Effects of water content and initiator composition on photopolymerization of a model BisGMA/HEMA resin

Abstract

Aims The purpose of this study was to evaluate the effects of photoinitiator type and water content on the polymerization rate ( R p) and degree of conversion (DC) of a model BisGMA/HEMA-based resin. Materials and methods The comonomer mixture consisted of BisGMA/HEMA (60/40 by weight). Different two- or three-component photoinitiator systems were incorporated. Two-component systems were 0.5% CQ (camphorquinone) and 0.5% DMAEMA (2-(dimethylamino) ethyl methacrylate) or 0.5% CQ and 0.5% 4E (ethyl 4-dimethylaminobenzoate). The three-component systems were added 1% DPIHP (diphenyliodonium hexafluorophosphate) to the above systems. Each system was tested as made, or after addition of 5, 10, 15 wt% water. When cured under a conventional dental light, the R p and DC of each formulation was determined using time-resolved attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectroscopy. Results For mixtures containing two-component initiator systems, when the hydrophobic initiator CQ was used in combination with hydrophilic DMAEMA, R ps and DCs were dramatically decreased as a function of water content. The R ps and DCs of the hydrophobic CQ/4E system were higher than those of the CQ/DMAEMA system in the presence of water. For three-component initiator systems, incorporation of DPIHP enhanced the polymerization of all mixtures in the presence of water compared to their counterpart two-component initiators. Interestingly, the CQ/DMAEMA caused greater DC and R p when DPIHP was used. Significance The hydrophobicity/hydrophilicity of photoinitiator components significantly affects both the DC as well as R p when in the presence of water. The results indicate that formulation of photoinitiator components should be based on the effectiveness of the bonding systems under both dry and wet conditions.