Extra Coronal Restorations: Crowns and Stages

Extra Coronal Restorations: Crowns and Laboratory Stages

  • Crown Definition: Full restoration that encompasses the entire tooth; constructed outside the mouth.
  • Key Terms:
    • Crown Preparation: The procedure to ready a tooth for a crown.
    • Height: Distance from margin to occlusal/incisal surface of preparation.
    • Taper: Degree of convergence of the walls of the preparation.
    • Crown Margin: The edge of the crown that fits against the tooth.
    • Retention & Resistance: Factors affecting the stability of the crown.
    • Luting Cement: Material used to bond the crown to the tooth.

Types of Crowns

1. Full Veneer Crown (FVC)

  • Material: Gold or non-precious metal.
  • Advantages:
    • Strong and similar hardness to enamel.
    • Inert (does not corrode in the mouth).
    • Minimal tooth reduction required.
    • Simple manufacturing process (lost wax technique).
  • Disadvantages:
    • Aesthetically less appealing (metal visible).
    • Gold is expensive.
    • Does not bond to tooth structure.
  • Indications:
    • To restore functionality in posterior teeth where aesthetics are not crucial.
    • In cases with limited starting height.
  • Manufacturing Process:
    • Lost Wax Technique:
    • Impression of crown preparation made.
    • Model and die preparation involves removing the tooth from the dental cast using a thin saw blade.
    • Die spacer applied to accommodate the luting cement.
    • Wax pattern constructed to mimic natural tooth anatomy with proper contact points.

2. Metal-Ceramic Crown (MCC)

  • Structure: Metal substructure with a porcelain facing.
  • Advantages:
    • Aesthetic appeal.
    • Strong and durable.
  • Disadvantages:
    • Patients may reject if aesthetics not met.
    • Substantial tooth preparation required due to thickness of porcelain needed to mask metal.
  • Usage: In cases where aesthetic demands do not allow for gold crowns.
  • Construction Process:
    • Use of clear silicone impressions.
    • Creation of wax patterns for the metal substructure.
    • Final restoration involves layering porcelain for a natural appearance.

3. All Ceramic Crown (ACC)

  • Material: Lithium Disilicate (e.MAX).
  • Advantages:
    • Strength and good aesthetics.
    • Can be manufactured using both lost wax and CAD/CAM techniques.

CAD/CAM Workflow

  • Stages:
    • Chairside scan of the crown preparation.
    • Design and milling of the crown directly in the surgery.
    • Ensuring marginal fit and contacts checked prior to cementation.

Conclusion

  • Successful crown restoration depends on understanding materials, types, procedures, and precise execution of the manufacturing process.