STRENGTH OF A DENTAL GLASS-CERAMIC AFTER SURFACE COATING

Clinical evidence suggests that using a resin luting agent rather than a traditional cement reduces the fracture incidence of glass-ceramic crowns. There is some evidence from stress analysis and fractography t o indicate that fracture failure is typically initiated from their int ernal surface. The objective of this study was to determine if surface treatments and cement coatings of the fracture-initiating surface aff ected fracture stresses of ceramic discs in vitro. Glass-ceramic discs were cast, crystallized, and given various treatments. The discs were fractured with a ball-on-ring of balls biaxial fixture in air. The ma ximum stresses at the ceramic-coating interface were calculated using the bi-layer material equations. ANOVA and Tukey's multiple range test revealed that resin coating the fracture-initiating surface increased the biaxial fracture strength of the glass-ceramic discs by 33%. The effect was not reduced by short-term water storage. Etching alone did not significantly alter strength. The results suggest that crack-bridg ing is the most likely mechanism for the strengthening. Selecting tech niques and materials that are likely to enhance crack-bridging may be a practical method of improving the performance of ceramic dental rest orations.