Effect of photodynamic therapy with two photosensitizers on Streptococcus mutants: In vitro study

Abstract Background and objectives Streptococcus mutans (S. mutans) colonizes the oral cavity and causes dental caries and periodontal diseases. Considering the importance of the treatments that decrease pathogenic microorganisms, the aim of the present research was the assessment of the antimicrobial effect of Photodynamic Therapy (PDT) with Methylene Blue (MB) and Indocyanine Green (IG) photosensitizers on S. mutans. Materials and methods In this In vitro experimental study, Sixty four caries-free first premolars were contaminated with 0.5 McFarland S.mutans suspension and were randomly assigned to 4 groups. The teeth in the first group were impregnated with 2% MB while the teeth in the second group were impregnated with 0.2% IG. The teeth in the first group were irradiated with continuous-wave 660 nm dod laser with 40 mw output power, energy density of 2.4 J/cm 2 and 100% duty cycle for 60 s, while the teeth in the second group were irradiated with continuous -wave 810 nm diode laser with 100 mw out power, density energy of 6 J/cm 2 and 100% duty cycle for 60 s in contact mode. In the third group, the teeth were suspended in 0.2% Chlorhexidine for 30 s. The fourth group was considered as the control. The teeth were sampled before and after the interventions and the samples were incubated in Blood Agar for 24 h. Afterwards, the number of S. mutans colonies were counted. Data were statistically analyzed by Kruskal-Wallis, Dunn's and Friedman tests. Results In the groups treated with a combination of MB and IG and laser irradiation and also in the Chlorhexidine group, the final number of S. mutans colonies equaled zero. In “MB and IG groups without laser irradiation”, although the amount of microorganisms decreased, but the number of colonies did not reach zero. Pair comparisons by Dunn's test showed that there was a significant difference between “MB and IG groups without laser irradiation” and the other experimental groups p = 0.03). Conclusion PDT with MB and IG photosensitizers and also Chlorhexidine mouthwash, have the ability to completely eradicate S. mutans bacterial colonies.