2011 Volume 22 Issue 2+3 Pages 77-84
The bactericidal effects of an Nd:YAG laser by using a reaction mediator of TiO2 are described. The laser beam was irradiated to the TiO2 suspension through a quartz optical fiber, and the generated induced dynamic stress was observed in the TiO2 particles which were absorbed by the laser beam. Our previous study demonstrated the bactericidal effect of an Nd:YAG laser due to thermal and induced dynamic stress. The aim of this study was to investigate the effect of different conditions of the Nd:YAG laser on induced dynamic stress. A pulsed Nd:YAG laser (STREAK-I ALTEK Co., Tokyo) and rutile type of TiO2 powder (TIO12PB Kojundo Chemical Lab. Co., Ltd., Saitama) were used. Streptococcus mutans ATCC 25175 was used for this experiment. Bacterial cell suspensions of the strain were irradiated by Nd:YAG laser with several different pulsed energies and times of exposure, then the samples were subjected to SEM investigation. After these treatments, the viable cell count was estimated in each sample under different conditions. Regarding the bactericidal effects of the Nd:YAG laser in the presence of TiO2, there was a significant reduction such as 90-99.9% of viable cells of S. mutans. SEM (JSM-6390LV JEOL Ltd. Tokyo) investigations revealed morphological damage according to the pulse energies and exposure times applied. It is suggested that the bactericidal action occurred as a result of the dynamic stress induced by the Nd:YAG laser irradiation and TiO2 as a reaction mediator.