Porcelain and Cast Crown Preparation

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.
• It 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 the restoration to conform to the original contours.
• Preservation: Tooth structure should be preserved whenever possible.
• Strength Consideration: Reduction of tooth structure should produce a crown with 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 of complete crowns 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 re-establishing the occlusal plane is necessary.

Disadvantages

• Extensive Tooth Structure Removal: Can cause 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 on specific teeth.
• Placement: May be limited to maxillary molars and mandibular molars and premolars.

Indications

• Extensive Coronal Destruction: Maximum retention is needed.
• Short Clinical Crowns: High displacement forces are anticipated.
• Correction of Axial Contours: Support for partial removable dental prostheses is needed.

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 aesthetic needs.

Special Considerations

• Endodontically Treated Teeth: Complete cast crowns are 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 the 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

(This section is a procedure, not specific details.)

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 mm 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 the permanent crown.

This quiz covers the preparation process for complete cast crowns, including tooth structure removal and the importance of preservation. You'll learn about the advantages of complete cast crowns, focusing on retention and resistance. Enhance your understanding of dental restorations with this informative quiz.