The rheological properties of Bis-GMA dispersions filled with fumed silica were investigated to optimize the manufacturing process and mechanical properties by using a Rheometrics Mechanical Spectrometer (RMS). Steady and dynamic measurements on the RMS were carried out to obtain shear viscosity and dynamic mechanical properties. The effect of several factors on the rheological properties of fumed silica dispersions was also examined. The factors were a concentration of a silane coupling agent (gamma-MPS), the methods of surface treatment of fillers, silica content, diluent concentration, shear rate, and operating temperature. From these studies, it was observed that shear viscosity showed an asymptotic phenomenon at a higher concentration than a uniform multi-layer coverage concentration of gamma-MPS. The silane coupling agent had a significant role in the reduction of tan 6, resulting from a decrease of loss modulus, while fillers decreased tan 6 by increasing the storage modulus. In cases where the silica content and diluent concentration increased simultaneously, the Barcol hardness of Bis-GMA/silica composites was increased, but there was no change in the viscosity of dispersions and diametral tensile strength of those composites.