Effect of the structure of silane coupling agent on sorption characteristics of solvents by dental resin-nanocomposites

Objective This work was aimed at the study of sorption characteristics of water or ethanol/water solution (75 vol%/25 vol%) by dental nanocomposites consisting of a Bis-GMA/TEGDMA (50/50, wt/wt) matrix and silica nanoparticles (Aerosil OX50) as filler, silanized with various silanes. The silanes used were 3-[(1,3(2)-dimethacryloyloxypropyl)-2(3)-oxycarbonylamido]propyltriethoxysilane, which is a urethane dimethacrylate silane (UDMS), 3-methacryloxypropyltrimethoxysilane (MPS), octyltrimethoxysilane (OTMS), blends UDMS/OTMS (50/50, wt/wt) or blends MPS/OTMS (50/50, wt/wt). Methods The composite specimens (15 mm diameter × 1 mm height) were immersed in water or ethanol/water solution at 37 ± 1 °C for 30 days. At fixed time intervals they were removed, weighed and returned to the liquid for the study of sorption kinetics. Then desorption kinetics was studied by heating the samples in a drying oven maintained at 37 °C. The sorbed or desorbed liquid at equilibrium, diffusion coefficients, solubility, and volume increase after sorption were calculated. The sorption/desorption cycle was repeated for a second time. Results The silane structure used for the silanization of nanosilica was found to affect the sorption behavior of water or ethanol/water solution (37 °C) by the composites. The composite containing the UDMS with the hydrophilic urethane group showed the highest amount of sorbed water. The composite with the OTMS, which does not contain a methacrylate moiety and cannot react with the dimethacrylate monomers showed the highest solubility both in water and ethanol/water. In all composites the amount of sorbed ethanol/water solution is much higher than that of water. OTMS-composite sorbed the highest amount of ethanol/water and the MPS-composite with the 3-methacryloxypropyltrimethoxysilane the lowest. Significance The silane structure used for the silanization of nanosilica has an effect on the solvent sorption and solubility of composites.