Class II Preparations Flashcards
What kind of cavities require class II preparations?
Interproximal cavities
How are class II restorations made to last long?
The operating field is isolated to control moisture
The preparation is correctly designed with the required charcteristics
A properly placed matrix and wedge are used when placing the restoration.
Restorative material is selected, manipulated, carved, and finished correctly
What are the walls of the preparatio cavity?
Distal
Facial
Lingual
Gingival
Pulpal
Axial
What are the clinical steps to a class II restoration?
A. Initial tooth preparation stage:
1) Outline form and initial depth
2) Primary resistance form
3) Primary retention form
4) Convenience form
– Proximal box - achieving clearance from the adjacent tooth
B. Final tooth preparation stage:
5) Removal of remaining defective tooth structure and restorative material
6) Pulp protection
7) Secondary resistance and retention form
8) Finishing walls
9) Final procedures: cleaning and inspecting the preparation
What are the important features of the occlusal box?
Occlusal convergence of buccal and lingual walls
Smooth and gentle curves
No angular contours
Extend far enough towards the buccal and lingual grooves to have gentle contours
- 5 - 2.0mm < isthmus < 1/3 - 1/4 intercuspal distance
- 5 - 2mm deep
Flat pulpal floor
Extend cavity towards the center of the tooth.
How is the proximal box created?
Extend into the involved marginal ridge
Leave a thin layer of enamel then break the contact point
How wide should the proximal box be?
Wider buccolingually than the occlusal box.
How much clearance should there be between the prep and adjacent teeth?
0.2 - 0.5 mm
What are the features of the axial wall and the gingival floor?
Axial wall:
Height should be 0.4 - 0.6mm
Parallel to the long axis of the crown
Straight or convex
From the occlusal view, it should follow the contour of the proximal surface.
Gingival floor:
Flat and perpendicular to the long axis of the crown
Width: 0.6 - 0.8mm premolars
0.8 - 1.0 mm molars
2/3 dentine and 1/3 enamel.
What are the features of the lingual and buccal walls of the proximal box?
Must be convergent towards the occlusal to improve retention form and marginal ridge strength.
What are the features of the internal and external angles of the proximal box?
All internal angles are rounded
Cavosurface angle - butt joint = provide 90 degree amalgam on the margin
Axiopulpal line angle should be rounded.
How should retention grooves be added to a preparation?
Axiolingual and axiobuccal line angles should have retention grooves in them while avoiding axial wall. They must be smooth.
How deep should retention grooves be?
0.2mm deep inside dentin
What are the retention form modifications for the class II preparation?
Occlusal convergence of the buccal and lingual walls of the preparation.
Retention grooves
What are the resistance form features of a class II preparation?
The pulpal and gingival floors are flat and perpendicular to forces directed with the long axis of the tooth
Minimal extension of outline form
Minimizing extension of walls to allow strong cusps and ridge areas supported by dentine
Minimizing occlusal contact where possible
Rounding the internal line angles to reduce stress concentration
Sufficient depth to provide bulk to the amalgam.
