Class I Amalgam Tooth Preparations

Question 1

Which requires more preparation: amalgam or composite restorations?

Answer 1

The amalgam requires much more preparation.
For composites, decay dictates the prep.
For amalgams, there is a min size/shape for the prep.

Question 2

Why does amalgam require a min thickness?

Answer 2

To offer the best mechanical strength and retention.

Question 3

For a small caries lesion, is amalgam or composite preferred?

Answer 3

Composite - much less tooth structure is removed.

Question 4

When is amalgam preferred over composite?

Answer 4

If:

1. the caries is moderate to large
2. Need strong foundation for partial dentures
3. when in areas of heavy occlusal contacts
4. placing a full coverage restoration - use amalgam as the foundation
5. the patient has many caries, high activity
6. the cost is an issue

Question 5

Why might you pay special attention to the outline form?

Answer 5

Consider the outline form carefully to prevent margins from being located at the occlusal contacts

Question 6

What are the steps to creating the preparation?

Answer 6

1. Create access to faulty structure
2. Remove the faulty structure
3. Create resistance, convenience, and retention forms

Question 7

Do internal line angles matter for amalgam?

Answer 7

Yes, they still matter. Avoid sharp internal line angles - these create points of high pressure that can crack the tooth.

Question 8

What does a class I amalgam outline look like?

Answer 8

Curvy!

Avoid sharp angles, preserve the cusp strength by avoiding triangular ridges, remove any weak or undermined enamel.

Question 9

What is the minimum depth for the amalgam prep? Why?

Answer 9

1.5 mm is deep enough to enter the dentin

Question 10

How should the bur be aligned when cutting?

Answer 10

The head of the handpiece should be parallel to the occlusal plane…bur is perpendicular to the occlusal plane.

Question 11

Is the pulpal floor in the dentin or the enamel?

Answer 11

Cut through to the dentin so that the pulpal floor is in the dentin.

Question 12

How much tooth structure should be left at the borders (marginal ridges) to withstand the forces of the amalgam?

Answer 12

1.6 mm!

Question 13

Should the mesial and distal walls be convergent or divergent.

Answer 13

Slightly divergent to conserve dentinal support (NOT for retention - there is no binding!)

Question 14

Does it matter if the pulpal floor is flat?

Answer 14

Yes. Need it to be flat for the restoration strength and to protect the tooth structure. Don’t want any focused forces on one point of the tooth.

Question 15

Should the facial and lingual walls be convergent or divergent.

Answer 15

They should be slightly convergent for mechanical retention.

Question 16

If the pulpal floor isn’t flat in the clinic, what can be done?

Answer 16

Fill the defect to create a level floor.