Comparative radical production and cytotoxicity induced by camphorquinone and 9-fluorenone against human pulp fibroblasts

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 remain 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. The free-radical production activity of CQ was measured by two different methods [using diphenylpicryl hydrazyl and galvinoxyl]. The phase-transition properties of dipalmitoylphosphatidyl choline (DPPC) liposomes, as a model for biomembranes, induced by CQ were investigated by differential scanning calorimetry. These findings were compared with those of 9-fluorenone (9F), an aromatic photo-initiator with long conjugated groups. Camphorquinone with VL irradiation increased the radical production, whereas 9F with VL irradiation increased ROS production, as well as effecting changes in the DPPC phase-transition properties. The cytotoxicity of CQ towards HPF cells was smaller than that of 9F despite greater radical production. The addition of DMA to the photosensitizer enhanced the free-radical production without increasing the ROS level or the cytotoxicity. Camphorquinone/DMA is a valuable combination for the polymerization of dental resins.