Dental Crown Preparation Principles

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Questions and Answers

What is the primary aim of preserving tooth structure during preparation?

To enhance aesthetic appearance

To avoid unnecessary weakening of the tooth (correct)

To increase the size of the tooth

To prevent gum recession

Which type of margin is considered less conservative during tooth preparation?

Shoulder margin (correct)

Sub-gingival margin

Chamfer margin

Supra-gingival margin

What is one consequence of excessive taper in tooth preparation?

Increased retention

Considerable loss of tooth structure (correct)

Improved aesthetic finish

Enhanced structural durability

What should axial surfaces of a tooth preparation be like?

As uniform as possible Signup and view all the answers

Which principle governs the prevention of the removal of the restoration along the path of insertion?

Retention and resistance Signup and view all the answers

How should occlusal reduction be performed?

By following anatomical planes Signup and view all the answers

What type of crown would be considered more conservative for tooth structure?

Partial veneer crown Signup and view all the answers

Which option represents a less destructive alternative to tooth preparation?

Onlays Signup and view all the answers

What problem can lack of functional cusp bevel lead to?

Thin area or perforation Signup and view all the answers

What is the consequence of inadequate axial reduction in restorative material?

Distortion of the restoration Signup and view all the answers

Which type of finish line is preferred for full veneer metal restoration?

Chamfer Signup and view all the answers

What should be avoided when placing a finish line for effective restoration?

Tearing or deformation of margins Signup and view all the answers

What is a key benefit of having smooth margins in restoration?

Easier restoration fabrication Signup and view all the answers

Which of the following is NOT a type of finish line configuration?

V-shaped edge Signup and view all the answers

What is the main purpose of the functional cusp bevel?

To provide space for metal thickness Signup and view all the answers

When should a sub-gingival margin be considered?

When caries are present Signup and view all the answers

What is the primary function of resistance in dental restorations?

To prevent dislodgement by forces from apical or oblique directions Signup and view all the answers

Which feature contributes to maximum retention in a dental preparation?

Minimal taper and a single path of insertion Signup and view all the answers

What is ideal taper for tooth preparation to optimize retention?

Minimum taper to maximize retention Signup and view all the answers

What must be adequately considered for structural durability of a restoration?

Occlusal reduction and functional cusp bevel Signup and view all the answers

What is the recommended clearance for occlusal reduction using gold alloys on the functional cusp?

1.5 mm Signup and view all the answers

What is a consequence of inadequate occlusal reduction in restorations?

It makes the restoration weaker Signup and view all the answers

Which of the following statements about retention is true?

Internal opposing surfaces can contribute to retention Signup and view all the answers

What should be avoided in tooth preparation for optimal retention?

Short and over-tapered preparations Signup and view all the answers

Study Notes

Tooth Preparation

There are 4 crown categories: all-metal, metal-ceramic, ceramic, and composite.
Different crown materials have different requirements regarding space and margin configuration.
Preparation for a cast restoration follows 5 principles: Tooth structure preservation, retention and resistance, structural durability, marginal integrity, preservation of the periodontium.

Tooth Structure Preservation

The goal is to avoid weakening the tooth unnecessarily and compromising the pulp.
The preparation should only remove what is necessary.
Less destructive preparation options include:
- Inlays and onlays instead of crowns.
- Partial veneer crowns instead of full veneer crowns.
- Supra-gingival margins instead of sub-gingival margins.
- Chamfer margins instead of shoulder margins.
Minimizing the taper of the preparation is important to avoid excessive tooth structure loss.

Retention and Resistance

Retention prevents the restoration's removal along its insertion path or the tooth preparation's long axis.
Resistance prevents dislodgement of the restoration by forces directed apically or obliquely and prevents movement under occlusal forces.
Retention is achieved with two opposing vertical surfaces, either on the external surfaces (sleeve retention) or internal surfaces (wedge retention).
Factors that improve retention and resistance include minimizing taper, limiting freedom of displacement, maximizing length, substituting internal features, and ensuring a single path of insertion.
Preparations with near-parallel axial walls and grooves maximize retention.
Over-tapered, short, and unprepared grooves lack retention.

Structural Durability

The preparation must withstand occlusal forces.
Consider these factors for structural durability:
- Occlusal reduction: 1.5mm clearance for functional cusps and 1mm clearance for nonfunctional cusps with gold alloys.
- Functional cusp bevel: provides space for an adequate metal bulk in areas of heavy occlusal contact.
- Axial reduction: ensures sufficient space for restorative material thickness.
Inadequate occlusal reduction weakens the restoration, can cause thin areas, hinders functional morphology, and may lead to perforation during finishing procedures.
Inadequate axial reduction results in thin restoration walls that distort and cause over contouring of the axial surface, potentially triggering periodontal issues.

Marginal Integrity

The restoration margin should closely adapt to the preparation's cavosurface finish line for its survival in the oral cavity.
Different finish line configurations include:
- Chamfer
- Heavy chamfer
- Shoulder
- Radial shoulder
- Shoulder with bevel
- Knife edge
Chamfer is the preferred gingival finish line for full veneer metal restorations as it exhibits the least stress on the underlying cement.

Preservation of the Periodontium

The placement of finish lines impacts the ease of fabrication and restoration success.
Margins should be as smooth as possible for optimal cleaning and success.
Ideally, finish lines should be placed in accessible areas, making finishing by the dentist and patient cleaning easy.
The impression should capture the finish lines without tearing or deformation.
Finish lines should be placed in enamel whenever possible.
Sub-gingival margins are sometimes necessary due to:
- Caries presence
- Increased retention requirements
- Esthetic concerns
- Extension of previous restorations
- Trauma

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Description

Explore the essential principles of tooth preparation for dental crowns, including the types of crowns, techniques for tooth structure preservation, and retention methods. This quiz covers critical concepts necessary for effective restorative dentistry practice.