PRINCIPLES OF TOOTH PREPARATION ppt given

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1. Principles of Tooth Preparataion in Fixed Partial Dentures Presented By Shabeena Mustafa PG-II Year

2. Contents Introduction Objectives of tooth preparation Principles of tooth Preparation Definition of FPD Types of Fixed prostheses Retainers Conservation of tooth structure Margin placement and Design Restorations and margins Porcelain fused metal crowns

3. INTRODUCTION Tooth preparation may be defined as the mechanical treatment of dental disease or injury to hard tissue that restores a tooth to the original form ( Tylman ). The mechanical preparation or the chemical treatment of the remaining tooth structure, which enables it to accommodate a restorative material without incurring mechanical or biological failure.( Marzouk ) The current focus is on conservative tooth preparation that is noninvasive and that minimally involves dentin. PRINCIPLES OF TOOTH PREPARATION . NAIR RR

4. Black’s principles of cavity preparation and Tylman’s principles of tooth preparation are both presently being modified to accommodate imaginative approaches i.e., acid etching with minimum reduction. Dentistry is changing from macro tooth preparation to an environment of molecular chemistry i.e., esthetic bonding. These techniques are not presently supported by any longitudinal studies, but are exciting and promising

5. Despite these advances, traditional crowns are still indicated for majority of patients. Diagnosis and disciplined tooth preparation are essential to successful fixed prosthetics.

6. OBJECTIVES OF TOOTH PREPARATION 1.Reduction of the tooth in miniature to provide retention. 2.Preservation of healthy tooth structure to secure resistance form. 3.Provision for acceptable finish line. 4.Performing pragmatic axial tooth reduction to encourage favorable tissue responses from artificial crown contour.

7. PRINCIPALS OF TOOTH PREPARATION According to Rosentsteil

8. FIXED PARTIAL DENTURES According to Glossary of Prosthodontic Terms - GPT 9 th edition (2005) fixed prosthodontics is defined as, “The branch of prosthodontics concerned with the replacement and/ restoration of the teeth by artificial substitutes that not readily removed from the mouth.”

9. TYPES OF FIXED PARTIAL PROSTHESES All metal crowns. b. Porcelain Fused Metal crowns c. All ceramic crowns. d. Acrylic crowns. e. Porcelain veneers. i Full veneer ii Partial Veneer g. Laminates h. Post and core i.Resin Bonded i. Resin Retained J .Anterior partial coverage Crowns k. Posterior Partial coverage crowns l.Cantilever Bridges

10. Retainers. “The part of a fixed dental prosthesis that unites the abutment(s) to the remainder of the restoration.” GPT – 9

11. RETAINERS CORONAL RADICULAR INTRA CORONAL EXTRA CORONAL INLAY ONLAY PARTIAL VENEER CROWN FULL VENEER CROWN POST AND CORE

12. FULL VENEER PARTIAL VENEER ONLAY INLAY LAMINATE VENEER TELESCOPIC CROWN

13. MESIAL HALF CROWN RESIN BONDED BRIDGES

14. CONSERVATION OF TOOTH STRUCTURE

15. Partial coverage rather than complete coverage

16. Preparation with minimum convergence angle (taper) between axial walls

17. In 1923 Prothero indicated that the convergence of surfaces should be 2-5 ◦ In 1955 Jorgenson tested the retention of crown and concluded that maximal retention was recorded at 5º.

18. Preparation of the occlusal surface: reduction follows the anatomic planes to give uniform thickness to the restoration.

19. Preparation of the axial surfaces: - tooth structure is removed evenly. - if necessary, teeth should be orthodontically repositioned

20. Selection of a conservative margin compatib le with the other principles of tooth preparation

21. Avoidance of unnecessary apical extension of preparation

22. MARGIN PLACEMENT Whenever possible, the margin of the preparation should be supragingival . Advantages of supragingival margins: They can be easily finished without trauma to soft tissues. They are more easily kept clean. Impressions are more easily made, with less potential for soft tissue damage. Restorations can be easily evaluated at recall appointments.

23. Indications of subgingival margin Dental caries, cervical erosion, or restorations extending subgingivally and a crown-lengthening procedure is not indicated. The proximal contact area extends to the gingival crest. Additional retention is needed. The margin of a metal-ceramic crown is to be hidden behind the labiogingival crest. Root sensitivity cannot be controlled by more conservative procedures. Modification of the axial contour is indicated (undercuts).

24. MARGIN ADAPTATION The junction between a cemented restoration and the tooth is always a potential site for recurrent caries because of dissolution of the luting agent and inherent roughness. A well-designed preparation has a margin that is smooth and even.

25. Rough, irregular, or "stepped" junctions greatly increase the length of the margin and substantially reduce the adaptation of the restoration.  

26. RATIONALE FOR COMPARISON OF PLAQUE-RETAINING PROPERTIES OF CROWN SYSTEMS JOHN A. SORENSEN(1989) The factors that mediate plaque accumulation and influence gingival health at the tissue-restoration interface are: Surface roughness : Since bacterial colonization originates in the protected sites of microscopic grooves, the crown micro-topography is crucial. The linearity of the marginal finish line, if irregular, increases roughness and hence plaque accumulation. Marginal fit : Marginal discrepancy determines the amount of exposed cement retaining plaque and/or the plaque niche between the crown and tooth. The degree of marginal rounding determines the area of exposed cement and possible plaque habitation. Contour : An over-contoured margin compromises oral hygiene and hinders professional scaling.

27. MARGIN GEOMETRY Guidelines for margin design: Ease of preparation without overextension. Readily identifiable in the impression and on the die. A distinct boundary to which the wax pattern can be finished. Sufficient bulk of material (to enable the wax pattern to be handled without distortion as well as give the restoration strength and, when porcelain is used, esthetics). Conservative of tooth structure (provided the other criteria are met).

28. PROPOSED MARGIN DESIGN CHISEL EDGE Advantage: conservative Disadvantage: location of margin difficult to control Indication occasionally on tilted teeth

29. PROPOSED MARGIN DESIGN FEATHER EDGE - Advantage: conservative - Disadvantage: does not provide sufficient bulk - Not recommended.

30. BEVEL EDGE Advantages: unsupported enamel removed, allows finishing of metal Disadvantage: extends preparation into sulcus if used on apical margin Indication: facial margin of maxillary partial coverage crowns

31. CHAMFER Advantage distinct margin, adequate bulk, easier to control Disadvantage care needed to avoid unsupported lip of enamel Indications cast metal restorations, lingual margin of metal ceramic crowns

32. SHOULDER Advantage bulk of restorative material, Disadvantage less conservative Indication facial margin of metal ceramic crowns, complete ceramic crowns

33. SLOPED SHOULDER Advantage bulk of material, Disadvantage less conservative Indication facial margin of metal ceramic crowns

34. SHOULDER WITH BEVEL Advantage bulk of material, advantages of bevel Disadvantage less conservative, extends preparation apically Indication facial margin of posterior metal ceramic crowns with supragingival margins

35. A study was conducted by Jung-zen et. al.in (1993IJP) on the influence of finish line geometry on the fit of the crown. Three tooth preparation were considered that had different labial finish line configuration shoulder, shoulder with bevel and chamfer. Result: marginal fit was not influenced by the type of finish line. Castings with well-fitting margins exhibited axial wall space between 15 and 33 μ m.

36. Grooves and boxes incorporation Adding grooves or boxes to a preparation with a limited path of withdrawal does not markedly affect its retention because the surface area is not increased significantly( Rosenstiel ). However other authors have reported that, where the addition of grooves or boxes limits the path of withdrawal, retention is increased

37. RETENTION AND RESISTANCE Retention prevents removal of the restoration along the path of insertion or long axis of the tooth preparation. Resistance prevents dislodgement of the restoration by forces directed in an apical or oblique direction and prevents any movement of the restoration under occlusal forces. Retention and resistance are interrelated and often inseparable qualities.

38. RESTORATIONS AND MARGINS

39. ALL METAL CROWN

40. PORCELAIN FUSED METAL CROWNS

41. PREPARATION FOR FULL VENEER CROWN

42. FULL VENEER CROWN Variations of the full veneer crown are Metal-ceramic crown. All-ceramic crown.

43. FULL VENEER CROWN INDICATIONS : Extensive coronal destruction due to caries or trauma. Endodontically treated tooth. Necessity for maximum retention and strength. To correct minor malinclination . To correct occlusal plane.

44. FULL VENEER CROWN Contra-indication : Full coverage should not be used in mouths with uncontrolled caries. It does not protect the tooth against the biological causes of caries. Caries must be controlled by other means before any restoration can be successful.a

45. FULL METAL CROWN PREPARATION ARMAMENTARIUM : Hand piece No : 171L bur Round-end tapered diamond Short needle diamond Torpedo diamond Torpedo bur Red utility wax

46. FULL METAL CROWN PREPARATION STEP NO :1 OCCLUSAL REDUCTION 1.5 mm of clearance of functional cusp and 1mm on the nonfunctional cusp. Depth orientation grooves are placed on the occlusal surface with round end tapered diamond.

47. Full metal crown preparation Occlusal reduction : A round-end tapered diamond is used to place the grooves on the ridges and the primary grooves of the occlusal surface. If there is already some clearance with the opposing tooth because of malposition- grooves should not be made as deep.

48. Full Metal Crown Preparation OCCLUSAL REDUCTION : The occlusal reduction should follow the configuration of the geometric inclines that make the occlusal surface of any posterior teeth.

49. Full Metal Crown Preparation STEP NO : 2 Functional cusp bevel with round-end tapered diamond. A wide bevel is placed on the functional cusp-depth orientation grooves are also helpful in this reduction. Functional cusp bevel is integral part of occlusal reduction. Failure to place this bevel can produce thin casting or poor morphology.

50. Full Metal Crown Preparation OCCLUSAL CLEARANCE : Is checked by having the patient to close on red utility wax held over the preparation.

51. Full Metal Crown Prep STEP NO : 3 Buccal and lingual walls are reduced with the round-end tapered diamond.The sides of the diamond will produce the desired axial reduction while the tip forms the chamfer.

52. Full Metal Crown Preparation STEP NO : 4 Initial proximal axial reduction with short needle diamond followed by the round-end tapered diamond.

53. Full Metal Crown Preparation STEP NO : 6 Seating groove with 171L bur.

54. Full Veneer Crown Preparation

55. Full Veneer Crown Preparation STEP NO : 5 Axial finishing- round-end tapered diamond. All axial surfaces are smoothed including all point angles. The finish line should be smooth and continuous.

56. Full Veneer Crown Preparation