Analyses of layer-thickness effects in bilayered dental ceramics subjected to thermal stresses and ring-on-ring tests.
OBJECTIVE
The purpose of this study was to analyze the stress distribution through the thickness of bilayered dental ceramics subjected to both thermal stresses and ring-on-ring tests and to systematically examine how the individual layer thickness influences this stress distribution and the failure origin.


METHODS
Ring-on-ring tests were performed on In-Ceram Alumina/Vitadur Alpha porcelain bilayered disks with porcelain in the tensile side, and In-Ceram Alumina to porcelain layer thickness ratios of 1:2, 1:1, and 2:1 were used to characterize whether failure originated at the surface or the interface. Based on (1) the thermomechanical properties and thickness of each layer, (2) the difference between the test temperature and the glass transition temperature, and (3) the ring-on-ring loading configuration, the stress distribution through the thickness of the bilayer was calculated using closed-form solutions. Finite element analyses were also performed to verify the analytical results.


RESULTS
The calculated stress distributions showed that the location of maximum tension during testing shifted from the porcelain surface to the In-Ceram Alumina/porcelain interface when the relative layer thickness ratio changed from 1:2 to 1:1 and to 2:1. This trend is in agreement with the experimental observations of the failure origins.


CONCLUSIONS
For bilayered dental ceramics subjected to ring-on-ring tests, the location of maximum tension can shift from the surface to the interface depending upon the layer thickness ratio. The closed-form solutions for bilayers subjected to both thermal stresses and ring-on-ring tests allow the biaxial strength of the bilayer to be evaluated.
Hsueh
C H
CH
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6068, USA. hsuehc@ornl.gov
Thompson
G A
GA
Jadaan
O M
OM
Wereszczak
A A
AA
Becher
P F
PF
D003776:Dental Porcelain; D003799:Dental Stress Analysis / Q000379:methods; D003801:Dental Veneers; D020342:Finite Element Analysis; D006358:Hot Temperature; D008422:Materials Testing; D018583:Pliability; D013499:Surface Properties; D013718:Tensile Strength; D044366:Transition Temperature
C483026:In-Ceram Alumina; C483027:vitadur alpha; D003776:Dental Porcelain