Three commercial dental composites with filler loading of 75-76 wt% were evaluated. The wear results were compared with those reported in an earlier study on a highly filled composite containing predominately alumino-silicate glass fillers and alumina at a filler loading of 92 wt%. The differences in wear rates between the three medium filled composites were not statistically significant indicating that the variations in filler particle size and slight differences in chemical composition of the glass fillers do not affect the wear rates of these composites. Wear rates of the medium filled composites, however, were significantly lower than the highly filled composite. WEM, FTIR and ICP-MS analyses suggested that wear in the medium filled composites occurs by a complex set of processes involving formation of surface films by tribochemical reactions and film detachment by microfracture as well as dissolution of the reaction products.