Coumarin-based iodonium hexafluoroantimonate as an alternative photoinitiator for experimental dental adhesives resin

The objective of this study was to evaluate the coumarin-based iodonium hexafluoroantimonate (P3C-Sb) in the polymerization kinetics of an experimental model adhesive resin both in presence of solvent and acid monomer content. A monomer mixture based on Bis-GMA, TEGDMA and HEMA was used as a model adhesive resin. Initially a screening was performed to evaluate P3C-Sb concentrations (0.25, 0.50, 1, 2, 4 mol%). Four photoinitiator systems using P3C-Sb at 2 mol% were evaluated: CQ + EDAB (control), P3C-Sb + CQ, P3C-Sb + EDAB and P3C-Sb + EDAB + CQ. Additionally, the performance of the photoinitiator systems in the presence of ethanol and acidic monomer at four different concentrations (0, 10, 20, 40 wt%) were evaluated. Real-time Fourier transform infrared spectroscopy was used to evaluate degree of conversion (DC) and rate of polymerization (RP). The ternary initiation system P3C-Sb + CQ + EDAB showed similar DC and RP to CQ + EDAB into the model adhesive resin without ethanol, however, in the presence of solvent, P3C-Sb + CQ + EDAB showed the highest polymerization kinetics. An inhibitory polymerization effect was observed when a solvent was introduced to adhesive resin using CQ + EDAB. Polymerization reaction was affected by the presence of acidic monomer irrespective of initiation system used. Adhesive resins with CQ + EDAB and P3C-Sb + CQ + EDAB as initiation systems showed similar DC to CQ + EDAB in presence of acidic monomer. The use of P3C-Sb as a third component of the initiation system seems to be an interesting alternative to improve the polymerization kinetics of simplified dental adhesives which showed to be less sensitive to the residual presence of solvent before photoactivation and it was similar polymerization behavior to CQ + EDAB in presence of acidic monomer.