Rheological properties of experimental Bis-GMA/TEGDMA flowable resin composites with various macrofiller/microfiller ratio

Objectives. The purpose of this study was to investigate the rheological behavior of resin composites and to evaluate the influence of each component, organic as well as inorganic, on their viscoelastic properties by testing model experimental formulations. Methods. Several unfilled mixtures of 2,2-bis-[4-(methacryloxy-2-hydroxy-propoxy)-phenyl]propane (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) were prepared as well as experimental flowable resin composites using a Bis-GMA/TEGDMA 50/50wt% mixture as organic fraction filled at 60% in weight with varying ratios of silanated barium glass (1 mu m) and partially hydrophobic fumed silica (0.1 mu m). Their rheological properties were investigated using dynamic oscillatory rheometers. Transmission electron microscopy (TEM) was also performed to investigate the spatial organization of the filler particles. Results. Unfilled Bis-GMA/TEGDMA mixtures all showed a Newtonian behavior. The experimental flowable resin composites were non-Newtonian, shear-thinning fluids. As the quantity of microfiller increased, the viscosity increased and the shear-thinning behavior increased as well. In addition, the experimental composites showed thixotropy, i.e. their viscosity is a function of time after deformation. All these properties were not specific-ally linked to the creation and destruction of a visible network between inorganic particles, as no difference could be seen between particles' spatial organization at the equilibrium rest state or immediately after deformation. Significance. The complex viscoelastic properties of resin composites are due to interactions between microfiller and monomer molecules. Modifying the chemical and physical properties of the particles' surface could possibly improve their flow properties and thus their clinical handling performances. (c) 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.