Objectives: This study evaluated the kinetics of water diffusion and percent conversion in neat versus acetone-solvated resins that were formulated to be used as dental bonding agents.
Methods: Five methacrylate-based resins (R1, R2, R3, R4 and R5) of known hydrophilicities were used as reference materials. These resins were evaluated as neat bonding agents (100% resin) or they were solvated with absolute acetone (95% resin/5% acetone or 85% resin/15% acetone). Specimens were prepared by dispensing the uncured resin into a circular brass mold (5.8 mm x 0.8 mm). Photo-activation was performed for 80 s. The water sorption/diffusion/solubility measurements were made gravimetrically, while the degree of conversion (DC) was calculated by infrared spectroscopy.
Results: Water sorption/diffusion increased with the hydrophilicity of the resin blends. In general, the acetone-solvated resins exhibited significantly higher water sorption, solubility and water diffusion coefficients when compared to their corresponding neat versions (p<0.05). The only exception was resin R1, the least hydrophilic resin, in which neat and acetone-solvated versions exhibited similar water sorption (p>0.05). Addition of acetone increased the DC of all tested resins, especially of the least hydrophilic, resins R1 and R2 (p<0.05). Despite of the increased DC of acetone–solvated methacrylate-based resins, it occurs at the expense of an increasing in their water sorption/diffusion and solubility values.
Conclusions: Negative effect of residual acetone on water sorption/diffusion was more critical for the most hydrophilic resin blends.