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 to indicate that fracture failure is typically initiated from their internal surface. The objective of this study was to determine if surface treatments and cement coatings of the fracture-initiating surface affected 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 maximum 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-bridging is the most likely mechanism for the strengthening. Selecting techniques and materials that are likely to enhance crack-bridging may be a practical method of improving the performance of ceramic dental restorations.