Inactivation of Streptococcus mutans Using Photo-activated Disinfection Therapy with Methylene Blue and Indocyanine Green Photosensitizers

Abstract

Background: Streptococcus mutans is one of the species in the biofilm adjacent to cariogenic lesions. Photo-activated disinfection (PAD) is a new method which reduces cariogenic bacterial without common side effects. The success of PAD depends on the sensitivity of the organism, type of dyes, a dose of dyes, and the depth of emitted laser. In this study, effect of PAD on S. mutans reduction using indocyanine green (ICG) compared with methylene blue was evaluated. Materials and Methods: The standard turbidity (0.5 McFarland) of S. mutans suspension was prepared. Bacterial suspensions were transferred to the wells. Then, samples were subsequently divided into 7 groups. 1: Negative control, 2: Only methylene blue without laser, 3: Only 640 nm laser, 4: PAD by methylene blue, 5: Indocyanine without laser, 6: Only 810 nm laser, and 7: PAD by ICG. Subsequently, the bacterial suspension from each well was cultured, colony counts were determined, and data were analyzed using one-way ANOVA and Tukey's tests (P < 0.05). Results: There was a significant decrease of S. mutans colony counts after PAD using by both methylene blue and ICG photosensitizers. The highest decreased amount belonged to the ICG (PAD group). Methylene blue group (without laser application) also had a significant decrease of S. mutans colony counts (less effective than both PAD groups). Other groups (laser applications alone and ICG dye without laser) showed no significant bacterial reduction. Conclusion: With the parameters of this study PAD by ICG seems to be more effective than PAD by methylene blue, in reducing S. mutans bacteria as etiological factors of dental caries.