The effect of irradiation wavelengths and the crystal structures of titanium dioxide on the formation of singlet oxygen for bacterial killing.

Safe and effective methods for oral bacterial disinfection have been desired, since bacteria cause many infectious diseases such as dental caries, periodontal disease, and endodontic infections. Singlet oxygen ((1)O(2)) is attractive, because it is toxic to prokaryotic cells, but not to eukaryotic cells. We selected irradiation of titanium dioxide (TiO(2)) as a source of (1)O(2), because it has been used in sunscreens and cosmetic products without complications. In order to establish the optimal oral photodynamic therapy conditions, we measured the rate of (1)O(2) formation from the irradiated anatase or rutile forms of TiO(2) using 365 or 405 nm lamps. The rate of (1)O(2) formation decreased in the following order: anatase, 365 nm > rutile, 405 nm > rutile, 365 nm > anatase, 405 nm. Therefore, we concluded that irradiation of the rutile form of TiO(2) by a 405 nm lamp is the most favorable photodynamic therapy condition, because visible light is more desirable than UV light from the viewpoint of patient safety. We also confirmed that there was no direct HO(•) formation from the irradiated TiO(2).

Stimulatory effects of low-concentration reactive oxygen species on calcification ability of human dental pulp cells.

The present study was conducted to investigate the effects of reactive oxygen species (ROS) on the calcification ability of human dental pulp (HDP) cells. HDP cells were treated with 100 mumol/L hydrogen peroxide (H(2)O(2)) for 5 or 10 minutes (5-min ROS group and 10-min ROS group) to investigate the mechanism of transmission to cells. Untreated cells were used as controls. Generation of free radicals was quantified by the electron spin resonance spin-trapping method and found to be increased by treatment with ROS. Formation of calcified nodules was also investigated by von Kossa staining and alizarin red S staining. Twenty-eight days after exposure, calcified nodules were present in cell cultures that had been treated with ROS for 5 or 10 minutes. Expression of mRNAs for osteopontin (OPN) and osteocalcin (OCN) was significantly greater in 10-min ROS group 6 and 9 days, respectively, after exposure than in controls. Production of OPN and OCN by 10-min ROS group was also greater 12 and 18 days, respectively, after exposure than in controls. These results suggested that calcification of HDP cells was stimulated by H(2)O(2) and by the ROS it generated.