Amalgam Cavity Preparation Class I

Question 1

What location groups are involved in class I lesions?

Answer 1

The occlusal surfaces of molars and premolars

The occlusal 2/3rds of buccal and lingual surfaces of molars

Lingual surfaces of anterior teeth

Question 2

What are the common predilection places of caries?

Answer 2

Plaque retentive locations that are not self-cleansable

Question 3

Where is a class 1 prep done in anterior teeth?

Answer 3

Convex protuberance at the cervical third of the anatomical crown

Question 4

What is a tooth cavity preparation?

Answer 4

Mechanical alteration of a defective injured or diseased tooth to receive a restorative material that re-establish the normal form, function and aesthetics.

Question 5

What are the aims of tooth restoration?

Answer 5

Removal of tooth structures affected by caries

Retention form + Resistance form (to know displacement)

Prevention of restoration deformation = Fracture

Protection of remaining tooth structures

Aesthetics

This is to:

Protect the pulp

Preserve strength of the tooth

Reduce the deterioration of amalgam structures

Question 6

What should we know about tooth before making a preparation?

Answer 6

Biology of tooth and periodontium

Enamel and Dentin structure

Properties of restorative material

Occlusion

Question 7

What are the advantages and disadvantages of amalgam restorations?

Answer 7

Advantages:

Strong and durable

Cheaper

Easy to use and less technique sensitive

Self-sealing ability meaning there is lower rate of microleakage

Wear resistance similar to tooth structure

Disadvantages:

Aesthetic

No bond to tooth structure - rely on mechanical retention

Safety issues - Mercury toxicity

Question 8

What are the features of a successful amalgam restoration?

Answer 8

Retentive and resistance form: Refers to macromechanical features such as convergence opposing walls, grooves, and mortise form.

Structural durability of restorative material (right angle butt joints, adequate bulk, smooth and flat walls)

Structural durability of tooth (Right angle butt joints, removal of unsupported enamel)

Proximal clearance: Break interproximal contact points with adjacent teeth

Question 9

What are the stages of preparation of cavity?

Answer 9

Initial cavity preparation stage involves extending the limits of the cavity to sound tooth structures: Enamel supported by sound dentine

Final cavity preparation stage: Remove infected carious dentine, old restorative material from the bottom of the cavity, protect the pulp (liner and base), incorporate cavity design features, finishing the prep walls.

Question 10

What should outline of the class 1 prep look like?

Answer 10

Smooth and gentle curves with no angular contours.

Question 11

Why should angular contours be avoided?

Answer 11

Restoration can chip during condensation

Concentrating the stress and leading to restoration fracture

Question 12

What is the danger of invagination of a preparation cavity?

Answer 12

It is susceptible to fracture

Question 13

What is the danger of evagination of a preparation cavity?

Answer 13

Difficult to condense material into the corners.

Question 14

What are the principles of extension of a class 1 preparation?

Answer 14

Encompass the carious lesion

Eliminate unsupported enamel

Encompass contiguous restoration

Encompass contiguous fissures

Question 15

What is the rationale behind extending a class 1 cavity?

Answer 15

To eliminate infected tissue

To eliminate weakened structures and protect remaining ones

To maximize restoration lifespan

To reduce the risk of secondary disease

Question 16

How far should bucco-lingual extension go?

Answer 16

Extend far enough towards buccal and lingual grooves to have gentle contours

Margin in sharp anatomy is difficult to polish and clean

Extend minimally to the ridge area and cusps to preserve cusp strength

Question 17

What is the purpose of medio-distal extension?

Answer 17

Narrow groove extension to preserve cusp strength.

Ensure you stay far from the marginal ridge to preserve its strength.

Question 18

What are the features of the occlusal class i preparation depth?

Answer 18

2mm deep

Sufficient bulk of restorative material to give mechanical resistance

Pulp protective

Convergent 6 degrees pulp-occlusally (retention form)

Question 19

What should the pulpal floor look like in a class 1 cavity?

Answer 19

Flat and smooth

Parallel to occlusal surface

Uniform thickness of amalgam to prevent fracture

Best resistance to occlusal stress and forces of condensation - better stress distribution

Question 20

How should cavity angles be in class 1 preparations?

Answer 20

Internal line angles should not be sharp and should be well defined.

This is to maximize amalgam resistance to dislodgement and to reduce stress concentration and subsequent risk of tooth fracture

Question 21

How should the cavosurface angle look in a class 1 preparation?

Answer 21

It should be well-defined and well supported.

This is easier to visualize and carve following condensation.

Optimize adaptation of amalgam to margins. Bevel poor defined margin.

Eliminates weak tooth structure

Question 22

How can we see the occlusal contact points and see whether they have been restored or not?

Answer 22

Articulating paper

Question 23

What is the clinical sequence of class 1 preparations?

Answer 23

Registration of occlusal contacts

Local anaesthesia (Topical, infiltration, nerve block)

Rubber dam

Tooth cavity preparation (removal of remaining infected dentin: Spoon escavator or slow speed round carbide burr)

Pulpal protection (Liner and base if needed)

Cavity cleanliness (free of debris and moisture, facilitate adaptation of amalgam to the cavity, improves the physical properties of the restoration by eliminating voids and foreign material)