Degradation of microfilled posterior composite.

The substantial improvement in the chemical, physical and mechanical characteristics of posterior composites has contributed to their increased use in recent years. However, some troubling characteristics of these materials are their susceptibility to wear, marginal leakage, and recurrent caries. Numerous studies have dealt with the wear resistance of posterior composites. Only a few have investigated the mechanisms of failure, particularly those containing submicron-sized fillers. The purpose of this study, therefore, was to analyze the clinical characteristics of a posterior composite to determine the mechanisms responsible for marginal degradation. Using a series of optical standards, it was determined that the generalized wear-rate was linear, averaging 8 microns/year. Furthermore, it was shown that the marginal defect was cohesive in nature and that this type of defect, which is inherent in submicron-type posterior composites, was probably due to tensile fatigue failure.