentedupper lip to help mask ihe unpleasant odor astrosurgery.Fig 16-32 Electrodes must be completely seated in the hand-piece (left). If bare metal is left exposed anyplace but at the tip(arrow), the patient or the operator could be burned.The number of reported cases involving flash firescaused by dental electrosurgery in the presence ofnitrous oxide-oxygen analgesia is minimal. Oringer76describes two such occurrences. Given the right circum-stances with an extremely dry mouth and an accumula-tion of oxygen, a small spark caused by the electrodetouching a metallic restoration could conceivably set offa dry cotton packing. Therefore, whenever electro-surgery is used in the presence of nitrous oxide-oxygenanalgesia, be sure that any cotton packing in the mouthis kept slightty moist,63if in fact it is not already that wayfrom absorption of oral fluids.Electrosurgery Armanientarium1. Electrosurgery unit2. Set of cutting electrodes3. Cotton pliers4. Mouth mirror5. Fischer Ultrapak Packer6. DE plastic filling instrument7. High-volume vacuum with plastic ti|8. Wooden tongue depressor9. Cotton rolls10. Cotton-tipped applicator11. Aromatic oil12. Hydrogen peroxide13. Dappen dish14. Alcohol sponges {gauze, 4x4)15. Retraction cordElectrosurgery TechniqueBefore an electrosurgical procedure is done, verify thatanesthesia is profound and reinforce it if necessary. Witha cotton-tipped applicator, place a drop of a pleasant-smelling aromatic oil, such as peppermint, at the vermil-ion border of the upper lip (Fig 16-31) The odor from itwill help to mask some of the unpleasant odor emanatingfrom the mouth during electrosurgery.Check the equipment to make sure all the connectionsare solid. Be especially certain that the cutting electrodeis seated completely in the handpiece (Fig 16-32). If anyuninsulated portion of it other than the cutting tip isexposed outside the handpiece chuck, it could producean accidental burn on the patients lip.Proper use of electrosurgery requires that the cuttingelectrode be applied with very light pressure and quick,deft strokes. The pressure required has been describedas the same needed to draw a line with an ink-dippedbrush without bending the bristles (Fig 16-33). It is obvi-ous that the electrode is being guided, and not pushed,through the tissue.To prevent lateral penetration of heat into the tissueswith subsequent injury, the electrode should move at aspeed of no less than 7 mm per second.54If it is neces-sary to retrace the path of a previous cut, 8 to 10 secondsshould be allowed to elapse before repeating thestroke.54This will minimize the buildup of lateral heat thatcould disrupt normal healing.Initially set the power selector dial at the level recom-mended by the manufacturer and make adjustments asnecessary. As the electrode passes through the tissue, itshould do so smoothly without dragging or charring thetissue. If the tip drags and collects shreds of clinging tis-sue, the unit has been placed on a setting that is too low.
    • Fluid Control and Soft Tissue ManagementFig 16-33 The cutting <light pressure used to dr,bending it (left). The pressure exerted on the brush on the rightwould be excessive.vooden tongue blade used as a tongue retractor.Fig 16-35 An alcohol spongthe tutting electrode.On the other hand, if the tissue chars or discolors, or ifthere is sparking, the setting is too high. If an error mustbe made initially, it is better to have a setting that is slight-ly too high. Moist tissue will cut best. If it dries out, sprayit lightly. Avoid collections of water, however, becausethat will increase resistance and decrease efficiency.A high-volume vacuum tip should be kept immediatelyadjacent to the cutting electrode at all times to draw offthe unpleasant odors that are generated (Fig 16-34). Thetip must be plastic to prevent any burns that might becaused by accidental contact with the electrode. For thesame reason, a wooden tongue depressor or plastic-han-dled mirror should be used rather than the metal-backedmouth mirror that would customarily be employed.Stop frequently to clean any fragments of tissue fromthe electrode by wiping it with an alcohol-soaked 4 x 4sponge (Fig 16-35) The electrode is completely safe assoon as the foot switch has been released. Proper tech-nique with the cutting electrode can be summed up inthree points:1. Proper power setting2. Quick passes with the electrode3. Adequate time intervals between strokesGingival Sulcus EnlargementBefore any tissue is removed, it is important to assess thewidth of the band of attached gingiva. The electrosurgerytip is a surgical instrument; it cannot restore lost gingiva.If there is unattached alveolar mucosa too near the gin-gival crest, periodontal surgery, probably in the form of agingival graft, must be employed to reinstate an ade-quate band of healthy, attached tissue.To enlarge the gingival sulcus for impression making, asmall, straight or J-shaped electrode is selected. It isused with the wire parallel with the long axis of the toothso that tissue is removed from the inner wall of the sul-cus.50If the electrode is maintained in this direction, theloss of gingival height will be about 0 1 mm « Holding theelectrode at an angle to the tooth, however, is likely toresult in a loss of gingival height.Around those teeth where the attached gingival tissueis thin and stretched tightly over the bone on the labialsurface, there is a greater chance for a loss of gingivalheight. This is frequently true of maxillary anterior teeth,and particularly the canines, and is worth bearing in mindif the esthetic requirements are greaf and any gingivalIIbeu ;eptable
    • Finish Line ExposureFig 16-36 Passes to be made withthe electrode can be practiced beforeturning on the power.Fig 16-37electrode, without repeating any strokesmade: A, facial; B, mesial; C, lingual; D, di
    • Fluid Control and Soft Tissue Manageme.Fig 16-39 The cuff of tissue adjacent to the edentulous spaointerferes with a cleanablc pontic and strong connectors.With the electrosurgery unit off, the electrode is heldover the tooth to be operated and the cutting strokes aretraced over the tissue (Fig 16-36). Depress the foot switchbefore contacting the tissue, and then move the electrodethrough the first pass. A whole tooth should be encom-passed in four separate motions: facial, mesial, lingual,and distal at a speed of no less than 7 mm per second(Fig 16-37, A to D).64If a second pass is necessary in anyone area, wait 8 to 10 seconds before repeating thatstroke.54This will minimize the production of lateral heat.Clean tissue debris off the electrode tip after each strokeUse a cotton pellet dipped in hydrogen peroxide to cleandebris from the sulcus (Fig 16-38). Better results are usu-ally obtained if retraction cord is loosely packed in theenlarged sulcus before the impression is made.Removal of an Edentulous CuffFrequently, the remnants of the interdental papilla adja-cent to an edentulous space will form a roll or cuff that willmake it difficult to fabricate a pontic with cleanableembrasures and strong connectors. Before a pontic isfabricated, an edentulous ridge should be examinedcarefully. If there are cuffs, they should be removed (Fig16-39). Malone and Manning43found in a bilateral com-parative study of gingivoplasties on 10 patients that therewas no difference in healing between conventionalsurgery and electrosurgery. A large loop electrode isused for planing away the large roll of tissue (Fig 16-40].When this larger electrode is used, it requires a higherpower setting of the unit.Crown LengtheningThere are circumstances in which it may be desirable tohave a longer clinical crown on a tooth than is present(Fig 16-41). If there is a sufficiently wide band of attachedgingiva surrounding the tooth, this can be accomplishedwith a gingivectomy using a diamond electrode (Fig 16-42). It is frequently necessary to do a second series ofcuts to produce a bevel around the first (Fig 16-43). Thiswill produce a better tissue contour without hard-to-cleanedges near the tooth (Fig 16-44). This "bevel" also mustbe done only on attached gingiva. When surgery leavesan extensive postoperative wound, as in this case, it isnecessary to place a periodontal dressing, which shouldbe changed in about 7 days.The lengthened tooth that results from this surgeryshould afford better retention for any crown placed on it,with margin placement in an area of the tooth moreaccessible for cleaning. If the band of attached gingivais too narrow, it must be made wider with a graft or analternative restoration must be made for the tooth.Fig 16-40 A large loop is used to remove the cuff.
    • Finish Line ExposureFig 16-43 The same instrument is used to shape the edges of the Fig 16-44 "Lengthened" tooth after completion of nprevious cut to prevent a ledge of gingival tissue adjacent to the givectomy.tooth.
    • Fluid Control and Soft TissReferencesI Noonan JE, Goldfogel MH, Lambert RL Inhibited set of thesurface of addition silicones in contact with rubber dam.Oper DenM985; 10:46-48.> Accepted Dental Therapeutics, ed 40. Chicago, AmericanDental Association, 1984, p 344-345.i. Sapkos SW: The use of antisialagogues in periodontal andrestorative dentistry. Int J Periodont Rest Dent 1984;4(4):43-49.1. Wilson EL, Whitsett LD, Whitsett TL: Effects of methanthelinebromide and clonidine hydrochloride on salivary secretion.J Prosthet Dent 1984; 52:663-665.>. Thompson MJ: Hydrocolloid—Its treatment and applicationin securing consistent accurate models for indirect inlaysand feed bridges- Bull Okla DentAssoc 1949, 387-24.i. Benson BW, Bomberg TJ, Hatch RA, Hoffman W: Tissue dis-placement methods in fixed prosthodontics. J Prosthet Dent1986; 55:175-181.. Hovestad JF: Practical Dental Porcelains. St Louis, CVMosby Co. 1924, p 34-36osthesis. J Prosthet Dent 1958,ssion technique. Dent Clin North). Ewing JE: Beautiful but glum—Porcelain jacket crowns. JProsthet Dent 1954; 4:94-103.I. Johnston JF, Mumford G, Dykema RW: Modem Practice inDental Ceramics Philadelphia, WB Saunders Co, 1967, p84-94.I. Ruel J, Schuessler PJ. Malament K, Mori D: Effect of retrac-tion procedures on the periodontium in humans. J ProsthetDenM980; 44:509-515.J. Coelho DH, Brisman AS: Gingival recession with modelling-plastic copper-band impressions. J Prosthet Dent 1974;31:647-650.1. Ingraham R, B