1. Class I Amalgam Preparations
Elizangela Bertoli, DDS, MS

2. Overview Indications and contraindications for amalgams
Advantages and disadvantages for amalgams
Conservative Class I Preparations
Bur Depth Cuts
Initial Tooth Preparation
Outline
Resistance
Retention
Convenience Forms
Final Tooth Preparation
Extensive Class II Preparations

3. Indications and Contraindications
Where esthetics is not highly important
Moderate to large preparations
Area that will have heavy occlusal contacts
Field cannot be well isolated
Root surface
Foundation for a full coverage restoration
Tooth that serves as an abutment for a removable partial denture

4. Indications and Contraindications
Esthetically prominent areas of posterior teeth
Small to moderate Class I and II defects that can be well isolated
Small Class VI defects

5. Advantages and Disadvantages
Ease of use and the simplicity of the procedure
Disadvantages
Complex and larger tooth preparations than composite resins
Non-esthetic

6. Conservative Class I Preparations
Outcomes
Protect the pulp: minimal pulp irritation
Preserve the strength of the tooth: remaining tooth structure is strong
Reduce deterioration of the amalgam restoration: enhances marginal integrity and restoration

7. Initial Tooth Preparations
Establish the outline form by extension of the external walls to sound tooth structure while maintaining a specified, limited depth (usually just inside the DEJ) and providing resistance and retention forms

8. Outline Form
Should include only the defective occlusal pits and fissures (in a way that sharp angles in the marginal outline are avoided)

9. Outline Form
Friable and/or weakened enamel should be removed Faulty and defective occlusal pits & fissures should be included in the preparation Margins preparation should be placed so the restoration margins can be easily finished and polished

10. Resistance Form Definition
Shape and placement of the preparation walls that best enable the remaining tooth structure and the restoration to withstand, without fracture, masticatory forces delivered principally in the long axis of the tooth.

11. Resistance Form Summary of Features Relatively flat floors Box shape
Inclusion of weakened tooth structure
Preservation of cusps and marginal ridges
Rounded internal line angles
Adequate thickness of restorative material
Reduction of cusps for capping

12. Resistance Form
Establish optimal, conservative depth of the pulpal walls
1.5 mm at the central fossa and 2.0 mm along the cuspal inclines
Resistance may be in the form of locks, grooves, or coves which are placed in line angles or point angles of your preparation
we usually think of locks, grooves, and coves as secondary resistance features

13. Retention Form
Definition of retention - The shape or form of the conventional preparation that prevents displacement or removal of the restoration by tipping or lifting forces for non-bonded restorations

14. Retention Form
Amalgam is retained in the tooth by developing external facial and lingual walls that converge occlusally (or are nearly parallel)

15. Retention Form Preparation is centered on major grooves
Facial-lingual width at isthmus does not exceed 1.5mm
Inclusion of mesial and distal pits
No extension to marginal ridges (1.5mm)
Tooth # 19
1.5 mm

16. Retention Form Occlusal internal form
Facial and lingual wall converse occlusally
Mesial and distal wall diverse occlusally
Pulpal depth is uniform ( mm)
Internal angles are defined but not sharp
Cavity is aligned with long axis of the anatomical crown

17. How do I begin my Class I Preparation?
Enter the deepest or most carious pit using a punch cut with a high speed handpiece
If M and D pits are carious, enter the distal pit first Why? Visibility

18. How do I begin my Class I Preparation?
Minimize extending into the marginal ridge. Why?
For strength of marginal ridge

19. Class I Preparation Depth Cuts
Keep the bur rotating until removed from the tooth
Dentinal caries initially spreads at the DEJ
the goal of the initial cut is to reach the DEJ
On posterior teeth, the approximate depth of the DEJ is located at 1.5 to 2 mm from the occlusal surface
Depth is 1.5 mm along the central fossa (or 1/2 length of a No. 245 bur)
Cuspal incline may extend up to 2 mm
Desired pulpal depth is mm into dentin
Most textbooks will state .5 mm

20. Bur Depth Cuts

21. Bur Depth Cuts
The No. 330 bur head length is 1 mm (1.5 mm) and it’s shorter than the No. 245 bur
Shape of No. 330 is also pear shaped (.8 mm diameter head)
No. 330 indicated for most conservative amalgam preparations

22. Mesiodistal longitudinal section
Faciolingual longitudinal section

23. Class I Preparation Depth Cuts
Distal extension into the distal marginal ridge to include a fissure or caries occasionally requires a slight tilting of the bur distally (≤10 degrees)
This creates a slight occlusal divergence to the distal wall to prevent undermining the marginal ridge of its dentin support

24. Class I Preparation
If the marginal ridge is 1.6 mm or greater, you can allow the M and D walls to converge. If the marginal ridge is less than 1.6 mm, then the M and D walls must diverge

25. Class I Preparation
The strongest and most ideal enamel margin will have full- length enamel rods resting on sound dentin, and supported by shorter rods on the restoration side
Enamel cavosurface angles, once again, should be close to 900
Remember: amalgam has a low edge strength (very brittle)

26. Summary Class I preparations Outline form
Preparation is centered on major grooves
Facial-lingual width at isthmus does not exceed 1.5mm
Inclusion of mesial and distal pits
No extension to marginal ridges (1.5mm)
Tooth # 19

27. Summary Class I preparations Occlusal internal form
Facial and lingual wall converse occlusally
Mesial and distal wall diverse occlusally
Pulpal depth is uniform ( mm)
Internal angles are defined but not sharp
Cavity is aligned with long axis of the anatomical crown

28. Summary Class I preparations Cavosurface angles and margins
Cavosurface angles are ˚
Cavosurface margins are definite & free of irregularities

29. Summary Class I preparations Finish
No gauges or large scratches in the lateral or pulpal walls

30. Initial Tooth Preparation
Occasionally for maxillary premolars, the outline may be butterfly-shaped (if you need to include all carious fissures facially or lingually)

32. Final Tooth Preparation
Caries may be removed
spoon excavator
round bur with a low speed handpiece
starting with the largest spoon excavator or the largest bur
Why the largest?
you’re less likely to get a pulp exposure and it allows visibility!

33. Final Tooth Preparation
Ensure all caries is removed from the DEJ. Why?
59% of the caries is missed at the DEJ

34. Deep Fissure on the Floor Tooth Preparation
Remove any defective enamel pit and fissure, but if the central fissure remains on the entire pulpal floor, go ahead and extend your preparation to maximum depth of 2 mm

35. Principles of Final Tooth Preparation
If there are isolated pit and fissure remnants and they are very small, simply use a small round bur (such as # ½, #1, or #2) to remove the caries

36. Final Tooth Preparation
Remember: don’t bevel amalgam occlusal preparations. Why?
Butt joint margins of enamel and amalgam approximating on the occlusal surface

37. Final Tooth Preparation
Remove any remaining defective(unsupported) enamel and infected dentin on the pulpal floor Secondary resistance & retention forms Finish the external walls (refine, remove scratches, etc) Clean and inspect your tooth preparation Consider pulpal protection (sealers, bases, or liners)

38. Conservative Class I Preparation Maxillary 2nd Molar

39. Conservative Class I Preparation Mandibular Second Premolar

40. Extensive Class I Amalgam Preparations
Extensive caries
The distance between infected dentin and the pulp is judged to be less than 1 mm
Wider faciolingual distances
Deeper and larger preparations
A more traditional indication for amalgam

41. Extensive Class I Amalgam Preparations
Procedure
Rubber dam isolation
Risk of pulp exposure
The preparation is extended laterally at the DEJ
to remove all enamel undermined by caries
For caries extending up the cuspal inclines:
it may be necessary to alter the bur's long axis to prepare a 90- to degree cavosurface angle while maintaining the initial depth

42. Tooth #30

43. What’s wrong with this preparation?

44. converging walls?
Rough pulpal floor
marginal ridge
width?

45. What’s this
black stuff?
rough
margin
Rough pulpal floor

46. What’s wrong with this preparation?

47. What’s wrong with this preparation?

48. What’s wrong with this preparation?

49. What’s wrong with this preparation?

50. What’s wrong with this preparation?

51. What’s wrong with this preparation?

52. What’s wrong with this preparation?

53. What’s wrong with this preparation?

54. Copyright
Most of pictures in this presentation comes from the text book adopted in the restoratives classes with permission from the publisher. No pictures may be reproduced without written permission from the publisher.
Sturdevant’s Art and Science of Operative Dentistry 6th Edition
Sturdevant’s Art and Science of Operative Dentistry 6th Edition
Fundamentals of Operative Dentistry 4th Edition