Mouth preparation for removable partial dentures /certified fixed orthodontic courses by Indian dental academy


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Mouth preparation for removable partial dentures /certified fixed orthodontic courses by Indian dental academy

  3. 3. DEFINITION Mouth preparations are identified as those procedures that are accomplished to prepare the mouth for reception of prosthesis. RENNER BOUCHER
  4. 4. More specifically they are the procedures that change or modify existing oral structures of conditions to    Facilitate placement and removal of prosthesis Facilitate its efficient physiologic function Enhance its long term success
  5. 5.  Mouth preparation follows preliminary diagnosis and development of tentative treatment plan.
  6. 6. OBJECTIVES IN PLANNING MOUTH PREPARATIONS FOR REMOVABLE PARTIAL DENTURES      To establish a state of health in the supporting and contiguous tissues To eliminate interferences or obstructions to the placement, removal and function of prosthesis To establish an acceptable occlusal scheme To establish an acceptable occlusal plane To alter natural tooth form to accommodate requirements of form and function of prosthesis
  7. 7.          Mouth preparation procedures are classified into Prosthodontic procedures which includes Procedures related to Occlusion Restorative dentistry (fixed partial dentures) Non prosthodontic procedures which includes Oral surgery Orthodontics Periodontics endodontics
  8. 8. Classification
  9. 9. Mouth preparation Non prosthodontic procedures Prosthodontic procedures •Procedures related to Occlusion •Restorative dentistry (fixed partial dentures) •Oral surgery •Orthodontics •Periodontics •Endodontics
  10. 10. PLANNING MOUTH PREPARATIONS       Thorough examination of patient including familial, general health and dental histories Thorough examination of oral structures including vitality testing, mobility records and periodontal evaluation A complete roentgenographic survey Making accurate diagnostic casts and mounting them on a suitable dental articulator in centric relation Diagnosis and evaluation of data gathered from examinations Surveying diagnostic casts
  11. 11.   The formation of an orderly, sequential treatment outline to meet patients specific needs this outline includes design of removable partial denture As the final design of removable partial denture evolves the need for specific mouth preparations is identified and recorded in an appropriate manner
  12. 12. RECORDING MOUTH PREPARATIONS   As mouth preparations must be accomplished before the impressions are made and removable partial denture is constructed there is often a considerable time lapse between the examination, diagnosis and treatment planning actual commencement of mouth preparations and construction of removable partial denture. Hence it is necessary to determine and record which mouth preparations must be accomplished before and during the removable partial denture phase of therapy
  13. 13.   Method of recording, listing or charting mouth preparations will depends on needs and desires of individual dentist Record can be placed in patients chart and become permanent part of patients record
  14. 14. RECORDING MOUTH PREPARATIONS ON DIAGNOSTIC CAST     Technique for recording mouth preparations on diagnostic cast is usually executed in a red pencil to identify the mouth preparations to be accomplished Teeth to be extracted are marked with an X Some dentists prefer to remove dental stone teeth from diagnostic cast and identify the extraction site with an X Areas of bony and soft tissue recontouring are outlined with closely spaced parallel lines or shaded with a red pencil
  15. 15.  Tooth structures to be altered are outlined or shaded including those areas necessary to prepare rest seats, guiding planes ,modification of survey lines, occlusal refinements and removal of interferences
  16. 16.
  18. 18. ADVANTAGES OF LISTING OR CHARTING MOUTH PREPARATIONS    It assures completeness It provides a quick and convenient records of what has to be accomplished to prepare patient for reception of removable partial denture When the record is properly prepared it serves as a road map guiding the dentist through all of the procedures that must be accomplished in proper sequence and providing sufficient detail to enhance the accuracy of those procedures that are accomplished
  19. 19.   It serves as a legal record as to the thoroughness of mouth preparations and of treatment plan It virtually ensures that all procedures will be executed in proper sequence before making impression for master cast is made since it leaves nothing to memory
  20. 20. TERM          ABBREVATION Survey line Guiding plane Interference Occlusal rest Incisal rest Incisal hook rest Cingulum rest Facial Lingual SL GP INT OR IR IHR CR F L
  21. 21. TERM        ABBREVATION Mesial Distal Line angle Raise survey line Lower survey line Reduce cusp tip Selectively grind M D LA RSL LSL RCT SG
  22. 22. SEQUENCE OF PROCEDURES TO BE FOLLOWED DURING MOUTH PREPARATIONS       Oral surgical preparation Periodontal preparation Orthodontic considerations Endodontic therapy Restorative dentistry Preparation of abutment teeth
  23. 23.    All preprosthetic surgical treatments for 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 accomplished during same time frame The longer the interval between surgery and impression procedure the more complete the healing and consequently more stable the denture bearing area
  24. 24. ORAL SURGICAL PREPARATION   EXTRACTIONS Extraction of non strategic teeth that would present complications or those that may be detrimental to design of partial denture is a necessary part of overall treatment plan
  25. 25. REMOVAL OF RESIDUAL ROOTS   All retained roots or root fragments should be removed particularly if they are in close proximity to the tissue surface or if there is evidence of associated pathologic finding Residual roots adjacent to abutment teeth may contribute to progression of periodontal pockets
  26. 26. IMPACTED TEETH    All impacted teeth including those in edentulous areas as well as those adjacent to abutment teeth should be removed Asymptomatic impacted teeth in elderly that are covered with bone with no evidence of pathologic condition should be left to preserve arch morphology If an impacted tooth is left it should be recorded in patients record and patient should be informed of its presence.`
  27. 27. TISSUE REACTIONS TO WEARING OF PROSTHESIS PALATAL PAPILLARY HYPER PLASIA  It is a lesion of mucosa that occurs more often on hard palate but may extend onto residual ridges  It is associated with poorly fitting prosthesis that has been worn for prolonged periods generally 24 hours per day  It is also associated with inadequate oral and prosthesis hygiene  Tissue conditioning and tissue rest may help to resolve some of the edema and inflammation but only surgery will eliminate the papillae
  28. 28. EPULIS FISSURATUM  It is a tumour like hyperplastic growth caused by an ill fitting or over extended border of a removable prosthesis  A relatively soft epulis may resolve if irritation is removed  The offending border should be adjusted until it is completely out of contact with lesion  Fibrosed epulis should be removed surgically
  29. 29.      DENTURE STOMATITIS It is characterised by generalised erythema including all the tissues covered by prosthesis Oral mucosa is swollen and inflammed Patient complains of burning or itching and pain It is caused by trauma from occlusion, poor fit of prosthesis, poor oral hygiene and continuous wearing of prosthesis Complete tissue rest and tissue conditioning procedures are effective in treating this condition
  30. 30.     CYSTS AND ODONTOGENIC TUMOURS Panoramic roentgenograms of jaws are recommended to survey jaws for unsuspected condition When suspicious area appears on survey film periapical radiograph should be taken to conform or deny the presence of lesion All radiolucencies and radioopacities observed in the jaws should be investigated Dentist should confirm the diagnosis by performing the biopsy of the area and submit the specimens to oral pathologist for microscopic study
  31. 31.    EXOSTOSIS, TORI ,UNDERCUTS Exostosis and undercuts in residual ridge areas that prevents proper extension of denture borders should be surgically corrected. Torus palatinus is a benign slowly growing protruberance of palatine process of maxilla Removal of torus palatinus is not necessary unless it is so large that it interferes with design and construction of prosthesis
  32. 32.     Torus mandibularis is an exostoses occuring bilaterally on lingual surface of body of mandible Mandibular tori should be removed if patient is to wear removable partial denture with comfort Modification of denture design to accommodate for exostoses results in additional stress to supporting elements and compromised function hence their removal is recommended Mucosa covering bony protruberances is extremely thin and friable partial denture components in close proximity to this type of tissue may cause irritation and chronic ulceration
  33. 33.       Undercut areas may be minimized by changing path of insertion of removable partial denture Undercuts that would seriously compromise prognosis should be surgically removed Surgical correction of under cuts should be accomplished if relieving denture base or reducing length of denture border would Significantly reduce support and stability of prosthesis Create a bothersome food impaction area Cause a denture border to be so far away from underlying tissues that it may affect function, compromise esthetics or cause discomfort for the patient
  34. 34. BONY SPINES AND KNIFE LIKE RIDGES    Sharp bony spicules should be removed and knife like crest gently rounded These procedures should be carried out with minimum bone loss If correction of knife edge alveolar crest results in insufficient ridge support for denture base dentist should consider vestibuloplasty
  35. 35. MUSCLE ATTACHMENTS AND FRENA    As a result of alveolar bone height muscle attachments may insert on or near alveolar crest Mylohyoid, buccinator, mentalis,genioglossus muscles are likely to introduce these problems Repositioning muscle attachments will enhance comfort and function of removable partial denture
  36. 36.     Maxillary labial frenum presents problem when anterior teeth are replaced with a removable partial denture If the frenum is attached near crest of ridge or if it is hypertrophic notch that must be placed in denture base to accommodate frenum it may be unsightly Hypertrophic lingual frenum can greatly compromise the rigidity and placement of major connector Frenectomy is done to correct these conditions
  37. 37.   All abnormal soft tissue lesions like polyps papillomas should be excised and submitted for pathologic examination before fabrication of removable partial denture All abnormal white, red or ulcerative lesions should be recognized and properly evaluated through biopsy
  38. 38.    Augmentation of alveolar bone with use of autogenous or alloplastic materials Use of osseointegrated devices (implants) Implants are placed using clean and controlled surgical procedures and are allowed to heal before surgical exposure and fabrication of dental prosthesis
  39. 39. PERIODONTAL PREPARATION OBJECTIVES OF PERIODONTAL THERAPY  Removal and control of all etiologic factors contributing to periodontal disease  Elimination or removal of all pockets with establishment of healthy gingival sulci  Establishment of functional and non traumatic occlusal relationships and tooth stability  Development of personalized plaque control programme and definitive maintainence schedule
  40. 40.   After a thorough examination of periodontium complete periodontal charting that include pocket depths, assessment of attachment levels, furcations, mucogingival problems and tooth mobility should be performed Extent of periodontal destruction must be determined by use of radiographs
  41. 41.       EXAMINATION FINDINGS`THAT INDICATE POSSIBLE NEED FOR PERIODONTAL TREATMENT INCLUDE THE FOLLOWING Pocket depth In excess of 3mm Furcation involvement Deviations from normal color and contours in gingiva indicating gingivitis Marginal exudate Potential abutment teeth with less than 2mm of gingiva
  43. 43. INITIAL DISEASE CONTRL THERAPY      Oral hygiene instructions Scaling and root planing is done for removal of calculus and plaque deposits from coronal and root surfaces of teeth Elimination of local irritating factors other than calculus like overhanging margins of amalgam alloy and inlay restorations Overhanging crown margins Open contacts leading to food impaction
  44. 44.     Elimination of gross occlusal interferences Selective grinding is procedure generally applied and coronal reshaping of teeth is done to produce simultaneous occlusal contacts or harmonizing cuspal relations Deflective contacts in centric path of closure are removed Balancing side or non chewing side interferences which are usually most destructive should be eliminated
  45. 45. CLINICAL SYMPTOMS OF TRAUMATIC OCCLUSION ARE    Excessive wear of teeth which may include chipping or fracture of teeth A change in loss of supporting structures which may include increased tooth mobility ,tooth migration and pain during and after occlusal contact Involvement of neuromuscular mechanism of temporomandibular joint which may include muscle spasm, muscle pain and joint symptoms
  46. 46. RADIOGRAPHIC SIGNS OF TRAUMATIC OCCLUSION ARE     Widening of periodontal ligament space with either thickening or loss of lamina dura Periapical or furcation radioluscency Resorption of alveolar bone Root resorption
  47. 47.    Extensive occlusal equilibration should never be initiated on a patient with temporomandibular joint dysfunction the symptoms and muscle spasm should be eliminated through the use of occlusal splint before occlusal adjustment is initiated The mere presence of occlusal abnormalities in the absence of demonstrable pathologic change associated with occlusion does not contribute indication for selective grinding Indication of occlusal adjustment is based on presence of pathologic condition
  48. 48.   If decision is made to equilibrate the occlusion it should be done before any definitive restorative procedures It is beneficial to perform occlusal equilibration on duplicate set of diagnostic casts to determine whether equilibration is feasible this serves as a blue print for selective grinding in mouth if the sequence of grinding is recorded
  49. 49. SPLINTING OF PERIODONTALLY WEAKENED TEETH REMOVABLE SPLINTING  Most patients who have periodontally weakened teeth are in their fourth, fifth or sixth decade of life and have major medical problems that contraindicate extensive treatment necessary for multiple fixed prosthesis are considered for removable splinting  Splint type guide plane removable partial denture continuous loop removable splint can be used
  50. 50. FIXED SPLINTING    It is done when an individual tooth or two adjoining teeth may have lost some periodontal support as a result of local conditions Fixed splinting must be accomplished with full or partial coverage crowns soldered together Splinting of periodontally weakened teeth in partially edentulous arch maintains continuity of arch avoids additional modification spaces simplifying construction and fitting of partial denture and improving prognosis
  51. 51. NIGHT GUARD    It is removable acrylic resin splint designed as an aid in eliminating deleterious effects of nocturnal clenching and grinding They may act as temporary splints if worn at night when partial denture has been removed Night guard is useful before fabrication of partial denture when one of abutment teeth has been unopposed for an extended period as night guard returns some functional stimulation to tooth periodontal ligament changes are reversed
  52. 52.
  53. 53. DEFINITIVE PERIODONTAL SURGERY GINGIVECTOMY :  It is indicated to eliminate supra bony pockets  Pocket depth confined to band of attached gingiva  PERIODONTAL FLAP PROCEDURES :  They may be used to perform osseous recontouring  Osseous recontouring may be indicated for pocket elimination, when crown lengthening is needed
  54. 54. MUCOGINGIVAL SURGICAL PROCEDURES :  They are considered when an abutment tooth for a removable partial denture lacks adequate attached keratinized gingiva and requires root coverage to facilitate partial denture construction and maintenance
  55. 55. RECALL MAINTANENCE   Frequency of recall appointments depends on susceptibility and severity of periodontal disease Patients with previous moderate to severe periodontitis should be placed on 3 to 4 months recall system
  56. 56. ADVANTAGES OF PERIODONTAL THERAPY    Elimination of periodontal disease removes primary etiologic factor in tooth loss Periodontium free of disease presents a much better environment for restorative correction Response of teeth to periodontal therapy provides an important opportunity for reevaluating their prognosis before final decision is made to include or exclude them in partial denture design
  57. 57.  Through periodontal surgical techniques environment of potential abutment teeth may be altered to point of making an otherwise unacceptable tooth to most satisfactory retainer for a partial denture
  58. 58.
  59. 59. ORTHODONTIC CONSIDERATIONS  Loss of individual tooth or groups of teeth may lead to extrusion, mesial drifting orthodontic appliances are used for correction
  60. 60. CORRECTION OF OCCLUSAL PLANE     Occlusal plane in most partially edentulous patients will be uneven Teeth that have been unopposed for a time tend to over erupt Maxillary molars if not opposed tend to migrate downward carrying bony tuberosity along in this condition surgery is indicated to reduce height of bone If space is extremely limited between overerupted teeth and opposing ridge a thin metal casting may be designed to cover the ridge in place of acrylic resin denturebase
  61. 61.
  62. 62. CLASSIFICATION OF SUPER ERUPTED TEETH    A class 1 super erupted teeth poses no appreciable problems in positioning the prosthetic replacement teeth in opposing dental arch and has no potential for creating occlusal trauma hence no treatment is needed A class 2 extruded posterior teeth poses definite problems of moderate magnitude that can be successfully managed by enameloplasty A class 3 extruded posterior teeth poses moderately severe problems that cannot be successfully managed without altering tooth to degree that enamel is penetrated thus requiring placement of restoration
  63. 63.     In class 3 (E) the degree of tooth reduction needed will cause pulpal exposure necessitating endodontic therapy in addition to complete cast crown restoration In class 4 tooth is severely extruded if tooth is considered non essential to success of removable partial denture it may be extracted A class 4 (E) extruded tooth is considered nonessential for retention but essential for support in eliminating a distal extension situation it may be treated endodontically and used as an overdenture abutment In class 4 (O) when the extruded teeth are considered to be essential for bracing ,retention and support of removable partial denture surgical orthodontics might be considered for repositioning teeth and alveolus
  64. 64.  In class 5 extruded teeth poses moderate to moderately severe problems relative to ideal plane of occlusion and space relation but cause no occlusal trauma because of their location in dental arch shortening of cusp tips by means of selective grinding is satisfactory to provide acceptable interarch space
  65. 65.   In case of infra erupted teeth lengthening of clinical crown is done to restore occlusal plane it is done by orthodontic treatment or placement of cast onlays or crowns Tipped molars also present problems in establishing harmonious occlusal plane treatment is to upright the teeth orthodontically if it is not possible occlusal plane may be reestablished by using crowns or inlays
  66. 66. ENDODONTIC THERAPY    A tooth with pulpal involvement or root end pathology may be considered a candidate for endodontic therapy USE OF PULPLESS TEETH AS AN ABUTMENT It is considered when pulpless teeth that has been treated endodontically is presented as a potential abutment in mouth of patient for whom a removable partial denture is to be made A potential abutment with an infected pulp is present in mouth of a candidate for partial denture
  67. 67.     A tooth that has been serving as an abutment for prosthesis that has developed pulpitis must be treated either endodontically or extracted TREATED PULPLESS TEETH To use them as abutment teeth they should satisfy same criteria used for teeth with normal healthy pulp Canals have been filled to apex with what appears radiographically to be well condensed filling material There is no radioluscency at apex tooth has been asymptomatic clinically since the therapy was accomplished
  68. 68.     INFECTED TEETH When this teeth are important to design of partial denture feasibility of endodontic therapy should be considered this should satisfy certain criteria like Access to canals If apicoectomy is needed if its apex is in maxillary sinus then tooth becomes poor candidate for endodontic therapy If apicoectomy is performed will it create an unfavorable crown root ratio
  69. 69. ABUTMENT TOOTH WITH PULPITIS      If tooth develops pulpitis while serving actively as an abutment for prosthesis several factors must be considered with regard to treatment Endodontic treatment should be considered only when abutment tooth with pulpitis is healthy from periodontal stand point Crown root ratio is favorable When prosthesis itself is satisfactory When mouth as a whole is in a state of good health and repair
  70. 70. RESTORATIVE DENTISTRY   It should be integrated with endodontic treatment when this type of therapy is part of treatment plan All restorative work including crowns , inlays and onlays should be programmed to contribute to restoration of best possible occlusal plane
  71. 71.   Caries lesions should be treated with suitable restorations Any defective restorations (restorations with broken contacts ,overhanging margins) should be repaired and replaced
  72. 72. PREPARATION OF ABUTMENT TEETH   Abutment is a tooth ,a portion of a tooth or that portion of implant that serves to support and retain a prosthesis After surgery ,periodontal treatment, endodontic treatment and tissue conditioning of arch involved abutment teeth may be prepared to provide support, stabilization and retention for partial denture
  73. 73. OBJECTIVES OF ABUTMENT TEETH PREPARATION     To prepare teeth that are to be clasped so that occlusal rest directs stress along long axis of tooth Recontouring of teeth when an altered contour will eliminate an interference or otherwise contribute to better design To create retention by simple alteration procedure To allow placement and removal of prosthesis without having it transmitting wedging or torsional types of stress against teeth with which it comes in contact
  74. 74. CLASSIFICATION OF ABUTMENT TEETH    Abutment teeth that require only minor modifications to their coronal portions Abutment teeth that are to have restorations other than complete coverage crowns Abutment teeth that are to have crowns
  75. 75. SEQUENCE OF ABUTMENT PREPARATIONS ON SOUND ENAMEL OR EXISTING RESTORATIONS    Proximal surfaces parallel to path of placement should be prepared to provide guiding planes Tooth contours should be modified lowering height of contour so that Origin of clasp arms may be placed well below occlusal surface preferably at the junction of middle and gingival third
  76. 76.    Retentive clasp terminals may be placed in gingival third of crown for better esthetics and better mechanical advantage Reciprocal clasp arms may be placed on or above height of contour Occlusal rest areas should be prepared that will direct occlusal forces along long axis of abutment tooth
  77. 77.  Proposed changes to abutment teeth should be made on diagnostic cast and outlined in red pencil to indicate area, amount of modification to be done
  78. 78.
  79. 79. PREPARATION OF GUIDING PLANES  Guiding planes are vertically parallel surfaces on abutment teeth oriented so as to contribute to the direction of the path of placement and removal of a removable partial denture
  80. 80.    The diagnostic cast mounted on surveying table at the tilt at which design of removable partial denture was drawn should be available at mouth preparation appointment It should be placed on table in front of patient and hand piece with appropriate diamond instrument in place positioned over the cast so that relation ship of hand piece and diamond stone to tooth can be visualized This same relationship can then be duplicated in patients mouth this ensures that guiding plane will be parallel to planned path of insertion
  81. 81.     A cylindric diamond point is generally the instrument used to make preparation A gentle light sweeping stroke from buccal line angle to lingual line angle should be used Flat surface created should be 2 to 4mm in occlusogingival height the reduction should follow curvature of surface so that uniform amounts of enamel are removed throughout buccolingual width of preparation All prepared tooth surfaces must be polished when contouring is complete
  82. 82.
  83. 83.
  84. 84. GUIDING PLANES ON ABUTMENT TEETH ADJACENT TO DISTAL EXTENSION EDENTULOUS SPACES   In these cases occluso gingival height of guiding plane is reduced to 1.5 to 2mm to permit partial denture to rotate slightly around distal occlusal rest as downward force occurs on artificial teeth The slight movement allows release of denture from guiding plane there by avoiding torquing or twisting forces on abutment tooth
  85. 85. GUIDING PLANES ON LINGUAL SURFACES OF ABUTMENT TEETH   The purpose is to provide maximum resistance to lateral stress Occluso gingival height of guiding plane is 2 to 4mm the plane ideally should be located in the middle third of clinical crown of tooth
  86. 86. GUIDING PLANES ON ANTERIOR ABUTMENT TEETH    Guiding planes on anterior teeth adjacent to edentulous spaces provides parallelism needed to ensure stabilization, minimize wedging action between teeth ,decrease undesirable space between denture and abutment teeth Special purpose is to increase or restore normal width of edentulous space as anterior teeth are lost and replacement teeth not provided immediately teeth adjacent to space will drift and tip into space Both actions reduce the size of space and make the esthetic replacement of missing teeth difficult
  87. 87.     Teeth that have tipped towards an edentulous space will exhibit a large undercut area below height of contour on proximal surface If height of contour is not reduced as guiding planes are established the undercut will appear as a large unsightly space between artificial tooth and restored tooth The space not only detracts from esthetic value of denture but also traps food If sufficient tooth structure cannot be removed to restore the space and reduce the undercut without penetrating the enamel layer a restoration must be planned
  88. 88. ENAMELOPLASTY TO CHANGE HEIGHT OF CONTOUR    Height of contour is changed most frequently to provide better positions for clasp arms or lingual plating Retentive clasp arm should be located no higher on crown of abutment tooth than function of gingival and middle thirds This position not only enhances esthetic quality of clasp but also provides mechanical advantage
  89. 89.     In maxillary arch molars and premolars if unsupported tend to tip in buccal direction this causes height of contour to be near occlusal surface on facial side of abutment tooth In mandibular arch molars and premolars if unsupported tip lingually this causes problems with positioning of reciprocal clasps and lingual plating If tipping is severe it causes problems in placement of lingual bar major connector Height of contour is best lowered by tapered diamond stones
  90. 90.   The amount of correction that can be accomplished by recontouring the enamel surface is limited by thickness of enamel If dentin is exposed restoration must be placed to protect the tooth
  91. 91.
  92. 92. ENAMELOPLASTY TO MODIFY RETENTIVE UNDERCUTS    Contouring the enamel surface to produce retentive undercut to be successful buccal and lingual surfaces of teeth must be nearly vertical `if both surfaces have a pronounced slope procedure is contraindicated If surface to receive undercut is sloped indentation would have to be excessively deep to be effective
  93. 93.      If opposing surface is sloped reciprocal arm could not brace the tooth sufficiently to prevent retentive clasp tip from being dislodged from undercut Retentive undercut must be created in the form of gentle depression it is prepared by using small round end tapered diamond stone The end of stone is moved in anteroposterior direction near line angle of tooth Preparation is made parallel to and as close as possible to gingival margin without encroaching on gingival crevice Depression should be 4mm in mesiodistal length and 2mm in occlusogingival height
  94. 94.
  95. 95. PREPARATION OF REST SEAT   Rest seat is prepared recess in a tooth or restoration created to receive the occlusal ,incisal, cingulum or lingual rest Rest is component of partial denture that is placed on an abutment tooth ideally in prepared rest seat so that it limits movement of denture in a gingival direction and transmits functional forces to tooth
  96. 96.     Outline form of occlusal rest seat is triangular with base of triangle at marginal ridge and apex towards centre of tooth An occlusal rest must be at least 1mm thick at its thinnest point if chrome alloy is used 1.5mm if gold is to be used Extension of occlusal rest seat preparation should vary from one third to one half the mesiodistal diameter of tooth Bucco lingual extent should be half the distance between buccal and lingual cusp tips
  97. 97.     Floor of occlusal rest must be inclined towards centre of tooth must be spoon shaped The enclosed angle formed by inclination of floor of rest and vertical projection of proximal surface of tooth must be less than 90 degrees so occlusal forces can be directed along vertical axis Occlusal rest seats in enamel should be prepared with round diamond stone First a channel of correct depth and at desired outline of preparation is created by using small round diamond stone to lower marginal ridge at either buccal or lingual extent of rest seat to continue inward towards centre of tooth and to return to marginal ridge
  98. 98.   Island of enamel that remains with in outline form can be removed with same diamond stone so that sufficient tooth structure is removed to provide the thickness of metal required for strength of rest Deepest portion of rest seat is towards centre of tooth preparation raises gradually towards marginal ridge it is called positive rest located in fossa area away from marginal ridge it is concave area it should be 0.5 to 1.0mm deeper than general base of rest seat.
  99. 99.
  100. 100.
  101. 101.
  102. 102.      Adequacy of occlusal rest seats can be checked before impression of master cast is made by Visual inspection Direct tactile contact By making imprints in red utility wax By making impression to create a diagnostic cast
  103. 103. OCCLUSAL REST SEAT PREPARATON IN EXISTING GOLD RESTORATION     It should always be placed in wax pattern after establishment of guiding planes After preparation for restoration is complete it is helpful to add a depression to preparation to accommodate depth of occlusal rest Rest seat can be carved with suitable wax instruments The anatomy of rest seat must not be destroyed during polishing procedure
  104. 104. OCCLUSAL REST SEAT PREPARATION IN EXISTING GOLD RESTORATION  If existing restoration display marginal integrity and occlusalharmony attempt should be made to contour them to satisfy requirement of proposed prosthesis
  105. 105. OCCLUSAL REST SEAT PREPARATION IN AMALGAM RESTORATION     Occlusal rest seat preparation in a multi surface amalgam restoration is less desirable as amalgam alloy tends to flow when placed under constant pressure Care must be taken not to weaken proximal portion of amalgam restoration at isthmus during preparation This may result in fracture during function Rest seats are prepared using no.4 round bur.
  106. 106. REST SEAT PREPARATION FOR EMBRASSURE CLASP    This preparation extends over occlusal embrassure of two approximating posterior teeth from mesial fossa of one tooth to distal fossa of other tooth Main problem with this preparation is failure to remove sufficient tooth structure over buccal slopes of preparation it leads to occlusal interferences between metal of clasp opposing cusps Relieving metal to gain occlusal freedom leads to breakage of clasp during function
  107. 107.     Small round diamond stone is used to establish outline form for normal occlusal rest in each of approximating fossae The contact point between the teeth should not be broken because a wedging action and food impaction between teeth may take place The same diamond stone is used to carry buccal and lingual extensions of occlusal rests over buccal and lingual embrassures Cylindrical diamond stone held horizontally from buccal surfaces of teeth pointing towards lingual surface
  108. 108.     Stone is held against distal incline of buccal cusp of one tooth and mesial incline of buccal cusp of other tooth for creating occlusal clearance The patient should be able to close without contacting metal As preparation passes over buccal and lingual embrassures it should be 1.5-2mm wide and 1 -1.5mm deep Buccal inclines of preparation must be rounded after preparation
  109. 109.
  110. 110. LINGUAL REST SEAT PREPARATION      Outline form of lingual rest seat is half moon shaped It should form a smooth curve from one marginal ridge to other crossing centre of tooth incisally to cingulum Rest seat is v shaped Labial incline of lingual surface of tooth makes one wall other wall of v shaped notch starts at top of cingulum and inclines linguo gingivally towards centre of tooth to meet other wall of preparation Sharp lines and angles must be avoided because they will interfere with fit of framework of partial denture
  111. 111.
  112. 112. LINGUAL REST SEAT PREPARATION IN CAST RESTORATION     Lingual rest seat should be carved in wax pattern LINGUAL REST SEAT PREPARATION IN ENAMEL Lingual rest seat may be prepared in enamel surface of an anterior tooth if tooth is sound Cingulum also should be prominent to present a gradual slope to lingual surface rather than steep vertical slope
  113. 113.      This is why mandibular canines are poor candidates for lingual rest A safe side ¼ inch diamond disk should be used it must be held so that it is parallel or slightly inclined labial to path of insertion The cut with disk should start low on one marginal ridge pass over cingulum and then pass gingivally to contour opposite marginal ridge this will produce half moon shape When space is not available to permit use of disk flat end large diamond cylinder is best choice Rest seat must always be gingival to contact level of opposing tooth
  114. 114. INCISAL REST SEAT PREPARATION      It should be done on only enamel surfaces Incisal rest seat is usually placed near one of incisal angles of canines If incisal rest is used with circumferential clasp rest should be placed at distal incisal angle If rest is used in conjunction with bar clasp rest should be placed at mesio incisal angle Incisal rests are least desirable rests for anterior teeth
  115. 115.       On incisor teeth an incisal rest is used as last resort to stabilize removable partial denture the prognosis for these teeth is usually poor An incisal rest seat is begun with small safe side diamond disk held parallel to path of insertion First cut is made vertically 1.5 -2mm deep in form of notch and approximately 2 -3mm inside proximal angle of tooth A small flame shaped diamond point is used to complete the preparation The notch created by disk is rounded slightly but not to level of base of notch The enamel wall created by disk toward centre of tooth must be rounded with flame shaped diamond point
  116. 116.     Base of notch is also rounded with tip of flame shaped diamond the groove that results after notch has been completely rounded must be carried slightly over onto labial surface This projection onto facial surface provides a locking device to prevent the tooth from being tipped or moved facially The groove should be continued part way down the lingual surface as an indentation this indentation will help accommodate minor connector Incisal hook rest seat is prepared as a modification of incisal rest seat by extending preparation 1.5 -2mm onto labial surface of tooth as concave depression advantage of it is greater stability
  117. 117.
  118. 118. ABUTMENT TEETH PREPARATIONS USING CONSERVATIVE RESTORATIONS   Proximal and occlusal surface that support minor connectors and occlusal rests require modification in restoration when an inlay is restoration of choice for an abutment tooth The extent of occlusal coverage depends on extent of caries ,presence of unsupported enamel walls ,extent of occlusal abrasion and attrition
  119. 119.     To prevent buccal and lingual proximal margins from lying at or near minor connector or occlusal rests these margins must be extended well beyond line angles of tooth this may be accomplished by widening the conventional box preparation The margin of cast restoration produced may be quite thin and may be damaged by the clasp during placement and removal of partial denture This hazard may be avoided by extending outline of box beyond line angle Pulp is particularly vulnerable unless the axial wall is curved to confirm with external proximal surface of tooth
  120. 120.    Gingival rest should be placed where it can be easily accessed to maintain oral hygiene The proximal contour necessary to produce proper guiding plane surface and close proximity of minor connector render this area vulnerable to future caries attack Every effort should be made to provide restoration with maximum retention and resistence which can be obtained by preparing opposing cavity walls 5 degrees or less from parallel and producing flat floors and sharp clean restorations
  121. 121.
  122. 122. ABUTMENT PREPARATIONS USING CROWNS   Crowns may be in the form of three quarter complete coverage cast crowns, porcelain veneer crowns Ideal crown restoration for a partial denture abutment is complete coverage crown which can be carved ,cast and finished to ideally satisfy all requirements for support , stabilization and retention
  123. 123.    Three quarter crown does not permit creating retentive areas as does complete coverage crown If buccal or labial surfaces are sound and retentive areas are acceptable or can be made so by slight modification of tooth surfaces three quarter crown is conservative restoration of merit Regardless of type of crown used preparation should be made to provide appropriate depth for occlusal rest seat this is best accomplished by creating depression in prepared tooth at occlusal rest area
  124. 124. CONTOURING WAX PATTERNS   To contour wax pattern to desired configuration die of tooth preparation in a cast of remainder of arch must be analyzed on surveyor Working cast should be mounted on surveyor at the same tilt that diagnostic cast was mounted once correct tilt has been established wax knife is substituted for analyzing rod and guiding plane is carved in wax pattern by shaving the wax
  125. 125.      Height of contour of crown can also be determined by use of analyzing rod Pattern must be hand carved to place the height of contour on middle third of lingual surface if tooth is to receive a reciprocal clasp and at junction of gingival and middle third if retentive clasp has been planned Position and depth of retentive under cut can be verified by means of undercut gauge 0.010 inch undercut gauge will be used for most cast chrome clasps The measured undercut should fall at distal or mesial line angle of tooth depending on type of clasp that has been designed
  126. 126.
  127. 127. REFINING CAST RESTORATIONS     After casting has been made it should be finished carefully so that contour that was carved in wax pattern must be maintained Working cast with die and casting in position should be returned to surveyor before final polish of restoration is complete Guiding planes on casting and any changes in contouring of axial surfaces should be refined using surveyor as machining device by attaching hand piece holder to the vertical arm of surveyor and straight hand piece holder A straight cylinder mounted stone is used in hand piece to accomplish machining procedure
  128. 128. LEDGES ON ABUTMENT CROWNS   Complete coverage restorations on teeth used as partial denture abutments offers an advantage that is not obtainable on natural teeth this is crown ledge or shoulder which provides effective stabilization and reciprocation True reciprocation is not possible with a clasp arm that is placed on occlusally inclined tooth surface because it does not become effective until prosthesis is fully seated
  129. 129.    When a dislodging force is applied reciprocal clasp arm along with occlusal rest breaks contact with supporting tooth surfaces they are no longer effective As the retentive clasp flexes over height of contour and exerts horizontal force on abutment reciprocation is nonexistent just when it is needed most True reciprocation can be obtained only by creating path of placement for reciprocal clasp arm that is parallel to other guiding planes
  130. 130.     Here inferior border of reciprocal clasp makes contact with its guiding surface before retentive clasp on other side of tooth begins to flex Thus reciprocation exists during entire path of placement and removal Presence of ledge on abutment crown acts as a terminal stop for reciprocal clasp arm Ledge on abutment crown has still another advantage usual reciprocal clasp arm is half round and therefore convex when superimposed on tooth increases bulk of already convex surface reciprocal clasp arm built on a crown ledge is inlayed into crown and reproduces more normal crown contours
  131. 131.     The patients tongue then contacts continuously convex surface rather than projection of clasp arm Crown ledge may be used on any full or three quarter crown restored surface that is opposite the retentive side of abutment teeth it is used most frequently on premolars and molars Ledge should be placed at junction of gingival and middle thirds of tooth curving slightly to follow curvature of gingival tissues In forming crown ledge wax pattern is completed after proximal guiding planes,occlusal rests and retentive contours are formed ledge is carved with surveyor blade
  132. 132.  Full effectiveness of crown ledge can only be achieved when crown is returned to surveyor for refinement after casting
  133. 133.
  134. 134. SHAPING VENEER CROWNS   Resin and porcelain veneered crowns are used on abutment teeth that would otherwise display an objectionable amount of metal Veneer crowns must be contoured to provide suitable retention this means veneer must be slightly over contoured and then shaped to provide desired undercut for location of retentive clasp arm
  135. 135.    If veneer is of porcelain this procedure must precede final glazing If it is of resin it must precede final polishing If this step is neglected excessive or inadequate retentive contours may result
  136. 136. THANK YOU