Evaluation of alternative photoinitiator systems in two-step self-etch adhesive systems

The aim of this study was to evaluate the effect of different photoinitiator systems on the cell viability and physico-chemical properties of an experimental adhesive resin of a two-step self-etch adhesive system.

Eight photoinitiators and coinitiators were evaluated, camphorquinone (CQ); ethyl-dimethylamino benzoate (EDAB); diphenyliodonium hexafluorophosphate (DPIHFP); 1,3-benzodioxole (BDO); piperonyl alcohol (AP); 1,3-diethyl-2-thiobarbituric acid (TBA); bisphenyl phosphinic oxide (BAPO); and diphenyl phosphinic oxide (TPO). Seven experimental adhesive resins (Bis-GMA:TEGDMA - 1:1 by wt%) were formulated by varying the initiation systems: R_CQ+EDAB (control), R_{CQ+EDAB+DPHFP}, R_CQ+BDO, R_CQ+AP, R_CQ+TBA, R_BAPO and R_TPO. The cell viability of the different photoinitiators in their isolated form and after being incorporated into the adhesive resins was evaluated using the MTT assay. The degree of conversion within the hybrid layer (DC in situ) was evaluated by micro-Raman spectroscopy; the polymerization kinetics, by FTIR spectroscopy. The water sorption (Wsp) and solubility (Wsl) were calculated by using percentage of gain and loss of mass. Data were analyzed using One-way ANOVA and Kruskal-Wallis tests (α=0.05).

When evaluated in their isolated form, the DPIHFP was considered cytotoxic in all concentrations evaluated. When incorporated into and adhesive resin, R_CQ+TBA presented higher cell viability values than control and the highest values of DC in situ (p<0.05). Additionally, the use of CQ+TBA showed a higher cell viability when compared with the conventional CQ+EDAB system.

The pair CQ+TBA could be potentially useful in the development of materials with improved biocompatibility.