The development of amalgam-substitute materials is a high research priority due to environmental concerns associated with mercury management. Dental composites are likely to be the substitute material of choice for the foreseeable future. Other alternative materials (e.g., ceramics) are excessively complex and expensive. Current use of directly placed dental composites is somewhat limited, however, due to excessive polymerization shrinkage and inferior fracture and wear resistance. These characteristics can potentially lead to microleakage and the development of secondary caries, and reduce the life expectancy of composite restorations in load bearing applications. Because of these factors, current dental composites are recommended only for conservative applications. The use of novel fillers is one approach to expand the range of applications for currently available dental composite technology. Three-dimensional "scaffold-like" filler has been investigated in a variety of dental materials in limited studies with mixed results. The overall objective of the proposed research is to test the hypothesis that incorporation of a "scaffold-like" fused-fiber filler will decrease dental composite shrinkage, increase composite fracture resistance, and produce no adverse effects on composite wear resistance of standard dental composite compositions. The specific aims of the proposed research are to: (1) determine the effect of additions of prepolymerized fused-fiber filler particles on the overall volumetric shrinkage of standard dental composite compositions, (2) determine the effect of additions of prepolymerized fused-fiber filler particles on the flexural strength and fracture toughness of standard dental composite compositions, (3) determine the effect of additions of prepolymerized fused-fiber filler particles on the in vitro wear behavior of standard dental composite compositions, and (4) determine if there is any correlation between the fracture toughness and wear rate of modified and unmodified dental composite compositions. Volumetric shrinkage will be measured using specific gravity techniques. Fracture toughness will be determined by a controlled flaw fracture strength technique and through fractographic evaluation of fracture-initiating flaws. Wear will be simulated using a modified Leinfelder wear testing apparatus and measured using standard profilometric techniques. In addition, SEM and AFM will be used to characterize the prepolymerized fused-fiber filler particles and the modified composite microstructures.