All Ceramic Crown Preparation in Fixed Prosthodontics Quiz

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Questions and Answers

Why is it important to have a deep chamfer or shoulder finish line in crown preparations?

To avoid stress concentration (correct)

To increase stress concentration

To reduce marginal integrity

To decrease structural durability

What is the recommended range for axial taper in the preparation of all ceramic crowns?

6-10 degrees (correct)

10-15 degrees

3-5 degrees

5-8 degrees

What is the purpose of using a putty index before tooth preparation?

To skip provisional restorations

To increase the amount of reduction

To check the amount of reduction (correct)

To speed up the process

Which type of diamond stone is recommended for incisal reductions in tooth preparation?

Tapered stone with round end Signup and view all the answers

What is the range for the amount of incisal reduction needed in crown preparations?

1.5-2 mm Signup and view all the answers

Why is it necessary to round line and point angles during crown preparation?

For structural durability Signup and view all the answers

Why is incisal reduction done with a slight inclination toward the lingo-gingival?

To preserve the retention & resistance features of the preparation Signup and view all the answers

What is the depth of reduction recommended for labial reduction?

1-1.5mm Signup and view all the answers

What is the purpose of making grooves in labial reduction?

To remove tooth structure between the grooves Signup and view all the answers

Why are depth grooves made before creating a straight plane for the incisal edge?

To guide the depth of preparation Signup and view all the answers

What is the precise direction for cutting during labial reduction for 2 plane reduction?

Starting with the incisal 2/3 after removal of maximum convexity, then gingival 1/3 Signup and view all the answers

What is the primary reason for performing two-plane reduction during labial reduction?

To enhance tooth durability Signup and view all the answers

What is the recommended depth of reduction for the palatal fossa area?

1.5 mm Signup and view all the answers

What is the ideal convergence angle for the proximal walls in a restoration preparation?

6-10 degrees Signup and view all the answers

What feature of the preparation is responsible for providing resistance and retention to the final restoration?

The curved horizontal surface between the lingual fossa and cingulum Signup and view all the answers

Which instrument is recommended for reducing the palatal fossa area?

Any of the above Signup and view all the answers

What is the purpose of rounding all sharp line and point angles in the preparation?

Both a and b Signup and view all the answers

Which feature of the preparation acts as an anti-rotation feature?

The curved horizontal surface between the lingual fossa and cingulum Signup and view all the answers

Which of the following is NOT an advantage of all-ceramic crowns?

More conservative than metal-ceramic crowns Signup and view all the answers

Which of the following is NOT a disadvantage of all-ceramic crowns?

Poor esthetic properties and color instability Signup and view all the answers

Which of the following is NOT an indication for all-ceramic crowns?

As a restoration for teeth with large pulp size and high epithelial attachment Signup and view all the answers

Which of the following is a limitation for all-ceramic crowns?

Patient with heavy bite, deep bite, or edge-to-edge occlusion Signup and view all the answers

Which of the following statements is TRUE regarding the preparation of all-ceramic crowns?

The preparation should be extensive, as all-ceramic crowns require more tooth reduction compared to partial coverage restorations. Signup and view all the answers

Which of the following statements is FALSE regarding the limitations of all-ceramic crowns?

All-ceramic crowns are not recommended for teeth with excessive short clinical crowns more than 1/3 of the occluso-gingival height. Signup and view all the answers

Study Notes

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.

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Description

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.