This study was designed to measure percentage of weight loss during simulated toothbrushing of five different composite resins. The surface roughness of each composite resin was also measured after each year of simulated toothbrushing for a period of 5 years. The following conclusions were reached: 1. Despite the loss of toothbrush efficiency, all composite resins tested tended to have a decreasing wear rate with the increasing time of toothbrushing. 2. Profile (with a soft filler) and Isopast (with a microsized filler) showed the greatest resistance to abrasion and retained the smoothest surface. 3. Prestige, which demonstrated the greatest percent weight loss, also has a soft barium filler. Loss of the filler as an alkaline reaction in water due to soluble barium compounds may cause the binder to release filler particles prematurely.