The wear resistance of posterior composites has improved dramatically over the last several years. Compared to the original formulations, many of the currently available composites exhibit wear rates of less than 10% of their early predecessors. Nevertheless, much research has been directed toward improving this property to a higher level. This investigation deals with a surface-penetrating sealant designed to increase the wear resistance and marginal integrity of posterior composites. In conjunction with a recently developed three-bodied wear testing device. it was shown that the effectiveness of this surface-penetrating sealant depends upon the mean particle size. Those composites in which the mean particle size is greater than 1 micrometer undergo nearly 40-50% reduction in wear. The wear of composites containing submicron-sized filler particles was not affected by the surface-penetrating sealant. Finally, regardless of the particle size of the composites, the surface-penetrating sealant enhanced marginal integrity.