Objectives: The aims of this study are firstly to demonstrate the limitations of a phenomenological model proposed for filler/resin dental composites, and secondly, to modify the model to accommodate these limitations.Methods: A power-law rule of mixtures (ROM) is established by a simple modification of the elastic contact mechanics. A scaling parameter from the modification links the composite modulus E-c to the filler and resin moduli, E-f and E-r. Computer simulation results available in the literature are used to determine the scaling parameter. Difference between the previous phenomenological model and the current approach is evaluated using correlation coefficients and standard errors.Results: The results demonstrate that the previous phenomenological model is deficient if the modulus ratio E-f/E-r is higher than 10 (the normal E-f/E-r, ratio for filler/resin dental composites is around 20-30). A modified approach keeps the simplicity of the previous model, gives much improved predictions for composite moduli and satisfies the boundary conditions for bulk filler and resin materials,Significance: Dental researchers investigating a variety of combinations of different fillers and resins can have accurate first-hand estimates of the potential composite modulus even before the composites are actually made. Therefore, the dental researchers will be able to tailor their composite modulus more purposefully to match either the dentin or enamel modulus, Such a useful design tool would obviously promote much wanted further research and application of polymeric dental composites, (C) 1999 Academy of Dental Materials. Published by Elsevier Science Ltd, All rights reserved.