Commercially available dental composite resins undergo polymerization shrinkage during curing, setting up internal stress that can result in debonding at the tooth-composite interface, tooth fracture and composite failure. Debonding can also lead to marginal leakage and recurrent decay. The presence of a compliant phase, in this case polybutadiene in aggregate form with fumed silica, is shown to reduce polymerization shrinkage in the bis-GMA/TEGDMA resin system. The addition of a small amount of the plasticizer triphenylethylene promoted additional reduction in cure shrinkage by reducing the glass transition temperature, T., A trend toward reduced cure shrinkage was noted as the polybutadiene: silica ratio decreased within each molecular weight of polybutadiene tested. The optimal formulation tested was determined to be 0.25 wt. % triphenylethylene in bis-GMA with aggregates formed from polybutadiene of molecular weight 2-3 million, in a polybutadiene: silica ratio of 0.005. Shrinkage reduction in this system was similar to 42% without loss of Knoop hardness. (c) 2005 Wiley Periodicals, Inc.