Synergistic Effect of Thermal Energy on Bactericidal Action of Photolysis of H ₂ O ₂ in Relation to Acceleration of Hydroxyl Radical Generation

Abstract

The purpose of the present study is to evaluate the effect of thermal energy on the yield of and the bactericidal action of hydroxyl radical generated by photolysis of H 2 O 2 . Different concentrations of H 2 O 2 (250, 500, 750, and 1,000 mM) were irradiated with light-emitting diodes (LEDs) at a wavelength of 400 ؎ 20 nm at 25°C to generate hydroxyl radical. The 500 mM H 2 O 2 was irradiated with the LEDs at different temperatures (25, 35, 45, and 55°C). Electron spin resonance spin trapping analysis showed that the yield of hydroxyl radicals increased with the temperature, as well as the concentration of H 2 O 2 . Streptococcus mutans and Enterococcus faecalis were used in the bactericidal assay. The LED-light irradiation of the bacterial suspensions in 500 mM H 2 O 2 at 25°C could hardly kill the bacteria within 3 min, while the bactericidal effect was markedly enhanced with the temperature rise. For instance, a temperature increase to 55°C resulted in >99.999% reduction of viable counts of both bacterial species only within 1 min. The photolysis of 500 mM H 2 O 2 at 55°C could reduce the viable counts of bacteria more efficiently than did the photolysis of 1,000 mM H 2 O 2 at 25°C, although the yields of hydroxyl radical were almost the same under the both conditions. These findings suggest that the thermal energy accelerates the generation of hydroxyl radical by photolysis of H 2 O 2 , which in turn results in a synergistic bactericidal effect of hydroxyl radical and thermal energy.A novel disinfection technique where artificially generated hydroxyl radical kills pathogenic fungi and bacteria has been developed in our laboratory (8, 9). The hydroxyl radical disinfection technique is based on the concept that the hydroxyl radical kills microorganisms as a result of oxidation of cellular components, such as cell membrane, nucleic acid, and other cell organelles. In our previous study, the bactericidal effect of photolysis of H 2 O 2 depended on the light irradiation time, indicating that bacteria were killed dependently on the amount of hydroxyl radical (8). Thus, the yield of hydroxyl radical is one of the most important factors which determine the bactericidal effect of the disinfection technique. The yield of hydroxyl radical is affected mainly by two factors when photolysis of H 2 O 2 is used as a hydroxyl radical generator. One is the potency of light to photolyse H 2 O 2 , which is controlled by wavelength and the energy density. The other is the concentration of H 2 O 2 . A high concentration of H 2 O 2 , however, might cause adverse effects when the disinfection technique is applied in the oral cavity (3,16,23). Hence, a low concentration of H 2 O 2 is preferable from a clinical point of view regarding safety issues. Especially, unlike a short-term disinfectant treatment, adverse effects on the normal tissue should be considered in a case of repetitive usage of disinfectant in a long-term treatment. One of the possible strategies to reduce the level of H 2 O 2 is thermal energy. For instance, it was ...

Microbicidal Activity of Artificially Generated Hydroxyl Radicals

“…This finding suggests that photolysis of H 2 O 2 can effectively kill not only bacteria but also fungi. Shirato et al evaluated the effect of thermal energy on the yield of and the bactericidal action of hydroxyl radicals generated by photolysis of H 2 O 2 [53]. The results demonstrated that thermal energy accelerated the generation of hydroxyl radicals by photolysis of H 2 O 2 , which in turn resulted in a synergistic bactericidal effect of hydroxyl radicals and thermal energy.…”

Corrosive effect of disinfection solution containing hydroxyl radicals generated by photolysis of H2O2 on dental metals

“…As a result, the amount of released ions was evaluated by weighing the specimens before and after immersion test using an electronic analytical balance (GH-200, A&D, Tokyo, Japan). Amount of released ions was calculated as µg/cm 2 14) . DMPO was the spin trapping agent.…”

“…In our previous studies 1,2) , we have developed a novel disinfection technique, based on hydroxyl radicals generated by photolysis of H 2O2, which could effectively kill bacteria in biofilms within 3 min. Therefore, this new disinfection technique can be used as an adjunctive treatment for caries, periodontitis, and root canal infection by delivering light together with H 2O2 to the lesion site.…”

Influence of a new denture cleaning technique based on photolysis of H2O2 the mechanical properties and color change of acrylic denture base resin

“…It is recommended that proper denture cleaning should include chemical disinfection [5][6][7] . In our laboratory, we developed a new chemical disinfection method based on the photolysis of hydrogen peroxide (H 2O2) 8,9) . When removable dentures were immersed in H2O2 irradiated with lightemitting diode (LED) light at a wavelength of 405 nm, microorganisms in denture plaque were rapidly and effectively killed by hydroxyl radicals generated from the photolysis of H 2O2 10) .…”