Influence of different initiators on the degree of conversion of experimental adhesive blends in relation to their hydrophilicity and solvent content

Abstract Objectives The aim of this study was to compare the curing reaction of five experimental adhesive blends containing different photo-initiating systems. The hypothesis tested was that degree of conversion (DC) of resin blends is affected by resin type, solvent content and photo-initiating system. Methods The experimental methacrylate resin blends were ranked from hydrophobic (R2) to hydrophilic (R3 and R4) and tested as neat, or solvated with 10% or 20% ethanol, or 10% ethanol and 10% water. Three different photo-initiators were used: IS-1 = 0.25% CQ (camphorquinone) + 1% EDMAB (ethyl 4-dimethylaminobenzoate); IS-2 = 1.25% TPO (diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide); IS-3 = 0.25% CQ + 0.50% EDMAB + 0.50% TPO. DC of resin blends was measured with a differential scanning calorimeter. Data were analyzed with a three-way ANOVA. Results Neat resin type influenced DC, as R4 showed the highest values compared to R2 and R3 ( p < 0.05). Solvent had a significant effect on DC ( p < 0.05): dilution of resin blends with 10% or 20% ethanol or 10% ethanol + 10% water increased the DC of all resins, except for R4. Initiators influenced the polymerization since neat resins and mixtures solvated with 10% or 20% ethanol showed their highest DC values when polymerized with IS-1 or IS-3 ( p > 0.05), while IS-2 or IS-3 increased the DC values of resins diluted with 10% ethanol and 10% water ( p < 0.05). Conclusions Water-compatible photo-initiators such as TPO should be included in the hydrophilic solvated adhesive formulation to ensure an appropriate DC of the adhesive layer.