1. MOUTH PREPARATION FOR REMOVABLE PARTIAL DENTURE
Presented by : Dr. Tehseen Zakir

2. CONTENTS Introduction Definitions
Objectives of mouth preparation in removable partial denture
Mouth preparation:
Relief of pain and infection
Oral surgical procedures
Conditioning of abused and irritated tissue
Periodontal therapy:
Oral hygiene instructions
Scaling & root planning
Provision of support for weakened teeth

3. Correction of occlusal plane Correction of malalignment
Abutment teeth preparation:
Reshaping teeth
Preparation of retentive areas for clasps in enamel
Inlays, onlays and crowns
Occlusal rest seat preparation
Rest seat preparation of anterior teeth
Conclusion
References

4. INTRODUCTION

5. Mouth preparation is fundamental to a successful removable partial denture prosthesis
It contributes to the philosophy: the prescribed prosthesis must not only replace what is missing, but also preserve the remaining tissue & structures that will enhance the prosthesis
Mouth preparation follows in logical sequence after oral diagnosis and tentative treatment planning
Final treatment planning may be deferred till the response to preparatory procedures can be ascertained

6. The extent of mouth preparation & the various procedures involved varies from person to person
Some patients might require minimal mouth preparation involving removal of interferences & preparation of rest seats
However a majority of the patients might require extensive treatment
It includes correction of occlusal plane, oral surgical preparation like extraction of non-restorable teeth, removal of tori or exostosis & preprosthetic surgeries

7. Periodontal preparation including oral prophylaxis, treatment of periodontal abscess etc. Also changes in gingival contour following periodontal treatment should be completed before working impressions are obtained
Orthodontic treatment, so that any required improvement in the position of the teeth can be achieved without delaying the prosthetic treatment unduly
Restorative treatment & root canal therapy to ensure that the remaining teeth are in a healthy state and preparation of abutment teeth so that the crown shape of the remaining teeth is improved to receive rests, retentive clasp arms, bracing & reciprocating elements

8. DEFINITIONS

9. GUIDING PLANES (GPT 8) :
Vertically parallel surfaces on abutment teeth or/and dental implant abutments oriented so as to contribute to the direction of the path of placement and removal of a removable dental prosthesis

10. PATH OF INSERTION (GPT 8) :
The specific direction in which a prosthesis is placed on the abutment teeth or dental implant(s)

11. SURVEY LINE (GPT 8) :
A line produced on a cast by a surveyor marking the greatest prominence of contour in relation to the planned path of placement of a restoration

12. ENAMELOPLASTY / OCCLUSAL RESHAPING (GPT 8) :
The intentional alteration of the occlusal surfaces of teeth to change their form 12

13. OBJECTIVES OF MOUTH PREPARATION IN REMOVABLE PARTIAL DENTURE
1.To establish a state of health in the supporting & contiguous tissues.  
2.To eliminate interferences or obstructions to the placement, removal, & function of the prosthesis.
3. To establish an acceptable occlusal scheme.
4. To establish an acceptable occlusal plane.
5. To alter natural tooth form to accommodate the requirements of form & function of the prosthesis.

14. PLANNING THE MOUTH PREPARATIONS
When a removable partial denture is preferred choice of treatment, an orderly, sequential plan of action should be thought of that should include:
A thorough examination of the patient including
 Patient’s medical & dental history:
The prognosis of a removable partial denture based on the health of the patient is less complicated when health is a considered in 3 classes

15. The 1st class patient is in good health, has healthy mucosa & lack of tooth mobility, even in the presence of occlusal disharmonies
The caries incidence is low or no history of caries is present
The properly designed restoration for this patient should not only provide years of masticatory function, but should provide preventive service

16. The Class2 patient is in average health & has health assets & disease liabilities that can either be corrected or eliminated
Usually demonstrates past or present caries
Gingivitis or periodontal pockets that can be eradicated are present from the occlusal imbalance caused by loss of teeth
Successful treatment depends on the patient’s cooperation in personal oral hygiene, periodontal stimulation, & prompt return for maintenance

17. The Class 3 patients are a poor risk with a history of predisposition to systemic disease
Correction or elimination of the liability is uncertain
Recurrent caries or periodontal pockets develop inspite of the best efforts of previous competent, professional care

18. Digital & visual examination:
Search for tissues intolerant to stress, which must be corrected to ensure success
Attention is directed to caries, erosion, abrasion, loose teeth, inflamed hypertrophic or ulcerated mucosa, knife-edge or unhealed ridges, & tori that interfere with lingual bar placement

19. Radiographs of teeth & edentulous spaces:
The alveolar & supporting tissues may reveal evidence of previous trauma that not only precludes the possibility of using the adjacent tooth for an abutment, but also may indicate its removal to restore a healthy foundation
The combined force of occlusion and the clasps, must be correlated to the alveolar support of the abutment teeth

20. Splinting the abutments when there is a doubt concerning their future stability is advised
The elimination of sequestra, root fragments & residual infections makes the patients adjustment less complicated
Eliminating foci of infection aids in restoring the patient to the health optimum to facilitation of the retention of the remaining natural teeth

21. Surveyed & occluded study casts:
Surveyed study casts mounted on an articulator provide an opportunity to preview the location of the metal framework.
Changes & improvements of design on the study cast are the least expensive to make.

22. Mouth Preparation

23. Dental conditions causing pain or discomfort due to caries or defective restoration should be treated as early in the treatment process as possible to eliminate the possibility of an acute episode or pain occurring during the treatment procedure
The gingival tissue should also be treated early to decrease the possibility of periodontal abscesses and other inflammatory responses
Calculus accumulation should be derided, plaque should be controlled and a preventive dental hygiene program should be started and vigorously monitored

24. ORAL SURGICAL PREPARATION
All Preprosthetic surgical treatment for the RPD patient should be completed as soon as possible
Generally includes manipulation of both hard & soft tissues which introduces the necessity of adequate healing time before the fabrication of the prosthesis

25. The longer the time interval between the surgery and the impression procedures, the more complete the healing and consequently the more stable the denture bearing areas
Necessary endodontic surgery, periodontal surgery and oral surgery should be planned so that they can be completed during the same time frame

26. EXTRACTIONS
The extraction of non-strategic teeth that would present complications or those that might be detrimental to the design of the prosthesis is necessary

27. Planned extractions should be done after careful evaluation of each remaining tooth
Each tooth should be evaluated for strategic position & potential contribution to the success of the prosthesis

28. REMOVAL OF RESIDUAL ROOTS
Generally all retained roots or root fragments should be removed, especially, if they are in close proximity to the tissue surface or if there is evidence of associated pathological findings

29. Residual roots adjacent to abutment teeth may contribute to the progression of periodontal pockets & compromise the results from subsequent periodontal therapy
The removal of root tips can be accomplished from facial or palatal surfaces without resulting in a reduction of alveolar ridge height or endangering adjacent teeth

30. IMPACTED TEETH
All impacted teeth, including those in edentulous areas & those adjacent to abutment teeth, should be considered for removal

31. The periodontal implications of impacted teeth adjacent to abutments are similar to those for retained roots
Early elective removal of impactions prevents later serious acute & 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 & prevent more extensive damage

32. Asymptomatic impacted teeth in the elderly, covered with bone & with no evidence of pathology should be left to preserve the arch morphology
If an impacted tooth is left, it should be recorded & patient informed of it
Radiographs should be taken at regular intervals to ensure that there are no adverse changes

33. MALPOSED TEETH
Loss of individual tooth or group of teeth may lead to extrusion, drifting or combination of malpositioning of the remaining teeth
In most cases, the alveolar bone supporting the extruded teeth also will be carried occlusally

34. Orthodontics may help to correct the occlusal discrepancy
Where it is not practical due to lack of teeth for anchorage of orthodontic appliances, or other reasons, surgical repositioning can be done as an out patient procedure

35. MISPLACED TEETH
Teeth that are grossly misplaced in the arch should be removed in the interests of both function and esthetics. Anteriorly misplaced teeth that are unsightly may be extracted and replaced on the denture

36. Sometimes cases present where no space retainer has been inserted after the extraction of a central incisor, and closure, up to half the width of the tooth, has occurred
Overlapping the replacing tooth may give a reasonable appearance but often the most satisfactory result is achieved by extraction of one of the contiguous teeth

37. Lower posterior teeth with gross lingual inclination may prevent the correct positioning of a bar and, therefore, warrant extraction.
A posterior tooth or teeth which have over-erupted into a space created by the extraction of their opponents may interfere with occlusion. When this displacement is more than slight and cannot be corrected by grinding, extraction is often necessary

38. Sometimes a lower molar is found impinging upon the tuberosity/upper impinging on the retromolar pad rendering the denture impossible unless the vertical dimension is increased, if this is not indicated the offending tooth should be extracted or surgical reduction of the lower tooth for support and retention

39. CYSTS & ODONTOGENIC TUMORS

40. Panoramic roentgenograms of the jaws are recommended to survey for unsuspected pathological conditions.
When present, a periapical radiograph should be taken to confirm or deny the presence of the lesion
Any radiolucency or radio-opacity observed in the jaws should be investigated and the diagnosis confirmed
The patient should be informed of the diagnosis & provided with the various options for resolution of the abnormality

41. EXOSTOSES & TORI
Presence of exostoses & tori compromise the design of the RPD
Modification of denture design at times can accommodate for exostoses, but more frequently resulting in additional stress to the supporting elements & compromised function

43. In addition, the mucosa covering the bony protuberances is extremely thin & friable. Thus, the removable partial denture components close to this type of tissue may cause irritation & chronic ulceration
Those approximating the gingival margins may complicate maintenance of periodontal health & eventually lead to loss of strategic abutment teeth
The removal of exostosis & tori is not a complex procedure & it is advantageous to remove them in contrast to the deleterious effects their continued presence can create

44. HYPERPLASTIC TISSUE
Often seen in the form of fibrous tuberosities, soft flabby ridges, folds of redundant tissue in the vestibule or floor of the mouth,& palatal papillomatosis

45. All theses forms of excess tissue should be removed to provide a firm base for the denture
This will also produce a more stable denture, reduce stress & strain on the supporting teeth & tissue & in many instances provide a more favorable orientation of the occlusal plane & arch form for the arrangement of artificial teeth
The surgical procedures should not result in reduction in the vestibular depth

46. The tissues can be removed by the use of scalpel, currette or even electrosurgery or laser
A surgical stent should always be used after the surgery to provide a more comfortable healing period

47. MUSCLE ATTACHMENT & FRENUM
Due to the loss of bone height, muscle attachments may insert on or near the residual ridge crest
Mylohyoid, buccinator, mentalis, & genioglossus muscles are most likely to cause problems of this nature
In addition, muscles such as the genioglossus & mentalis often produce bony protuberances at their attachment, that may also affect removable partial denture design

48. Appropriate ridge extension procedures can reposition attachments & remove bony spines, which will enhance the comfort & function of the prosthesis
Maxillary labial & mandibular lingual frenae are most common source of interference, & can be easily modified with surgery

49. BONY SPINES & KNIFE-EDGE RIDGES
Sharp bony spicules must be removed & knife-like crests gently rounded
It is very important to perform these procedures with utmost care to cause minimum bone loss

50. In case the procedure leads to insufficient ridge support, we can consider vestibular deepening for the correction of deficiency or insertion of various graft materials

51. POLYPS, PAPILLOMAS & TRAUMATIC HEMANGIOMAS
All abnormal soft tissue lesions should be excised & submitted for pathological examination before the fabrication of the prosthesis
New or additional stimulation to the area introduced by the prosthesis may produce discomfort or even malignant changes in the tumor

52. HYPERKERATOSES, ERYTHROPLASIA, & ULCERATIONS
All abnormal white, red or ulcerative lesions should be investigated
The lesions should be removed & healing accomplished before fabrication of the prosthesis

53. In some cases, the removable prosthesis design will have to be modified to prevent areas of possible sensitivity, such as after irradiation treatments or the excoriation of erosive lichen planus

54. DENTOFACIAL DEFORMITY
Often patients with dentofacial deformity have multiple missing teeth and the correction of the jaw deformity can simplify the dental rehabilitation

55. Overall problems faced by the patient should be addressed to, before correcting problems related to the dentition
Prosthodontist, orthodontist, periodontist, oral surgeon & general dentist may play a role in the patient’s treatment
A sequential treatment plan should be formulated for the patient

56. Surgical correction of jaw deformity can be made in the horizontal, sagittal or frontal planes
Mandible & maxilla may be positioned anteriorly or posteriorly & their relationship to the facial planes may be surgically altered to achieve improved appearance

57. AUGMENTATION OF ALVEOLAR BONE
Can be performed with the use of autogenous or alloplastic materials
Clinical results depend on careful evaluation of the need for augmentation, projected volume of required material & site and method of placement

58. CONDITIONING OF ABUSED & IRRITATED TISSUE
Required in patients often demonstrating the following symptoms:
-Inflammation & irritation of mucosa covering the denture bearing areas
-Distortion of normal anatomic structures, such as incisive papilla, rugae and retromolar pads
-Burning sensation in the residual ridge areas, tongue and cheeks and lips

59. Differential diagnosis of these conditions would include:
These conditions are often associated with ill-fitting or poorly occluding removable partial dentures
Differential diagnosis of these conditions would include:
Nutritional deficiencies
Endocrine imbalances
Severe health problems (diabetes or blood dyscrasias)
Bruxism

60. A good home care program should be introduced that would include:
These conditions should be corrected before fabricating a new prosthesis or relining the present denture
Patient should be informed of the delay in treatment, till the tissues attain a healthy state
A good home care program should be introduced that would include:
Rinsing mouth thrice daily with prescribed saline solution
Massaging residual ridge areas, palate & tongue with soft toothbrush
Removing prosthesis at night
Using prescribed multivitamin with prescribed high protein, low- carbohydrate diet.

61. Some inflammatory conditions can be resolved by removing the dentures for extended periods of time

62. USE OF TISSUE CONDITIONING MATERIALS
Permit distorted tissues to rebound & assume normal form
Have a massaging effect on the irritated mucosa
Occlusal forces are more evenly distributed

63. Maximum benefit of these materials can be obtained by :
Eliminating deflective or interfering contacts of old dentures
Extending denture bases to proper form to enhance support, retention & stability
Relieving tissue side of denture bases sufficiently (2mm) to provide space for even thickness & distribution of conditioning material
Applying material in amounts sufficient to provide support & cushioning effect
Following manufacturer’s directions for manipulation & placement of conditioning material

64. Conditioning procedure should be repeated till supporting tissues are healthy
In cases positive results are not noticed 3-4 weeks, should suspect more serious health problems, and should be investigated for

65. PERIODONTAL PREPARATION
The periodontal preparation of the mouth usually follows any oral surgical procedure and simultaneously with tissue conditioning procedures
Gross debridement is recommended before procedures such as extraction to prevent dislodgement of calculus in the extraction socket leading to infection

66. Periodontal therapy should be completed before restorative procedures, as the ultimate success of the restoration depends directly on the health and integrity of the supporting structures of the remaining teeth
The objective is to return the health of the supporting structures of the teeth, creating an environment in which the periodontium may be maintained

67. Criteria to satisfy the objective are:
Removal & control of all etiological factors contributing to periodontal disease, along with a reduction or elimination of bleeding on probing
Elimination of, or reduction in pocket depths, with the establishment of healthy gingival sulci whenever possible
Establishment of functional atraumatic occlusal relationships and tooth stability
Development of a personal plaque control program and definitive maintenance schedule

68. PERIODONTAL DIAGNOSIS AND TREATMENT PLANNING
The diagnosis is based on a systematic & carefully accomplished examination of the periodontium
It includes:
Health history of the patient
Investigation using direct vision
Palpation
Periodontal probe
Mouth mirror
Other auxiliary aids, such as curved explorers, furcation probes, diagnostic casts & appropriate radiographs

69. It is most important to carefully explore the gingival sulcus & record the probing pocket depth & sites that bleed on probing

70. GRADED ACCORDING TO EASE AND EXTENT OF TOOTH MOVEMENT
Normal mobility : 0.05 – 0.1 mm
Grade I mobility : <1mm movement in buccolingual (B-L) direction
Grade II mobility : 1–2 mm movement in B-L direction
Grade III mobility : >2 mm mobility in B-L direction &/or tooth is vertically depressible

71. Each tooth should be evaluated for mobility, which is an indication of the condition of the supporting structures, namely the periodontium, & is usually caused by inflammatory changes in the periodontal ligament, traumatic occlusion, loss of attachment, or a combination of the 3 factors
In many cases, if the etiological factor can be removed, grade I & II mobile teeth can become stable & may be used successfully to help support, stabilize & retain the prosthesis

72. Mobility is not an indication of extraction, unless it cannot aid in support or stability of the denture or the mobility cannot be reduced

73. TREATMENT PLANNING
Periodontal treatment planning can be usually divided into 3 phases.

74. FIRST PHASE (DISEASE CONTROL OR INITIAL THERAPY)
The objective is to essentially eliminate or reduce local etiological factors before any periodontal surgical procedures are accomplished
It includes:
Oral hygiene instruction
Scaling & root planing & polishing
Occlusal adjustment
Temporary splinting if indicated

75. ORAL HYGIENE INSTRUCTION
For the oral hygiene routine to be successful, the patient must be convinced to follow the prescribed procedure regularly
The most effective motivation techniques require good understanding by the patient of his/her periodontal condition
Thus, an explanation of the disease, it’s cause, initiation & progression is important
Instruct patient to use:
Disclosing tablets/wafers
Soft / medium bristle toothbrush
Unwaxed / waxed dental floss

76. On subsequent visits, oral hygiene can be evaluated & other oral hygiene aids, such as, interdental brushes can be incorporated, if needed
A satisfactory level of plaque control should be achieved

79. SCALING & ROOT PLANING

80. Careful scaling & root planing are fundamental to reestablishment of periodontal health
Without meticulous removal of calculus, plaque & toxic material in the cementum, other forms of periodontal therapy cannot be successful
The use of ultrasonic instrumentation is recommended for calculus removal followed by root planing with sharp periodontal curettes

81. ELIMINATING OF LOCAL IRRITATING FACTORS OTHER THAN CALCULUS:
Overhanging restoration margins & open contacts allow food impaction, and should be corrected before beginning definitive prosthetic treatment

82. ELIMINATION OF GROSS OCCLUSAL INTERFERENCES
Can lead to rapid loss of periodontal attachment due to bacterial plaque accumulation
Can be corrected by various techniques, of which, selective grinding is the generally applied procedure

83. GUIDE TO OCCLUSAL ADJUSTMENTS USE OF A NIGHT GUARD
Removable acrylic resin splint with flat occlusal plane can be used effectively as a form of temporary stabilization and means to eliminate excessive lateral forces due to clenching and grinding habits
Particularly useful before fabrication of denture, when one of the abutment teeth has been unopposed for an extended period

84. MINOR TOOTH MOVEMENT
Malposed teeth can be corrected by orthodontically repositioning it to favorable positions to improve function & / or aesthetics

85. SECOND PHASE (DEFINITIVE PERIODONTAL SURGICAL PHASE)
Patient is reevaluated after initial therapy. In case, oral hygiene is at optimum level, but there is presence of pockets and osseous defects, periodontal surgery is considered
Includes:
Free gingival grafts
Osseous grafts
Pocket reduction

86. Periodontal flap surgery

87. Usually involves elevation of Full thickness flap
Most important goal is:
To allow access to bone and root surfaces for complete instrumentation
Access for pocket elimination, caries control, crown lengthening, root amputation or hemisection, as required and access to furcation of the tooth.
Osseous resection involves both osteoplasty and ostectomy
Osteoplasty is reshaping of the bone without removing tooth- supporting bone
Ostectomy on the other hand involves removing of tooth- supporting bone

88. GUIDED TISSUE REGENERATION
Procedures that attempt at regeneration of the lost periodontal structures through different tissue responses
Rationale is based on the physiological healing response of the tissue after periodontal surgery

89. PERIODONTAL PLASTIC SURGERY / MUCOGINGIVAL SURGERY
Procedures used to resolve problems involving inter-relationship between the gingiva & alveolar mucosa
Objective:
Elimination of pockets that traverse the mucogingival junction
Creation of an adequate zone of attached gingiva
Correction of gingival recession
Relief of pull of frena & muscle attachments on gingival margins
Correction of osseous defects

90. Commonly used procedures:
Lateral sliding flaps
Free gingival grafts
Pedicle grafts
Subepithelial connective tissue grafts
Edentulous ridge augmentation

91. THIRD PHASE (RECALL MAINTENANCE PHASE)
Includes reinforcement of plaque control measures and thorough debridement of all root surfaces of supragingival & subgingival calculus & plaque
The frequency of recall appointments should be customized for the patient depending on the susceptibility & severity of periodontal disease

92. Patients with moderate to severe periodontitis should be recalled 3-4 monthly

93. Advantages of periodontal therapy:
Elimination of periodontal disease removes a primary etiological factor in tooth loss
Provides a better environment for restorative correction
Response of strategic, but questionable teeth provides an important opportunity to reevaluate their prognosis before final decision is made to include/exclude them in the denture design
Overall patient response indicates the degree of cooperation to be expected in the future

94. PROVISION FOR PERIODONTALLY WEAKENED TEETH - TEMPORARY SPLINTING
Cause for tooth mobility should be determined, and eliminated
Temporary immobilization can be done and the response observed, that may be an indicator in establishing a prognosis of these teeth

95. A tooth that has lost 50% of its bony support & is being considered as a terminal abutment tooth for a class I & II partial denture would be a poor candidate for splinting to the adjacent tooth
In a situation such as this the usual result is that the stronger of the teeth is weakened by splinting procedure rather than the weaker tooth being strengthened

96. Secondary mobility due to inflammatory disease may be reversible, if the disease has not destroyed too much of the attachment apparatus
Primary mobility due to occlusal interferences may be resolved after selective grinding

97. In some cases, teeth must be stabilized due to the loss of supporting structures
This can be achieved by
Acid etching teeth with composite resin
Fiber reinforced resins
Cast removable splints
Intracoronal attachments (require cutting tooth surfaces & embedding rigid connection between adjacent teeth).

99. PERMANENT SPLINTING
After periodontal treatment, permanent splinting can be achieved with 2 or more cast restorations, soldered or cast together, that may be cemented with either a permanent or temporary cement
Major drawback of fixed splinting is inability of patient to adequately clean the splinted teeth

100. It is important to recognize that fixed splinting of posterior teeth provide additional resistance to antero-posterior forces, but not medio-lateral forces
Thus, to obtain improved resistance, splinting should extend to include 1 or more anterior teeth

101. Better method to obtain resistance to lateral forces is by obtaining cross-arch stabilization by a removable prosthesis, in the form of wide palatal strap (maxillary arch) and lingual plate (mandibular arch)
The major connector may be retained with extracoronal (clasps) or intracoronal attachments

102. OVERDENTURE ABUTMENTS
Teeth that have lost atleast 50% supporting bone, but are strategically positioned in the arch, should be retained for support to the prosthesis
Resist tissue-ward forces

103. CORRECTION OF MALALIGNMENT
Teeth that are malposed facially or lingually are frequently more difficult to correct than overerupted or submerged teeth
Malaligned teeth compromise the contours & positions of removable partial denture components
While minor malalignment corrections can be tried by altering design of partial denture

104. ORTHODONTIC REALIGNMENT
Orthodontically moving the malpositioned tooth should be considered first, whenever possible

105. In some cases, where a large number of teeth are missing, the number, distribution & periodontal consideration of remaining teeth may not provide sufficient anchorage for orthodontic correction
Some patients may be unwilling or unable to undergo orthodontic therapy

106. Other forms of treatment that must be considered include:
Minor malalignment: recontouring axial surfaces of malposed teeth
Moderate malalignment: placement of crowns, where, tooth preparation should permit correction of malalignment
In cases, where tooth preparation is such that it encroaches pulp, endodontic therapy should be opted prior to reduction, where post & core is used to restore the crown
In cases of severe malalignment, extraction should be considered

108. OCCLUSAL CONSIDERATIONS
Here one must evaluate the patients occlusion, that is:
Type of occlusion patient has
Whether there is a need to change or modify the patients existing occlusion
Whether the intercuspal position is in harmony with the patients centric jaw relation
The status of the plane of occlusion and of the occlusal curve

109. To evaluate the existing occlusal plane or occlusal curve on the diagnostic cast an occlusal template is used

110. CORRECTION OF OCCLUSAL PLANE
The occlusal plane in most partially edentulous mouths will be uneven
The severity of the irregularity will determine the treatment necessary to correct the condition
Teeth unopposed for a prolonged time tend to supraerupt
Most often encountered in the posterior dental arch segments
Such teeth should be treated in relation to the magnitude of the problems they create & the importance of the teeth to the success of the RPD

111. The problems encountered by posterior supraerupted teeth are usually
Insufficient space in positioning the opposing prosthetic teeth
Their potential for causing occlusal trauma .

112. Extruded teeth in the anterior dental arch segment pose an additional problem of esthetics
Depending on the degree of extrusion the probable treatment varies
When there is slight extrusion the tooth poses no appreciable problems in positioning the prosthetic replacement in the opposing dental arch & has no potential for creating occlusal trauma, no treatment is needed

113. When tooth extrusion is moderate, the extruded posterior tooth poses definite problems, of moderate magnitude, that can be successfully managed by various techniques

114. ENAMELOPLASTY/ SELECTIVE GRINDING OF THE TOOTH CUSPS

115. ENAMELOPLASTY / OCCLUSAL RESHAPING (GPT 8)
The intentional alteration of the occlusal surfaces of teeth to change their form

116. It consists of reducing cusp height in order to level or harmonize the curve of the occlusal plane
Amount of correction accomplished by this technique is limited
When cusp height is reduced, the anatomy of the occlusal surface should be preserved
Functional cusp with accessory grooves and sluiceways must be restored to the teeth once the necessary reduction has been made

117. It is best accomplished by using tapered diamond cylinder stones in the high speed handpiece
Air-water spray should always be used to prevent creating excess heat during the procedure
Cut enamel surface should be polished to remove scratches, using carborandum containing rubber wheel or points

118. When tooth extrusion is moderately severe, the tooth cannot be successfully managed without altering the tooth to such a degree that the enamel is penetrated, thus requiring the placement of a restoration (usually a cast restoration)

119. CAST CROWNS
When crown height of the tooth must be changed to harmonize with the occlusal plane, the facial, lingual or proximal surfaces must be altered to produce a more desirable height of contour, guiding plane or retentive undercut, a full crown is normally the restoration of choice

120. When restoring the tooth with a surveyed crown, one can create retentive undercuts & guiding planes surfaces in the wax pattern precisely where they will be most advantageous to the overall design
The surface of the tooth that is to support the reciprocal arm of the clasp likewise can be ideally contoured

122. Before reduction, the casts should be mounted to ascertain the amount of reduction required
In case, reduction is so great as to endanger the pulp, endodontic treatment should be done

123. When tooth extrusion is severe & the tooth is considered nonessential to the success of the prosthesis, it may be extracted

124. INFRAERUPTED TEETH
Infraerupted teeth create defects in the plane of occlusion & they can be successfully managed by:
Orthodontic treatment
Placement of cast restoration on the tooth to increase the clinical crown
Use of an occlusal onlay as a part of the RPD or as an onlay rest to restore the clinical crown to the plane of occlusion

125. ORTHODONTIC TREATMENT

126. PLACEMENT OF CAST RESTORATION ON THE TOOTH TO INCREASE THE CLINICAL CROWN

127. USE OF AN OCCLUSAL ONLAY AS A PART OF THE RPD OR AS AN ONLAY REST TO RESTORE THE CLINICAL CROWN TO THE PLANE OF OCCLUSION

128. The occlusal surface of a tooth to be covered by an onlay rest should be free of pits & fissures or should be made so by eliminating the defects with small burs or stone
The smooth occlusal surface helps prevent caries caused by dental plaque & other debris trapped & held against vulnerable tooth surfaces
Use of this rest in mouths with poor oral hygiene can lead to destruction of teeth

129. If the onlay rest is to be constructed of chrome alloy, any opposing natural teeth should not occlude directly against the rest
Chrome alloy, being extremely hard, will cause rapid wear of the opposing enamel surfaces

130. If the onlay rest must be used under these circumstances, the chrome metal should be constructed short of occlusal contact & the surface of the metal covered with projections of metal beads
Tooth colored acrylic resin may be processed on the surface of the onlay rest with the beads used to retain the resin
However the acrylic resin will wear fairly rapidly & will require replacement more frequently than an acrylic denture tooth

131. Tipped molars also present problems in establishing a harmonious occlusal plane

132. The design requirements for the RPD can usually be met by selective grinding procedures when the degree of tilt is moderate (50-100)
Molars with severe tilts (150 or more) require a more careful appraisal

133. Such molars are best repositioned orthodontically
This better allows the forces from the RPD to be distributed along the long axis of the tooth & eliminates the possibility of interferences from clasp assemblies & major & minor connectors

134. Severely tipped mandibular molars with a lingual tilt may considerably interfere with a lingual bar major connector during placement & removal of the prosthesis when the lingual bar is to be extended to the distal surface of the tooth to support a clasp assembly
In such instances, when the RPD framework is fully seated there will be a significant space between the lingual bar & the alveolar mucosa

135. A major connector so placed will interfere with tongue function, create the potential for food entrapment & in general be annoying to the patient
Tooth modifications generally cannot be done without penetrating the enamel, which will require one to place a cast restoration on the tooth

136. Preparation of abutment teeth
Abutment teeth may be grouped as follows:
1.Those requiring only minor modifications to their coronal portions.
2.Those requiring to have restorations other than complete coverage crowns &
3.Those requiring to have crowns (complete coverage).

137. Abutment teeth that require only minor modifications include teeth with Sound enamel

138. Those with small restorations not involved in the RPD design

139. Those with acceptable restoration that will be involved in the RPD design

140. Those that have existing crown restoration requiring minor modification that will not jeopardize the integrity of the crown, that is, an individual crown or as the abutment of a fixed partial denture.

141. Complete coverage restorations provide the best possible support for occlusal rests.
An amalgam alloy restoration if properly condensed is capable of supporting an occlusal rest without appreciable flow over a long period.
In case of any doubt about the existing amalgam restoration is there, it should be replaced with a new restoration.

142. Sequence of abutment preparation 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 circumferential clasp arms may be placed well below the occlusal surface, preferably at the junction of the middle and gingival third

143. -Retentive clasp terminals may be placed in the gingival third of the crown for better esthetics and better mechanical advantage
-Reciprocal clasp arms may be placed on and above a height of contour that is no longer higher than the cervical portion of the abutment tooth.

144. After alterations of axial contours and before rest seat preparations are instituted, an impression of the arch should be made in irreversible hydrocolloid and cast formed, that is surveyed to determine the adequacy of axial alterations before proceeding with rest seat preparations. If axial surfaces require additional recontouring, it can be done at the same appointment.

145. Occlusal rest areas should be prepared that will direct the occlusal forces along the long axis of the abutment tooth. Mouth preparation should follow removable partial denture design outlined on the diagnostic cast. Proposed changes to the abutment teeth should be made on the diagnostic cast and outlined to indicate the area, amount & angulation of modification to be done.

146. Abutment preparations using conservative restorations
Conventional inlay prepartations are permissible on proximal surface of a tooth not to be contacted by minor connector.
The proximal & occlusal surfaces that support minor connectors require different treatment.

147. Extent of coverage is governed by factors, such as, extent of caries, presence of unsupported enamel walls & extent of occlusal abrasion & attrition.
When an inlay is restoration of choice, certain modifications of outline form are necessary.

148. To prevent buccal & lingual proximal margins lying at or near minor connector or occlusal rest, these margins must be extended well beyond the line angles of the tooth, that might be accomplished by widening the conventional box preparation.
However, the margin of cast restoration produced may be quite thin & may be damaged by the clasp when placing or removing the prosthesis.
Prevented by extending outline of box beyond line angle.

149. Pulp in these preparations is endangered unless, axial wall is curved to conform to the external proximal curvature of the tooth.
Gingival seat should be so placed, to ensure access to maintain good oral hygiene.
Every effort should be made to provide restoration with maximum resistance & retention & clinically imperceptible margins.
This can be achieved by preparing opposing cavity walls 50 or less from parallel & producing flat floors & sharp, clean line angles.

150. Abutment preparation using crowns
When multiple crowns are to be restored as abutments, it is best that all wax patterns be made at the same time.
This can be accomplished with either removable dies or solid cast with individual dies to refine the margins.

151. After cast is placed on the surveyor to conform to the selected path of placement & after wax patterns have been preliminary carved for occlusion,& contact, the proximal surfaces that are to act as guiding planes are carved parallel to the path of placement with a surveyor blade.
Guiding planes are extended from marginal ridge to the junction of the middle and gingival 3rd of the involved tooth surface.

152. Guiding plane should not be extended to the gingival margin, as the minor connector must be relieved when it crosses the gingiva.
After the guiding planes are parallel & any other contouring is accomplished to accommodate the removable partial denture design, occlusal rest seats are carved in the wax pattern.

153. Preparing guiding planes

154. Guiding planes are naturally occurring or prepared parallel areas on vertical tooth surfaces that are contacted by certain rigid parts of the RPD framework during the placement & removal of the prosthesis .

155. Guiding planes should be prepared on sound enamel or on appropriately restored tooth surfaces.
The instrument used to prepare guiding planes is generally a smooth diamond stone with either a cylindric or tapered point. Keeping the long axis of the diamond instrument parallel with the path of placement when the selective grinding procedures are performed usually creates effective guiding surfaces.

156. Length
Guiding planes should be longer (occlusogingivally) for tooth supported than for distal extension prostheses .
Proximal guiding planes for all tooth-supported prostheses should be approximately one half –two thirds the length of the occlusogingival dimension of the coronal enamel. The guiding plane should extend from the marginal ridge cervically.
Guiding planes on teeth that serve, as abutments for distal extension prostheses should be one- third to one half the occlusocervical dimension of the coronal dimension of the coronal enamel.

157. Width
From an occlusal view, guiding planes on proximal tooth surfaces may be slightly curved buccolingually to more or less follow the natural tooth contour. Buccolingually, guiding planes on proximal tooth surfaces should be about two-thirds as wide as the distance between the buccal & lingual cusp tips.

158. Modifying survey lines
Survey lines can be modified by
1.Changing the tilt of the diagnostic cast
2.Selectively grinding the tooth
3.Placing an appropriate cast restoration
4.Placing an enamel bonded resin veneer.

159. Tilting the diagnostic cast

160. When survey lines are modified by tilting the diagnostic cast ,the survey lines on all abutment teeth are affected.One cannot alter the survey lines on one abutment tooth by tilting the diagnostic cast without affecting the survey line on all other abutment teeth. Once the final diagnostic cast position has been selected & additional survey line modifications needed are accomplished by

161. Selective grinding
Tooth alterations by selective grinding are often necessary to achieve acceptable survey lines for appropriate clasp placement.
Survey lines can be lowered but not raised by selective grinding. When survey lines are extremely high & the degree of undercut is severe, teeth are often selectively ground to lower the survey line,thus reducing the degree of undercut so that the retentive arm tip can be placed more gingivally.

162. Selective grinding procedures to modify survey lines should be accomplished within the thickness of the enamel.
It is not generally possible to raise a survey line on natural tooth structure by selective grinding.The amount of enamel that would have to be removed to effectively raise a survey line would undoubtedly expose the dentin.

163. Changing survey lines by placing an appropriate cast restoration.
-When survey line on an abutment tooth needs to be changed significantly to meet design requirements ,a cast restoration may be employed.

164. Creating an acceptable undercut for clasp retention with an enamel bonded resin veneer:
-When the enamel of an abutment tooth is sound but presents an inadequate survey line relative to the chosen path of placement & removal ,the survey line may be appropriately changed by veneering an enamel bonded resin to a portion of the enamel surface.This technique of changing a survey line is generally employed to enhance an inadequate undercut.

165. Preparation of composite retentive areas.

166. Preparing rest seats

167. Rest seats are specially prepared tooth surfaces designed to accommodate the metal rest of the RPD framework.
The preparation of the rest seats should follow all selective grinding procedures, because if the rest seats were prepared first the selective grinding to create guiding planes would alter the character of the rest preparation .
Attempts to redesign the rest seat often result in severe compromises in the rest preparation.

168. It is the rest seat that basically determines the outline, form, size, shape, width, & thickness of the metal rest. If the rest seat is inappropriately prepared, the metal rest cannot possibly accomplish the function for which it is intended.

169. Basic types of rest seats: 2 general types of rest seats-
Intra coronal &
Extra coronal

170. Intracoronal rest preparations are prepared in a restoration such as a crown or inlay. They are never placed in natural tooth structure.
Extra coronal rest preparations are placed on natural or restored tooth surfaces.

171. Rest seats can also be identified according to their location on the tooth surface, that is, occlusal, incisal, cingulum, mesial, distal, facial, or lingual.
Most rest seats can further be identified as either Proximal rest seats or Embrasure rest seats .

172. A proximal rest seat is one located on a proximal surface of a tooth adjacent to an edentulous area.

173. An embrasure rest seat is once located on a tooth surface adjacent to another tooth.

174. Combination terms to describe various rest seats are
1.proximal occlusal rest
2.embrasure occlusal rest
3embrassure incisal rest
4.proximal incisal hook rest

175. Requirements of occusal rest seats
Rest seats should be prepared in a manner that will permit the metal rest to direct functional vertical forces along the long axis of the abutment tooth.
Rest seats should provide a positive seating of the metal rest in the rest seat on the abutment tooth.
A rest seat should have gradual sloping walls; it should be smooth and polished.

176. A rest seat should not have undercuts, sharp angles, or edges.
Cavosurface margins should end on self cleansing surfaces.
A rest seat should provide adequate space for sufficient bulk of metal to provide strength in the rest.
Rest seats for distal-extension RPDs should allow slight rotation of the metal rest in the rest seat without wedging or torquing of the abutment tooth.

177. Basic occlusal rest
Location: mesial or distal fossa of the occlusal surface of molars & premolars.
Outline: spoon shaped.It also resembles a printed U that has been spread apart slightly at its open end.
Width: at the marginal ridge should be one half-two thirds the distance b/w the tips of the buccal & lingual cusps.

179. The deepest portion of the rest seat is located in the fossa area away from the marginal ridge.
This concave area is called the positive seat.
It should be mm deeper than the general base of the rest seat.
The base of the rest seat should be at right angles to or should make an acute angle with the long axis of the abutment tooth.

180. The preparation for all occlusal rest seats can be made with a no
The preparation for all occlusal rest seats can be made with a no.6 or 8 round carbide bur or a diamond instrument of a similar size & shape, using either conventional or high speed instrumentation.

181. Assessment of the adequacy of occlusal rest seats:
The adequacy of occlusal rest seats can & should be checked before the impression for the master cast is made.
visual inspection
direct tactile contact
by making wax imprints or patterns
by making an impression to create a diagnostic cast.

182. Visual inspection
The basic outline of the rest seat should be envisioned on the tooth surface mentally as the first amount of tooth structure is removed and this image should be maintained & intensified until the rest seat evolves. The dark contrast of the irregular base demonstrates an inadequate rest seat preparation.

183. VISUAL INSPECTION

184. An explorer or the bur that was used to prepare the rest seat can be helpful in direct tactile evaluation of the rest seat.
Another technique to test the adequacy of the rest seat is placing soft wax over the preparation and having the patient bite in to tight occlusion. This makes a wax pattern of the rest preparation. Its thickness, size & shape can be evaluated by the dentist.

185. Perhaps the best way to assess the adequacy of rest seats and the accuracy of other tooth alterations is to make an irreversible hydrocolloid impression, pour it in dental stone and obtain diagnostic cast from which the evaluation can be made.

186. INCISAL REST SEATS Location : On the incisal edge of anterior teeth .
Minimum depth mm
Width-2.5 mm
Mesiodistally: rest should be
Concave.

187. They may be used on any anterior tooth if they can be employed without interfering with the existing occlusion.
They may be safely employed on anterior teeth that have adequate bony support.
Major disadvantage –aesthetics
An alternative to placing an incisal rest is the use of a resin bounded cast restoration.

188. From an incisal view the axial wall should flare lingually
From an incisal view the axial wall should flare lingually. This will provide an extra bulk of metal for strength without increasing the display of metal from labial view.

189. Incisal hook rest seats
Prepared as a modification of incisal rest seat.
Most often used on mandibular canines.
Preparation extends 1.5 –2.0 mm onto the labial surface of the tooth as a concave depression.

190. It provides greatest stability than the incisal rest.
Disadvantage-Greater metal display
The incisal rest seat and the incisal hook rest seat are very similar when viewed from the labial and incisal aspects.
The only difference is that the incisal hook rest seats extend on to the labial surface for an additional 1.5 –2.0 mm as a concave depression

191. Proximal incisal rest seat on maxillary canines
Usually employed when the anterior teeth have a deep vertical overlap and canine is located adjacent to an edentulous space.

192. Cingulum rest seats
Should follow general contour of the cingulum. No.2 or 4 round diamond instruments. The base of the rest seat should be placed about 1mm cervical to the height of the cingulum. The preparation can be finished with a rounded point cylindric diamond instrument.

193. From the lingual view the cingulum rest seat should follow the natural contour of the cingulum & slope cervically as the preparation approaches the mesial and distal line angles of the tooth.

194. From the proximal view the base of the rest seat is concave or U shaped. Care must be exercised so that there are no undercuts on the lingual axial wall. The rest seat should be mm deep.

195. Lingual ledge rest seats
Usually employed on anterior teeth without a cingulum or on anterior teeth with a cingulum that is not sufficiently prominent to accommodate the cingulum rest preparation.

196. The most satisfactory lingual rest seats are placed on cast restoration,where the ledge can be made wider and the rest can be located more cervically to avoid occlusal interferences.

197. Width 1-1.5mm at the central portion of the lingual surface & tapers to blend with mesial and distal line angles of the tooth.
Lingual ledge rest seats are prepared with a cylindric,wheel shaped,or inverted-cone carborandum stone or diamond instruments.

198. References

199. Clinical Removable partial prosthodontics –second Edition. Kenneth L
Clinical Removable partial prosthodontics –second Edition. Kenneth L. Stewart, Kenneth D. Rudd & William A. Kuebker
Stewart’s Clinical Removable Partial Prosthodontics – Third Edition. Rodney D. Phoenix, David R. Cagna & Charles F. DeFreest
Removable partial prosthodontics – Eleventh Edition. McCracken’s.

200. William L.mcCraken (1956) mouth preparation for partial dentures
George Ward Glann & Ralf Carson (1960): mouth preparation for removable partial dentures.
David G Jochen (1972) achieving planned parallel guiding planes for removable partial dentures

201. Apostolos Al Krikos (1977) preparing guide planes for removable partial dentures 
Bange AA, Montalvo R(1980) Preparing teeth to receive a removable partial denture
Sansom BP, Flinton RJ, Parks VJ, Pelleu GB Jr Kingman A(1987) Rest seat designs for inclined posterior abutments

202. Berg T Jr, Caputo AA.(1987) Anterior rests for maxillary removable partial dentures
Seibert JS, Cohen DW. (1990) Periodontal considerations in preparation for removable prosthodontics.
Altay OT, Tsolka P, Preiskel HW.(1992) Abutment teeth with extracoronal attachments: the effects of splinting on tooth movement 

203. Hansen CA, Clear K.(1997) Removable partial denture design considerations where periodontally compromised teeth exist.
Caputo AA, Wylie R, Berg T.(1998) Effects of periodontal support and fixed splinting on load transfer by removable partial dentures