Rheological properties of resin composites according to variations in monomer and filler composition

Objectives The aim of this study was to investigate the effects of monomer and fitter composition on the rheological properties related to the handling characteristics of composites. Methods A resin matrix in which Bis-GMA was blended with TEGDMA at a ratio of 6:4, was mixed with silane-treated Barium glass (0.7 and 1.0 mu m), 0.04 mu m fumed silica or 0.5 mu m round silica. The type and content of incorporated filters were varied to achieve different viscosity Levels of the experimental composites. Steady shear and dynamic oscillatory shear tests were performed with a rheometer. The viscosity (77) of the resin matrix, the storage shear modulus (G'), Loss modulus (G"), complex modulus (G*), loss tangent (tan delta), phase angle delta and complex viscosity (eta*) of the composites were evaluated as a function of frequency omega=0.1-100 rad/s. To investigate the effect of temperature on viscosity, a temperature sweep test was also performed. Results Resin matrices were Newtonian fluids and all experimental composites exhibited pseudoplasticity. The viscosity exponentially increased as the percentage of filter volume was increased, but decreased with increasing temperature. For identical filter volumes, as the filter size decreased, viscosity increased. The effect of filter size on the viscosity was intensified with increasing filter content, and the increased filter content reduced the tan delta. Significance The rheological properties of composites related to handling characteristics were greatly influenced by the formulation of the monomer and filter, shear rate and temperature. The locus of frequency domain phasor plots, G* (omega)e(i delta) = G* (omega) angle delta, in a complex plane was a valuable method for representing the viscoelastic properties of the composites. (C) 2002 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.