An array of polyhedral oligomeric silsesquioxane (POSS) compounds, including metal, methacrylate, and amine functional POSS, and POSS copolymers were incorporated into aromatic and aliphatic dental resins. Heptaphenyl-propylamine POSS and methacrylate derivatives were synthesized by corner-capping and Michael addition reactions, respectively. The POSS compounds were tested for solubility in commercial resins at concentrations of 1, 5, 10, and 15 wt %, followed by UV polymerization of all soluble combinations. The POSS compounds generally increased modulus and had an unpredictable effect on T-g. The modulus of the aliphatic resin increased 83% by incorporation of 15 wt % aluminum-phenyl POSS, while aromatic resins saw a maximum modulus improvement of 18% at 30 degrees C and 72% at 160 degrees C by incorporating 1 wt % of heptaphenyl-methacrylate POSS. (c) 2006 Wiley Periodicals, Inc.