AbstractThe intent of this project was to evaluate the elastic modulus and hardness of four composites with different fillers, a microfill, a hybrid, a dental resin cement, and a fiber filler, using nanoindentation. An indentation load of 0.001 N was used and 100 indents per specimen were taken. The elastic modulus measured for the Choice composite was 30.2–30.3 GPa, 15.9–16.0 GPa for Micronew, 24.6–27.1 GPa for Renew, and 36.4–47.1 GPa for Restolux. The statistical analysis indicated a significant difference in the elastic modulus for all four composites. Micronew had the lowest hardness (1.2–1.3 GPa) followed by Renew (1.6–1.8 GPa), Choice (2.6–2.8 GPa), and Restolux (2.7–4.0 GPa). The statistical analysis indicated a significant difference between Choice and Restolux from Micronew and Renew, with Renew and Micronew not being significantly different from each other. Nanoindentation of dental composites, using a 10 × 10 matrix of indentations, resulted in a wide range of measured values for the elastic modulus and hardness because of the size of the filler particle, the location of the indenter within the filler particle, the composition of the filler particles, and the location of the indenter within the filler/resin matrix. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006