Antimicrobial photodynamic therapy using a plaque disclosing solution on Streptococcus mutans.

OBJECTIVES: Photodynamic therapy with a bactericidal action is called antimicrobial photodynamic therapy (aPDT),which is a method of staining an object with a photosensitizing dye and then sterilizing by irradiating the dye at it's excitation wavelength. In this study, we aimed to investigate a caries pathogenic bactericidal method in a site difficult to mechanically remove, by examining aPDT effect on Streptococcus mutans (S. mutans), which is a typical caries pathogenic bacteria by applying the plaque disclosing solution as photosensitizing dye. METHODS: The absorption wavelength spectrum of irradiating plaque staining agent phloxine B (PB) was analyzed using UV-vis. Reactive oxygen species (ROS) generated by photo excitation with blue LED irradiation was measured by electron spin resonance technique. S. mutans was cultured according to a conventional method and the effect of aPDT after PB staining was evaluated by a Colony Forming Unit (CFU). In addition, protein carbonyl (PC), an oxidative stress marker, was also measured by western blotting. RESULTS: Singlet oxygen was generated by PB with blue light. As a result of aPDT treatment on S. mutans under this condition, it was recognized that CFU was suppressed dependent on irradiation intensity of blue light. In addition, the expression of PC was enhanced by aPDT. CONCLUSIONS: aPDT is demonstrated by staining S. mutans with PB and irradiating blue light used for resin polymerization and tooth bleaching to generate ROS. Therefore, plaque-disclosing solution-based aPDT against S. mutans might represent a new method for cleaning pit and fissure grooves.

Blue light irradiation-induced oxidative stress in vivo via ROS generation in rat gingival tissue.

It has been reported that oxidative stress with reactive oxygen species (ROS) generation is induced by blue light irradiation to a living body. Only limited research has been reported in dental field on the dangers of blue light, mostly focusing on cytotoxicity associated with heat injury of dental pulp. We thus performed an in vivo study on oral tissue exposed to blue light. ROS generated upon blue light irradiation of flavin adenine dinucleotide were measured by electron spin resonance spectroscopy. After blue light irradiation, the palatal gingiva of Wistar rats were isolated. Collected samples were subjected to biochemical analysis of lipid peroxidation and glutathione. Singlet oxygen was generated by blue light irradiation, but was significantly quenched in an N-acetyl-L-cysteine (NAC) concentration-dependent manner. Blue light significantly accelerated oxidative stress and increased the oxidized glutathione levels in gingival tissue. These effects were also inhibited by NAC pre-administration. The results suggest that blue light irradiation at clinical levels of tooth bleaching treatment may enhance lipid peroxidation by the induction of oxidative stress and the consumption of a significant amount of intracellular glutathione. In addition, NAC might be an effective supplement for the protection of oral tissues against blue light irradiation-induced oxidative damage.