Effect of preheating on mechanical properties of a resin-based composite containing elastomeric urethane monomer

This study investigated the effect of preheating an elastomeric urethane monomer (Exothane-24) experimental resin composite on its physicochemical properties. Two resin matrices were formulated: (a) 50 wt% Bisphenol-glycidyl methacrylate (Bis-GMA) and 50 wt% triethylene glycol dimethacrylate (TEGDMA); and (b) 20 wt% Exothane-24, 40 wt% Bis-GMA and 40 wt% TEGDMA. A photoinitiator system (0.25 wt% camphorquinone and 0.50 wt% ethyl-4-dimethylamino benzoate) and 65 wt% of the inorganic filler (20 wt% 0.05 μm silica and 80 wt% 0.7 μm BaBSiO₂ glass) were added to both matrices. These formulations were then assigned to four groups: Exothane-24 (E); Exothane-24 plus preheating (EH); no Exothane-24 (NE); and no Exothane-24 plus preheating (NEH). NEH and EH were preheated at 69 °C. The dependent variables were as follows: film thickness (FT); polymerization shrinkage stress (PSS); gap width (GW); maximum rate of polymerization (Rp_max); and degree of conversion (DC). Data were statistically analyzed by two-way ANOVA and Tukey's test (α = 0.05). Preheating reduced FT for both composites. PSS and GW were significantly lower for EH, when compared with E. The DC for EH and NEH and the Rp_max for EH increased significantly. Preheating improved most of the physicochemical properties (FT, PSS, GW, and DC) of the experimental resin composite containing Exothane-24.