Fatigue of zirconia under cyclic loading in water and its implications for the design of dental bridges

Objectives The aim of this study was to evaluate the cyclic fatigue behavior of zirconia (3Y-TZP) in water and derive guidelines for the design of zirconia-based dental bridges with extended lifetime. Methods The subcritical crack growth parameters under aqueous and cyclic loading conditions were determined from Weibull distributions of the initial mechanical strength and of the lifetime of TZP specimens. The strength and lifetime data were obtained using a specially designed bending machine under simple and oscillatory loading conditions, respectively. Results The TZP components submitted to cyclic loading in water exhibited subcritical crack propagation at stress levels significantly (not, vert, similar50%) lower than the critical stress intensity factor (KIC = 5.6 MPa m1/2). In spite of this susceptibility to subcritical crack growth, calculations based on the fatigue parameters and on the stress applied on the prosthesis indicate that posterior bridges with zirconia frameworks can exhibit lifetimes longer than 20 years if the diameter of the bridge connector is properly designed. Significance This in vitro study indicates that partially stabilized zirconia (3Y-TZP) can withstand the severe cyclic loading and wet conditions typically applied in the molar region of the mouth and is therefore an appropriate material for the fabrication of all-ceramic multi-unit posterior bridges.