MOUTH PREPARATION FOR REMOVABLE PARTIAL DENTURES.pptx

mouth preparation is imp procedure in rpd

1. MOUTH PREPARATION FOR REMOVABLE PARTIAL DENTURES Presented by- Dr vaishali shrivastava 1 st year post graduate student department of prosthodontics, crown & bridge and implantology 1

2. CONTENTS Introduction Objectives Preparation of Mouth A) NON PROSTHODONTIC PREPARATION B) PROSTHODONTIC PREPARATION Preparation of Abutment tooth Conclusion References 2

3. INTRODUCTION Mouth preparation are identified as those procedures that are accomplished to prepare the mouth for reception of prosthesis prescribed prosthesis not only must replace what is missing but also must preserve the remaining tissues and structures that will enhance the removable partial denture Mouth preparation follows the preliminary diagnosis and the development of a tentative treatment plan, following this the master cast is made. 3

4. OBJECTIVES 4 the objectives of the procedures involved are to create optimum health and eliminate or alter any condition that would be detrimental to the functional success of the removable partial denture

5. NON PROSTHODONTIC PREPARATION Relief of pain and infection Pre-Prosthetic Considerations in Partially Edentulous Mouths Periodontal Preparation Optimization of the Foundation for Fitting and Function of the Prosthesis Endodontic and restorative treatment Orthodontic treatment 5 Preparation of Mouth

6. Relief of pain and infection Dental conditions that are causing discomfort should be addressed as soon as possible. Necessary endodontic and surgical procedures should be completed. 6

7. Pre-Prosthetic Considerations in Partially Edentulous Mouths Extractions Impacted teeth Malposed teeth Cysts and odontogenic tumours Exostoses and tori Hyperplastic tissue Muscle attachments and freni Bony spines and knife edge ridges Polyps, papillomas and traumatic haemangiomas Hyperkeratoses, Erythroplasia and ulcerations Dentofacial deformity Augmentation of Alveolar bone Dental implants 7

8. Extractions - Extraction of nonstrategic teeth that would present complications or those that may be detrimental to the design of the removable partial denture is a necessary part of the overall treatment plan. . 8

9. 9 Diagnostic mounting allows confirmation of the need for extraction after clinical examination.

10. Removal of residual roots- Generally, all retained roots or root fragments should be removed . Residual roots adjacent to the abutment teeth may contribute to the progression of periodontal pockets and compromise the results of subsequent periodontal therapy. 10

11. 11 Impacted teeth- All impacted teeth, including those in edentulous areas, as well as those adjacent to abutment teeth, should be considered for removal.

12. Malposed teeth The loss of individual tooth or groups of teeth may lead to extrusion, drifting, or combinations of malpositioning of remaining teeth. Surgical repositioning of these teeth is contemplated only after orthodontic treatment is ruled out. 12

13. Cyst and Odontogenic tumours OPG should be taken for ruling out unsuspected pathology . If there is any pathology surgical removal should be done. Exostoses and Tori the existence of abnormal bony enlargements should not be allowed to compromise the design of the removable partial denture. Removable partial denture components in proximity to this type of tissue may lead to irritation and chronic ulceration. 13

14. Hyperplastic tissue Hyperplastic tissues are seen in the form of fibrous tuberosities, soft flabby ridges, folds of redundant tissue in the vestibule or floor of the mouth, and palatal papillomatosis. Removal of this excess tissue provides a firm base for the denture and reduces stress on supporting teeth and tissues. 14

15. As a result of the loss of bone height, muscle attachments may insert on or near the residual ridge crest. The mylohyoid, buccinator, mentalis, and genioglossus muscles are most likely to introduce problems of this nature. Maxillary labial and mandibular lingual frenum most commonly interfere with denture design. Muscle attachments and freni 15

16. Bony spines and knife edge ridges Sharp bony spicules should be removed and knife like crests gently rounded. 16

17. Polyps, Papillomas, and Traumatic Hemangiomas all abnormal soft tissue lesions should be excised and submitted for pathologic examination before a removable partial denture is fabricated 17 polyps papilloma hemangioma

18. Hyperkeratoses, Erythroplasia, and Ulcerations hyperkeratoses erythroplasia ulcerations All abnormal white, red, or ulcerative lesions should be investigated, regardless of their relationship to the proposed denture base or framework. The lesions should be removed and healing accomplished before the removable partial denture is fabricated. 18

19. Dentofacial Deformities Cleft palate Patients with these deformities have multiple missing teeth and malocclusion as a part of the problem. Correction of the deformity should form part of the treatment plan to replace teeth and develop a harmonious occlusion 19

20. Ridge augmentation is done for atrophic ridges, flat palatal vault and mild to moderate anteroposterior ridge relation discrepancy. It is done with graft materials It enhances the support and stability of denture Augmentation of Alveolar Bone 20

21. Dental Implants Implants are carefully placed using controlled surgical procedures and, in general, bone healing to the device is allowed to occur before a dental prosthesis is fabricated. Hobo S, Ichida E, Garcia LT: Osseointegration and occlusal rehabilitation, Tokyo, 1989 These devices offer a significant stabilizing effect on dental prostheses through a rigid connection to living bone. 21

22. fig 22

23. fig A, An anterior implant-supported bar demonstrating excellent access for hygiene and a parallel relationship to opposing occlusion . B, Prosthesis with implant bar space (housing three retentive male components for retention and a flat surface for bar contact and support) and bilateral posterior embrasure clasps. C, Prosthesis seated and in occlusion. (Courtesy of Dr. N. Van Roekel, Monterey, CA.) 23

24. A Class II, modification 1, maxillary arch with a posterior implant at the distal location of the extension base . B, Maxillary gold framework with broad palatal coverage, maximum stabilization through palatal contacts of multiple maxillary teeth, and implant position at the distal extension base. A single implant should be protected from excessive occlusal forces; consequently the broad palatal coverage and maximum bracing are important features of the overall design. The ball attachment abutment was used for retentive purposes. C, Occlusal view of the prosthesis with implant (see A), which provides improved retention to the distal extension base. (Courtesy of Dr. James Taylor, Ottawa, Ontario. 24

25. Periodontal Preparation *Vanchit John, DDS, Associate Professor and Chair, Department of Periodontics and Allied Dental Programs, Indiana University School of Dentistry, Indianapolis, Indiana The periodontal health of the remaining teeth, especially those to be used as abutments, must be evaluated carefully by the dentist and corrective measures instituted before a removable partial denture is fabricated. 25

26. Periodontal Preparation Objectives of Periodontal Therapy Periodontal Diagnosis and Treatment Planning Initial Disease Control Therapy (Phase 1) Definitive Periodontal Surgery (Phase 2) Recall Maintenance (Phase 3) Advantages of Periodontal Therapy 26

27. Objectives of Periodontal Therapy 1. Removal and control of all etiologic factors contributing to periodontal disease along with reduction or elimination of bleeding on probing 2. Elimination of, or reduction in, the pocket depth of all pockets with the establishment of healthy gingival sulci whenever possible 3. Establishment of functional atraumatic occlusal relationships and tooth stability 4. Development of a personalized plaque control program and a definitive maintenance schedule 27

28. Periodontal Diagnosis and Treatment Planning The diagnosis of periodontal diseases is based on a systematic and carefully accomplished examination of the periodontium. Depending on the extent and severity of the periodontal changes present, a variety of therapeutic procedures ranging from simple to relatively complex may be indicated. 28

29. Initial Disease Control Therapy (Phase 1) Oral Hygiene Instruction Scaling and Root Planing Elimination of Local Irritating Factors Other Than Calculus Elimination of Gross Occlusal Interferences Temporary Splinting Use of a Nightguard Minor Tooth Movement 29

30. Definitive Periodontal Surgery (Phase 2) Periodontal Surgery After initial therapy is completed, the patient is reevaluated for the surgical phase. If oral hygiene is at an optimum level, yet pockets with inflammation and osseous defects are still present, a variety of periodontal surgical techniques should be considered to improve periodontal health. 30

31. Periodontal flaps Periodontal flap surgery involves the elevation of either mucosa alone or both the mucosa and the periosteum Other goals of the flap approach include access for pocket elimination, caries control, crown lengthening to allow for optimum restorative dental treatment, root amputation or hemisection, as required and access to the furcation of the tooth Guided Tissue Regeneration. GTR has been defined as those procedures that attempt regeneration of lost periodontal structures through differing tissue responses. This technique has the potential to lead to substantial improvement of the periodontal condition when used around carefully selected two and three-walled osseous defects and mandibular furcation involvements 31

32. 32 Guided tissue regeneration (GTR) procedure performed to address a furcation involvement. .

33. Periodontal Plastic Surgery 33 Mucogingival surgery consists of plastic surgical procedures that are used for correction of gingiva–mucous membrane relationships that complicate periodontal disease and may interfere with the success of periodontal treatment. Gingival recession addressed with subepithelial connective tissue graft procedure

34. Recall Maintenance (Phase 3) This is very important in maintaining periodontal health It includes reinforcement oral hygiene measures and thorough scaling and root planning patients with a history of moderate to severe periodontitis should be placed on a 3- to 4-month recall system to maintain results achieved by nonsurgical and surgical therapy 34

35. OPTIMIZATION OF THE FOUNDATION FOR FITTING AND FUNCTION OF THE PROSTHESIS Conditioning of Abused and Irritated Tissues Use of Tissue Conditioning Materials Abutment Restorations Contouring Wax Patterns Rest Seats 35

36. Conditioning of Abused and Irritated Tissues Conditioning of tissue is required if: • Inflammation and irritation of the mucosa covering denture-bearing areas • A burning sensation in residual ridge areas, the tongue, and the cheeks and lips These conditions are usually associated with ill-fitting or poorly occluding removable partial dentures. Tissue conditioners are used to provide a soothing effect on irritated mucosa 36

37. Use of Tissue Conditioning Materials Maximum benefit from using tissue conditioning materials may be obtained by (1) extending denture bases to proper form to enhance support, retention, and stability (2) relieving the tissue side of denture bases sufficiently (2 mm) to provide space for even thickness and distribution of conditioning material (3) applying the material in amounts sufficient to provide support and a cushioning effect (4) following the manufacturer’s directions for manipulation and placement of the conditioning material. 37

38. A, Mandibular removable partial denture with underextended bases, which contributed to tissue irritation. B, Denture bases properly extended to enhance support, stability, and retention 38

39. Abutment Restorations Esthetic veneer types of crowns should be used when a canine or premolar abutment is to be restored or protected. when preparing abutments that will receive surveyed crowns, it is important to plan for the tooth reduction necessary to allow placement of sufficient restorative material for durability, contour, and esthetics, as well as the contours prescribed for the desired clasp assembly (fig). 39

40. 40 Diagnostic cast at an orientation best for all abutments considered. The buccal survey line is too close to the marginal gingival. A surveyed crown is indicated. Cast of seated crown demonstrate desired contours for clasp design chosen

41. Contouring Wax Patterns 41 All abutment teeth to be restored with castings can be prepared at one time and an impression made that will provide an accurate stone replica of the prepared arch. Wax patterns may then be refined on separated individual dies or removable dies. All abutment surfaces facing edentulous areas should be made parallel to the path of placement by the use of the surveyor blade

42. 42 Completed prosthesis splinted between retainer crowns and across the midline. Splint bar with added vertical support provides indirect retention.

43. Rest Seats 43 Buccal and lingual contours have been established to satisfy the requirements of stability and retention with the best possible esthetic placement of clasp arms, the occlusal rest seats should be prepared in the wax pattern rather than in the finished restoration spoon shape or saucer shape can permit locking of the occlusal rest and the transmission of tipping forces to the abutment tooth.

44. Endodontic and restorative treatment 44 Teeth with pulpal involvement and root end pathology are candidates for endodontic therapy. Restorative therapy like – crowns, inlays, onlays, restoration of carious lesions and replacement of defective restorations should be integrated with endodontic treatment.

45. Orthodontic treatment 45 Orthodontic preparation is carried out to achieve the following: • Reduce the need for prosthetic teeth as much as possible. • Position the teeth to allow the most natural prosthetic replacement of teeth. • Create sufficient vertical height to allow room for placement of artificial teeth. Allow sufficient occlusal guidance on natural teeth

46. Prosthodontic preparation 46 Correction of occlusal plane 1) Enameloplasty 2) onlay 3) crowns 4) Endodontics with crown or coping 5) Extraction 6) surgery Correction of malalignment 1) orthodontic realignment 2) Crown 3) Enameloplasty Provision of support for weakened teeth 1) Removable splinting 2) fixed splinting 3) overdenture abutment

47. Correction of occlusal plane 47 Uneven occlusal plane is common in partially edentulous situations due to: • Supraeruption and infraeruption • Mesial migration • Tipping of teeth • Malrelationship of jaws

48. 48 Enameloplasty- occlusal reshaping, Esthetic Reshaping (GPT9) The intentional alteration of the surfaces of teeth to change their form The enamel is contoured using high-speed tapered diamonds and polished with carborundum wheels or points. Fluoride treatment of the tooth surface increases its resistance to caries. Irregular occlusal plane Enameloplasty done to correct the occlusal plane.

49. 49 onlay It is a conservative method of correcting occlusal plane as minimal tooth preparation is required compared to a full veneer crown. It maintains the natural contours of facial and lingual enamel surfaces as only occlusal surface is prepared. The occlusal surface of the tooth being prepared should be free of pits and fissures. It can be made of chrome or gold alloy. If chrome alloy is used, the occluding surface should be processed with tooth colored acrylic resin to prevent attrition of opposing tooth. Disadvantages: • Less retention • More metal display

50. 50 crowns When the height of contour, retentive undercut or guiding plane needs to be altered, crown is preferred to change the occlusal plane

51. 51 Retaining teeth in strategic positions will greatly improve the prognosis of the partial denture. Retaining mandibular second or third molars to serve as posterior abutments will support the prosthesis and will prevent it from being a more complicated distal extension situation Endodontics followed by crown or overdenture coping will restore occlusal plane and allow the teeth to be retained. Endodontics with crown or coping Retaining a distal abutment will prevent a distal extension situation .

52. 52 Extraction Malposed teeth and teeth interfering with placement of major connector require extractions to correct occlusal plane as they compromise the success of treatment Surgery Surgical repositioning of one or both jaws, fully or partly, can be contemplated to correct occlusal plane. These include osteotomies and repositioning procedures.

53. Correction of malalignment 53 Malaligned teeth create the following difficulties: • Maintenance of oral hygiene. • Determining a simple path of insertion. • Establishing guiding planes. • Placement of clasp arms of direct retainers.

54. 54 Teeth which are malposed facially or lingually are more difficult to correct than supraerupted teeth I . Orthodontic realignment - it is the treatment choice , multiple missing teeth can not be corrected • Partial or full veneer crowns may be used. • Indicated to correct buccal or lingual tipping. • If tipping is extensive, endodontic treatment followed by a post will correct the same. However, long axis of crown and root should not be too dissimilar, as undesirable horizontal forces will occur on tooth. Hence, severe malposition cannot be corrected by crowning II. Crown

55. 55 this is always considered first, but amount of correction that is possible is limited. • Enameloplasty can be used to recontour buccal or lingual surfaces to eliminate the interferences to the path of placement of major connector. III. Enameloplasty

56. Provision of support for weakened teeth 56 Over denture abutment Teeth strategically positioned in the arch with more than 50% bone loss can be retained as overdenture abutments. They resist the tissueward forces and provide support. Retaining such a tooth distal to edentulous space will convert a potential distal extension base into a tooth supported situation, improving the function of denture.

57. 57 splinting Fixed splinting with crowns. Removable splinting with clasps

58. Preparation of abutment teeth Objectives Classification of abutment teeth Preparation 58

59. Objectives 59 Direct stress along the tooth axis Eliminate interferences by recontouring of teeth Create retention by simple alteration procedure Allow placement and removal of prosthesis

60. 60 Sequence of preparation Preparation of guiding planes Modification of height of contour Preparation of retentive undercuts 4. Rest seat preparation Enameloplasty: conservative procedure involve only minor modification and reshaping of enamel

61. Preparation of guiding planes 61 Two or more vertically parallel surfaces on abutment teeth and/or fixed dental prostheses oriented so as to contribute to the direction of the path of placement and removal of removable partial denture(GPT9)

62. 62 Abutments adjacent to tooth supported segments cylindrical diamond or carbide bur is used for the preparation (fig a) The chosen bur is placed in a high-speed handpiece. Diagnostic cast mounted on surveying table at the desired tilt, handpiece with bur is positioned over abutment tooth on cast to visualize the correct angulation, same is reproduced in the mouth. Stewart’s clinical removable partial prosthodontics 4 th edition

63. 63 A light, sweeping stroke from the facial line angle to the lingual line angle is then used to create a gently curving plane. (fig b) Surface should be 2 to 4 mm in occlusogingival height , not resemble a straight slice when viewed from the occlusal or incisal surface. Instead, it should follow the natural curvature of the tooth surface(fig2). All prepared surfaces are polished with carborundum impregnated rubber point or wheel in low speed handpiece

64. 64 Fig a Fig b Fig3

65. 65 Abutments adjacent to distal extension bases Occlusogingival height of preparation is (1.5- 2mm) fig i The reduced height results in decreased contact with the associated minor connector (i.e. proximal plate) and permits greater freedom of movement for the associated removable partial denture (fig ii) As a result, potentially destructive torquing forces are minimized Fig ii Fig i Stewart’s clinical removable partial prosthodontics 4 th edition

66. 66 Lingual surface of abutment 1)To enhance reciprocation Reciprocation -Mechanism by which lateral forces generated by retentive clasp passing over a height of contour are counterbalanced by reciprocal clasp passing along a reciprocal guiding plane (GPT9) 2) preparing lingual guiding planes is to minimize the number of pathways by which the prosthesis may enter and exit its fully seated position Stewart’s clinical removable partial prosthodontics 4 th edition

67. 67 3) preparing guiding planes on the lingual surfaces of the remaining teeth is to provide maximum resistance to lateral forces. The more teeth that are used to stabilize the removable partial denture, the less stress will be transmitted to any individual tooth. Occlusogingival height of preparation is 2-4 mm located in the middle third of crown fig2

68. 68 Lingual surface of abutment If reciprocation is ineffective, potentially destructive lateral forces (arrow) will be transferred to the abutment. (b) A properly prepared guiding plane permits sustained contact between the reciprocal element and the abutment and prevents the application of unopposed lateral forces A properly prepared lingual guiding plane should be 2 to 4 mm in occlusogingival height and should be located in the middle third of the clinical crown.

69. 69 Anterior abutment teeth Guiding planes may be prepared on anterior teeth to enhance stabilization of the prosthesis, to decrease undesirable space between the prosthesis and an abutment tooth, and to increase retention through frictional resistance Stewart’s clinical removable partial prosthodontics 4 th edition

70. Modification of height of contour 70 Enameloplasty is necessary when teeth have drifted or tipped. Maxillary posterior teeth often tip in a facial (buccally) direction, while mandibular teeth generally tip in a lingual direction Preparation is best done with tapered diamond stone

71. 71 before after polishing

72. Preparation of retentive undercuts 72 The facial and lingual surfaces of the tooth must be nearly vertical. Under these circumstances, a gentle depression may be created on one of these surfaces(fig1) fig1 A depression should exhibit smooth, flowing contours. Sharply defined dimples and pits should be avoided since retentive clasps cannot flex into and out of these indentations Stewart’s clinical removable partial prosthodontics 4 th edition

73. 73 A gentle depression is prepared using a round diamond bur in a high-speed handpiece. The bur is moved in an anteroposterior direction The depression should be approximately 4 mm in mesiodistal length and 3 mm in occlusogingival height. More importantly, it should establish an undercut of 0.010 inches relative to the proposed path of insertion Preparation should be polished with a carborundum-impregnated rubber point. Stewart’s clinical removable partial prosthodontics 4 th edition

74. Rest seat preparation 74 Rest seats must always be prepared after preparation of guiding planes The function of a rest is to direct the forces of mastication parallel to the long axis of the associated abutment If rest seats are not adequately prepared, the forces transmitted from the prosthesis to the abutments may not be directed within the long axis of these teeth. This may result in irreparable damage to the abutments.

75. 75 Rest Seat Preparations for Posterior Teeth Occlusal rest seats in enamel Occlusal rest seats as part of a new cast-metal restoration Occlusal rest seats on the surface of an existing cast-metal restoration Occlusal rest seats on an amalgam restoration Embrasure rest seats

76. 76 Occlusal rest seats in enamel The outline form of an occlusal rest seat is basically triangular, the base of the triangle at the marginal ridge the apex pointing toward the center of the tooth The apex of the triangle should be rounded, as should all external margins of the preparation (fig) the floor of the occlusal rest seat must be inclined toward the center of the tooth and should display gently rounded contours. The enclosed angle formed by the floor of the rest seat and the proximal surface of the tooth must be less than 90 degrees (Fig).

77. 77 A variety of burs may be used in the preparation of rest seats . These include round burs and tapered cylinders. When using a round bur, care must be taken to ensure that mechanical undercuts are not created. (a) Round bur positioned above enamel surface. (b) Round bur moved vertically into enamel. (c) Bur moved laterally. (d) Upon removal of the bur, a distinct overhang is present

78. 78 A tapered cylinder may help eliminate mechanical undercuts. (a) Tapered bur positioned above enamel surface. (b) Tapered bur moved vertically into the enamel. (c) Bur moved laterally. (d) Upon removal of bur, no overhang is present

79. 79 An occlusal rest should be at least 1 mm thick at its thinnest point.. Failure to achieve sufficient reduction may make a rest more susceptible to fracture The outline form for an occlusal rest seat is established using a rounded-end, tapering bur in a high-speed handpiece . The form and depth of an occlusal rest seat is evaluated using red boxing wax . Boxing wax should be formed into a disk approximately 4 mm in thickness and 15 mm in diameter

80. 80 . Available space is evaluated by measuring rest seat areas with a wax thickness gauge . The boxing wax should be at least 1 mm thick in rest seat areas. Finishing procedures are performed using a green stone in a low-speed handpiece. The green stone is intended to round sharp angles (represented by the solid line at periphery of preparation) and to eliminate scratches produced by the diamond bur

81. 81 The completed rest seat should exhibit smooth, gently rounded surfaces

82. 82 Occlusal rest seats as part of a new cast-metal restoration No. 4 or No. 6 round bur is used to begin preparation of the rest seat occlusal rest seats for cast gold restorations should always be placed during the wax pattern stage. Required rest seats are carved into the wax pattern following placement of guiding planes The rest seat is then refined with a rounded carver. At this stage, the wax pattern may be sprued, invested, and cast in an appropriate alloy

83. 83 Occlusal rest seats on the surface of an existing cast-metal restoration Crown restoration has adequate marginal integrity and occlusal harmony. During preparation if perforation of crown occurs, new restoration must be made. Adequate tooth preparation is essential, otherwise it will results insufficient framework thickness and failure of the removable partial denture. Procedure is same to rest seat preparation on enamel .

84. 84 Occlusal rest seats on an amalgam restoration Amalgam alloys tend to deform when a sustained load is applied. conservative amalgam restorations are quite capable of providing support for removable partial dentures. Therefore, rest seats may be prepared on conservative single- and multiple-surface amalgams. The instrumentation and procedures for preparing rest seats on amalgam restorations are the same as those for preparing rest seats on enamel surfaces.

85. 85 Embrasure rest seats this preparation crosses the occlusal embrasure of two approximating posterior teeth, from the mesial fossa of one tooth to the distal fossa of the adjacent tooth diamond bur with a rounded end and tapering sides is ideal for preparing embrasure rest seats

86. 86 same bur is used to prepare the facial and lingual extensions of the embrasure rest seat Clearance may be evaluated by placing two pieces of 18-gauge wire across the preparation The patient should be able to close without contacting these wires

87. 87 the form and depth of the rest seat is evaluated using red boxing wax and a wax-thickness gauge. At the facial and lingual embrasures, the embrasure rest seat should be 3.0 to 3.5 mm wide and 1.5 to 2.0 mm deep. All contours should be gently rounded and no undercuts should be present

88. 88 Rest Seat Preparations for Anterior Teeth Cingulum rest seats in enamel Cingulum rest seats in a new cast-metal or metal-ceramic restoration Placement of cingulum rest seats using dental bonding techniques An alternative cingulum rest seat incisal rest seats in enamel

89. 89 Cingulum rest seats in enamel if tooth contours are favorable, sufficient enamel is present, and the patient exhibits good oral hygiene, the cingulum rest prepared. The outline form of a cingulum rest seat should be crescent shaped when viewed from the lingual aspect (a)cingulum rest seat as viewed from the lingual surface (b)the proximal surface. An inverted cone bur is used to establish the outline form of a cingulum rest seat. The preparation begins on one marginal ridge, passes over the cingulum, and terminates on the opposite marginal ridge

90. 90 The preparation is finished using a green stone in a low-speed handpiece. Care must be taken to round sharp angles (denoted by solid line). The preparation is then polished using a carborundum containing rubber point in a low-speed handpiece. cingulum rest seat .

91. 91 Lingual rest placed nearer the centre of rotation of supporting tooth and so it does not tip the tooth.

92. 92 Cingulum rest seats in a new cast-metal or metal-ceramic restoration a fixed restoration is to be placed on an anterior abutment, a cingulum rest seat should be incorporated into the wax pattern. This rest seat should exhibit ideal contours and should direct forces along the long axis of the abutment A mandibular metal-ceramic restoration with a cingulum rest seat A cingulum rest seat may be placed in a wax pattern. This is easily accomplished using a cleoiddiscoid carve

93. 93 mandibular canines do not display prominent cingula, nor do they have appreciable thicknesses of enamel on their lingual surfaces. Attempts to prepare cingulum rest seats on mandibular canines often result in exposure of the underlying dentin and greatly increase the risk of caries. Placement of cingulum rest seats using dental bonding techniques

94. 94 initial stages of tooth preparation are accomplished using a small, tapering diamond bur in a high-speed handpiece. A limited area on the lingual surface of the proposed abutment is prepared to a depth of 0.5 to 0.7 mm. indentations are prepared using a No. 2 carbide bur and should be no deeper than one third to one half the bur’s diameter

95. 95 The preparation for a bonded cingulum rest seat includes a shallow indentation (arrow) and two or three circular indentations . The depression helps disguise the thickness of the metal, while the circular indentations guide placement of the completed restoration. The wax pattern must exhibit a properly contoured cingulum rest seat and excellent adaptation at its margins

96. 96 Bonded cingulum rest seats are shown. (Courtesy of Dr Scott Schmitt.)

97. 97 An alternative cingulum rest seat alternative cingulum rest seat may be described as a crescent-shaped depression located in the middle and apical thirds of the clinical crown in many ways, this rest seat resembles an inverted cingulum rest seat. The alternative cingulum rest seat is prepared using a No. 38 carbide bur or a small diamond disk in a high-speed handpiece

98. 98 An inverted cone bur is used to prepare an alternative cingulum rest seat The preparation begins within the enamel of one marginal ridge, progresses apically to the level of the cingulum, and then sweeps incisally within the enamel of the remaining marginal ridge

99. 99 Incisal rest seats in enamel incisal rest seats are the least desirable rest seats for anterior teeth . The accompanying rests are unesthetic and may interfere with occlusion. More importantly, incisal rests are located far from the rotational centers of the abutments. Hence, these teeth may be damaged by tipping or torquing forces An incisal rest seat is usually placed near a proximal surface (Fig) (A)An incisal rest seat as viewed from the facial surface (B)lingual surface

100. 100 Incisal rest seat preparation is begun with a flame shaped diamond bur in a high-speed handpiece. The bur is oriented parallel to the proposed path of insertion, and a notch is created This notch should be located 2 to 3 mm from the proximal angle of the tooth and should be 1.5 to 2.0 mm in depth

101. 101 The notch is extended slightly onto the facial surface of the tooth. This provides a method to prevent facial movement of the abutment. On the lingual surface of the tooth, a small channel is created. This channel helps disguise the thickness of the associated minor connector

102. Abutment teeth that have cast restoration 102 Cast restorations like inlays, onlays and crowns are planned on abutments in the following situations: • If Enameloplasty does not achieve usable natural contours, as in tipping, rotation, malalignment, supra- and infraeruption of abutment. • Presence of caries, defective restorations, tooth fracture and endodontic treatment in abutment tooth. • The guiding planes, height of contour, retentive undercuts and occlusal rests are prepared on the wax patterns of these restorations with mounted casts on the surveyor.

103. 103 When inlay is the restoration of choice, proximal and occlusal surface that support minor connectors and occlusal rests require modification in preparation. • Buccal and lingual proximal margins must be extended well beyond line angles of tooth. • Axial wall is carved to confirm with external proximal curvature of tooth. • There should be 1–1.5 mm of restorative material between occlusal rest and inlay margin. • The rest is made on the wax pattern of inlay Inlays

104. 104 View of distal surface of MOD preparation for lower left second premolar showing broad extension of box, where occlusal rest with minor connector will be placed. (B) View of mesial surface, not as broad where there is only contact with adjacent tooth with no rest Occlusal view showing axial wall curvature in conformity with external proximal tooth curvature There should be 1–1.5 mm of restorative material between occlusal rest and inlay margin.

105. 105 Crowns • Three quarter crowns, complete coverage cast crowns and porcelain veneer crowns can be used. Ideal for partial denture is complete coverage crown. • Preparation should be made to accommodate the depth of occlusal rest, which is seen as a depression in the prepared tooth, in the rest area. • If crowns are to be veneered with acrylic resin or porcelain, they are surveyed again after veneering to confirm the established contours.

106. conclusion The success or failure of a RPD depends on how well the mouth preparations are accomplished. It is only through intelligent planning and competent execution of mouth preparations that the partial denture can satisfactorily restore lost dental functions and contribute to the health of the remaining oral tissues 106

107. References McCracken WL. Mouth preparations for partial dentures. J Prosthet Dent 1956;6:39–52 Stewart’s clinical removable partial prosthodontics 4 th edition McCracken's removable partial prosthodontics 13 th edition. Glann GW, Appleby RC. Mouth preparation for removable partial dentures. The Journal of Prosthetic Dentistry. 1960 Jul 1;10(4):698-706 107

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