BDS4 principles of Crown prep

Question 1

when to provide extra coronal restorations?

Answer 1

• protect weakened tooth structure
• improve or restore aesthetics
• retainer for bridge
• design of RPD
• Restore tooth function

Question 2

what are principles of tooth prep?

Answer 2

1- Preservation of tooth structure
2- Retention and resistance
3- Structural durability
4- Marginal integrity
5- Preservation of the periodontium
6- Aesthetic considerations

Question 3

what is involved with preservation of tooth structure?

Answer 3

• where possible preserve sound tooth structure
• balance against needs for retention, resistance and structural durability

Question 4

what does under prep result in?

Answer 4

Poor aesthetics
Over built crown with periodontal and occlusal consequences

Question 5

what does over prep result in?

Answer 5

Pulp and tooth strength being compromised

Question 6

what is retention for prep? how is it improved?

Answer 6

• Prevents removal of the restoration along the path of insertion or the long axis of the tooth preparation
• limit number of paths of insertion

Question 7

what is resistance for prep?

Answer 7

Prevents dislodgement of the restoration by forces directed in an apical or oblique direction and prevents any movement of the restoration under occlusal forces

Question 8

what is involved with retention and resistance of prep stage?

Answer 8

• taper - 6 degrees
• length walls
• extra means retention (grooves, slots)
• path of insertion

Question 9

effect of longer walls?

Answer 9

interefere with tipping displacement

Question 10

what must be decided before prep?

Answer 10

path of insertion
- imaginary line - where rest will be placed and removed from prep
- all features of prep must coincide with line

Question 11

what is structural durability stage and how is it acheived?

Answer 11

• rest must contain bulk of material that i enough to withstand occlusal forces
• achieved through
  *occlusal reduction
  *functional cusp bevel
  *axial reduction

Question 12

what are finish line configurations for marginal integrity stage of prep?

Answer 12

(a) Knife edge
(b)Bevel
(c) Chamfer
(d)Shoulder
(e) Bevelled shoulder

Question 13

what is this?

Answer 13

chamfer finish line

Question 14

What is this?

Answer 14

shoulder finish line

Question 15

how is the preservation of periodontium stage done?

Answer 15

margins of rest must be
- smooth and exposed to clean
- dentist can finish them and patient can clean
- placed at gingival margin
*potential subginigval may be required

Question 16

what is this? what is size?

Answer 16

biological width - 2mm from CT to sulcular epithelium

Question 17

what should you consider regarding aesthetic consideration stage?

Answer 17

smile lines

Question 18

what are reductions for crown prep?

Answer 18

• axial reduction
• occlusal reduction
  *functional cusp
  *non-functional cusp
  -finish line

Question 19

what is reductions for metal crown

Answer 19

(e.g gold)

axial - 0.5mm
occlusal
*functional cusp - 1.5
*non-functional cusp - 0.5
finish line - chamfer 0.5mm

Question 20

what is reductions for ceramic crown

Answer 20

(e.g traditional porcelain)

axial - 1mm
occlusal
*functional cusp - 1.5
*non-functional cusp - 1
finish line - shoulder (1mm)

Question 21

what is reductions for MCC?

Answer 21

axial - 1.3mm
occlusal
*functional cusp - 1.8
*non-functional cusp - 1.3
finish line -
A) chamfer 0.5mm where only metal required
B) shoulder 1.3mm (metal 0.4mm) (porcelain 0.9mm)

Question 22

what is reductions for all ceramic crowns?

Answer 22

(e.g porcelain bonded to aluminia or zirconia)

axial - 1.5mm
occlusal
*functional cusp - 2
*non-functional cusp - 1.5
finish line - chamfer (1-1.5mm)

Question 23

what are stages in prep?

Answer 23

1. Occlusal reduction
2. Separation (long tapered diamond bur)
3. Buccal reduction (prepare in 2 planes)
4. Palatal or lingual reduction (diamond chamfer)
5. Shoulder and chamfer finish
6. Check occlusal surface and clearance

Question 24

degree of taper for separation?

Answer 24

5-10 degrees

Question 25

how do you check occlusion and what is most common reason lab can’t construct crown?

Answer 25

• check in ICP and excursive movement
• insufficent occlusal clearance. -lab