Strain energy density approach for failure evaluation of occlusal loaded ceramic tooth crowns

The crown notch-like geometry creates a strong stress concentration, which is characterised by high stresses and severe stress gradient at the tip of the notch. In the vicinity of such stress concentrations the traditional approach based on a critical stress magnitude analysis may lead to unrealistic values for the critical load and failure conditions. At the same time, the crown geometry represents a relatively shallow rounded notch with the notch radius comparable with the tooth dimensions. Because of these geometrical features the popular approaches based on the critical stress gradient (notch stress intensity factor) could also lead to misleading results. Therefore, in this paper an alternative approach based on the averaged strain energy density over a defined volume is applied in order to predict and thus potentially avoid clinical failures in ceramic pre-molar tooth crowns. A two-dimensional finite element method is employed to investigate the stress state for various crown occlusal geometries, similar to those which were previously fabricated and subjected to mechanical testing. Then, the critical loads are calculated from the energy density approach and are compared with the results of an experimental study. The comparison of the predicted and calculated critical loads strongly supports the validity of strain energy density approach for failure assessment of tooth crown failures in the case of monotonic loading.