24 Questions
What is the purpose of cutting into the proximal area from both sides until a few mm of interproximal island remains?
To protect the neighboring tooth
What should be done to the adjacent proximal surface if it is damaged?
Polish with white stone, silicon stones, and prophylaxis paste
What is evaluated during the preparation step?
All of the above
What type of bur is typically used for axial reduction?
Thin round tipped diamond bur
What is the purpose of placing a non-functional cusp bevel?
To create additional retention features
Why is it important to take care not to injure the adjacent tooth?
To prevent damage to the adjacent tooth
What is the recommended speed for using a fine girt diamond or carbide bur?
Any of the above
What should be the condition of the chamfer finish line?
Smooth and glassy
What is the recommended reduction for the incisal edge to allow for translucency in the final restoration?
2mm
Why is less reduction required for posterior teeth?
Because esthetic is not critical
How many imaginary parts is the facial surface divided into?
1/3 and 2/3
What is the depth of the grooves placed on the facial surface?
1.3mm
How should the cervical grooves and reduction be angled?
Parallel to the long axis of the tooth and/or the intended path of insertion
What is the purpose of the incisal portion following the facial contour?
To provide space for porcelain layering
Where is the shoulder FL typically placed?
1 mm above the gingival crest
What is the purpose of using a retraction cord during finishing?
To retract the gingiva and place the FL more apically
What is the primary purpose of proper manipulation of the gingival tissue in metal-ceramic crown preparation?
To prevent gingival recession and exposure of the metal collar
What is the recommended width of the chamfer finish line in metal-ceramic crown preparation?
0.5 mm
What is the purpose of guiding grooves in anterior teeth preparation for metal-ceramic crowns?
To guide the bur during preparation
What is the primary function of the interproximal margin in metal-ceramic crown preparation?
To follow the gingival contour
What is the recommended tool for reducing the lingual surface of anterior teeth in metal-ceramic crown preparation?
Football-shaped diamond bur
What is the primary purpose of the shoulder finish line in metal-ceramic crown preparation?
To extend well into the proximal embrasures
What is the recommended depth of concavity removal in metal-ceramic crown preparation?
1.0 mm
What is the primary purpose of finishing and evaluating the reduction in metal-ceramic crown preparation?
To ensure the margin provides distinct resistance to vertical displacement of an explorer tip
Study Notes
Axial Reduction
- Remove remaining tooth structure while placing chamfer margin, reducing half of axial surface first and leaving the other as reference.
- Take care not to injure adjacent tooth in interproximal area.
- Use enamel lip technique: cut into proximal area from both sides until a few mm of interproximal island remains, then remove contact with a fine needle diamond.
Protecting Adjacent Tooth
- If adjacent proximal surface is damaged, polish with white stone, silicon stones, and prophylaxis paste.
- Apply fluoride to prevent demineralization.
Finishing
- Use fine grit diamond or carbide bur for finishing, operating at reduced speed or with low speed handpiece.
- Smooth internal line angles, chamfer finish line should be glassy smooth.
- Add non-functional cusp bevel if necessary, and additional retention features with tapered carbide bar if needed.
Evaluation
- Evaluate preparation for smooth, even, and continuous chamfer finish line.
- Check for 6° taper, gradual transition between prepared surfaces, and no undercuts.
- Assess occlusal and proximal clearance.
Occlusal/Incisal Reduction
- Reduce incisal edge by 2mm for adequate material thickness and translucency.
- Posterior teeth require less reduction (1.5mm).
Buccal/Labial Reduction
- Divide facial surface into 2 imaginary parts: 1/3 cervical and 2/3 incisal.
- Place 3 grooves: mesial, distal, and middle, with a depth of 1.3 mm.
- Cervical grooves and reduction are parallel to the long axis of the tooth and/or the intended path of insertion.
- Incisal grooves are parallel to the facial contour.
Shoulder Finish Line
- Place shoulder finish line 1 mm above the gingival crest.
- Retract gingiva using a retraction cord to place the finish line more apically.
- Manipulate gingival tissue to prevent recession and exposure of metal collar.
Axial Reduction of Proximal and Lingual Surfaces
- Remove sufficient tooth structure to provide a distinct, smooth chamfer finish line (0.5 mm in width).
- Use round-end tapered diamond bur held parallel to the intended path of insertion.
- Place guiding grooves on anterior teeth and remove concavity with wheel or football diamond bur.
- Follow gingival contour for interproximal margin and extend lingual chamfer buccally to blend with interproximal area.
This quiz covers the preparation steps for a complete metal crown, including axial reduction and protection of adjacent teeth.
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