Mechanisms of cytotoxicity by initiators for dental polymerizing resin systems and application for photodiamic therapy.

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Camphorquinone (CQ) is widely used as a photo-initiator in dental materials ; however, its cytotoxicity against human pulp fibroblasts (HPF) and particularly the effects of 2-dimethylaminoethyl methacrylate (DMA), a reducing agent, and visible-light (VL) irradiation on it remains unknown. So we investigated the cytotoxic and reactive oxygen species (ROS)-producing effects of CQ with or without DMA, in the presence or absence of VL on HPF cells. Also, the free-radical production activity of CQ was measured by 2 different methods (using diphenylpicryl hydrazyl, DPPH, and galvinoxyl). Furthermore, the phase-transition properties of dipalmitoylphosphatidyl choline (DPPC) liposomes, as a model for biomembranes, induced by CQ were investigated by differential scanning calorimetry (DSC). These findings were compared with those of 9-fluorenone (9F), an aromatic photo-initiator with long conjugated groups. CQ with VL irradiation increased the radical production, whereas 9F with VL irradiation increased ROS production, as well as changes in the DPPC phase-transition properties. The cytotoxicity of CQ toward HPF cells was smaller than that of 9F despite greater radical production. The addition of DMA to photosensitizer enhanced the free-radical production without in creasing ROS and cytotoxicity. In conclusion, CQ/DMA is valuable for polymerization of dental resins.