Photoinitiator system and water effects on C=C conversion and solubility of experimental etch-and-rinse dental adhesives

The purpose of this study was to determine the influence of the photoinitiator system and moisture condition on the degree of C=C conversion (DC), the water sorption (Wsp), and the solubility (Wsl) of experimental two-step etch-and-rinse dental adhesives. Different photoinitiator systems were added at 0.5 mol% to an experimental adhesive blend (55:45 wt% Bis-GMA:HEMA), defining the experimental groups: camphorquinone (CQ)+ethyl-4-dimethylaminobenzoate (EDMAB), 9,10-phenanthrenequinone (PQ), PQ+EDMAB, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO). The adhesives were tested in two moisture conditions: neat and wet (with the addition of 10 wt% D2O). The DC (n=6) was evaluated by Fourier-transformed infrared spectroscopy (FTIR). Wsp and Wsl were determined (n=10) after successive weighting procedures. Data were submitted to two-way ANOVA and Tukey׳s post hoc test (α=0.05). Pearson׳s correlation tests were used to analyze the correlation between DC and Wsp or Wsl. TPO and BAPO presented the highest DC in the neat condition while CQ+EDMAB presented the highest in the wet condition. Wsp and Wsl were both dependent on the photoinitiator system and moisture condition. PQ-based materials presented the highest Wsp and Wsl in both neat and wet conditions. Pearson׳s tests were not able to detect any significant correlation between DC and Wsp or DC and Wsl. Within the limitations of the present study, it can be concluded that the photoinitiator system and moisture condition influenced the DC, Wsp, and Wsl of experimental two-step etch-and-rinse adhesives.