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Mouth preparation for rpd /certified fixed orthodontic courses by Indian dental academy


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Mouth preparation for rpd /certified fixed orthodontic courses by Indian dental academy

  2. 2. Contents of the seminar Introduction History Oral surgical preparation, Conditioning of abused and irritated tissue Periodontal preparation Preparation of abutment teeth 1.Correction of Occlusal Plane 2.Correction of Malalignment 3.Provision of support for weakened teeth 4.Reshaping Teeth 5.Occlusal rest seat preparation 6.Lingual or incisal rest seat preparation 2
  3. 3. INTRODUCTION The preparation of the mouth is fundamental to a successful removable partial denture service. Mouth preparation, perhaps more than any other single factor, contributes to the philosophy that the prescribed prosthesis must not only replace what is missing but also preserve the remaining tissue and structures that will enhance the removable partial denture. 3
  4. 4. The treatment plan for the patient who is to receive a removable partial denture can be finalized only after diagnostic casts have been mounted on an articulator and surveyed and the proposed partial denture has been designed. The design procedure will have disclosed procedures that are necessary to prepare the mouth to receive a removable partial denture like reshaping of enamel to produce more favorable contours. After the examination, diagnosis, and treatment planning phase, the sequence of mouth preparation appointments must be planned with the goal of conserving as much time as possible. 4
  5. 5. HISTORY The design philosophies of RPDs have progressed considerably since the first published description in 1711. The earliest description of the use of occlusal rests for removable partial dentures is usually credited to Bonwill The development of the surveyor circa 1915 contributed immeasurably to current concepts of RPDs. The first instrument specially developed for surveying RPDs was designed by Weinstein and Roth, and it was made available commercially in 1921. In 1940, Applegate wrote on the use of the paralleling surveyor in modern partial denture fabrication: “Perhaps no step in the construction of a clasp-retained partial denture has more direct bearing upon the ultimate result than that of surveying the model of the dental arch for which the appliance is to be made.” The preparation of the mouth, path of insertion, tilts of a cast, shapes and tapers of clasps, fulcrum line, and design of major and minor connectors are described in several manuals and have been known for many years. 5
  6. 6. Mouth preparation follows the preliminary diagnosis of the development of a tentative treatment plan. Final treatment planning may be deferred until the response to the preparatory procedures can be ascertained. In general, mouth preparation includes procedures in four categories: Oral surgical preparation, Conditioning of abused and irritated tissue, Periodontal preparation, and Preparation of abutment teeth. Objectives of the procedures involved in all four areas are to return the mouth to optimum health and eliminate any condition that would be detrimental to the success of the removable partial denture. 6
  7. 7. Naturally, mouth preparation must be accomplished before the impression procedures that will produce the master cast on which the removable partial denture will be fabricated. Oral surgical and periodontal procedures should precede abutment tooth preparation and should be completed far enough in advance to allow the necessary healing period. If at all possible, at least 6 weeks, but preferably 3 to 6 months, should be provided between surgical and restorative dentistry procedures. This depends on the extent of the surgery and its impact on the overall support, stability, and retention of the proposed prosthesis. 7
  8. 8. Relief of Pain and Infection As early in the treatment process as possible all teeth that are causing pain or discomfort because of caries or defective restorations should be treated to eliminate the possibility of an acute episode of pain occurring during the treatment procedure. Asymptomatic teeth with advanced carious lesions should be treated in the same way and restored with an intermediate restorative material until definitive treatment is accomplished. The gingival tissues should also be treated early in the treatment sequence to eliminate the possibility of exacerbation of periodontal abscesses and other inflammatory responses. Definitive periodontal therapy need not be performed until the complete treatment plan is accomplished, but calculus accumulations should be debrided, plaque should be controlled and a preventive dental hygiene program should be started and vigorously monitored. 8
  9. 9. ORAL SURGICAL PREPARATION As a rule, all pre-prosthetic surgical treatment for the removable partial denture patient should be completed as early as possible. When possible, necessary endodontic surgery, periodontal surgery, and oral surgery should be planned so that they can be completed during the same time frame. The longer the interval between the surgery and the impression procedure, the more complete the healing and consequently the more stable the denture bearing areas. 9
  10. 10. A variety of oral surgical techniques can prove beneficial to the clinician in preparing the patient for prosthetic replacements. In this seminar attention is called to some of the more common oral conditions or changes in which surgical intervention is indicated as an aid to removable partial denture design and fabrication, and as an aid to the restoration's successful function. The important consideration is that the patient not be deprived of any treatment that would enhance the success of the removable partial denture. 10
  11. 11. Extractions Planned extractions should occur early in the treatment regimen but not before completion of a careful and thorough evaluation of each remaining tooth in the dental arch. Regardless of its condition, each tooth must be evaluated concerning its strategic importance and its potential contribution to the success of the removable partial denture. Heroic attempts to salvage seriously involved teeth or those with doubtful prognoses, for which retention would contribute little if anything, even if successfully treated and maintained are contraindicated. The extraction of non-strategic teeth that would present complications or those that may be detrimental to the design of the removable partial denture is a necessary part of the overall treatment plan. 11
  12. 12. Removal of Residual Roots Generally, all retained roots or root fragments should be removed. This is particularly true if they are in close proximity to the tissue surface or if there is evidence of associated pathological findings. Residual roots adjacent to abutment teeth may contribute to the progression of periodontal pockets and compromise the results from subsequent periodontal therapy. The removal of root tips can be accomplished from the facial or palatal surfaces without resulting in a reduction of alveolar ridge height or endangering adjacent teeth 12
  13. 13. Impacted Teeth All impacted teeth, including those in edentulous areas and those adjacent to abutment teeth, should be considered for removal. The periodontal implications of impacted teeth adjacent to abutments are similar to those for retained roots. These teeth are often neglected until serious periodontal implications arise. Asymptomatic impacted teeth in the elderly that are covered with bone, with no evidence of a pathological condition, should be left to preserve the arch morphology. 13
  14. 14. If an impacted tooth is left, it should be recorded in the patient's record and the patient should be informed of its presence. Roentgenograms should be taken at reasonable intervals to be sure that no adverse changes occur. Alterations that affect the jaws can result in minute exposures of impacted teeth to the oral cavity via sinus tracts. Resultant infections can cause considerable bone destruction and serious illness for persons who are elderly and not physically able to tolerate the debilitation. Early elective removal of impactions prevents later serious acute and chronic infection with extensive bone loss. Any impacted teeth that can be reached with a periodontal probe must be removed to treat the periodontal pocket and prevent more extensive damage 14
  15. 15. Malposed Teeth The loss of individual teeth or groups of teeth may lead to extrusion, drifting, or combinations of malpositioning of the remaining teeth. In most instances the alveolar bone supporting extruded teeth will be carried occlusally as the teeth continue to erupt. Orthodontics may be useful in correcting many occlusal discrepancies, but for some patients, such treatment may not be practical because of a lack of teeth for anchoring orthodontic appliances or for other reasons. In such situations individual teeth or groups of teeth and their supporting alveolar bone can be surgically repositioned. This type of surgery can be accomplished in an outpatient setting and should be given serious consideration before condemning additional teeth or compromising the design of removable partial dentures. 15
  16. 16. Cysts and Odontogenic Tumors Panoramic roentgenograms of the jaws are recommended to survey for unsuspected pathological conditions. When a suspicious area appears on the survey film, a periapical roentgenogram should be taken to confirm or deny the presence of a lesion. All radiolucencies or radiopacities observed in the jaws should be investigated. Although the diagnosis may appear obvious from clinical and roentgenographic examinations, the dentist should confirm that diagnosis through appropriate consultation and if necessary perform a biopsy of the area and submit the specimens to a pathologist for microscopic study. The patient should be informed of the diagnosis and provided with various options for resolution of the abnormality as confirmed by the pathologist's report. 16
  17. 17. Exostoses and Tori The existence of abnormal bony enlargements should not be allowed to compromise the design of the removable partial denture. Although modification of denture design can at times accommodate for exostoses, more frequently this results in additional stress to the supporting elements and compromised function. The removal of exostoses and tori is not a complex procedure, and the advantages to be realized from such removal are great in contrast to the deleterious effects their continued presence can create. Ordinarily the mucosa covering bony protuberances is extremely thin and friable. Removable partial denture components in proximity to this type of tissue may cause irritation and chronic ulceration. Also, exostoses approximating gingival margins may complicate the maintenance of periodontal health and lead to the eventual loss of strategic abutment teeth. 17
  18. 18. Hyperplastic Tissue Hyperplastic tissue is seen in the form of fibrous tuberosities, soft flabby ridges, folds of redundant tissue in the vestibule or floor of the mouth, and palatal papillomatosis. All these forms of excess tissue should be removed to provide a firm base for the denture. This removal will produce a more stable denture, reduce stress and strain on the supporting teeth and tissue, and in many instances will provide a more favorable orientation of the occlusal plane and arch form for the arrangement of the artificial teeth. 18
  19. 19. The appropriate surgical approaches should not reduce vestibular depth. Hyperplastic tissue can be removed with any preferred combination of scalpel, curette, electrosurgery, or laser. Some form of surgical stent should always be considered for these patients so that the period of healing is more comfortable. An old removable partial denture properly modified can serve as a surgical stent. Although hyperplastic tissue has no great malignant propensity, all such excised tissue should be sent to an oral pathologist for microscopic study. 19
  20. 20. Muscle attachment and frena As a result of the loss of bone height, muscle attachments may insert on or near the residual ridge crest The mylohyoid, buccinator, mentalis, and genioglossus muscles are those most likely to introduce problems of this nature. In addition to the problem of the attachments of the muscles themselves, the mentalis and genioglossus muscles occasionally produce bony protuberances at their attachments, which may also interfere with removable partial denture design. Appropriate ridge extension procedures can reposition attachments and remove bony spines, which will enhance the comfort and function of the removable partial denture. 20
  21. 21. Repositioning of the mylohyoid is successfully achieved by several methods. The genioglossus is more difficult to reposition, but careful surgery can reduce the prominence of the genial tubercles and provide some sulcus depth in the anterior lingual area. Surgical procedures that use skin or mucosal grafts have largely replaced secondary epithelialization procedures for the facial aspect of the mandible. Mucosal grafts using the palate as a donor site offer the best possibility for success. Transplanted skin can be used when large areas must be grafted. The maxillary labial and mandibular lingual frena are the most common sources of frenum interference with denture design. These can be modified easily with any of several surgical procedures. Under no circumstances should a frenum be allowed to compromise the design or comfort of a removable partial denture. 21
  22. 22. Bony Spines and Knife-Edge Ridges Sharp bony spicules should be removed and knifelike crests gently rounded. These procedures should be carried out with minimum bone loss. If, however, the correction of a knifeedge residual crest results in insufficient ridge support for the denture base, the dentist should resort to vestibular deepening for correction of the deficiency or insertion of the various bone grafting materials that have demonstrated successful clinical trials. 22
  23. 23. Polyps, Papillomas, and Traumatic Hemangiomas All abnormal soft tissue lesions should be excised and submitted for pathological examination before the fabrication of a removable partial denture. Even though the patient may relate a history of the condition having been present for an indefinite period, its removal is indicated. New or additional stimulation to the area introduced by the prosthesis may produce discomfort or even malignant changes in the tumor. 23
  24. 24. Hyperkeratoses, Erythroplasia, and Ulcerations All abnormal, white, red, or ulcerative lesions should be investigated regardless of their relationship to the proposed denture base or framework. A biopsy of areas larger than 5 mm should be completed, and if the lesions are large (more than 2 cm in diameter), multiple biopsies should be taken. The biopsy report will determine whether the margins of the tissue to be excised can be wide or narrow. The lesions should be removed and healing accomplished before fabrication of the removable partial denture. On occasion the removable partial denture design will have to be radically modified to prevent areas of possible sensitivity, such as after irradiation treatments or the excoriation of erosive lichen planus. 24
  25. 25. Dentofacial Deformity Patients with a dentofacial deformity often have multiple missing teeth as part of their problem. Correction of the jaw deformity can simplify the dental rehabilitation. Before specific problems with the dentition can be corrected, the patient's overall problem must be evaluated thoroughly. Several dental professionals (prosthodontist, oral surgeon, periodontist, orthodontist, and general dentist) may play a role in the patient's treatment. These individuals must be involved in producing the diagnostic database and in planning treatment for the patient. 25
  26. 26. Osseointegrated Devices A number of implant devices to support the replacement of teeth have been introduced to the dental profession. These devices offer a significant stabilizing effect on dental prostheses through a rigid connection to living bone. The system that pioneered clinical prosthodontic applications with the use of commercially pure (CP) titanium endosseous implants is that of Branemark and co-workers. This titanium implant was designed to provide a direct titanium-to-bone interface (osseointegrated), with the basic laboratory and clinical results supporting the value of this procedure. 26
  27. 27. Implants are carefully placed using controlled surgical procedures, and in general bone healing to the device is allowed to occur before fabrication of a dental prosthesis. Long-term clinical research has demonstrated good results for the treatment of complete and partially edentulous patients using dental implants. Although there has been very limited research on implant applications with removable partial dentures, the inclusion of strategically placed implants can significantly control prosthesis movement 27
  28. 28. 28
  29. 29. 29
  30. 30. Augmentation of Alveolar Bone Considerable attention has been devoted to ridge augmentation with the use of autogenous and alloplastic materials, especially in preparation for implant placement. Larger ridge volume gains necessitate consideration of autogenous grafts; however, these procedures are accompanied with concerns for surgical morbidity. Although alloplastic materials have displayed short-term success, no randomized controlled trials have been conducted to provide evidence of long-term increases in ridge width and height for removable prostheses. Clinical results depend on careful evaluation of the need for augmentation, the projected volume of required material, and the site and method of placement. Considerable emphasis must be placed on sound clinical understanding that some of the alloplastic materials can migrate or be displaced under occlusal loads if not appropriately supported by underlying bone and contained by buttressing soft tissue. Careful clinical judgment, with sound surgical and prosthetic principles, must be exercised. 30
  31. 31. CONDITIONING OF ABUSED AND IRRITATED TISSUE Many removable partial denture patients require some conditioning of supporting tissue in edentulous areas before the final impression phase of treatment. Patients who require conditioning treatment often demonstrate the following symptoms: 1. Inflammation and irritation of the mucosa covering the denture-bearing areas 2. Distortion of normal anatomic structures, such as incisive papillae, the rugae, and the retromolar pads 3. A burning sensation in residual ridge areas, the tongue, and the cheeks and lips 31
  32. 32. These conditions are usually associated with ill-fitting or poorly occluding removable partial dentures. However, nutritional deficiencies, endocrine imbalances, severe health problems (diabetes or blood dyscrasias), and bruxism must be considered in a differential diagnosis. If a new removable partial denture or the relining of a present denture is attempted without first correcting these conditions, the chances for successful treatment will be compromised because the same old problems will be perpetuated. The patient must be made to realize that fabrication of a new prosthesis should be delayed until the oral tissue can be returned to a healthy state. 32
  33. 33. If there are unresolved systemic problems, removable partial denture treatment will usually result in either failure or limited success. The first treatment procedure should be an immediate institution of a good home care program. A suggested home care program includes rinsing the mouth three times a day with a prescribed saline solution; massaging the residual ridge areas, palate, and tongue with a soft toothbrush; removing the prosthesis at night; and using a prescribed therapeutic multiple vitamin along with a prescribed highprotein, low-carbohydrate diet. Some inflammatory oral conditions caused by ill-fitting dentures can be resolved by removing the dentures for extended periods. However, few patients are willing to undergo such inconveniences. 33
  34. 34. Use of Tissue Conditioning Materials The tissue conditioning materials are elastopolymers that continue to flow for an extended period, permitting distorted tissue to rebound and assume its normal form. These soft materials apparently have a massaging effect on irritated mucosa, and because they are soft, occlusal forces are probably more evenly distributed. Maximum benefit from using tissue conditioning materials may be obtained by (1) Eliminating deflective or interfering occlusal contacts of old dentures (by remounting in an articulator if necessary); (2) Extending denture bases to proper form to enhance support, retention, and stability 34
  35. 35. 3) Relieving the tissue side of denture bases sufficiently (2mm) to provide space for even thickness and distribution of conditioning material; (4) Applying the material in amounts sufficient to provide support and a cushioning effect following the manufacturer's directions for manipulation and placement of the conditioning material. 35
  36. 36. The conditioning procedure should be repeated until the supporting tissues display an undistorted and healthy appearance. Many dentists find that intervals of 4 to 7 days between changes of the conditioning material are clinically acceptable. An improvement in irritated and distorted tissue is usually noted within a few visits, and in some patients a dramatic improvement will be seen. Usually three or four changes of the conditioning material are adequate, but in some instances more changes are required. If positive results are not seen within 3 to 4 weeks, one should suspect more serious health problems and request a consultation from a physician 36
  37. 37. PERIODONTAL PREPARATION The periodontal preparation of the mouth usually follows any oral surgical procedure and is performed simultaneously with tissue conditioning procedures. Ordinarily, tooth extraction and removal of impacted teeth and retained roots or their fragments are accomplished before definitive periodontal therapy. However, it is strongly recommended that a gross debridement be performed before tooth extraction when patients have significant calculus accumulation. This helps limit the possibility of accidentally dislodging a piece of calculus into the extraction socket, which could lead to an infection. The elimination of exostoses, tori, hyperplastic tissue, muscle attachments, and frena, on the other hand, can be incorporated with periodontal surgical techniques. In any situation, periodontal therapy should be completed before restorative dentistry procedures are begun for any dental patient. 37
  38. 38. The periodontal health of the remaining teeth, especially those to be used as abutments, must be evaluated carefully by the dentist and corrective measures instituted before removable partial denture fabrication. It has been demonstrated that following periodontal therapy and with a good recall and oral hygiene program, properly designed removable partial dentures will reduce the progression of periodontal disease or carious lesions. 38
  39. 39. Objectives of Periodontal Therapy The objective of periodontal therapy is the return to health of the supporting structures of the teeth, creating an environment in which the periodontium may be maintained. The specific criteria for satisfying this objective are as follows: 1. Removal and control of all etiological factors contributing to periodontal disease, along with a reduction or elimination of bleeding on probing 2. Elimination of, or reduction in, pocket depths of all pockets, with the establishment of healthy gingival sulci whenever possible 3. Establishment of functional atraumatic occlusal relationships and tooth stability 4. Development of a personal plaque control program and definitive maintenance schedule 39
  40. 40. Prosthetic Mouth Preparation 40
  41. 41. The prosthetic mouth preparation will be discussed under the following: Correction of Occlusal Plane Correction of Malalignment Provision of support for weakened teeth Reshaping Teeth Occlusal rest seat preparation Lingual or incisal rest seat preparation 41
  42. 42. Correction of the Occlusal Plane The dentition in the arch opposing the RPD, and the teeth in the arch being treated, must be returned to as normal an occlusal plane as possible, which is defined in the Glossary of Prosthodontic Terms as “The average plane established by the incisal and occlusal surfaces of the teeth…it is not a plane, but represents the planar mean of the curvature of these surfaces”. The occlusal plane in most partially edentulous mouths will be uneven. The severity of this irregularity will determine the extent of the treatment necessary to correct the condition. Teeth that have been unopposed for a time will tend to overerupt. Maxillary molars, if not opposed. tend to migrate downward, carrying the bony tuberosity along. Problems such as this should be recognized following the diagnostic mounting procedure, and the partial denture should be designed to circumvent the problem if surgical correction is impossible. 42
  43. 43. Normally the occlusal plane is corrected by reducing the height of overerupted teeth. There are times however, when the clinical crown requires lengthening to restore the correct occlusal plane, such as when teeth fail to erupt fully because of interferences from other teeth or lack of stimulation. This condition is most often corrected by orthodontic treatment or the placement of cast onlays or crowns. Tipped molars also present problems in establishing a harmonious occlusal plane. The ideal solution is to upright the teeth orthodontically. 43
  44. 44. Enameloplasty Enameloplasty is a coined word used to describe the removal of a portion of the enamel surface of a tooth to accomplish specific purposes. For the correction of the occlusal plane, the enameloplasty consists of reducing cusp height in order to level or harmonize the curve of the occlusal plane . 44
  45. 45. When cusp height is reduced the anatomy of the occlusal surface should not be mutilated. Functional cusps with accessory grooves and sluiceways must be restored to the teeth once the necessary reduction has been made. The actual reduction of enamel surface is best accomplished by using tapered diamond cylinder stones in the high speed handpiece 45
  46. 46. Onlay It is a conservative method of correcting the plane of occlusion. The occlusal surface of a tooth to be covered by an onlay rest should be free of pits and fissures or should be made so by eliminating the defects with small burs or stones. Use of this restorations in mouths with poor oral hygiene can lead to destruction of teeth. One of the simplest methods of reestablishing the plane of occlusion is by the use of cast gold onlays, which an either lengthen or shorten the crown height of a tooth. 46
  47. 47. One of the main advantages of the onlay is that the natural contours of the facial and lingual enamel surfaces can be maintained. This is normally an objective if the periodontal health of the tooth is optimal under the existing conditions. If the tooth bearing the onlay is also to be a primary abutment for the removable partial denture (that is, is to have a retentive extracoronal clasp), the retentive clasp tip should not engage an undercut in the onlay; it must be on the enamel surface. If this is not possible the onlay is not indicated and a full crown should be planned for that tooth. 47
  48. 48. Crowns When the crown height of the tooth must be changed to harmonize the occlusal plane. and the facial, lingual, or proximal surfaces must be altered to produce a more desirable height of contour, a guiding plane, or a retentive undercut, a full crown is normally restoration of choice. Before the tooth is prepared to receive the crown, mounted diagnostic casts should be measured to ascertain how much crown reduction is necessary to correct the occlusal plane. If the reduction of tooth structure will be so great as to endanger the dental pulp, a decision must be made as to whether endodontic treatment is indicated or whether this extent of treatment is not warranted and extraction would be the treatment of choice. 48
  49. 49. Endodontics with Crown or Coping If strategically positioned teeth in the dental arch are retained, the prognosis of the partial denture is improved markedly. These teeth include mandibular second or third molars that may be used to serve as posterior abutment so as the prosthesis may be all tooth supported. This greatly improves patient acceptance of the denture. Other vitally important teeth are those in the center of a long anterior edentulous span either mandibular or maxillary. The presence of a usable abutment tooth in that location offers a great advantage in controlling vertical movement of the denture. 49
  50. 50. If the overeruption has been so gross as to obliterate the remaining interarch space, the crown of the tooth can be removed at the gingival crest and a coping constructed. The tooth will serve as a vertical stop, preventing excessive vertical or horizontal movement of the prosthesis. 50
  51. 51. Extraction It should be the goal of a designer of removable partial dentures to retain as many of the remaining teeth as possible. However, at times retaining certain teeth can greatly complicate or even compromise the success of the treatment. For example, if orthodontic treatment cannot be accomplished to realign severely malposed molars or premolars, extraction must be considered. When teeth interfere with the placement of the major connector and no other solution (such as crowning the tooth) feasible, extraction must be planned. 51
  52. 52. Surgery Surgical repositioning of one or both jaws or of segments of one or both jaws can be performed to correct malrelationship of teeth. Various forms of mandibulectomies, usually to correct gross prognathic jaw relationships, have been performed. Maxillary segmental osteotomy is done to superiorly repositioning posterior segments of maxillae. This is one of the most effective methods of regaining interarch space lost due to downward migration of the teeth and tuberosity 52
  53. 53. Correction Of Malalignment Teeth that are malposed facially or lingually are frequently more difficult to correct than overerupted or submerged teeth. There are definite limitations to repositioning of these malposed teeth, Often it is the design of the removable partial denture that must be altered rather than the tooth position. 53
  54. 54. Orthodontic Realignment The technique of orthodontically moving the malpositioned tooth should be considered first. Whenever it is possible, it is the treatment of choice. Unfortunately it is often not possible to use this method. In many mouths where a large number of teeth are missing there may not be enough remaining teeth to serve as an anchor from where the moving force can be applied. There must be some means of applying force and resisting the equal and opposite counter force that will be generated. 54
  55. 55. Crowns Teeth that are not grossly out of position facially or lingually can occasionally be improved by a partial or full crown restoration. The teeth to be considered for this form correction are those that are tipped either buccally or lingually. It is possible to treat the tooth endodontically and use a post and core to restore the crown in a nearly normal position. It must be remembered however that the long axis of the remaining root and the crown must not be too dissimilar or undesirable forces will take place on the structure supporting the root. Thus crown restorations may be used, but they will not cure severe malalignment. 55
  56. 56. Enameloplasty The concept of reshaping or reducing enamel surfaces or cusps of teeth to correct the occlusal plane can be used to a lesser degree to correct malaligned teeth. It is possible to recontour buccal or lingual surfaces to eliminate interferences to the path of placement of a major connector. It is possible in certain instances to reshape the facial or lingual surfaces of tipped or malposed teeth to allow better placement of clasps or lingual plating. 56
  57. 57. PROVISION OF SUPPORT FOR WEAKENED TEETH In many partially edentulous mouths some or all the remaining teeth have lost varying amounts of the supporting periodontal ligament and alveolar bone. To use these teeth to help support and stabilize a removable partial denture, it will be necessary to provide additional support for these teeth by splinting the teeth together or by using overdenture abutments. Removable Splinting The premise behind splinting teeth with removable restorations is that the mobility will either decrease or remain the same. 57
  58. 58. Fixed splinting There are times that an individual tooth or two adjoining teeth may have lost some periodontal support as a result of local conditions. The decision must be made as to the value of retaining such teeth as opposed to the extraction of the teeth and the inclusion of the teeth in the removable partial denture. To be considered a permanent form of treatment, fixed splinting must be accomplished with full or partial coverage crowns soldered together or pin-ledge restorations that provide additional retention for the splint. Teeth that require splinting usually exhibit mobility. This mobility, if not completely controlled may over time cause a break in the cementing medium with ultimate adverse effects on the tooth and surrounding tissues. To attempt to control mobility with inlay restorations is ill adviced . If the teeth cannot be held totally immobile, splinting should not be attempted. 58
  59. 59. Overdenture Abutments Certain teeth that have lost at least 50% of the supporting bone but are strategicallv positioned in the arch should be retained to provide support for a removable prosthesis. The support providing will consist principally of resisting tissueward forces. If such teeth at the posterior end of an edentulous space are retained and used as vertical stops for the denture base, the prosthesis will be converted from a Class I or II partial denture to a functioning Class III prosthesis. This change improves the function of the denture, and the patient acceptance is consistently excellent. 59
  60. 60. RESHAPING OF TEETH Tooth surfaces often need to be reshaped to accomplish specific purposes. This changing of tooth contour may be accomplished in the enamel, on the surface of an existing restoration, or by placing a new restoration. Enameloplasty Conservatism must be the rule when tooth preparation is to be accomplished on enamel surfaces for a removable partial denture. Sufficient tooth reduction must be accomplished to ensure adequate space or proper contour, but never at the expense of overcutting the tooth 60
  61. 61. Enameloplasty to Develop Guiding Planes Guiding planes are those surfaces on the teeth, of sufficient area and parallel relationship to each other, so that they may serve to determine positively the direction of appliance movement (Applegate 1954). McCracken (2005) describes them as two or more vertical parallel surfaces of abutment teeth, so shaped to direct a prosthesis during placement and removal. The Glossary of Prosthodontic Terms (1999) defines them as two or more vertically parallel surfaces of abutment teeth, so orientated as to direct the path of placement of removable partial dentures. 61
  62. 62. Functions of guiding planes Six functions are attributed to guiding planes (McCracken 2005) -To provide one path of placement and removal -To ensure planned and intended action of the retentive and bracing components of the partial denture -To eliminate detrimental strain to the abutment teeth and the components of the framework in placing and removing the prosthesis -To eliminate gross food traps between the abutment teeth and the denture base -To provide retentive characteristics against dislodgement of the denture when the dislodging force is other than parallel to the path of removal -To provide bracing characteristics against horizontal rotation of the denture 62
  63. 63. Guiding Planes On Abutment Teeth Adjacent to Tooth Supported Segments The diagnostic cast mounted on the surveying table at the tilt at which the design of the removable partial denture was drawn, should be available at the mouth preparation appointment. It should be placed on the table in front of the patient, and the hand piece, with the appropriate diamond instrument in place, positioned over the cast so that the relationship of the hand piece and diamond stone to the tooth can be visualized. A cylindrical diamond point is generally the instrument to make the preparation. A gentle, light sweeping stroke from the buccal line angle to the lingual line angle should be used 63
  64. 64. The flat surface created should ideally be 2 to 4mm in occluso-gingival height As a general rule five or six light strokes of the diamond stone are sufficient to produce the desired reduction. More strokes usually will remove excessive tooth structure. The reduction must not be a straight slice across the tooth surface; rather it should follow the curvature of the surface so that nearlv uniform amounts of enamel are removed from through out the bucco-lingual width of the preparation. 64
  65. 65. Guiding Planes on Abutment Teeth Adjacent to Distal Extension Edentulous Spaces The tooth preparation on the proximal surface of abutment teeth adjacent to distal extension edentulous spaces is accomplished in the same manner with a cylindrical diamond stone held parallel to the path of insertion. The importance of maintaining parallelism in this instance is critical. The principal difference between this guiding plane and the planes on teeth bordering a tooth-supported segment is that the occluso-gingival height of the plane is reduced to 1.5 to 2 mm to permit the partial denture to rotate slightly around the distal occlusal rest as downward force occurs on the artificial teeth. This slight movement allows the release of the denture from the guiding plane, thereby avoiding the creation of torquing or twisting forces on the abutment tooth. 65
  66. 66. Guiding Planes On Lingual Surfaces Of Abutment Teeth Mandibular posterior teeth are usually inclined lingually with a resultant high lingual survey line. Minor recontouring can frequently improve the position of the survey line to allow placement of the reciprocal clasp arm in its proper position The purpose of providing guiding planes on lingual surfaces of teeth is to provide maximum resistances to lateral stresses. The more teeth involved in guiding plane preparation, the less will be the stress transmitted to each individual tooth. 66
  67. 67. The occluso-gingival height of the preparation is 2 to 4 mm. The plane ideally should be located in the middle third of the clinical crown of the tooth. Special care must be shown to avoid changing the contour of the gingival third of the tooth because damage to the marginal gingiva through the improper shunting of food may occur if the normal morphology of the gingival third of the crown is lost 67
  68. 68. When it is not possible to recontour the tooth sufficiently for proper placement of the reciprocal arm, lingual plating may be used to provide the necessary reciprocation. Unless the tooth is recontoured, a large undesirable undercut will be present to trap food Recontouring will reduce the amount of undercut and will result in less torque on the tooth. Occasionally, mandibular posterior teeth have been severely worn or the occlusal surface adjusted in such a manner as to leave a flat occlusal surface that meets the lingual surface at an acute angle. The bracing arm of the clasp cannot go to place because it contacts a flat horizontal surface rather than an inclined plane preventing the partial denture from seating in the mouth. Rounding occlusal-lingual line angle allows clasp arm to open as it is seated in mouth. 68
  69. 69. Guiding Planes on Anterior Abutment Teeth Guiding planes on anterior teeth adjacent to edentulous spaces provide the parallelism needed to ensure stabilization, minimize wedging action between the teeth, decrease undesirable space between the denture and the abutment tooth, and increase retention through frictional resistance. Another special purpose of such guiding planes is to increase or restore the normal width of edentulous space. In addition teeth that have tipped towards an edentulous space will exhibit a large undercut area below the height of contour on the proximal surface. 69
  70. 70. If the height of contour is not reduced as the guiding planes are established, the undercut will appear as a large, unsightly space between the artificial tooth and the restored tooth. The space not only detracts from the esthetic value of the denture, but also traps food. If sufficient tooth structure cannot be removed to restore the space and to reduce the undercut without penetrating the enamel layer a restoration must be planned Use a cylindrical smooth cut carbide fissure bur such as a no. 57 or 52, or a fine diamond instrument (bur) of a comparable shape, to recontour the proximal surfaces. Original facial-lingual contour of the proximal surfaces should be maintained 70
  71. 71. Applegate suggested that the abutment teeth may be paralleled by eye to the planned path of insertion by grinding the proximal enamel of restoration facing the edentulous area. Jochen suggested an alternative method by preparing an acrylic index constructed upon a previously modified cast on which the desired guiding planes have been cut. After gross enamel reduction the index is fitted to the crown and disclosing wax is used to reveal interferences requiring further milling. Stern (1975) subjectively tested the retention of clasp assemblies on laboratory models with rest preparations only, mesial, proximal and mesiolingual guide planes, and mesial and lingual guide planes. He found that retention for the same degree of clasp undercut was greater where guide planes had been prepared. Johnston (1961) wrote that guiding planes should be prepared on all tooth surfaces which would contact minor connectors and reciprocal clasp arms. On approximal surfaces they should be parallel to the path of insertion or converge 2-5 degrees occlusally to avoid leverage during mastication. The guiding planes should be full length for tooth supported dentures but full length planes should be avoided for extension base dentures. 71
  72. 72. Enameloplasty to Change Height of Contour The height of contour is changed most frequently to provide better positions for clasp arms or 4 lingual plating. Ideally the retentive clasp arm should be located no higher than the juncture of the gingival and the middle thirds. This position not only enhances the esthetic quality of the clasp, but also provides a definite mechanical advantage 72
  73. 73. The amount of correction that can be accomplished by recontouring the enamel surface is limited by the thickness of the enamel. Care has to be taken not to penetrate the enamel and expose dentin The height of contour is best lowered by using tapered diamond stones Judicious facial contouring can be used to allow placement of clasp lower on tooth. A tapered cylindrical diamond rotary instrument used to reduce the enamel to lower survey line on mesial-facial surface of tooth. Bracing portion of clasp can be lower on tooth and remain in full contact with tooth surface. 73
  74. 74. Enameloplasty to Modify Retentive Undercuts Occasionally a proposed abutment tooth has less than a sufficient retentive undercut. If the oral hygiene of the patient is adequate and if the caries index is low, some of these teeth may be treated to increase the amount of retentive undercut by contouring the enamel surface. This technique does not have universal application, but in a few instances it may be beneficial. This method of developing retentive undercuts should not be substituted for adequate design procedures. Retentive undercuts may exist on other surfaces that could be utilized by other forms of clasps. Relying on creating undercuts in enamel surfaces can lead to potentially damaging consequences for the patient. 74
  75. 75. In order for the technique of contouring the enamel surface to produce a retentive undercut to be successful, the buccal and lingual surfaces of the tooth must be nearly vertical. If either or both surfaces have a pronounced slope, the procedure is contraindicated. If the surface to receive the undercut is sloped, the indentation would have to be excessively deep to be effective . If the opposing surface is sloped, the reciprocal clasp arm could not brace the tooth sufficiently to prevent the retentive clasp tip from being dislodged from the undercut 75
  76. 76. The retentive undercut must be created in the form of a gentle depression not a pit or hole. The term dimpling has been applied to this technique, but the name it appears to be misleading, implying a definite pit rather than a gentle depression. The depression or undercut is prepared by using a small, round-ended, tapered diamond stone. The end of the stone is moved in an antero- posterior direction near the line angle of the tooth. The preparation is made parallel to and as close as possible to the gingival margin without actually encroaching on the gingival crevice. The purpose is to create a slight concavity approximately 0.010 inch deep measured from a vertical line paralleling the path of insertion. The depression should be approximately 4 mm in mesiodistal length and 2 mm in occlusogingival height. Care must be taken not to develop a ledge or shoulder in the enamel . 76
  77. 77. Henderson and Steffel(1972) recommended that heights of contour should be changed by reshaping the teeth to place the clasp in the gingival third and the root of the clasp with a direct approach from the occlusal rest to the clasp tip. This enabled clasps to be simple and long enough to be flexible as well as sturdy. Morris (1962) wrote that over-contoured teeth led to poor gingival health as under-contoured teeth were conducive to health. Demer (1976) suggested that when the surfaces did not exhibit undercuts, these could be created by dimpling or utilisation of a groove in a restoration. Maroso et al (1981) showed that little or no wear occurred when clasps were placed on porcelain. 77
  78. 78. Inlays, Onlays and Crowns If the remaining teeth do not possess usable natural contours and the enamel surfaces cannot be corrected to reduce these contours, cast restorations must be planned. The guiding planes, height of contour, and retentive undercuts can be placed in these restorations as the wax patterns are being developed. In addition ,many teeth that are to serve as abutments for removable partial dentures will require restorations for more routine reasons such as the presence of caries or effective restorations, tooth fracture, or endodontic therapy. These restorations also must be planned to satisfy the requirements of the partial denture. 78
  80. 80. OCCLUSAL REST SEAT The functions of a rest are (Stewart 1997): 1. To direct the forces of mastication parallel to the long axis of the abutment tooth. The form of the rest seat preparation helps carry out this function. 2. It acts as a stop against gingival displacement of the denture, maintains the clasp in its properly surveyed position 3. Functions as an indirect retainer in a distal extension partial denture. 4. Used to close a small space between teeth, thus restoring the continuity of the arch 5. Preventing food impaction between the minor connector and the proximal surface of an abutment tooth 6. It is used to onlay on abutment tooth to establish a more 80 acceptable occlusal plane and to prevent extrusion of tooth
  81. 81. Conventional rest preparations in posterior teeth View from occlusal shows facial-lingual width of rest seats that should be as wide as possible but approximately one half distance between cusp tips of teeth and in length about one fourth mesial-distal crown length of tooth. 81
  82. 82. Proximal view of preparations show spoon shape of rest seat, maximum depth of 1 to 2 mm, and that they flare at marginal ridge. 82
  83. 83. Cross-section of teeth showing that deepest part of preparation is in the fossae (A) and that marginal ridge (B) is higher than fossae. Angle formed between inclination of floor of rest and vertical projection of greatest contour of proximal surface (C) must be less than 90 degrees. 83
  84. 84. A metal rest should never be placed on a tooth that has not been adequately prepared to receive that rest. When a rest is placed on an unprepared or improperly prepared tooth, the action will be as if 2 inclined planes were placed opposing each other. 84
  85. 85. Properly prepared rest seats change direction of applied force, by 180 degrees, to pull tooth and RPD toward each other to make them mutually supportive. 85
  86. 86. The earliest description of the use of occlusal rests for removable partial dentures is usually credited to Bonwill Darling (1959) wrote that research had shown that any damage of the surface zone of the enamel would render that surface very susceptible to caries. Seiden (1958) wrote that where dentine was exposed by grinding, caries could be minimised by polishing, the use of caries inhibiting agents and good oral hygiene. Krol (1973) said that where dentine was exposed in rest preparation, the preparation should be deepened and modified for gold foil, amalgam or other restoration. 86
  87. 87. Rests in posterior teeth Occlusal rests should be prepared with a no. 4 round bur or diamond bur of approximately the same size. For larger teeth, a slightly larger round bur may be used.  Start the bur in the floor of the fossa and make a cut about one half the depth of the bur. Extend the cut the same depth along the facial wall of the rest seat and over the marginal ridge  Repeat the procedure for the lingual wall of the fossa to make an inverted V-shape of the remaining marginal ridge  Observe the cuts from the proximal surface to determine the depth of the cut 87
  88. 88.   When the cut is at the desired depth, remove the enamel left between the 2 cuts to form the base of the rest preparation. Blend the outside edges of the bur cuts with the contours of the occlusal surface to eliminate undercuts Flare the cuts slightly as they cross the facial and lingual aspects of the marginal ridge 88
  89. 89.   Verify the depth of the rest preparation by having the patient close on a small piece of red utility wax placed over the preparation. Remove the wax and measure the depth of the preparation with a thickness gauge made to measure wax. (The most critical dimension is the amount of reduction over the marginal ridge. The wax may also disclose undercuts in the preparation if any are present.) Round the marginal ridge to eliminate any sharp angles. 89
  90. 90. Dimensions of rest seat preparations The shape and dimensions of rest seat preparations in anterior teeth seem to have been governed by clinical experience. Most authors state that forces should be directed down the long axes of the abutment teeth. In posterior teeth, this was achieved by making the rest seat deeper towards the centre of the tooth (Zarb et al 1978; Henderson and Steffel 1981; Miller and Grasso 1981). Henderson and Steffel (1981)suggested that rest seats should be 2.0-2.5 mm in width. Perry (1956) and Miller and Grasso (1981) related dimensions to tooth size and said that the width of a rest should be equal to one half of the distance between lingual and buccal cusp tips whereas Glann and Appleby (1960) said that the width should be equal to one-third of the buccolingual width of the tooth. Glann and Appleby (1960) also wrote that a rest seat preparation should be a triangular saucer-like depression 1.0-1.5 mm deep. Miller and Grasso (1981) said that rest seats should provide ample strength by being wide and 90 comparatively thin, rather than being narrow and thick.
  91. 91. Occlusal Rest Preparation in Enamel The outline form of an occlusal rest seat is basically triangular, with the base of the triangle at the marginal ridge and the apex pointing toward the center of the tooth. The apex of the triangle should be rounded as, should all external margins of the preparation. The outline form of the occlusal rest essentially follows the shape of the mesial or distal fossa of the surface of the tooth in which the rest is prepared . 91
  92. 92. An occlusal rest must be at least 1 mm thick at its thinnest point if chrome alloy is used for the framework, 1.5 mm if gold is to be used. The extension of the rest seat preparation should vary from one-third to one-half the mesiodistal diameter of the tooth, seldom less than 3 mm. The buccolingual extent should be half the distance between the buccal and lingual cusp tips. The floor of the occlusal rest seat must be inclined toward the center of the tooth and must be spoon shaped. 92
  93. 93. Occlusal Rest Seat Preparation In Existing Gold Restorations There will be times when a removable partial denture is indicated for a patient who has cast restorations on teeth that must serve as abutments for the prosthesis. Although it would be easier and more accurate to replace these restorations with ones specifically designed and prepared for the new prosthesis, economically it would not be in the patients best interest. The greatest problem arises in developing adequate rest seats Patients must always be thoroughly warned of the possibility of needing to replace existing restorations before mouth preparation. If an existing crown, onlay, or inlay is penetrated during the rest seat preparation, the restoration must be replaced. 93
  94. 94. Occlusal Rest Seat Preparation In Amalgam Restorations An occlusal rest preparation in a multi surface amalgam restoration is less desirable than that in either sound enamel or a gold restoration . Amalgam alloy tends to flow when placed under constant pressure. Care must be taken not to weaken the proximal portion of the amalgam restoration at the isthmus during the preparation. This may result in fracture during function. 94
  95. 95. Rest Seat Preparation For Embrasure Clasp This preparation extends over the occlusal embrasure of two approximating posterior teeth, from the mesial fossa of one tooth to the distal fossa of other. There is probably more difficulty encountered in making this preparation correctly than with any of the others. The main problem is failure to remove sufficient tooth structure over the buccal slopes of the preparation. Insufficient tooth removal will generally lead to occlusal interferences between the metal of the clasp and the opposing cusps. Relieving the metal to gain occlusal freedom ultimately leads to breakage of the clasp during function. Repair of the embrasure clasp is usually difficult. 95
  96. 96. The occlusal clearance may be checked by laying two pieces of I8-gauge wire side by side across the preparation. The patient should be able to close without contacting the metal. A normal verification of space available should be made by making an impression with red utility wax and measuring the thickness of the wax with a Boley gauge. As the preparation passes over the buccal and lingual embrasures, It should be approximately 1.5 to 2 mm wide and 1 to 1.5 mm deep. The buccal inclines of the preparation must be rounded after the preparation is complete. 96
  97. 97. Rest Seat Preparation On Anterior Teeth An occlusal rest on a molar or a premolar is preferred over a lingual or an incisal rest on anterior teeth to provide support for a partial denture. Forces are better directed down the long axis of the abutment tooth by an occlusal rest than by a lingual or incisal rest. A canine is preferred over an incisor for support of a denture. When a canine is not present, multiple rests on incisor teeth are needed in place of a single rest on a single incisor tooth. A lingual rest is preferred to an incisal rest. 97
  98. 98. Lingual Rest Seat preparation In Enamel A lingual rest seat may be prepared in the enamel surface of an anterior tooth if the tooth is sound, the patient practices good oral hygiene, and the caries index is low. The cingulum should also be prominent to present a gradual slope to the lingual surface rather than a steep vertical slope. This is the principal reason why mandibular canines are poor candidates for a lingual rest. The lingual surface of the tooth normally has too great a vertical slope to permit the rest seat to be prepared without penetrating into dentin. In some instances a lingual rest can be placed on maxillary central incisors that have prominent cingulum. but most, often this is a compromise effort unless it is placed in a cast restoration. 98
  99. 99. The lingual rest can be prepared nearer the center of the tooth, preventing the tipping action that an incisal rest may produce. Lingual rests are also more acceptable esthetically and less subject to breakage and distortion. The most satisfactory lingual rest from the stand-point of support is one that is placed on a prepared rest seat in a cast restoration. This should be used wherever possible. A lingual rest on a cast restoration may be used on any anterior tooth, either maxillary or mandibular. A lingual rest prepared in a enamel surface should be used primarily on maxillary canines and on a limited number of maxillary incisor teeth. 99
  100. 100. The outline form of lingual rest is half-moon shaped. It should form a smooth curve from one marginal ridge to the other, crossing the center of the tooth incisally to the cingulum. The rest seat itself is V-shaped. The labial incline of the lingual surface of the tooth makes up one wall and the other wall of the V-shaped notch starts at the top of the cingulum and inclines linguogingivally toward the center of the tooth to meet the other wall of the preparation 100
  101. 101. Lingual rest seat preparation in cast restorations If a cast restoration is to be placed on abutment tooth, the rest seat should be carved in the wax pattern and not cut in the cast restoration. A definite rest seat thus developed will direct the forces of occlusion through the long axis of the abutment tooth. 101
  102. 102. Incisal Rest Seat Preparation. Incisal rest seats should be used only on enamel surfaces. If a cast restoration is planned for the abutment tooth a lingual rest seat should be included in the restoration. Although incisal rests are the least desirable rests for anterior teeth, they may be used successfully on select patients if the abutment tooth is sound. The incisal rest seat is usually placed near one of the incisal angles of canines. If the incisal rest is used in conjunction with a circumferential clasp, the rest should be placed at the distal incisal angle. If the rest is used in conjunction with a vertical projecion or bar clasp that uses a distal buccal undercut for retention, the preparation should be made at the mesial incisal angle. In this position the mesial incisal rest will reciprocate the action of the bar clasp more effectively than if it were 102 positioned at the distal incisal angle.
  103. 103. Although the incisal rest may be used on maxillary canines, it is not the rest of choice for that tooth because too much must be sacrificed in esthetics and in mechanical advantage. On incisor teeth an incisal rest is usually used as a last resort to stabilize the removable prosthesis. The prognosis for these teeth is usually poor. 103
  104. 104. Summary The benefits of careful planning, designing, and executing mouth preparations are substantial. Properly prepared rest seats and accurately fitting rests will direct the forces of mastication so that the teeth and the partial denture will mutually support each other. Properly balanced and distributed forces can contribute to enhanced longevity of both the remaining oral structures and the restoration. The principles presented in this seminar can result in saving considerable chair time in seating the framework and completed removable partial denture. They can provide more comfort for the patient by reducing repeated procedures and follow-up appointments. Finally, they can ensure a predictable, favorable prognosis for the restoration. 104
  105. 105. Brief outline of the seminar Relief of pain and infection Oral surgical preparation, Conditioning of abused and irritated tissue, Periodontal preparation, and Preparation of abutment teeth. 105
  106. 106. Oral surgical preparation Extractions Removal of Residual Roots Impacted Teeth Malposed Teeth Cysts and Odontogenic Tumors Exostoses and Tori Hyperplastic Tissue Bony Spines and Knife-Edge Ridges Polyps, Papillomas, and Traumatic Hemangiomas Hyperkeratoses, Erythroplasia, and Ulcerations Dentofacial Deformity Osseointegrated Devices Augmentation of Alveolar Bone 106
  107. 107. Conditioning of abused and irritated tissue Periodontal preparation Removal and control of all etiological factors Elimination of, or reduction in, pocket depths Establishment of functional atraumatic occlusal relationships and tooth stability Development of a personal plaque control program and definitive maintenance schedule 107
  108. 108. Preparation of abutment teeth 1.Correction of Occlusal Plane Enameloplasty Onlay Crowns Endodontics with Crown or Coping Extraction Surgery 2.Correction of Malalignment Orthodontic Realignment Crowns Enameloplasty 3. Provision of support for weakened teeth Removable Splinting Fixed splinting Overdenture Abutments 108
  109. 109. 4.Reshaping Teeth Enameloplasty a) b) c) Enameloplasty to Develop Guiding Planes Enameloplasty to Change Height of Contour Enameloplasty to Modify Retentive Undercuts Inlays, Onlays and Crowns 5.Occlusal rest seat preparation 6.Lingual or incisal rest seat preparation 109
  110. 110. THANK YOU 110