Principles of Cavity Preparation Flashcards
Fundamental concepts for all tooth preparations
1- Removal of dental caries
2- Removal of weak tooth structure to provide well supported sound hard tissue
3- Pulp protection
Cavity Preparation
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.
Healthy state is reestablishing….
- Tooth is not diseased anymore
- Normal function and form
- Esthetically pleasing where indicated (anterior zone of the oral cavity)
Line angles
junction of two surfaces
Point angles
Junction of three surfaces
Cavosurface margin
Junction between the external walls of the cavity preparation and the uncut tooth surface.
Dovetail
-In class I cavity preparations, isthmus connects the 2
dovetails
-Dovetail design includes each marginal fossa and the
developmental grooves around the marginal pits
Isthmus
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
External wall
extend to the outer tooth surface
- mesial
- distal
- buccal
- gingival
Internal wall
do not extend to the outer tooth surface
Axial walls
parallel to the long axis
- gingival
- pulpal
Cavosurface angle
angle formed between tangent formed of hitting cavosurface margin at one point and the external cavity wall
6 Basic Principles of Cavity Preparation
- Outline form
- Resistance form
- Retention form
- Convenience form
- Finishing
- Debridement
Outline Form
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
Resistance Form
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.
Primary resistance
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
Removal of undermined surface enamel
Cavosurface margin should not terminate on unsupported or undermined enamel to prevent its fracture
Flat pulpal floor and Cavity wall angulation
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
Cavity preparation depth
- Adequate depth to provide enough thickness of amalgam to prevent its fracture under load.
- Minimum amalgam thickness to withstand forces=1.5mm
Well defined rounded internal line and point angles
-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
Type of restorative material
- 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
Type of restorative material
- 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
Retention Form
- 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
Convenience Form
• 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
Finishing
- Finishing the cavosurface margin (enamel margin) to prevent jagged or rough outline
- To achieve the best marginal seal
Debridement
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)
