Fatigue of zirconia and dental bridge geometry: Design implications

Zirconia is currently used as a framework material for posterior all-ceramic bridges. While the majority of research efforts have focused on the microstructure and corresponding mechanical properties of this material, clinical fractures appear to be largely associated with the appliance geometry. Objective The objective of this study was to estimate the maximum stress concentration posed by the connector geometry and to provide adjusted estimates of the minimum connector diameter that is required for achieving 20 years of function. Methods A simple quantitative description of the connector geometry in an all-ceramic 4-unit bridge design is used with published stress concentration factor charts to estimate the degree of stress concentration and the maximum stress. Results The magnitude of stress concentration estimated for clinically relevant connector geometries ranges from 2 to 3. Using previously published recommendations for connector designs, adjusted estimates for the minimum connector diameter required to achieve 20 years of clinical function are presented. Significance To prevent clinical fractures the minimum connector diameter in multi-unit bridges designs must account for the loads incurred during function and the extent of stress concentration posed by the connector geometry.