2011 #2 Achievable Convergence Angle and the Effect of Preparation Design on the Clinical Outcome of Full Veneer Crowns in Dogs Author: Soukup and Snyder

Question 1

What is retention form?

Answer 1

The ability of a restoration to resist forces along the long axis, or path of insertion of the tooth

Question 2

What is taper?

Answer 2

The angle between once axial wall of the preparation and the long axis of the preparation

Question 3

What is convergence angle?

Answer 3

The angle between the two opossosing axial walls of a preparation and equals the sum of the taper of two opposing axial walls

Question 4

What is the limiting average taper?

Answer 4

The point at which resistance form is lost

T=1/2arcsin(H/D)

Question 5

In this study was the limiting average CA utilized or the limiting average taper?

Answer 5

Limiting average CA

Question 6

For teeth with a H/D greater than 1.0 what is the limiting CA?

Answer 6

The height is greater than or equal to the base diameter and therefore no CA lim exists

Question 7

What were two forms of failure in this study?

Answer 7

Adhesive/Cohesive failure

Tooth Fracture failure

Question 8

What were the results of the study?

Answer 8

3/31 crowns had adhesive/cohesive failure
3/31 crowns had tooth fracture failure
Overall 6/31 or 20% failure

Question 9

What were the results for achievable convergence angle in this study?

Answer 9

Mesial-distal angle= 35.5 degrees
Facial-lingual angle= 18.5 degrees
Overall convergence angle= 26.7 degrees

Question 10

What were the results for the preparation height and diameter?

Answer 10

Mesial-distal diameter= 9.1 mm
Facial-lingual diameter = 5.94 mm
Overall preparation diameter=7.53
Overall preparation height= 11.24mm

Question 11

What were the H/D ration results?

Answer 11

Mesial-distal H/D= 1.26
Facial-lingual H/D= 1.91
Overall H/D= 1.59

Question 12

In the study, how many had calculable CA lim?

Answer 12

Mesial-distal 9/32 teeth, 87.5% under CA lim
Facial-lingual 0/32 teeth 100% under CA lim
Overall 4/32 teeth had CA lim, 100% under CA lim

Question 13

What were two observations from the study (although not statistically significant) ?

Answer 13

Restorations that failed via adhesive/cohesive failure had numerically higher mean CA’s than those that failed via tooth fracture or did not fail

Those preparations with a CA that exceeded CAlim were 2.7 times more likely to suffer an adhesive/cohisive failure

Question 14

For a given tooth diameter and convergence angle, preparation height is directly proportional to dislodgement resistance? True or False?

Answer 14

True

Question 15

For a given height and diameter, covergence angle is inversely proportional to dislodgement resistance? True or False?

Answer 15

True

Question 16

What is the role of cements and retention?

Answer 16

Restoration cemented with a resin-based cement onto a preparation with a 35 degree taper had higher retention compared to a restoration cemented with zinc phosphate onto a prep with 12 degree taper

Question 17

What cement was used in this study?

Answer 17

Resin based cement

Question 18

What 5 recommendation can be made based on this study?

Answer 18

1 The ideal 12 degree CA can rarely be achieved for a dog and a CA exceeding 12 degrees usually has acceptable retention
2 The more clinical crown available , the less concerned the vet dentists needs to be with CA
3 A resin based cement is always recommended
4 As H/D increases the chance of tooth fracture may increase
5 Ca lim, can be used as a guide for determining the necessary CA for retention