L2 Treatment planning, restorability and execution Flashcards
What should be included as part of the intra-oral examination?
- Identifying disease risk
- Caries, toothwear, failing restorations, parafunction
- Periodontal condition
- Sensibility testing
- Impressions for study models
- Fracfinder: hard plastic tool to identify cracked teeth
At what stage of treatment are crowns completed?
After dealing with pain and disease stabilisation e.g. caries and perio controlled.
What radiograph is requierd before crowning a tooth and why?
IOPA
- Need to see entire crown and apex
- Provides pulp dimensions, status of periapical tissues, status of root filling if present, status of periodontal tissues
- BWs are not sufficient as the entire tooth is not visible
- OPTs are not sufficient as they don’t provide enough detail
What considerations need to be made regarding the crown of a tooth before restoring it?
- Has the tooth previously been restored, is this restoration sound?
- Is the tooth caries/disease free?
- Is there an acceptable core or does it need to be replaced?
- Is the tooth vital or root filled?
- Clinical crown height, require sufficient core height
- Occlusal relationships, how does the opposing arch interact with the teeth? Heavy contacts = more problems
Why are study models required prior to crown production?
- Assess pre-operative occlusion, keep or change?
- Assess occlusal space for crown
- Assess clinical crown height (too short = risk of crown becoming uncemented/debonded)
- Used to construct special tray where required
What framework should be used to determine the restorability of a tooth and whether it is suitable for crowning?
The Dental Practicality Index (Br Dent J)
What are the general considerations when deciding to complete an intra or extra coronal restoration?
General rule of thumb:
- More than 50% remaining tooth structure consider direct restoration
- Less than 50%, indirect restoration should be considered
What is a ferrule?
The amount of tooth above where the crown margin finishes.
Must be at least 2mm of sound tooth structure.
What are the issues with the teeth shown in the illustration?
- Lateral load is created
- Red dot = loading cusp
- Lateral load creates stress in the upper corner of the restoration causing crack propagation palatally
- Tooth fractures
What are the 6 principles of crown preparation?
- Tooth reduction: keep balance between sufficient space for crown material and pulp protection
- Non-undercut preparation: crown requires path of insertion
- Retentive preparation: 6-10 degree taper
- Resistant to lateral forces
- Occlusal reduction: occlusal clearance/space for crown
- Margin type: feather < chamfer < shoulder (most destructive)
Why is 6 degress of taper the ideal?
- Improves resistance to vertical displacement and rotation
- 6 degrees provides enough space to seat the crown fully (less taper would mean more resistance when trying to place crown)
- Less reliant on adhesive forces
What is the maximum taper you may create and what issues does this create?
- 20 degrees
- Approaching over tapered
- More likely to rotate, fall off, more tooth tissue removed
- More reliant on adhesive forces
What is combination compromise?
Combining tapers in teeth that are already tapered.
- 20 degree taper coronally
- 6 degress closer to CEJ
Why is margin type important?
- Dictates amount of tooth reduced
- Must be retentive, resistant and non-undercut
Describe the 3 types of crown margin.
- Shoulder: square profile, shoulder bur used
- Chamfer: rounded tip
- Feather edge: least destructive, not used often
Why is 2-3 plane reduction required for buccal surfaces?
- Preserves more natural tooth tissue
- Less risk of pulp trauma/exposure
- Follows the contour of the tooth curvature
What is the functional cusp bevel?
- Functional cusps are the cusps that occlude with the opposing teeth in centric occlusion
- Normal occlusion: palatal cusps of upper molars and buccal cusps of lower molars are the functional cusps
- Need to remove more tooth tissue from the functional cusp so that a bulky enough crown can be fitted, and the increased load can be tolerated by the tooth
Which 5 burs are used most frequently in crown preparation?
+ parallel bur
Shoulder bur thickness at tip is 1.2mm
What is the recommended anterior crown preparation order?
What is the recommended posterior crown preparation order?
