Properties of a silica-reinforced polymer for dental restorations.

An esthetic and permanent restorative material that could be placed directly into the cavities prepared in anterior. teeth would be an important contribution to dental practice and public well-being. Such a material, which would have less solubility, sensitivity to desiccation, and brittleness than the silicate cements/• 2 and have greater dimensional stability than do the methyl methacrylate direct filling resins,3•4 has been in demand for many years. The present lack of a material complying with these requirements is a problem worthy of extensive investigation. The tests reported here were undertaken to determine whether the desired properties could be obtained with a reinforced organic polymer. In industry, plastics are commonly reinforced with fibers,. particles, or a combination of these. The term "reinforcement" usually is reserved for instances where the physical properties are improved; the term "filler" often implies no improvement of physical or chemical properties. Particles, rather than fibers, were selected for use in the material described here. Irregular shaped particles of vitreous silica (General Electric Co.'s Clear Fused Quartz Powder) , with special surface treatment, were used for the reinforcement. Except where otherwise specified, the particles were vinylsilane-coated and were fine enough to pass through a no. 100 sieve of the United States standard sieve series, having dimensions of approximately 150 microns (about 0.006 inch) and smaller. The organic binder for this reinforcement was specially prepared for this study, because the commercially available monomers and comonomers did not appear to be as promising, with respect to polymerization shrinkage, as the comonomer system to be described. This system was especially designed to have low polymerization shrinkage.