All Ceramic Crown Preparation in Fixed Prosthodontics Quiz

Incisal Reduction

• Incisal reduction is done with a slight inclination of 45° towards the lingo-gingival to oppose the forces perpendicularly on the incisal edge.
• Start by making 1.8 mm depth grooves and connect them to make the incisal edge into one straight plane.

Labial Reduction

• Two sets of depth grooves are made cervically and incisally using a tapered flat-end diamond stone instrument.
• Tooth structure in between the grooves is removed.
• Instrument: flat-end tapered diamond stone.
• Depth of reduction: 1-1.5 mm (1.2 mm with an extra 0.3 mm added during the finishing process).
• Finish line: 90-degree rounded shoulder or deep chamfer 1-1.5 mm.
• Grooves directions: Cervical 1/3 (parallel to the long axis of the tooth) and incisal 2/3 (parallel to the contour of the labial surface).
• Labial reduction direction: start with the gingival 1/3 parallel to the long axis of the tooth, then adjust to follow the direction of the incisal 2/3.

Purpose of Two-Plane Reduction

• To follow the anatomy of the surface (conservative reduction, preserving retention and resistance features).
• To avoid pulp encroachment.
• To allow enough space for a uniform porcelain layer, displaying proper esthetics and avoiding an overcontoured restoration.

General Guidelines for Preparation of All Ceramic Crowns

• Axial taper: 6-10 degree occlusal convergence to give a common path of insertion.
• Finish line: deep chamfer or shoulder with a round internal angle to avoid stress concentration.
• Thickness: 1 mm.
• Location: supra-gingival.
• Should be smooth and continuous for marginal integrity, structural durability, and periodontal preservation.

Preparation of Anterior Teeth

• Make a putty index before preparation to check the amount of reduction and make provisional restorations.
• Diamond stones needed:
  • Needle stone
  • Tapered stone with round end for axial and incisal reductions
  • Flame stone or football for palatal fossa
  • Wheel stone for incisal reductions
  • Finishing stones for rounding line and point angles of the preparation

Incisal Reduction Amount

• Amount of incisal reduction: 1.5-2 mm, giving bulk for translucency of the incisal restoration.

Advantages and Disadvantages of All Ceramic Crowns

• Advantages:
  • Excellent esthetic, translucency, and color stability
  • Highly compatible with soft tissues
  • More conservative than metal ceramic
  • Can be bonded to tooth structure
• Disadvantages:
  • High brittleness and liability to fracture
  • More expensive than full metal and PFM
  • Extensive amount of reduction compared to partial coverage and full metal
  • Pulp vitality cannot be done
  • Radiographic examination cannot be done to detect caries under the restoration

Indications and Limitations of All Ceramic Crowns

• Indications:
  • Single restoration in cases with high esthetic demands
  • As a retainer for all ceramic anterior bridge
  • In case of bad oral hygiene, root canal treated teeth, malposed teeth, and badly decayed teeth
  • Fractured anterior teeth that cannot be restored with another more conservative restoration
  • Proximal or facial caries that cannot be restored with another restoration
  • Favorable occlusal forces
• Limitations:
  • Young patient with large pulp size and high epithelial attachment
  • When more conservative treatment can be done
  • Unfavorable occlusal loads
  • Excessive short teeth more than 1/3 occluso-gingival height

Proximal Reduction

• Direction: opposing proximal walls should converge incisally 6-10 degree.
• Instrument: tapered stone with flat end.
• Depth of reduction: 1-1.5 mm.

Palatal Reduction

• Palatal fossa:
  • A sloping surface offers little resistance to tipping.
  • The curvature of the palatal fossa should be maintained following the original concavity.
  • Instrument: wheel diamond stone or football stone.
• Cingulum:
  • Reduced to have minimal convergence with the cervical portion of the labial surface.
  • Instrument: tapered stone with flat end.
  • Depth of reduction: 1 mm.

Finishing of the Preparation

• All sharp line and point angles are rounded to avoid stress concentration.
• End cutting stone may be used to safely place the finish line subgingivally to improve aesthetics or retention of short abutments.

Test your knowledge on all ceramic crown preparation in fixed prosthodontics from the lecture by Dr. Alaa El-Ashkar. Learn about the instruments, steps, and criteria for all ceramic crown preparation, as well as the advantages of this method.