Method: The model adhesives consisted of HEMA/BisGMA with a mass ratio of 45/55. The following hydrophobic (h'phobic) and hydrophilic (h'philic) photoinitiators were used: h'phobic: camphorquinone (CQ) and ethyl-4-(dimethylamino)benzoate (EDMAB); h'philic: 3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-2-hydroxypropyl] trimethyl ammonium chloride (QTX), 2-(dimethylamino) ethyl methacrylate (DMAEMA) and diphenyliodonium hexafluorophosphate (DPIHP). CQ was included in all of the formulations; the amount of CQ was fixed at 0.5 wt% with respect to the total amount of monomer. When DMAEMA and DPIHP were included the amount was 0.5 wt%. EDMAB was 0.5 or 0.25 wt% and QTX was 0.25 or 0.125 wt%. Water was added at 33 wt% into the neat resins. Shaking, sonication and centrifugation were required to yield well-separated resin/aqueous phases. Degree of conversion (DC) and polymerization kinetics of neat resin, aqueous phase and resin phase were determined by a time-resolved ATR/FTIR spectrometer.
Result: The aqueous and resin phases of the phase-separated adhesive showed 0 and 85.4% DC, respectively with h'phobic photoinitiator system. CQ plus h'philic components only: DC in aqueous phase 12.9-25.4% and resin phase 65.1-47.8%. CQ/DMAEMA/EDMAB 0.25%/DPIHP/QTX 0.25% provided DC of 31.5 and 92.1% in the aqueous and resin phases, respectively.
Conclusion: The concentration and composition of initiators must be optimized for polymerization of both the h'philic and h'phobic rich phases in dentin adhesive exposed to overwet environments.