Two formulations of posterior composite resin (P-30 and Bisfil-P) were evaluated and compared to a high-copper, dispersed-phase amalgam (Dispersalloy). One hundred twenty-eight restorations were placed in 27 patients so that each patient received at least one of each material. After 3 years of clinical service, all three restorative materials produced clinically acceptable restorations, according to US Public Health Service and Leinfelder criteria. The amalgam restorations, however, underwent less wear (44 microns) than did the posterior composite resin restorations (60 to 74 microns). Stratification of data by type of tooth, class of restoration, and size of restoration produced the same ranking of wear from lowest to highest: Dispersalloy, Bisfil-P, and P-30. Resin restorations showed 45% more wear in molars than in premolars, and more wear was associated with moderately sized restorations than with conservative restorations. The surface texture of restorations of composite resin with porous strontium glass filler was nearly as smooth as that of enamel and was significantly smoother than that of the restorations of composite resin with zinc glass filler or of unpolished amalgam.