L2 Treatment planning, restorability and execution

Question 1

What should be included as part of the intra-oral examination?

Answer 1

• Identifying disease risk
• Caries, toothwear, failing restorations, parafunction
• Periodontal condition
• Sensibility testing
• Impressions for study models
• Fracfinder: hard plastic tool to identify cracked teeth

Question 2

At what stage of treatment are crowns completed?

Answer 2

After dealing with pain and disease stabilisation e.g. caries and perio controlled.

Question 3

What radiograph is requierd before crowning a tooth and why?

Answer 3

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

Question 4

What considerations need to be made regarding the crown of a tooth before restoring it?

Answer 4

• 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

Question 5

Why are study models required prior to crown production?

Answer 5

• 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

Question 6

What framework should be used to determine the restorability of a tooth and whether it is suitable for crowning?

Answer 6

The Dental Practicality Index (Br Dent J)

Question 7

What are the general considerations when deciding to complete an intra or extra coronal restoration?

Answer 7

General rule of thumb:
- More than 50% remaining tooth structure consider direct restoration
- Less than 50%, indirect restoration should be considered

Question 8

What is a ferrule?

Answer 8

The amount of tooth above where the crown margin finishes.
Must be at least 2mm of sound tooth structure.

Question 9

What are the issues with the teeth shown in the illustration?

Answer 9

• 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

Question 10

What are the 6 principles of crown preparation?

Answer 10

• 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)

Question 11

Why is 6 degress of taper the ideal?

Answer 11

• 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

Question 12

What is the maximum taper you may create and what issues does this create?

Answer 12

• 20 degrees
• Approaching over tapered
• More likely to rotate, fall off, more tooth tissue removed
• More reliant on adhesive forces

Question 13

What is combination compromise?

Answer 13

Combining tapers in teeth that are already tapered.
- 20 degree taper coronally
- 6 degress closer to CEJ

Question 14

Why is margin type important?

Answer 14

• Dictates amount of tooth reduced
• Must be retentive, resistant and non-undercut

Question 15

Describe the 3 types of crown margin.

Answer 15

• Shoulder: square profile, shoulder bur used
• Chamfer: rounded tip
• Feather edge: least destructive, not used often

Question 16

Why is 2-3 plane reduction required for buccal surfaces?

Answer 16

• Preserves more natural tooth tissue
• Less risk of pulp trauma/exposure
• Follows the contour of the tooth curvature

Question 17

Where should crown margins be positioned?

Answer 17

Supra-gingival wherever possible.
Sub-gingival can cause gingival inflammation and recession.

Question 18

What is the functional cusp bevel?

Answer 18

• 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

Question 19

Which 5 burs are used most frequently in crown preparation?

Answer 19

+ parallel bur

Shoulder bur thickness at tip is 1.2mm

Question 20

What is the recommended anterior crown preparation order?

Answer 20

Question 21

What is the recommended posterior crown preparation order?

Answer 21