Crown preparation

Question 1

4 indications of extra-coronal restorations?

Answer 1

• To protect weakened tooth structure
• improve or restore aesthetics
• to restore tooth function
• retainer for bridges
• when indicated by RPD design

Question 1

What 3 things you can include in a crown indicated for RPD design?

Answer 1

• Rest seats
• Clasps
• guideplanes

Question 2

What are the 6 principles of tooth preparation for crowns?

Answer 2

1. preservation of tooth structure
2. retention and resistance
3. marginal integrity
4. structural durability
5. preservation of the periodontium
6. aesthetic considerations

Question 3

2 reasons why to preserve tooth structure?

Answer 3

• to avoid weakening tooth structure
• to avoid damaging the pulp

Question 4

2 things under preparation will result into?

Answer 4

• Poor aesthetics
• overbuilt crown leading to occlusal and periodontal consequence

Question 5

what will over-preparation lead to?

Answer 5

Pulp and tooth strength being compromised

Question 6

What is retention in crowns?

Answer 6

Prevents the removal of restoration along the path of insertion

Question 7

What is resistance in crowns?

Answer 7

• prevents dislodgment of restorations by oblique or apical forces
• prevents movement of restoration under occlusal forces

Question 8

What is the ideal taper of crown walls?

Answer 8

6 degrees

Question 9

2 modifications in preparation to increase crown retention?

Answer 9

• Grooves
• Slots

Question 10

What 3 aspects of a crown preparation contribute to its retention?

Answer 10

• Taper - 6 degree
• Path of insertion
• length of walls

Question 11

What is the problem with short crown preparation walls?

Answer 11

• more prone to tipping displacement

Question 12

How is retention achieved by path of insertion in crown prep?

Answer 12

limiting the number of paths of insertion

Question 13

What 3 things achieve crown structural durability?

Answer 13

• occlusal redection
• functional cusp bevel
• Axial reduction

Question 14

How is marginal integrity achieved?

Answer 14

By finish line configurations

Question 15

Give 5 examples of finish line configurations?

Answer 15

• knife edge
• bevel
• chamfer
• shoulder
• bevelled shoulder

Question 16

Give 3 features of a good margin finish to preserve the periodontium?

Answer 16

• smooth and fully exposed to cleansing action
• placed where the patient can clean them and the dentist can finish them
• placed at the gingival margin whenever possible

Question 17

What is the biological width?

Answer 17

• the dimension of the junctional epithelium and connective tissue above the bone crest
• 2mm

Question 18

What line should you note to achieve good aesthetics for anterior restorations?

Answer 18

Smile line

Question 19

What 4 most common materials are crowns made of?

Answer 19

• Metal - gold
• Ceramic - porcelain
• Metal ceramic
• All ceramic - porcelain bonded to zirconia or alumia framework

Question 20

What are the 6 stages in crown preparation?

Answer 20

1. occlusal reduction
2. separation
3. buccal reduction
4. palatal or lingual reduction
5. shoulder and chamfer finish
6. check occlusion and clearance

Question 21

What degree of taper you want to achieve when separating in crown prep?

Answer 21

5-10

Question 22

How would you prepare the buccal aspect of crown prep?

Answer 22

in two planes ( coronal and apical)

Question 23

How would you prepare the palatal/lingual aspect of a crown in premolars and molars?

Answer 23

in one plane

Question 24

How would you prepare the palatal/lingual aspect of a crown in canines and incisors?

Answer 24

follow palatal contour

Question 25

What should you retain during occlusal reduction?

Answer 25

Occlusal morphology (cusps and marginal ridges)

Question 26

What anatomical structure should you avoid during buccal reduction?

Answer 26

Pulp horns especially in premolars

Question 27

What is the most common reason for technicians being unable to construct a crown?

Answer 27

• insufficient occlusal clearance