Introduction to crowns course Flashcards
What is a crown
An artificial replacement that restores missing tooth structure by surrounding part or all of the remaining structure with a material like cast metal alloy, metal ceramics, ceramics, resin or a combo of materials
Give some examples about when a crown in required
- When tooth is heavily restored and existing tooth tissue is undermined
- Root canal treated molars
- Abutments for fixed/removable partial dentures
- Cuspal protection for a tooth under extreme occlusal forces
- Extremely discoloured teeth
- Part of extensive restorative treatment
- Aesthetic concerns
- Failing existing extra coronal restoration
What preparation is needed before a crown preparation is done on a tooth
- Up to date PA radiograph to rule out apical pathology or unsatisfactory root filling
- Sensibility testing
- Periodontal tissue assessment (healthy periodontal health required)
- Core assessment (replace if needed)
- Occlusal assessment
- Diagnostic wax up if indicated
Name some types of crown
- Full Gold Crown
- Ceramo-metal crowns
- Composite crowns
- Partial gold crowns
- All ceramic crowns
What stages of crown treatment are there
- Tooth prep
- Impression of prepared tooth
- Wax pattern made and dat
- Casting of restoration
- Porcelain applicaiton
- Polishing and finishing of restoration
What does resistance mean
- This is the ability to withstand compresive and oblique displacing forces
What does retention mean
- The ability to withstand occlusally directed displacing forces
- Theoretically parallel walls = max retention but that’s impossible to make so slight undercuts are made to prevent the restoration from seating
What is a taper and what is the ideal taper in a tooth prep
This is the angle from a perpendicular dropped through the centre of the tooth to the wall of the preparation.
Ideally this should be 2-3 degrees
What is the convergence angle and what should this angle be ideally
This is the angle between 2 opposing walls if you extended them out entirely and is ideally 6 degrees
What kinds of crown are chamfer finishing lines used for
- Full metal crowns
- Lingual margin of cereal-metal crowns if unveneered
What kinds of crown are shoulder finishing lines used for
Facial margin (veneered) of ceramo-metal crowns, all ceramic crowns
Describe the Chamfer finishing line
This is where there is an obtuse angle at the finishing line and is the most conservative of finishing lines
Describe the shoulder finishing line
Where a right angle is at the finish line
What should we ensure happens in the tooth prep to ensure the crown has enough structural durability
- Adequate occlusal reduction to allow bulk of metal
- Functional cusp bevel to allow for adequate thickness of metal
- Sufficient axial reduction
- Rounded angles
Where should the margin of a restoration be placed
At least 2mm above the alveolar crest
What can invasion of the biological width by a crown result in
- Gingival inflammation
- Loss of alveolar bone
- Pocket formation
What are the advantages of a Full Metal Crown
- best retention and resistance form of all indirect restorations
- reduces less tooth tissue than porcelain fused to metal or all porcelain restorations
- best control of occlusion
- best marginal fit
- kindest to opposing tooth tissue
What are the disadvantages of a Full Metal Crown
- Not the most aesthetic material
- Can be too soft in some situations
- Some non-precious metals can cause allergy or can corrode
What are the advantages of all ceramic crowns
- Excellent aesthetics
- Preservation of tooth structure in some areas
- Good material selection
What are the disadvantages of all ceramic crowns
- Increased destruction of tooth tissue in some areas
- Longevity questionable
- Moderate strength
What are the advantages of ceramo-metal crowns
- Good aesthetics
- Longevity
- Preservation of tooth structure in some areas
What are the disadvantages of ceramo-metal crowns
- Increased destruction of tooth structure in some areas
What steps of treatment should be taken during a crown preparation appointment
- Shade selection
- LA
- 2 putty indices
- Crown prep
- Temp crown ready
- Tray selection and adhesive
- Retraction cord (tf??)
- Impression and disinfection of impression
- Cementation of temp crown and OHI instructions
- Lab card prescription
What steps should be taken in the fit and cementation of the crown appt.
- Check lab work
- Remove temp restoration
- Clean underlying prepared tooth
- Try in restoration
- Check marginal fit, contact points and occlusion
- Check pt is happy with fit and appearance
- Cement with appropriate cement
- Remove excess cement
- recheck occlusion
