Degree of conversion of resin blends in relation to ethanol content and hydrophilicity

Objectives: To evaluate the degree of conversion of five experimental adhesive systems in relation to their hydrophilicity. The resin blends ranged from hydrophobic to hydrophilic and were tested as neat bonding agents, or solvated with increasing percentages of ethanol. The hypothesis tested was that extent of polymerization of resin blends is affected by resin hydrophilicity, solvent concentrations or time of polymerization. Methods: Five light-curing versions of neat experimental resin blends were submitted to investigation: (1) 70% E-BisADM, 28.75% TEGDMA; (2) 70% BisGMA, 28.7% TEGDMA; (3) 70% BisGMA, 28.7% HEMA; (4) 40% BisGMA, 30% TCDM, and 28.75% TEGDMA; (5) 40% BisGMA, 30% BisMP, and 28.75% HEMA. All blends included 1% EDMAB and 0.25% CQ. Ethanol in different weight percentages (A: 0%, B: 30%, C: 50%, D: 70% and E: 90%) was added to these resin blends simulating different formulation of adhesives. A differential scanning calorimeter was used to measure the degree of conversion of resin blends as a function of resin hydrophilicity, solvent concentration and time of curing. Data were analyzed with three-way ANOVA and Tukey's post hoc test. Results: Exotherms showed that degree of conversion was influenced by the hydrophilicity of the blends resin (p < .05), percentage of ethanol dilution (p < .05) and time of curing (p < .05). 30% ethanol dilution increased degree of conversion compared to neat compounds irrespective to resin type and curing time, showing the highest degree of conversion values of the study design. Significance: This study supports the hypothesis that high ethanol percentages (>50 mass%) may compromise extent of polymerization kinetics of dental adhesives.