This document discusses the steps involved in cavity preparation, including establishing the outline form, obtaining resistance form, obtaining retention form, obtaining convenience form, removing remaining carious dentin, finishing enamel walls and margins, and performing the toilet of the cavity. The key principles for each step are outlined, such as ensuring all undermined enamel is removed, providing box-shaped cavities with rounded internal angles to resist stresses, and using beveled margins for certain restorative materials. Thorough cleaning of the prepared cavity is emphasized before placement of restorative materials.

1. Cavity Preparation
University of Dental Medicine, Yangon
3rd B.D.S (1/2018) 52nd Batch
Min Thant
1Min Thant2/7/2018

2. Steps in Cavity Preparation
1. Establishing Outline form
2. Obtaining Resistance form
3. Obtaining Retention form
4. Obtaining Convenience form
5. Removing remaining carious dentine
6. Finishing enamel walls & margins
7. Performing the toilet of cavity
2Min Thant2/7/2018

3. ESTABLISHING OUTLINE FORM
Min Thant
3Min Thant2/7/2018

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
4Min Thant2/7/2018

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
5Min Thant2/7/2018

6. Rules for establishing outline form for
pit & fissure
1) Extend the cavity margin until the sound
tooth structure is obtained
• Removal of unsupported enamel
6Min Thant2/7/2018

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

8. 3) 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
8Min Thant2/7/2018

9. 5) Minimally extend into the proximal ridges
• To prevent the ridges from being undermined
6) Extend the margins just to provide
adequate convenience form
9Min Thant2/7/2018

10. Rules for establishing outline form for
smooth surface
1) Extend the cavity margin until the sound
tooth structure is obtained
• Removal of unsupported enamel
2) Avoid ending the margin on cuspal heights
or ridge crests
10Min Thant2/7/2018

11. 3) Extend the margin to provide the
convenience form
4) 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)
11Min Thant2/7/2018

12. 5) 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)
12Min Thant2/7/2018

13. OBTAINING RESISTANCE FORM
Min Thant
13Min Thant2/7/2018

14. Obtaining Resistance Form
It is the shape created to the cavity
by the placement of the cavity walls
- which best enables the tooth (& the
restoration) to resist or counteract the stress
falling on the restoration & the remaining
tooth structure during mastication process
14Min Thant2/7/2018

15. General Principles
1. The cavity should be box shape with flat floor
• To resist the occlusal loading at Rt. angle
15Min Thant2/7/2018

16. 2. Restrict the extension of the walls
• To allow strong cusp & ridge areas
• To remain with sufficient dentin support
16Min Thant2/7/2018

17. 3. 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)
4. Make the internal angles curved or
rounded to reduce stress conc:
17Min Thant2/7/2018

18. 18Min Thant2/7/2018

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

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

24. 6. Using adhesive systems as acid etching
technique for micromechanical retention
7. 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
1) To provide the best marginal seal possible at
tooth-material interface
2) To afford a smooth marginal junction
3) To provide marginal strength of both enamel
& restorative material at the margin
2/7/2018 Min Thant 35

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

37. 3) 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
4) Location of the margin
5) 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