Crown Preparation

Question 1

What are the principles of tooth preparation?

Answer 1

1. Preserve tooth structure
2. Retention and resistance
3. Structural durability
4. Marginal integrity
5. Preservation of periodontium
6. Aesthetics considerations

Question 2

What will under preparation result in?

Answer 2

• Over built crown with periodontal and occlusal consequences
• Poor aesthetics

Question 3

What will over preparation result in?

Answer 3

Pulp and tooth strength compromised

Question 4

Define retention

Answer 4

Prevention of removal of rest along path of insertion or long axis of tooth prep

Question 5

Define resistance

Answer 5

• Prevention of dislodging of rest in apical/ oblique direction
• Prevention of any movement under occlusal forces

Question 6

How is retention and resistance increased?

Answer 6

• Taper of opposing walls (ideally 6 deg)
• Length of walls (longer = more resistance)
• Extra means of retention (slots, grooves)
• Path of insertion (limit)

Question 7

How is structural durability of the restoration achieved?

Answer 7

Adequate preparation of

• Occlusal reduction
• Fuctional cusp bevel
• Axial reduction

Question 8

What are the type of finish line configurations?

Answer 8

1. Knife edge
2. Bevel
3. Champfer
4. Shoulder
5. Bevel shoulder

Question 9

How is the periodontium persevered?

Answer 9

• Preparations of margins;
  
  • -> smooth
  • -> placed where pt can readily clean
  • -> at gingival margin whenever possible

Question 10

What are the preparation dimensions for a metal crown (incl gold)?

Answer 10

Axial reduction = 0.5mm

Occlusal reduction

• Functional cusp = 1.5mm
• Non-functional cusp = 0.5mm

Finish line = Chamfer (0.5mm)

Question 11

What are the preparation dimensions for a traditional ceramic crown?

Answer 11

Axial reduction = 1mm

Occlusal reduction

• Functional cusp = 1.5mm
• Non-functional cusp = 1mm

Finish line = Shoulder (1mm)

Question 12

What are the preparation dimensions for a MCC (metal ceramic crown)?

Answer 12

Axial reduction = 1.3mm

Occlusal reduction

• Functional cusp = 1.8mm
• Non-functional cusp = 1.3mm

Finish line

a. Chamfer (0.5mm); where metal required
b. Shoulder (1.3mm); 0.4mm for metal and 0.9mm for porcelain

Question 13

What are the preparation dimensions for a all ceramic crown (alumina/ zirconia reinforced framework)?

Answer 13

Axial reduction = 1.5mm

Occlusal reduction

• Functional cusp = 2mm
• Non-functional cusp = 1.5mm

Finish line = Chamfer (1-1.5mm)

Question 14

What are the stages of preparation?

Answer 14

1. Occlusal reduction
2. Separation (axial reduction)
3. Buccal reduction
4. Palatal/lingual reduciton
5. Finish line
6. Check occlusal surface and clearance