Mechanical performance of a dental composite: probabilistic failure prediction

In clinical situations, the mechanical performances of dental structures--for example, composite restorations--depend on many factors. Most of them have a probabilistic character. Because composites are brittle materials, their strength should also be considered as a probabilistic quantity. For successful prediction of mechanical failure of structures consisting of these materials, a probabilistic approach is indispensable, and a suitable definition of equivalent stress must be introduced. An equivalent stress facilitates the transfer of strength data of laboratory specimens to situations where the stress state is much more complicated. The tensile and compressive strengths of composites differ considerably. Of two equivalent stress definitions that potentially describe this experimental fact (the Drücker-Prager and the Modified von Mises equivalent stress), the predictive capacity was investigated for a microfine composite. In a probabilistic approach to failure, use of the Drücker-Prager equivalent stress appeared to be superior, because the average failure load of notched beams was predicted with an error smaller than 8%.