Lifetime of alumina- and zirconia ceramics used for crown and bridge restorations.

The lifetime of a ceramic is dependent on the presence of incidental cracks and their gradual propagation under the conditions of the oral cavity. The objective of this study was to examine the long-term strength of glass-infiltrated alumina- and various zirconia ceramics currently used in CAD/CAM systems to manufacture crown and bridge frameworks. Fracture mechanics were applied to determine characteristic strength (sigma(omicron)), Weibull modulus (m), fracture toughness (K(Ic)), and the subcritical crack growth parameters n and B. Based on these parameters, lifetime diagrams were generated which allowed the evaluation of the long-term behavior. The results showed that in a moist environment, the glass-infiltrated alumina- and some zirconia ceramics have a high susceptibility to subcritical crack growth. Zirconia ceramics with an alumina oxide content of 0.25 wt %, however, exhibited the highest initial and most favorable long-term strength, and should therefore be suitable for crown and bridge restorations.