General rules for Cavity Preparations

Steps in tooth cavity preparations

1. Cavity Preparation University of Dental Medicine, Yangon 3 rd B.D.S (1/2018) 52 nd Batch Min Thant 1 Min Thant 2/7/2018

2. Steps in Cavity Preparation Establishing O utline form Obtaining Resistance form Obtaining Retention form Obtaining Convenience form Removing remaining carious dentine Finishing enamel walls & margins Performing the toilet of cavity 2 Min Thant 2/7/2018

3. Establishing outline form Min Thant 3 Min Thant 2/7/2018

4. Establishing Outline Form Outline form is the form given to the cavity which will determine the final location of the enamel-restoration interface of the completed restoration 4 Min Thant 2/7/2018

5. General Principles All undermined enamel should be removed All margins should be placed in a position to afford good finishing of the margins of the restoration 5 Min Thant 2/7/2018

6. Rules for establishing outline form for pit & fissure Extend the cavity margin until the sound tooth structure is obtained Removal of unsupported enamel 6 Min Thant 2/7/2018

7. Extend the cavity margin to include all the fissures, placing the margin on relatively smooth, sound tooth sturct : When 2 pit & fissure cavities are < 0.5 mm Join them weak enamel b/w them   2/7/2018 Min Thant 7

8. Go around the cusp to conserve tooth struct : To prevent the internal line angles from approaching the pulp horns too closely Cavity should be ¼ of intercuspal distance (or) 1/3 of the cuspal slope 8 Min Thant 2/7/2018

9. Minimally extend into the proximal ridges To prevent the ridges from being undermined Extend the margins just to provide adequate convenience form 9 Min Thant 2/7/2018

10. Rules for establishing outline form for smooth surface Extend the cavity margin until the sound tooth structure is obtained Removal of unsupported enamel Avoid ending the margin on cuspal heights or ridge crests 10 Min Thant 2/7/2018

11. Extend the margin to provide the convenience form Extend gingival margins apically of the contact area To provide specified clearance b/w gingival margin & adjacent tooth (at least 0.5 mm below the contact area ) 11 Min Thant 2/7/2018

12. In proximal cavities, extend the facial & lingual margins → receptive embrasures to provide specificed clearance b/w the margins & the adjacent tooth (Margin should be 0.2 mm away from the adjacent tooth so that the margins can be visualized, instrumented & better cleaned) 12 Min Thant 2/7/2018

13. Obtaining resistance form Min T hant 13 Min Thant 2/7/2018

14. Obtaining Resistance Form It is the shape created to the cavity by the placement of the cavity walls w hich best enables the tooth (& the restoration) to resist or counteract the stress falling on the restoration & the remaining tooth structure during mastication process 14 Min Thant 2/7/2018

15. General Principles The cavity should be box shape with flat floor To resist the occlusal loading at Rt. angle 15 Min Thant 2/7/2018

16. Restrict the extension of the walls To allow strong cusp & ridge areas To remain with sufficient dentin support 16 Min Thant 2/7/2018

17. Prepare adequate depth of the cavity to provide sufficient thickness of the restorative material That prevent bulk fracture under load ( minimal occlusal thickness of amalgam restoration = 1.5 mm ) Make the internal angles curved or rounded to reduce stress conc : 17 Min Thant 2/7/2018

18. 18 Min Thant 2/7/2018

19. Obtaining retention form Min Thant 2/7/2018 Min Thant 19

20. Obtaining Retention Form It is the shape or form of the cavity that best permits the restoration To resist displacement through tipping or lifting forces 2/7/2018 Min Thant 20

21. General Principles Having sufficient length of parallel walls that allow enough frictional resistance & mechanical locking of the restorative material in minute irregularities of the cavity wall 2/7/2018 Min Thant 21

22. Slight convergence of the facial & lingual walls ( 85 undercut ) occlusally to provide mechanical locking against vertical displacement   2/7/2018 Min Thant 22

23. Placing a small channel or groove at the line angles in the proximal portion of the cavity Placing small undercut areas at the point Dovetail preparation for class II cavities To prevent lateral displacement of the restoration by occlusal F   2/7/2018 Min Thant 23

24. Using adhesive systems as acid etching technique for micromechanical retention Pins for additional retention 2/7/2018 Min Thant 24

25. Obtaining convenience form Min Thant 2/7/2018 Min Thant 25

26. Convenience Form The shape given to the cavity To provide reasonable access for the removal of caries To allow proper instrumentation & Placement of the lining & restoration 2/7/2018 Min Thant 26

27. Should allow Accessibility Visibility Ease of operation Extension of facial margins on ant. Teeth for ESTHETIC REASON 2/7/2018 Min Thant 27

28. Removing carious dentin removal of remaining caries Min Thant 2/7/2018 Min Thant 28

29. Removing Carious Dentin The elimination of any infected carious tooth structure or faulty restorative material left in the tooth after initial cavity preparation 2/7/2018 Min Thant 29

30. Infected dentin - dentin occupied by micro-org with their toxins Affected dentin - dentin without micro-org but contain toxins from the infected dentin 2/7/2018 Min Thant 30

31. If the pulp is not at risked, affected dentin → should be removed [ until sound dentin is visible] Otherwise, infected dentin removed affected dentin remained Clinical description of exactly where infected dentin stops & affected dentin begins IMPOSSIBLE 2/7/2018 Min Thant 31

32. Remaining carious dentin is removed by Smooth diamond round burs rotating at slow spd Excavator , if carious dentin is too close to pulp 2/7/2018 Min Thant 32

33. Sometimes, carious dentin is detected by Fusayama solution However, this method is unreliable [ rapidly developed caries → sometimes relatively unstained (or) The dye may also stain sound dentin ] 2/7/2018 Min Thant 33

34. Finishing the enamel walls & margins Min Thant 2/7/2018 Min Thant 34

35. Finishing the Enamel Walls & Margins Purposes To provide the best marginal seal possible at tooth-material interface To afford a smooth marginal junction To provide marginal strength of both enamel & restorative material at the margin 2/7/2018 Min Thant 35

36. The following should be considered Directions of the enamel rod Margins that end enamel rods have strongest R [d/t 90 (or) butt joint margin] Support of enamel rods both at DEJ & laterally Undermined enamel margins liable to fracture under occlusal load   2/7/2018 Min Thant 36

37. Types of restoration to be placed in preparation 90 butt joint for amalgam restoration 45 bevel for gold inlay Rounded or beveled margin for composite restorations Location of the margin Smoothness Desire for metal restorations Smooth marginal preparation is of paramount importance   2/7/2018 Min Thant 37

38. Performing toilet of the cavity Min Thant 2/7/2018 Min Thant 38

39. Performing the Toilet of the Cavity Procedure involved in Removing all chips & loose debris Drying the cavity Making a final complete inspection of the preparation for any remaining caries Unsound enamel margins Any condition that renders the cavity unacceptable to receive restorative material 2/7/2018 Min Thant 39

40. This procedure facilitates Adaptation of the lining & restoration against clean cavity walls Removal of chips & debris can be accomplished by air-water spray Cleaning by medicament should be careful As some agents can harm the pulp irreversibly 2/7/2018 Min Thant 40