The objective of this work is to quantify nanomechanical and nanotribological properties of nano- and micro- particles filled polymer composites used for the dental restorative applications. Nanotribological performances of the two polymer composites with different reinforcing particulates were investigated using advanced microscopy techniques. Both the polymer composites composed of same dimethacrylate based monomeric mixture, Bisphenol-A-glycidyldimethacrylate (Bis-GMA), triethylene glycoldimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), as matrix. It was found that the elastic modulus, hardness, particle size, shape, distribution and agglomeration significantly influence the friction and wear characteristics of the polymer composites. The results show that nanotribological performance of nanoparticle reinforced polymer composites is better than the microparticle reinforced polymer composites. Copyright © 2007 by ASME.