Fundamentals in Tooth Preparation

1. Fundamentals in Tooth Preparation Dr. RameshBharti Assistant Professor Conservative Dentistry &Endodontics King George’s Medical University Lucknow

2. Definition of Operative Dentistry Operative dentistry is the ART and SCIENCE of the diagnosis, treatment, prognosis of defects of teeth which do not require full coverage restorations for correction, such treatments should results in the restoration of proper tooth form, function, and esthetics while maintaining the physiologic integrity of the teeth in harmonious relationship with adjacent hard and soft tissue, all of which enhance the general health and welfare of the patient.

3. Objectives of Cavity Preparation • Remove all defects and give the necessary protection to pulp. • Locate the margins as conservatively as possible. • Form the cavity so that both the restoration and tooth can withstand the load of mastication. • Allow for the esthetic and functional placement of a restorative material.

4. Need of Restoration • Caries • Malformed, discolored or fractured teeth • Restoration replacement

5. Factors affecting tooth preparation 1. General Factors • Pulpal & periodontal status • Occlusal relationship 2.Dental anatomy • Direction of enamel rods • Thichness of enamel /dentin • Size and positionof pulp • Relationship of tooth to its supporting tissues

6. 3.Patient factors • Age • Esthetic consideration • Economic status • Patients with high risk caries 4.Affected & infected Dentine 5. Restorative material factors

7. Approach of Operative. cont….. • Cavity preparation • Matrix application • Preparation of materials • Insertion and carving of materials • Finishing and Polishing

8. Cavity Preparation The mechanical alteration of a defective, injured, or diseased tooth in order to best receive a restorative material which will re-establish a healthy state for the tooth including esthetic corrections where indicated, along with normal form and function.

9. Cavity Structure • walls • angles • Floor

10. Classification of cavity • Class I • Class II • Class III • Class IV • Class V • Class VI —G.V.Black in 1908

11. Cavity • Simple cavity: only one tooth surface is involved. • Compound cavity: two surfaces are involved. • Complex cavity: three or more surfaces are involved.

12. Class 1 Class 6 Class 1 Class 4 Class 3 Class 2 Class 2 Class 5

13. Stages and Steps in Cavity preparation • Initial cavity preparation stage • Final cavity preparation stage

14. Initial cavity preparation stage Step 1 Outline form and initial depth Step 2 Primary resistance form Step 3 Primary retention form Step 4 Convenience form

15. Final cavity preparation stage Step 5 Removal of any remaining infected dentin if indicated Step 6 Pulp protection Step 7 Secondary resistance & retention form Step 8 Procedure for finishing external walls Step 9 Final procedures

16. Outline Form and Initial Depth Definition: • placing the cavity margins in the positions they will occupy in the final preparation. • preparing an initial depth of 0.2~0.8 mm pulpally of the dentinoenamel junction position or normal root surface position.

17. Maxillary Class Ⅰ outline form

18. Mandibular Class Ⅰ outline form

19. Maxillary Class Ⅱ outline form

20. Mandibular Class Ⅱ outline form

21. Common Error

23. Outline Form and Initial Depth Principles: • all friable and/or weakened enamel should be removed • all faults should be included • all margins should be placed in a position to afford good finishing of the margins of the restoration. • Margins of the preparation will be located on finishable, self –cleansing area.

24. Outline Form and Initial Depth Features: • preserving cuspal strength • preserving marginal ridge strength • minimizing facio-lingual extension • using enameloplasty • connecting two close faults or cavities • restricting the depth of the preparation into dentin.

25. Auxillary Factors • Conservation • Adjacent enamel cracks or decalcification could be involved in the preparation. • Type of restorative material. • Extension for access. • anatomy and alignment. • If possible, no margins will be in occlusion with opposing teeth. • Esthetics

29. Outline Form and Initial Depth for pit and fissure cavities Controlled by three factors 1- Extension to which enamel has been involved by caries. 2- Extension to achieve sound and smooth margins. 3- Limited bur depth while extending the preparaton

30. Rules • Capping of cusp should be done when cavity extension is two-third from central fissure to cuspal eminence. • Include all fissures that cannot be eliminated by enameloplasty. • Restrict the depth. • Join two lesions if they are less than 0.5 mm apart.

31. Outline Form and Initial Depth for smooth surface cavities • Extension of cavity. • Sufficient access. • Depth. • Sufficient clearance with adjacent tooth.

32. Initial cavity preparation stage Step 1 Outline form and initial depth Step 2 Primary resistance form Step 3 Primary retention form Step 4 Convenience form

33. Primary Resistance Form Definition: The shape and placement of the cavity walls that best enable both the restoration and the tooth to withstand, without fracture, masticatory forces delivered principally in the long axis of the the tooth.

34. Primary Resistance Form Principles: • To utilize the box shape with a relatively flat floor to resist occlusal loading by virtue of being at right angles to mastication force. • To restrict the extension of the external walls (keep as small as possible) to allow strong cusp and ridge areas to remain with sufficient dentin support.

35. Primary Resistance Form Principles: • To have a slight rounding of internal line angles to reduce stress concentration in tooth structure; • The presence of sharp internal line angles in GOLD FOIL resist the movement of the restoration • Sharp internal line and point angles in dentin serve as convenient “starting” points for compacting of direct gold. • To provide enough thickness of restorative material to prevent its fracture under load.

36. Primary Resistance Form Feature: • Box shape • Relatively flat floors • Inclusion of weakened tooth structure • Preservation of cusps and marginal ridges • Rounded internal line angles • Adequate thickness of restorative materials • Reduction of cusps for capping if indicated

37. Primary Resistance cont…. • Designing the outline form so that minimal of restoration is exposed to occlusal stress. • Seat on sound dentin.

38. Vale Experiments • 1 MR at 1/4th ICD -10% Loss of FR • 2 MR at 1/4th ICD - 15% Loss of FR • 1 MR at 1/3th ICD -30% Loss of FR • 2 MR at 1/3th ICD -35% Loss of FR • 1 MR at 1/2 of ICD -40% Loss of FR • 2 MR at ½ of ICD -45% Loss of FR

40. Initial cavity preparation stage Step 1 Outline form and initial depth Step 2 Primary resistance form Step 3 Primary retention form Step 4 Convenience form

41. Primary Retention Form Definition: The shape or form of the prepared cavity that resists displacement or removal of the restoration from tipping or lifting forces.

42. Primary Retention Form Principles:depending on the materials • Amalgam restoration: developing external cavity walls that converge occlusally and dovetail design

43. The devotail design provide retention form to the occlusal portion of the cavity. The occlusal convergence of the walls offers retention in the proximal portion of the cavity against displacement occlusally.

45. Primary Retention Form Principles:depending on the materials • Composite restoration: a mechanical bond between the material and conditioned, prepared tooth structure.

46. Dentin etched with 32% phosphoric acid Collagen exposed by the acid.

47. FIG Bonding of resin to dentin, using a "total-etch" technique

48. 16 Bonding to dentin using a self-etching primer.

49. Scanning electron micrograph of the transition between composite resin (C) adhesive (A), adhesive-hybrid layer (H), and hybrid layer-dentin.

50. Initial cavity preparation stage Step 1 Outline form and initial depth Step 2 Primary resistance form Step 3 Primary retention form Step 4 Convenience form