Tooth preparation

OPERATIVE DENTISTRY

1. Tooth Preparation By Dr Ambalika Raj

2. Contents Definition Objectives Terminology Tooth preparation terminology Classification of tooth preparation Initial stage of tooth preparation Final stage of tooth preparation Additional concepts in tooth preparation

3.                  Definition Tooth preparation is the mechanical alteration of a defective, injured, or diseased tooth such that placement of restorative material reestablishes normal form (and therefore function) including esthetic corrections, where indicated. ( Sturdevant )

4.                  Objectives

5.                Terminology Anatomic crown Clinical crown Crystalline restorative material Polymeric restorative material Intracoronal  tooth preparation Extracoronal tooth preparation

6.           Extracoronal preparation

7. Simple tooth preparation -  only one tooth surface is involved , eg , O Compound  -  two or three surfaces are involved , e.g. MO Complex – 4 or more surfaces involved , e.g. MODL

8. 4. Internal wall – A prepared surface that does not extend to the external tooth surface. E.G. axial wall , pulpal wall. A. Axial wall - an internal wall that is oriented parallel to the long axis of the tooth. B. Pulpal wall - an internal wall that is oriented perpendicular to the long axis of the tooth and is located occlusal to the pulp. 5. External wall - A prepared surface that extends to the external tooth surface.

9. 12. Cavosurface angle - The angle of tooth structure formed by the junction of a prepared wall and the external surface of the tooth. The actual junction is referred to as cavosurface margin.

10. Classification of tooth preparation

11.       G.V. Black's Classification

12.     Stages of cavity preparation

13.   Steps in initial tooth preparation

14. Step 1 – Outline form and initial depth Establishing the outline form means  (1) placing the preparation margins in the positions they will occupy in the final preparation except for finishing the enamel walls and margins (2) preparing an initial depth of 0.2 to 0.8 mm pulpally of the DEJ position or normal root – surface position ( no deeper initially whether in tooth structure , air , old restorative material , or caries unless the occlusal enamel thickness is minimal , and greater dimension is necessary for strength of the restorative material ).

15. 1 . Outline form for pit and fissure caries Avoid terminating the margin on extreme eminence such as cusp height. Extend to include all fissure mot eliminated by enameloplasty. Restrict the depth to 0.2mm into dentin . For amalgam , depth of 1.5 mm prepared first . If < 50 % enamel pit or fissure on pulpal floor present - removed in final   tooth preparation stage. If enamel pit and fissure  on > 50% of pulpal floor , entire flor is deepened.

16. Outline form for conventional amalgam preparation is = butterfly type preparation As much of the cuspal incline as possible should be preserved in any preparation involving the occlusal surface. All developmental grooves should be included.This may necessitate   extending onto the facial or lingual SURFACES .

17. 2.Outline form for smooth surface lesion In 2 locations - Proximal surfaces Gingival portion of facial and lingual surfaces A. Proximal surface -   Extend preparation to sound tooth structure Avoid terminating margins on extreme eminences Restrict axial wall pulpal depth of proximal preparation to 0.2 to 0.8 mm into dentin. Gingival margins = apical to proximal contact to provide a clearance of atleast 0.5 mm between adjacent teeth. Facial and lingual margins of proximal preparation extended into embrasures ( self cleansing) 

18. B. Gingival portion of facial and lingual surfaces ( Class V ) -  Outline form is determined by extent of caries except pulpally. Depth of 0.8 to 1.25 mm pulpally. In class III restoration , when extending the proximal surface incisally , the incisal margin may be placed in the area of contact ,  esp .when an esthetic material is used.

19. To do enameloplasty or not -

20. Step 2 – Primary resistance form   It is defined as the shape and placement of the preparation walls that best enable the restoration and the tooth to withstand , without fracture , masticatory forces delivered principally in the long axis of tooth.

21.        Stress bearing areas on tooth

22. Principles of resistance form -  1. Box shaped cavity with flat floor ( resist forces by being at right angles to masticatory loads ) 2. Restrct the extension of external walls to preserve ridge and cusp. 3.Slight rounding of internal line angle 4. Cap weak cusps 5. Provide enough thickness of restorative material to prevent its fracture under load. 6.Bond the material to tooth structure.( whenever possible ) - Conventional and bevelled conventional preparation have these features- require a specific form , depth andmarginal configuration, eg. Amagam , cast meatl and ceramic. - Modified preparation design – small, medium composite restoration , no uniform depth – scooped design.

23.          Modified cavity preparation

24. Minimally extended facial and lingual walls conserve dentin supporting the cusps and facial and lingual ridges. Amalgam - 1.5 mm  Cast metal - 1 to 2 mm Porcelain – 2mm Composite – 1 to 2 mm usually ( acute marginal angles )

25. Step 3 – Primary retention form Primary retention form is the shape or form of the preparation that prevents displacement or removal of the restoration by tipping or lifting forces. Principles - - Depends on the restorative material used, - Hence different principles for different material.

26. 2. Composite - >90 degrees cavosurface angle Micromechanical bond between material and etched tooth structure. 3. Cast metal - Almost parallel vertical walls  Greater vertical height of walls Occlusal divergence in inlay and onlay preparation.

27.       Step 4 – Convenience form Convenience form is the shape or form of the preparation that provides for adequate observation, accessibility, and ease of operation in  preparing and restoring the tooth. Ideally a tooth preparation fulfilling all requirements for outline , resistance , retention form will be convinient to instrumentation. E.g.  Extension of the proximal walls, so as to obtain clearance with an adjacent proximal surface, may aford better access for the inishing of preparation walls, the placement of the matrix, and the inishing of the restoration margins.