2016 #3 The Influence of Axial Groves on Dislodgment Resistance of Prostetic Metal Crowns in Canine Teeth of Dogs Goldschmidt, Collins, Soukup

Question 1

What was the objective of the study?

Answer 1

To evaluate the application of axial grooves in an effort to develop a crown preparation design that enhances the retention of full veneer crowns in dogs.

Question 2

How was the study designed?

Answer 2

Canine teeth prepared with unfavorable retention features 14 canine teeth prepared with grooves 15 canine teeth prepared without grooves

Question 3

How were the canine teeth “unfavorable”?

Answer 3

Low H/D (4/10) and high CA (35 degree)

Question 4

What was the angle of force and in what direction was it applied in this study?

What was it replicating?

Answer 4

45 degrees

Oblique direction from distal to mesial replicating the biting-pulling action

Question 5

What was the load direction attempting to replicate?

Answer 5

The vector encountered during biting-pulling action

Question 6

What is the reported rate of failure for full veneer crowns in dogs?

Answer 6

Nearly 20% over follow up time of 3.6 years (Does this seem high to you guys? I have placed over 60 crowns and in 5 years and I have only had 2 come off)

Question 7

What are 3 pertinent dimensions for crwon retention?

Answer 7

1 CA (the angle between 2 opposing axial walls) 2 H/D (crown height to diameter ratio)

Question 8

What is the ideal morphology for crown retention?

Answer 8

Columnar shape (near parallel opposing axial walls) resulting in a small CA of <12 degrees A large height to diameter ration (H/D)

Question 9

What is the reality of crown morphology in veterinary dentistry?

Answer 9

• most teeth have lost crown height secondary to fracture leading to small and unfavorable H/D
• conical rather than columnar shaped teeth with CA of 35-70 degrees
• High torque placed on dental prostheses
• Variable force vectors

Question 10

What are two advantages of axial grooves?

Answer 10

• Counteract dislodgement forces
• Increase overall tooth surface area for cement bonding

Question 11

What axial walls were the retention grooves placed on the canine teeth?

Answer 11

Labial and palatal

Question 12

What was the height and the diameter of the crowns?

Answer 12

4 mm heigh

10 mm diameter

Resulting in an unfavorable H/D and a CA of 35 degrees

Question 13

What type of cement was used for the study?

Answer 13

Resin-Modified Glass Ionomer

Question 14

How was maximum force defined?

Answer 14

The peak of the force versus deflection curve prior to failure

Question 15

What were the results for force required for crown dislodgement in each group

Answer 15

No Grooves Mean= 156 N, Range=45-265 N

Grooves Mean= 900 N Range= 525-1516N

6-fold increase in crown dislodgment force in teeth prepared with axial grooves

Question 16

Was there a significant correlation between load to failure and length of the force application point?

Answer 16

No

Question 17

What is CAlim?

Answer 17

The mathematically calculated limit at which any measured CA above the CAlim does not have resistance form and any measured CA below the CAlim does have resistance form

Question 18

What was the CAlim calculated at for this study?

Answer 18

The CAlim for teeth with the dimensions used was 22 degrees The crown prep of 35 degrees ensured poor retention features

Question 19

What were 3 proposed causes of variability in the load required to cause clinical failure?

Answer 19

1 Minor differences in the casting of the crowns 2 Human error 3 Length of the force application points on the individual crown

Question 20

Why was resin modified glass ionomer cement used in the study?

Answer 20

To allow repeated crown dislodgement and cement removal from the die as only one die was used for all crowns

Question 21

What are two key differences between resin modified glass ionomer cement and resin cement?

Answer 21

RMGI cement has lower tensile and flexural strength

RMGI has weaker bond strength

*the paper points out that there are some recent studies showing that RMGI and resin cements may have similar values for crown retention

Question 22

Which type of cement is more commonly used currently in veterinary dentistry?

Answer 22

Resin Cement

Question 23

What are 3 weaknesses of the study?

Answer 23

1 A less commonly used cement type that is known to be weaker 2 The use of 1 test die 3 The study was between a metal crown and metal die rather that metal crowns and teeth