Evaluation of the Effect of Antimicrobial Photodynamic Therapy on Streptococcus Mutans; An In vitro Study

Introduction: Increased resistance of oral pathogens to conventional antimicrobial agents has led to the use of alternative methods to overcome microbial resistance. The purpose of this in vitro study was to evaluate the effect of antimicrobial photodynamic therapy on Streptococcus mutans. Materials & Methods: In this in vitro study, a diode laser emitting a wavelength of 810nm was used in association with EmunDo as a photosensitizing agent. Suspensions of Streptococcus mutans were prepared and divided into six groups by treatment: 1) EmunDo, 2) diode laser irradiation (100mW, 90 seconds), 3) diode laser irradiation (300mW, 30 seconds); 4) EmunDo+diode laser irradiation (100mW, 90seconds), 5) EmunDo+diode laser irradiation (300mW, 30 seconds), 6) control (no treatment). Immediately and 24 hours after photodynamic therapy, the bacterial suspensions were cultured. After incubation at 37°C, viable microorganisms of Streptococcus mutans were counted and the results were reported in colony-forming units (CFU). Data were analyzed by repeated measures analysis of variance at significance level of 0.05. Results: According to the repeated measures analysis, no significant between-group differences were found in the number of Streptococcus mutans colonies, either immediately or 24 hours after photodynamic therapy (P>0.05). The number of Streptococcus mutans colonies increased significantly at 24 hours after photodynamic therapy compared to immediately after treatment in all groups (P<0.001). Conclusion: Under the conditions used in this study, photodynamic therapy had no effect on viability of Streptococcus mutans. However, more evidence-based data are required regarding different photosensitizing agents and laser parameters for a definite conclusion.