Eisei Hayashi

Synergistic Effect of Thermal Energy on Bactericidal Action of Photolysis of H2O2 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 H2O2. Different concentrations of H2O2 (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 H2O2 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 H2O2. Streptococcus mutans and Enterococcus faecalis were used in the bactericidal assay. The LED-light irradiation of the bacterial suspensions in 500 mM H2O2 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 H2O2 at 55°C could reduce the viable counts of bacteria more efficiently than did the photolysis of 1,000 mM H2O2 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 H2O2, which in turn results in a synergistic bactericidal effect of hydroxyl radical and thermal energy.

In vitro and in vivo anti-Staphylococcus aureus activities of a new disinfection system utilizing photolysis of hydrogen peroxide

The present study aimed to evaluate in vitro and in vivo antibacterial activity of hydroxyl radical generation system by photolysis of H(2)O(2), which is a new disinfection system for the treatment of oral infection diseases such as periodontitis developed in our laboratory. Firstly, generation of the hydroxyl radical by the photolysis of H(2)O(2) in which 1 mol l(-1) H(2)O(2) was irradiated with a dual wavelength-light emitting diode (LED) at wavelengths of 400 and 465 nm was confirmed by applying an electron spin resonance-spin trapping technique. Secondly, the bactericidal effect of the system was examined under a similar condition in which Staphylococcus aureus suspended in 1 mol l(-1) H(2)O(2) was irradiated with LED light, resulting in substantial reduction of the colony forming unit (CFU) of the bacteria within a short time as 2 min. Finally, in vivo antibacterial effect of the photolysis of H(2)O(2) on a rat model of S. aureus infection was evaluated by a culture study. Since a significant reduction of recovered CFU of S. aureus was obtained, it is expected that in vitro antibacterial effect attributable to hydroxyl radicals generated by photolysis of H(2)O(2) could be well reflected in in vivo superficial bacterial infection.

Topical treatment of oral cavity and wounded skin with a new disinfection system utilizing photolysis of hydrogen peroxide in rats.

The present study aimed to evaluate the acute locally injurious property of hydroxyl radical generation system by photolysis of H(2)O(2), which is a new disinfection system for the treatment of periodontitis developed in our laboratory. Firstly, generation of the hydroxyl radical by a test device utilizing the photolysis of H(2)O(2) was confirmed by applying an electron spin resonance (ESR)-spin trapping technique. Secondly, the bactericidal effect of the device was examined under a simulant condition in which Staphylococcus aureus suspended in 1 M H(2)O(2) was irradiated with laser light emitted from the test device, resulting in substantial reduction of the colony forming unit of the bacteria within a short time as 2 min. Finally, acute topical effect of the disinfection system on rat oral mucosa and wounded skin was evaluated by histological examination. No abnormal findings were observed in the buccal mucosal region treated three times with 1 M H(2)O(2) and irradiation. Similarly, no abnormal findings were observed during the healing of skin treated with 1 M H(2)O(2) and irradiation immediately after wounding. Since topical treatment with the novel disinfection technique utilizing the photolysis of H(2)O(2) had no detrimental effect on the oral mucosa and the healing of full thickness skin wounds in rats, it is expected that the acute locally injurious property of the disinfection technique is low.

Synergistic interaction between wavelength of light and concentration of H2O2 in bactericidal activity of photolysis of H2O2

The present study aimed to evaluate the interaction between wavelength of light in the range of ultra violet A-visible and concentration of H2O2 in the reaction of photolysis of H2O2 from the point of view of hydroxyl radical (·OH) generation and the bactericidal activity. Light emitting diodes (LEDs) emitting the light at wavelengths of 365, 385, 400 and 465 nm were used at an irradiance of 1000 mW/cm(2). H2O2 was used at the final concentrations of 0, 250, 500, and 1000 mM. Quantitative analysis of ·OH generated by the LED irradiation of H2O2 were performed using an electron spin resonance-spin trapping technique. In a bactericidal assay, a bacterial suspension of Staphylococcus aureus prepared in sterile physiological saline was irradiated with the LEDs. The bactericidal activity of each test condition was evaluated by viable counts. When H2O2 was irradiated with the LEDs, ·OH was generated and bacteria were killed dependently on the concentration of H2O2 and the wavelength of LED. The two-way analysis of variance revealed that the wavelength, the H2O2 concentration and their interaction significantly affected the yield of ·OH and the bactericidal activity of the photolysis of H2O2. Therefore, it is suggested that bactericidal activity of photolysis of H2O2 could be enhanced by controlling the wavelength and the concentration of H2O2, which may contributes to shortening the treatment time and/or to reducing the concentration of H2O2.

Booster Effect of Thermal Energy on Bactericidal Action of Hydroxyl Radical Generated by Photolysis of H2O2

The effect of thermal energy on the yield of and the bactericidal action of hydroxyl radical generated by photolysis of H2O2 is discussed in this review article.

Transmitted laser beam power of the resin washed by experimental washing machine for dentures

We had developed the experimental washing machine for denture, and had examined the cleansing property of the machine. The washing machine was using hydrogen peroxide as cleansing solution activated by LED (375 nm) and ultrasonic energy. However, the effect of long-term use of this machine was not examined. The purpose of this study was to examine the color alteration using measurement of transmitted laser beam. This study showed that there was not a change in the measurement of transmitted laser beam after 100 h for washing. If the color alteration in the surface of the samples had occurred because of washing, it was thought that absorption and dispersion of the laser light were influenced. Consequently, this study indicated that this washing machine might not change on the surface of the resin.

Denture plaque removal efficacy of denture cleansing device utilizing radical disinfection ability of activated low concentration H2O2

The purpose of this study was to evaluate the plaque removal and disinfection effect of an experimental denture cleaning device applying radical disinfection system. An experimental denture cleaning device, which would be able to produce the hydroxyl ramdical by means of irradiation of light-emitting diodes (wavelength: 405 nm) to low concentration hydrogen peroxide was made.

The evaluation of the dental disinfection device with low concentration of H2O2 and laser diode

The purpose of the present study was to evaluate the experimental dental disinfection device, which is equipped with laser diode (LD) emitting visible radiation of wavelength (405 nm) and would be able to kill dental bacteria by effectively producing the hydroxyl radical by means of irradiation of LD to a low concentration (0.125–1 M) of the hydrogen peroxide (H2O2). The fungous suspension of Candida albicans (C. albicans) was exposed to the LD with an energy dose from 120 J/cm2 (5 min at 50 mW) to 720 J/cm2 (5 min at 300 mW). The results of this study indicate that the H2O2, even if the concentration is low, can effectively kill C. albicans when it is exposed to LD with a wavelength of 405 nm and an energy dose of over 360 J/cm2.

Bactericidal effect of photodynamic therapy

Photodynamic therapy (PDT) is a procedure whereby undesired tissue can be destroyed by the combined action of light, oxygen, and a photosensitizer. It is thought that a photosensitizer excited by light with a specific wavelength transfers its excitation energy to ground state oxygen molecules resulting in the generation of singlet oxygen. Singlet oxygen is a reactive oxygen species with high oxidative reactivity. Therefore, the reaction of singlet oxygen with cellular constituents can result in oxidative damage leading to cell death. Although PDT is mainly used in cancer treatment, several studies have shown that PDT also has antimicrobial properties. It has been proposed that the bactericidal effect of singlet oxygen generated by PDT could be used in clinical dentistry. Applications of PDT for the treatment of periodontitis and peri-implantitis, endodontic disease, and caries are now under study.