No abstract

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 (1O2) is attractive, because it is toxic to prokaryotic cells, but not to eukaryotic cells. We selected irradiation of titanium dioxide (TiO2) as a source of 1O2, 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 1O2 formation from the irradiated anatase or rutile forms of TiO2 using 365 or 405 nm lamps. The rate of 1O2 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 TiO2 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 TiO2.

Background and aim : The aims of the present study were to investigate the relationship between 1 O 2 generated via rutile-TiO 2 and its bactericidal effect on oropathogenic microorganisms, and to evaluate whether antimicrobial photodynamic therapy (a-PDT) via rutile-TiO 2 is applicable to dental treatment. Materials and methods : The experimental groups were defined as follows: only physiological saline without lightemitting diode (LED) irradiation; control group, physiological saline with LED irradiation; LED group, physiological saline including TiO 2 (4 mg/ mL) with LED irradiation; and the photocatalyst (PC) group. The LED irradiation time periods were set to 1, 2 and 3 min. A control group was placed without irradiation at room temperature. Reactive oxygen species and the amount of 1 O 2 generated were measured. A representative bacterial species selected from each oral infectious disease was used for bactericidal testing, including Streptococcus mutans (S. mutans) , Enterococcus faecalis (E. faecalis) , Porphyromonas gingivalis (P. gingivalis) , Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) , and Tannerella forsythia (T. forsythia). The colonyforming units per milliliter (CFU/mL) present after incubation was examined by experimental group, and the relative relationships between the amount of 1 O 2 generated and the various sterilization rates were examined. Results : Whereas S. mutans and E. faecalis were hardly sterilized in all groups, there were remarkable bactericidal effects in the LED group and PC group for A. actinomycetemcomitans, T. forsythia, and P. gingivalis. Conclusion : It appears that, by controlling the amount of 1 O 2 , one can select the bactericidal effect, and theses findings contribute to the development of an evidencebased medicine approach to a-PDT.