Full Metal Crown

Full Metal Crown

• Definition: An extracoronal metallic fixed restoration covering all coronal surfaces of the prepared clinical crown, restoring function, anatomy, and contour.

Types

• Construction Techniques:
  • Cast (lost wax technique)
  • Swaged (ready-made)
  • CAD/CAM milling
• Materials of Construction:
  • High noble alloys
  • Noble alloys
  • Base metal alloys

Advantages

• High strength
• Great retention and resistance form
• Good protection for teeth to be restored
• Ideal restoration for teeth with developmental defects
• Modifies occlusion (over eruption)
• Modifies tooth contour (open contact & retainer for PD)
• Has the best longevity of all fixed restorations

Disadvantages

• Bad esthetics
• Extensive amount of tooth reduction
• Pulp vitality cannot be detected
• Incipient caries cannot be detected

Indications

• Posterior teeth only
  • As a single crown:
    • Patient with a high caries index
    • Badly broken-down tooth
    • Endodontically treated teeth
    • When maximum retention and resistance are needed
    • For correction of malalignment teeth (change contour)
    • Fractured teeth
    • To support a removable partial denture
  • As a bridge retainer:
    • Long span bridge
    • Short OG height
    • High occlusal forces

Contraindications

• Anterior teeth
• Another conservative preparation made (buccal surface intact ¾ crown).
• Less maximum retention and resistance needed (long clinical crown, short span bridge)

Tooth Preparation

• Preparation Criteria:

  • Finish Line: Chamfer, supra gingival, 0.5 mm
  • Axial reduction: Parallel to the long axis of the tooth with a 6-degree angle taper

• Steps of Preparation:

  • 1. Occlusal Reduction & Functional Cusp Bevel: Using a tapered stone with a rounded end, wheel, or flame-shaped diamond stone. The cutting follows occlusal anatomy, ensuring 1.5mm of clearance on functional cusps and 1mm on non-functional cusps.
  • 2. Depth Orientation Grooves: Placing 1mm grooves using a fissure bur or rounded-end tapered diamond to cut and create orientation grooves needed. Grooves will be located at central, mesial and distal fossa, marginal ridges, buccal and lingual developmental grooves. Tooth structure between these grooves is removed.
  • 3. Proximal Reduction: Using a fine taper diamond stone (needle stone). Depth made is 0.3-0.5 mm cervically.
  • 4. Smoothing & Roundation: Using a diamond stone with finer grits to cut and smooth the sharp line angles, point angles, and undercut areas. The chamfer should be smooth, rounded, continuous, and follow the gingival contour. Cervical undercuts should be removed at the line angle.

• Additional Details:

  • Check Occlusal clearance by using utility wax, registration material, and reduction gauge.
  • Functional Cusp Bevel: Slant the bur at a flatter angle than the cusp angulation for additional reduction.
  • Axial Reduction: Use chamfers, and maintain a depth of 0.3-0.5 mm (base metal) or 0.5 mm (gold alloys) supragingivally. Maintain a 6-degree taper. Follow the gingival contour.
  • Over/Under Tapering: Over-tapering of opposing axial walls can result in reduced retention. Possible solutions include adding grooves to improve retention, or restricting the taper to a maximum of 6 degrees.
  • Auxiliary Retention and Resistance Forms: Possible forms like groves, boxes and pinholes are best placed at the proximal center, but they can also be placed buccal and lingual.

• Important Considerations:

  • Adequate metal thickness
  • Checking for undercuts
  • Ensuring proper occlusal clearance
  • Measuring proper axial reduction
  • Correct instruments are selected to reduce risk of over-/under-preparation

Explore the definition, types, advantages, and disadvantages of full metal crowns in dentistry. This quiz assesses your understanding of the materials of construction and their indications for use. Perfect for dental students and professionals looking to enhance their knowledge of fixed restorations.