Abstract

Background and aims This study was done to compare the antibacterial effect of Photodynamic therapy (PDT) on () using two different light sources and photosensitizers (PS). Materials and methods Five groups were studied in this research:no light and no toluidine blue ortho (TBO) as PS for control group, irradiation only (CO laser or Nd:YAG laser), and irradiation with PS (CO laser and TBO or Nd:YAG laser and TBO). Standard suspensions of , based on the type of group, were used in different PDTs. Bacterial suspension from each treatment was subcultured onto the surface of Mueller-Hinton agar plates, and bacterial growth was assessed. The results were analyzed by analysis of variance (ANOVA). Results There was a statistically significant reduction in the viability of in TBO with CO laser and TBO with Nd:YAG laser groups (p value < 0.05). However, there was no significant difference between control and groups treated with lasers only. The highest number of the colonies of in treated groups was observed in CO laser irradiation only and the lowest number was seen in CO laser with TBO. In the groups irradiated alone (without TBO), no significant reduction of colonies was observed. There was no significant difference between the experimental groups. Conclusions The colonies of were susceptible to either CO laser or Nd:YAG laser in the presence of TBO with no significant difference. So these lasers with this photosensitizer may be useful in prevention of dental caries and antimicrobial treatment protocols.