Principles of Cavity Preparation in Dentistry

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Questions and Answers

What is the primary purpose of resistance form in cavity preparation?

To remove unsupported enamel to prevent fracture

To restrict the extension of the walls for strong cusp and ridge support

To shape the cavity walls to withstand the force of mastication without fracture (correct)

To create a smooth pulpal floor to resist restoration movement

Why should the pulpal floor be flat and perpendicular to the long axis in cavity preparation?

To allow for easy removal of unsupported enamel

To reduce stress concentration at internal line angles

To resist restoration movement and prevent wedging action on the tooth (correct)

To prevent the spread of caries in dentin

What is the significance of slightly curved (rounded) internal line angles in cavity preparation?

To restrict the extension of the walls for strong cusp and ridge support

To reduce the spread of caries in dentin

To allow for easy removal of unsupported enamel

To prevent stress concentration and fracture of tooth structure (correct)

Why should unsupported enamel be removed during cavity preparation?

Enamel is brittle and will fracture easily when subjected to force Signup and view all the answers

What should be restricted by controlling the width of the cavity in cavity preparation?

The extension of the walls to allow strong cusp and ridge with sufficient dentin support Signup and view all the answers

What is the typical depth of the cavity when caries is present in the pulpal floor or axial wall or both?

1.5 mm Signup and view all the answers

What instrument should be used to remove caries when present in the pulpal floor or axial wall or both?

Spoon excavator Signup and view all the answers

How can caries dentin be detected?

By tapping on it with a metal instrument Signup and view all the answers

What can result from removing all of the pulpal floor due to caries?

Both A and B Signup and view all the answers

What are the objectives of finishing the cavity walls?

To provide maximum strength of both the tooth and restorative material at and near the margin Signup and view all the answers

What factors must be considered in the finishing of enamel walls and margins?

Direction of enamel rods, support of enamel rods, type of restorative material, location of margins, and desired smoothness Signup and view all the answers

What is the purpose of toilet of the cavity?

To clean the cavity from small chips of cutting tooth structure and remove carious lesion Signup and view all the answers

How should toilet of the cavity be performed?

Using a dry cotton pellet followed by oil-free air spray for drying Signup and view all the answers

What should be used to detect caries dentin?

Sharp probe or metal instrument Signup and view all the answers

What is the result of removing all pulpal floor?

Unnecessary cutting of tooth structure and increased possibility of hitting the pulp Signup and view all the answers

What should be used to remove caries when present in pulpal floor or axial wall?

Spoon excavator Signup and view all the answers

What must be considered in finishing enamel walls and margins?

Direction of enamel rods, support of enamel rods, type of restorative material, location of margins, and desired smoothness Signup and view all the answers

What is the aim of the retention form in restorative dentistry?

To resist displacement or removal of the restoration against tipping or lifting forces Signup and view all the answers

Why should the width of the cavity be 1/4 of the intercuspal distance?

To preserve sound tooth structure and prevent weak remaining tooth structure Signup and view all the answers

What is the purpose of a smooth pulpal floor in cavity preparation?

To avoid concentrating occlusal force on irregular areas and causing fracture Signup and view all the answers

Why should the mesial and distal walls of the cavity be made parallel or slightly diverge?

To prevent unsupported enamel and fracture under occlusal load Signup and view all the answers

What is the minimum thickness of amalgam required to withstand the load applied without being fractured?

1-1.5 mm Signup and view all the answers

What is the purpose of box form in cavity preparation?

To provide flat, smooth, and plane walls and floors for the restoration Signup and view all the answers

What is the aim of convenience form in restorative dentistry?

To allow adequate observation, accessibility, and ease of operation in preparing and restoring the cavity Signup and view all the answers

What is the recent trend in conservative restorative dentistry regarding retention?

Depend on adhesive materials capable of bonding all restorative materials to tooth structure Signup and view all the answers

What is the function of an axial groove in restorative dentistry?

To provide secondary or auxiliary retention Signup and view all the answers

What is the purpose of reverse bevel in gold inlays?

To resist displacement or removal of the restoration against tipping or lifting forces Signup and view all the answers

Why should convergence of buccal and lingual (palatal) walls be about 50 degrees?

To prevent unsupported enamel and fracture under occlusal load Signup and view all the answers

What is the advantage of reducing dependence on mechanical interlocking for retention?

Reduces unnecessary tooth cutting and destruction for creating dove tails and undercuts Signup and view all the answers

Study Notes

Cavity Preparation

Primary purpose of resistance form is to prevent fracture of tooth structure.
Pulpal floor should be flat and perpendicular to the long axis to allow for even distribution of stress and reduce the risk of fracture.

Cavity Design

Slightly curved (rounded) internal line angles help to reduce stress concentrations and prevent fracture.
Unsupported enamel should be removed to prevent fracture and ensure structural integrity.

Width and Depth of Cavity

Width of cavity should be restricted to 1/4 of the intercuspal distance to prevent excessive removal of tooth structure.
Typical depth of cavity when caries is present in pulpal floor or axial wall is 0.5-1.5 mm.

Caries Removal

Caries dentin can be detected using a caries detector dye.
Excavators or round burs should be used to remove caries when present in pulpal floor or axial wall.

Finishing the Cavity

Objectives of finishing the cavity walls are to provide a smooth surface, remove any sharp edges, and ensure a tight seal.
Factors to consider when finishing enamel walls and margins include beveling, smoothing, and polishing.

Toilet of the Cavity

Purpose of toilet of the cavity is to remove any debris or residue, ensuring a clean surface for restoration.
Toilet of the cavity should be performed using a soap and water followed by an alcohol rinse.

Retention Form

Aim of retention form is to provide mechanical interlocking between the tooth and the restoration.
Width of the cavity is restricted to allow for adequate retention without excessive removal of tooth structure.

Other Considerations

Smooth pulpal floor helps to reduce stress concentrations and prevent fracture.
Mesial and distal walls of the cavity should be made parallel or slightly divergent to allow for even distribution of stress.
Minimum thickness of amalgam required to withstand the load applied without being fractured is 1.5 mm.
Box form provides additional retention through mechanical interlocking.
Convenience form provides easy access for restoration placement and removal.

Trends in Restorative Dentistry

Recent trend in conservative restorative dentistry is to reduce dependence on mechanical interlocking for retention.
Axial groove serves as a guide for the placement and removal of the restoration.
Reverse bevel in gold inlays helps to increase the strength of the restoration.
Convergence of buccal and lingual (palatal) walls should be about 50 degrees to allow for easy removal of the restoration.

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Description

Learn about the resistance form and the shaping and placement of cavity walls to withstand mastication force. Understand the importance of a flat pulpal floor in preventing restoration movement and tooth fracture.