2016 #3 The Influence of Axial Groves on Dislodgment Resistance of Prostetic Metal Crowns in Canine Teeth of Dogs Goldschmidt, Collins, Soukup Flashcards
What was the objective of the study?
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.
How was the study designed?
Canine teeth prepared with unfavorable retention features 14 canine teeth prepared with grooves 15 canine teeth prepared without grooves
How were the canine teeth “unfavorable”?
Low H/D (4/10) and high CA (35 degree)
What was the angle of force and in what direction was it applied in this study?
What was it replicating?
45 degrees
Oblique direction from distal to mesial replicating the biting-pulling action
What was the load direction attempting to replicate?
The vector encountered during biting-pulling action
What is the reported rate of failure for full veneer crowns in dogs?
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)
What are 3 pertinent dimensions for crwon retention?
1 CA (the angle between 2 opposing axial walls) 2 H/D (crown height to diameter ratio)
What is the ideal morphology for crown retention?
Columnar shape (near parallel opposing axial walls) resulting in a small CA of <12 degrees A large height to diameter ration (H/D)
What is the reality of crown morphology in veterinary dentistry?
- 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
What are two advantages of axial grooves?
- Counteract dislodgement forces
- Increase overall tooth surface area for cement bonding
What axial walls were the retention grooves placed on the canine teeth?
Labial and palatal
What was the height and the diameter of the crowns?
4 mm heigh
10 mm diameter
Resulting in an unfavorable H/D and a CA of 35 degrees
What type of cement was used for the study?
Resin-Modified Glass Ionomer
How was maximum force defined?
The peak of the force versus deflection curve prior to failure
What were the results for force required for crown dislodgement in each group
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
Was there a significant correlation between load to failure and length of the force application point?
No
What is CAlim?
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
What was the CAlim calculated at for this study?
The CAlim for teeth with the dimensions used was 22 degrees The crown prep of 35 degrees ensured poor retention features
What were 3 proposed causes of variability in the load required to cause clinical failure?
1 Minor differences in the casting of the crowns 2 Human error 3 Length of the force application points on the individual crown
Why was resin modified glass ionomer cement used in the study?
To allow repeated crown dislodgement and cement removal from the die as only one die was used for all crowns
What are two key differences between resin modified glass ionomer cement and resin cement?
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
Which type of cement is more commonly used currently in veterinary dentistry?
Resin Cement
What are 3 weaknesses of the study?
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
