Effect of photodynamic therapy on accumulation of Streptococcus mutans on the surface of orthodontic composite used in fixed retainers: An in vitro study

Abstract

OBJECTIVES: This study aimed to assess the effect of antimicrobial photodynamic therapy (PDT) on accumulation of Streptococcus mutans (S. mutans) on the surface of orthodontic composite used in fixed retainers. MATERIALS AND METHODS: In this in vitro study, 60 Ortho Connect Flow composite discs were evaluated in two groups (n = 30) of fresh and aged (by thermocycling and toothbrushing). Composite discs in each group were inoculated with S. mutans, and evaluated in 5 subgroups (n = 6) of control, diode laser alone (660 nm, 200 mW, 400 mW/cm(2), 24 J/cm(2), continuous-wave mode, for 60 s), methylene blue (MB = 100 microg/mL), PDT with diode laser (with the aforementioned parameters) and MB, and 0.2 chlorhexidine (CHX). After the treatments, S. mutans colonies were counted, and data were analyzed by three-way and two-way ANOVA (alpha = 0.05). RESULTS: The CHX group showed the lowest colony count. The effects of 660 nm diode laser, MB, and their interaction (PDT) on colony count were all significant (P < 0.05). The PDT group also showed a significantly lower colony count than other groups (P < 0.05). The difference in colony count between the fresh and aged discs was not significant (P > 0.05). CONCLUSION: The results of this in vitro study showed that PDT with 660 nm diode laser (with the aforementioned parameters) and MB significantly prevented the accumulation of S. mutans on the surface of orthodontic composite, and may be suitable as an adjunct for biofilm control.