Principles of Cavity Preparation

Question 1

Fundamental concepts for all tooth preparations

Answer 1

1- Removal of dental caries
2- Removal of weak tooth structure to provide well supported sound hard tissue
3- Pulp protection

Question 2

Cavity Preparation

Answer 2

mechanical alteration of a diseased or a defective part of the tooth to receive a restorative material to ultimately restore healthy state of the tooth, longevity and patient comfort.

Question 3

Healthy state is reestablishing….

Answer 3

• Tooth is not diseased anymore
• Normal function and form
• Esthetically pleasing where indicated (anterior zone of the oral cavity)

Question 4

Line angles

Answer 4

junction of two surfaces

Question 5

Point angles

Answer 5

Junction of three surfaces

Question 6

Cavosurface margin

Answer 6

Junction between the external walls of the cavity preparation and the uncut tooth surface.

Question 7

Dovetail

Answer 7

-In class I cavity preparations, isthmus connects the 2
dovetails
-Dovetail design includes each marginal fossa and the
developmental grooves around the marginal pits

Question 8

Isthmus

Answer 8

In a class I: narrowest portion of a
cavity preparation

Class II: a portion of the cavity
connecting an occlusal portion
and a proximal portion together

Question 9

External wall

Answer 9

extend to the outer tooth surface

• mesial
• distal
• buccal
• gingival

Question 10

Internal wall

Answer 10

do not extend to the outer tooth surface

Question 11

Axial walls

Answer 11

parallel to the long axis

• gingival
• pulpal

Question 12

Cavosurface angle

Answer 12

angle formed between tangent formed of hitting cavosurface margin at one point and the external cavity wall

Question 13

6 Basic Principles of Cavity Preparation

Answer 13

1. Outline form
2. Resistance form
3. Retention form
4. Convenience form
5. Finishing
6. Debridement

Question 14

Outline Form

Answer 14

The shape of the cavity preparation;
perimeter of the tooth preparation in
width, length and depth

factors:
- Conservation of tooth structure
- Location and the extent of the carious lesion
- Position of pit and fissure dictate the outline

Question 15

Resistance Form

Answer 15

Design features of cavity preparation
allowing the remaining tooth structure & the restoration to withstand
forces that are principally directed towards the long axis of the tooth.

Question 16

Primary resistance

Answer 16

1- Removal of undermined surface enamel
2-Flat pulpal floor and Cavity wall angulation
3- Cavity preparation depth
4- Well defined rounded Internal line angles
5- Type of restorative material

Question 17

Removal of undermined surface enamel

Answer 17

Cavosurface margin should not terminate on unsupported or undermined enamel to prevent its fracture

Question 18

Flat pulpal floor and Cavity wall angulation

Answer 18

Cup shaped cavity: Rotation of the restoration (micromovement) results in a wedging effect on the supporting dentin bridge

Box shaped: pulpal floor perpendicular to the long axis of the tooth

Question 19

Cavity preparation depth

Answer 19

• Adequate depth to provide enough thickness of amalgam to prevent its fracture under load.
• Minimum amalgam thickness to withstand forces=1.5mm

Question 20

Well defined rounded internal line and point angles

Answer 20

-Placing line angles to delineate the walls
-Sharp line angles are not recommended in any restoration
-Sharp line angles act as stress concentration areas.
Sarah S Mikhai

Question 21

Type of restorative material

Answer 21

• Amalgams has a low edge strength
• Thus amalgam margin is of prime importance

Cavosurface margin has to establish a 90⁰ (Butt-joint Margin) amalgam margin
Reinforcement of the amalgam restoration at the margin by maintaining an angle of 80-90⁰

Question 22

Type of restorative material

Answer 22

• Amalgams has a low edge strength
• Thus amalgam margin is of prime importance

Cavosurface margin has to establish a 90⁰ (Butt-joint Margin) amalgam margin

Reinforcement of the amalgam restoration at the margin by maintaining an angle of 80-90⁰

Question 23

Retention Form

Answer 23

• Design features of the cavity preparation that prevent dislodgement of the restoration by lifting or tipping forces
• Amalgam does not bond to tooth structure thus increasing the surface area of the walls that contacts the amalgam (increased friction)
• Making opposing walls parallel or slightly converging toward the occlusal

Question 24

Convenience Form

Answer 24

• Sufficient access to the cavity, to facilitate visibility and instrumentation of the cavity preparation and the insertion of the restorative material.
• Visibility: for complete removal of decay
• Access the preparation for instrumentation
• Insertion of the restorative material
-The diameter of the small end (1.0mm) of the smallest condenser should fit passively into the prepared cavity

Question 25

Finishing

Answer 25

• Finishing the cavosurface margin (enamel margin) to prevent jagged or rough outline
• To achieve the best marginal seal

Question 26

Debridement

Answer 26

This is the final step before the cavity preparation receives the restoration
• Rinsing the cavity is done with air/water spray syringe and high suction evacuation
• To remove debris and wash away dentinal shavings (smear layer)
• Free the cavity from moisture (blood and saliva)