Evaluation of the effect of two types of laser on the growth of streptococcus mutans .

Background and aims: This study was done to compare the antibacterial effect of Photodynamic therapy (PDT) on streptococcus mutans ( S. mutans ) 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 (CO2 laser or Nd:YAG laser), and irradiation with PS (CO2 laser and TBO or Nd:YAG laser and TBO). Standard suspensions of S. mutans , 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 S. mutans in TBO with CO2 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 S. mutans in treated groups was observed in CO2 laser irradiation only and the lowest number was seen in CO2 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 S. mutans were susceptible to either CO2 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.