Dental Crown Preparation Techniques

Complete Cast Crown, Porcelain Fuse to Metal, and All Ceramic Preparation

• A complete cast crown is a durable restoration for badly damaged posterior teeth
• It covers all axial walls and the occlusal surface
• This restoration offers excellent longevity and can be used for single teeth or as retainers for fixed dental prostheses

Preparation Process

• Tooth Structure Removal: Adequate tooth structure must be removed to allow restoration to original contours
• Preservation: Tooth structure should be preserved when possible
• Strength Consideration: Reduction should produce a crown of acceptable strength

Advantages: Retention and Resistance

• Greater Retention: Complete cast crowns have superior retention compared to conservative restorations
• Improved Resistance: They offer better resistance form than partial-coverage restorations
• Strength: The cylinder-like configuration provides superior strength

Advantages: Contour Modification

• Axial Tooth Contour: Complete cast crowns allow modification of axial tooth contour
• Malaligned Teeth: Especially beneficial for malaligned teeth, within periodontal limits
• Furcation Access: Improved access to furcations through recontouring of buccal and lingual walls

Advantages: Special Requirements

• Partial Removable Dental Prostheses: Allows creation of properly shaped survey lines, guide planes, and occlusal rests
• Occlusion Modification: Permits easy modification of occlusion, important for supraerupted teeth
• Occlusal Plane: Helpful when reestablishing the occlusal plane is necessary

Disadvantages

• Extensive Tooth Structure Removal: Can have adverse effects on pulp and periodontium
• Gingival Inflammation: Proximity to gingiva may cause inflammation of gingival tissues
• Vitality Testing: Electric vitality testing is no longer feasible after cementation

Esthetic Considerations

• Patient Objection: Patients may object to the display of metal
• Smile Line: Normal smile line may restrict use to specific teeth
• Placement: May be limited to maxillary molars and mandibular molars and premolars

Indications

• Extensive coronal destruction: Maximum retention needed
• Short clinical crowns: High displacement forces anticipated
• Correction of axial contours: Support for partial removable dental prosthesis

Contraindications

• Conservative Options: Contraindicated if treatment objectives can be met with a more conservative restoration
• Intact Walls: Not recommended if intact buccal or lingual wall exists
• Esthetic Needs: Contraindicated for anterior teeth with high esthetic needs

Special Considerations

• Endodontically Treated Teeth: Complete cast crown is indicated on endodontically treated teeth for superior strength
• Additional Retentive Features: Grooves can be included for additional retention in specific cases

Cast Crown Preparation: Key Principles

Occlusal Reduction Guidelines

• Non-functional Cusps: Minimum 1 mm clearance required
• Functional Cusps: Minimum 1.5 mm clearance needed
• Anatomic Contours: Follow natural tooth shape for conservative preparation

Axial Reduction and Margin Design

• Axial Reduction: Parallel to tooth's long axis. 6° taper recommended
• Margin Configuration: Chamfer design. Ideally supragingival. 0.5 mm metal thickness
• Smoothness: Ensure distinct, smooth margins for optimal fit

Functional Cusp Bevel

• Placement: Directly beneath crown cusps for optimal contour
• Angle: Flatter than external surface, typically 45 degrees
• Purpose: Ensures durability and conserves tooth structure

Nonfunctional Cusp Considerations

• Clearance: Minimum 0.6 mm at occlusoaxial line angles
• Additional Bevel: Often needed for maxillary molars
• Mandibular Molars: May not require additional reduction due to inclination

Key Takeaways for Crown Preparation

• Precise Measurements: Follow recommended clearances for each area
• Anatomic Contours: Maintain natural tooth shape during reduction
• Margin Quality: Ensure smooth, distinct chamfer margins
• Proper Bevels: Angle functional and nonfunctional cusps correctly

Step By Step Procedure For Preparing a Tooth (Image-Based)

• This section describes a step-by-step visual guide to tooth preparation.

Guiding Grooves for Occlusal Reduction

• Central Groove: Place 1 mm deep holes in fossae, connect along central groove
• Developmental Grooves: Place guiding grooves in buccal and lingual developmental grooves
• Functional Cusp Bevel: Place 1.5 mm deep groove for centric stop, diminishing cervically

Occlusal Reduction Technique

• Place Guiding Grooves: Ensure accurate position, depth, and angulation of grooves
• Remove Tooth Structure: Use carbide or diamond to remove structure between grooves
• Check Clearance: Verify 1.5 mm clearance on functional cusps, 1.0mm on nonfunctional

Alignment Grooves for Axial Reduction

• Placement: Three grooves on buccal and lingual walls
• Instrument Angle: Diamond bur parallel to restoration path of placement
• Depth Control: Tip buried to midpoint to avoid unsupported enamel
• Path of Placement: Grooves determine restoration's path of placement

Axial Reduction Technique

• Remove Islands: Remove tooth structure between alignment grooves
• Interproximal Care: Prevent damage to adjacent teeth during reduction
• Chamfer Placement: Place 0.5 mm wide cervical chamfer during axial reduction

Finishing the Preparation

• Smooth Transitions: Create smooth transitions from occlusal to axial surfaces
• Margin Refinement: Use fine-grit diamond for smooth chamfer margin
• Surface Finishing: Round line angles and place nonfunctional cusp bevel
• Additional Features: Add retentive features like grooves or boxes if needed

Evaluation of Preparation

• Taper Assessment: Check for overtapering of opposing axial walls
• Undercut Check: Ensure no undercuts between opposing axial walls
• Clearance Verification: Assess occlusal and proximal clearances for adequacy

Common Errors and Corrections

• Error: Overtapering
• Correction: Upright walls or add retentive features
• Error: Undercuts
• Correction: Eliminate with diamond instrument
• Error: Inadequate clearance
• Correction: Adjust before making interim restoration

Tools and Instruments

• Diamond Burs: For initial reduction and finishing
• Carbide Burs: For occlusal reduction and retentive features
• Periodontal Probe: For measuring reduction depth
• Wax Caliper: For checking occlusal clearance

Final Steps

• Interim Restoration: Create temporary crown after preparation is complete
• Impression Making: Take final impression for fabrication of permanent crown

This quiz covers the preparation techniques for complete cast crowns, porcelain fused to metal, and all-ceramic restorations. Learn about tooth structure removal, retention and resistance advantages, and the importance of contour modification. Test your knowledge on creating durable restorations for posterior teeth.