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

The aim of this study was to investigate the effects of monomer and filler composition on the rheological properties related to the handling characteristics of composites. 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 μm), 0.04 μm fumed silica or 0.5 μm round silica. The type and content of incorporated fillers 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 ( η) of the resin matrix, the storage shear modulus ( G′), loss modulus ( G″), complex modulus ( G*), loss tangent (tanδ), phase angle δ and complex viscosity ( η*) of the composites were evaluated as a function of frequency ω=0.1–100 rad/s. To investigate the effect of temperature on viscosity, a temperature sweep test was also performed. Resin matrices were Newtonian fluids and all experimental composites exhibited pseudoplasticity. The viscosity exponentially increased as the percentage of filler volume was increased, but decreased with increasing temperature. For identical filler volumes, as the filler size decreased, viscosity increased. The effect of filler size on the viscosity was intensified with increasing filler content, and the increased filler content reduced the tan δ. The rheological properties of composites related to handling characteristics were greatly influenced by the formulation of the monomer and filler, shear rate and temperature. The locus of frequency domain phasor plots, G * ( ω ) e i δ = G * ( ω ) ∠ δ , in a complex plane was a valuable method for representing the viscoelastic properties of the composites.