Crown Preparation and Indications Quiz

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

• A complete cast crown is a durable restoration for 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. Tooth structure needs to match original shape for a good fit.
• Preservation: Tooth structure should be preserved whenever possible, keeping as much natural tooth as practical during preparation.
• Strength Consideration: Reduction should produce a crown with acceptable strength.

Advantages: Retention and Resistance

• Greater Retention: Complete cast crowns have superior retention compared to conservative restorations. This better retention is important for preventing looseness of the restoration.
• Improved Resistance: These crowns offer better resistance form than partial-coverage restorations, helping to prevent dislodgement of the restoration.
• Strength: The cylinder-like configuration provides superior strength. The streamlined shape makes the restoration resistant to various forces.

Advantages: Contour Modification

• Axial Tooth Contour: Complete cast crowns allow modification of axial tooth contours. Shape can be adjusted for a better fit.
• Malaligned Teeth: Particularly beneficial for malaligned teeth, within periodontal limits. The restoration can be adjusted to compensate for misalignments.
• Furcation Access: Improved access to furcations allows for recontouring of buccal and lingual walls. Accesses deep into the tooth are readily possible.

Advantages: Special Requirements

• Partial Removable Dental Prostheses: Allows creation of properly shaped survey lines, guide planes, and occlusal rests. These are important features in removable partial dentures.
• Occlusion Modification: Permits easy modification of occlusion, important for supraerupted teeth. Helps with maintaining a good bite alignment.
• Occlusal Plane: Helpful when re-establishing the occlusal plane is necessary. Important for ensuring optimal jaw position.

Disadvantages

• Extensive Tooth Structure Removal: Can have adverse effects on pulp and periodontium. This might cause damage to the pulp or periodontium (supporting tissues) if excessive reduction occurs.
• Gingival Inflammation: Proximity to gingiva may cause inflammation of gingival tissues. Inflammation may occur if the margins are too close to the gums.
• Vitality Testing: Electric vitality testing is no longer feasible after cementation. Electrical testing of tooth vitality is not useful after the crown has been cemented.

Esthetic Considerations

• Patient Objection: Patients may object to the display of metal. Restoring the visible aspect of the tooth is an important aim to prevent patients from noticing the underlying metal.
• Smile Line: Normal smile line may restrict use to specific teeth. Careful attention must be made to restore in accordance with patient's usual smile line.
• Placement: May be limited to maxillary molars and mandibular molars and premolars. Some teeth locations in the mouth may not be suitable for this type of restoration.

Indications

• Extensive coronal destruction: Maximum retention needed for restorations in teeth with extensive damage..
• Short clinical crowns: High displacement forces anticipated.
• Correction of axial contours: Support for partial removable dental prostheses.

Contraindications

• Conservative Options: Contraindicated if treatment objectives can be met with more conservative restoration.
• Intact Walls: Not recommended if intact buccal or lingual wall exists. Should not be used if either the buccal or lingual wall is still intact..
• Esthetic Needs: Contraindicated for anterior teeth with high esthetic needs. Not suitable for front teeth for visual purposes.

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.

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

• Detailed, illustrated step-by-step procedure is not provided; but the images show images of the process.

Guiding Grooves for Occlusal Reduction

• Central Groove: Place 1mm deep holes in fossae, connect along central groove.
• Developmental Grooves: Place guiding grooves in buccal and lingual developmental grooves.
• Functional Cusp Bevel: Place 1.5mm 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 1.5mm 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 0.5mm 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.

II-Metal-Ceramic Crown

• Widely used fixed restoration combining metal and porcelain.
• Offers durability and esthetics in dental practices.

Composition and Structure

• Metal Substructure: Complete coverage cast metal crown as base.
• Porcelain Veneer: Fused layer mimics natural tooth appearance.
• Thickness Requirements: Considerable reduction needed to mask metal color.

Fabrication Process

• Waxing and Casting: Special metal-ceramic alloy used for substructure.
• Preparatory Finishing: Framework prepared for porcelain application.
• Porcelain Fusing: Dental porcelain fused at 960° C.

Indications

• Complete Coverage Needs: Suitable for teeth requiring full crown restoration.
• Esthetic Demands: Meets high cosmetic requirements, especially for anterior teeth.
• Versatility: Can serve as retainer for fixed dental prosthesis.
• Structural Support: Ideal for endodontically treated teeth with post-core.

Contraindications

• Active Dental Issues: Not suitable for patients with active caries.
• Young Patients: High risk of pulp exposure in large chambers.
• Conservative Options Available: Avoid when more conservative restorations are feasible.

Advantages of Metal-Ceramic Crowns

• Strength: Cast metal substructure reinforces brittle ceramic.
• Aesthetics: Natural appearance achieved through characterization techniques.
• Retention: Excellent retention due to full axial wall coverage.

Preparation Considerations

• Tooth Reduction: Significant reduction required for material thickness.
• Margin Placement: Subgingival margins for aesthetics, potential periodontal concerns.
• Difficulty Level: Comparable to posterior complete cast crown preparation.

Aesthetic Considerations and Challenges

• Shade Selection: Accurate color matching crucial for natural appearance.
• Communication: Clear instructions to ceramist essential for desired outcome.
• Porcelain Layering: Multiple steps required for optimal aesthetics..

Limitations and Alternatives

• Brittle Fracture: Risk of porcelain chipping due to glasslike nature.
• Cost Factors: Higher laboratory expenses due to complex fabrication process.
• All-Ceramic Option: Consider for superior aesthetics in low stress situations.

III-All-Ceramic Restorations

• Esthetically pleasing prosthodontic restorations with superior color and translucency.

Types and Fabrication

• Platinum Foil Matrix: Original technique using foil to support porcelain during firing..
• Hot-Pressing: Modern fabrication process for ceramic restorations.
• Slip-Casting: Another popular method for creating all-ceramic restorations.

All-Ceramic Crowns

• Thickness: 1 to 1.5 mm circumferentially.
• Incisal Thickness: May require greater thickness for esthetic results—2mm.
• Preparation Design: Minor differences exist among various fabrication techniques..

Advantages of Ceramic Crowns

• Esthetics: Superior appearance and excellent translucency.
• Conservation: Allows more conservative facial reduction than metal-ceramic crowns.
• Customization: Appearance can be modified with different luting agent colors.

Disadvantages of Ceramic Crowns

• Strength: Reduced strength due to absence of metal substructure.
• Tooth Reduction: Significant reduction needed for shoulder type margin circumferentially.
• Brittleness: Porcelain brittleness requires careful preparation design.
• Fitting: Difficulties may occur in obtaining well-fitting margins.

Critical Preparation Design

• 90-Degree Angle: Cavosurface angle needed to prevent unfavorable stress distribution.
• Incisal Support: Preparation should support entire incisal edge of porcelain.
• High-Strength Core: Exception for systems with high-strength core materials.

Limitations in Fixed Dental Prostheses

• Retainer Ineffectiveness: Not effective as retainers for fixed dental prostheses.
• Connector Size: Large connectors (4x4 mm minimum) required for strength.
• Periodontal Risk: Large connectors may impinge on interdental papilla.

Indications for Ceramic Crowns

• Esthetic Requirement: High esthetic demand areas where conservative restoration is inadequate.
• Tooth Structure: Relatively intact coronal structure to support restoration.
• Occlusal Load: Favorable distribution of occlusal load required.

Contraindications for Ceramic Crowns

• Conservative Options: When more conservative restorations can be used.
• Molar Teeth: Rarely recommended for molar teeth due to occlusal load.
• Unfavorable Load: When occlusal loading is unfavorable.
• Inadequate Support: If unable to provide adequate support or even shoulder.

Considerations for Opposing Teeth

• Issue: Wear
• Specific Concern: Mandibular incisors can exhibit significant wear over time.
• Observation: Natural teeth opposing porcelain may show wear..

Suggested Preparation Features for Posterior Crowns

• Metal: 0.5-1.0mm occlusal reduction, 0.5mm marginal preparation.
• PFM: 1.5-2.0mm occlusal reduction, 1.2mm labial shoulder or heavy chamfer (0.5mm chamfer for lingual metal collar) marginal preparation.
• All-ceramic: 1.5-2.0mm occlusal reduction, 1.5mm rounded shoulder marginal preparation.