L6 Posterior crown preparations Flashcards
What are the functions of posterior crowns?
- Maintenance of existing tooth structure for extensively damaged teeth
- Maintenance of occlusion with teeth of the opposing arch
- Maintain contact points with adjacent teeth to prevent drifitng
- Maintain functional mastication
- Aesthetics
What is Amber Mill?
- Lithium disilicate milled blocks
- Used for veeners and crowns
- Minimal preparation
- Relatively strong in thin sections (0.3-1mm thickness)
- Digital milling, high fit accuracy
- Good longevity
- Durable
- Bio-inert
- Good aesthetics
What measurements of Amber Mill are used for veneers vs crowns.
- 0.3mm for anterior veneers
- At least 1mm for posterior crowns
Describe posterior metal ceramic crowns.
- CoCr bse layer with ceramic overlay
- Heavier preparation required, greater risk of pulp exposure
- Relatively strong, but not as strong as a full veneer metal crown
- Good longevity, durable, bio-inert
- Good aesthetics, not as vibrant as an ACC, appears flatter due to how light reflects off it
What can full veneer metal crowns be made of?
- Gold
- White gold
Non-precious alloys:
- Nickle-chromium (risk of nickel allergy)
- Cobalt-chromium and titanium
More difficult to cast. Can be milled nowadays.
Describe white gold as a full veneer metal crown material.
- Less expensive than gold
- More difficult to cast
- Corrossion, tarnishes
- Au 30%, Pd 10-35%, Ag 35-60%
Describe gold as a full veneer metal crown material.
- Type III gold alloy (75% gold)
- Expensive
- Gold is malleable in thin sections and minimal preparation is required
- Minimises risks of pulp damage
- Strong in thin sections
- Easy to cast
- Good longevity, durbale, bio-inert
- Poor aesthetics
How do the principles of posterior crown preparation differ compared to general crown prep principles?
- Increased reduction required for MCC
- Chamfer margin for metal or ceramic alone, shoulder for both together
- Sometimes helpful to use a study model to do a test preparation to see whether or not the form will be sufficiently retentive and resistant
What type of margins are used for posterior crown types?
- MCC: shoulder and chamfer
- ACC: chamfer
- FVC: thin chamfer (metal is strong in thin sections)
What happens to the amount of tooth reduction as amount of cermaic increases for an MCC?
Tooth reduction increases.
What are the measurements of reduction for a full veneer metal crown?
- 0.5mm chamfer margin
- 1-1.5mm occlusal reduction
What is the required taper for a FVC?
6-10 degrees
Describe the functional cusp bevel for a full veneer metal crown.
- 1.5mm functional cusp reduction due to high force applied to the area causing flexion of material and risk of fracture.
Outline the preparation steps for a full veneer metal crown.
Make sure to check which cusp is the functional cusp, don’t just assume.
Refine any sharp points.
Walk Williams probe around the margins to check taper and check for undercuts before using an active bur.
How does occlusal reduction change for different posterior crown types?
What types of reduction can be used for the occlusal surface of posterior teeth?
- Planar reduction. Bur used in the direction of each incline.
- Depth grooves. Grooves in fissure pattern, then remove material between each groove.
Why is a functional cusp bevel required?
Allows adequate bulk of the crown in region of high stress.
Bur should follow the incline of the cusp when creating functional cusp bevel.
How does margin preparation differ for different posterior crown types?
