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

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.

Fungicidal effect of combined nano TiO2 with erythrosine for mediated photodynamic therapy on Candida albicans: an in vitro study

“…This dye molecule, which was stimulated by light, transfers electrons to the conduction band of semiconductor (TiO 2 ) and then reacts with oxygen molecule on the TiO 2 surface to generate superoxide anion and hydroxyl radicals [18]. Unfortunately, in our study, we could not measure the amount of superoxide anion, partly due to the lower amount of TiO 2 compared with previous studies [17,19]. Moreover, the suitable light for stimulating TiO 2 to generate free radicals, especially superoxide anions, is not visible by UV light [20].…”

Bactericidal Effect of Antimicrobial Photodynamic Therapy Using Visible Light-responsive Titanium Dioxide -the First Report

“…Also besides, recent studies have reported the promotion of osseointegration by applying the ROS generated in a photofunctionalization reaction to remove carbon accumulated in TiO 2 formed on the surface of the implant body by ultraviolet (UV) irradiation (17,18) . cal, which is the most oxidative ROS, was generated directly from irradiated rutile -TiO 2 , it was also confirmed that a -PDT via rutile -TiO 2 could be safely applied to dental treatment (19) .…”

Photodynamic therapy: An adjunct to conventional root canal disinfection strategies

“…Its photocatalysis is able to promote the peroxidation of the polyunsaturated phospholipid component of the microbial lipid membrane, induce loss of respiratory activity, and elicit cell death. While with those organisms implicated in oral infections, including A. nucleatum, growth inhibitory and killing concentrations under anaerobic conditions are in the same order at 0.25-2.5 and >2.5 mg/mL, respectively (51).…”

“…It has two structures, the anatase and rutile (51). It is widely used in a number of applications as a powder and increasingly in a nanoparticulate form, and is generally considered to be non-toxic at the concentrations normally employed.…”