Antibacterial activity of a visible light-responsive photocatalytic titanium dioxide coated on the orthodontic bracket

Objectives: In orthodontic treatment with the multi-bracket appliance, it is critically important to remove biofilm attached around the appliance in order to prevent oral diseases such as caries and periodontal disease. Several studies have been reported on antibacterial activity of photocatalystic titanium dioxide coating under ultraviolet light (UV), but UV is not suitable for clinical application, because of baneful influence of UV on the human body. The purpose of this study was to examine antibacterial activity of a visible light-responsive photocatalystic titanium dioxide coated on the orthodontic bracket.
Methods: Streptococcus mutans ATCC 25175 and Streptococcus sobrinus ATCC 33478 were used in this study. Stainless steel disks with 3 mm in thickness and 5 mm in diameter were also used as the material of orthodontic bracket. The disks were coated with a visible light-responsive photocatalystic titanium dioxide. A LED light with a wavelength of 405 nm, which was within visible light region,　was irradiated to the disks. Antibacterial activities of the coated and uncoated disks were determined with radial diffusion assay. Antibacterial activities of both disks after the LED irradiation for 2 hours were also examined by counting colony forming unit on the agar plate. Furthermore, viability of the bacteria after the LED irradiation was examined with the LIVE/DEAD kit and observed by fluorescent microscopy.

Results: In the radial diffusion assay, a significant antibacterial activity was observed in the coated group, compared to the uncoated. In addition, coated group showed a significant decrease in the number of bacterial colony. In the fluorescent microscopy, many dead bacterial cells were observed in the coated group.
Conclusions: The visible light-responsive photocatalystic titanium dioxide coating have antibacterial activity against Streptococcus mutans and Streptococcus sobrinus.