Effect of TEGDMA/BisGMA ratio on stress development and viscoelastic properties of experimental two-paste composites

In this study, we explored the reduction of shrinkage stresses in restored teeth by stimulating viscous flow of adhesive restoratives during curing, by increasing the TEGDMA/BisGMA ratio in the resin of composite restoratives. We studied a series of experimental two-paste composites with different amounts of TEGDMA (30, 50, 70 wt%, respectively) in the resin by mechanical testing, infrared spectroscopy, and dilatometry, to determine how comonomer composition affects the mechanical and chemical properties of the composite during curing. It was found that the polymerization rate of BisGMA-TEGDMA composites is indicative of the viscoelastic behavior during curing: The higher the reactivity, the higher the stiffness and viscosity development. Composites with 50 wt% TEGDMA in the resin displayed the highest maximum polymerization rate. High amounts of TEGDMA in the resin only modestly increased the pre-gel viscous flow (= lowered viscosity) property of composites. Of these composites, high post-gel shrinkage is the decisive factor in high shrinkage stress development.