Antimicrobial activity of low level laser in presence of photosensitizer

Objectives: The purpose of this study was to determine whether low power laser light in the presence of a photosensitizer can kill oral microorganisms in three different experiments. Methods: Suspensions of Streptococcus mutans, Streptococcus sobrinus, Streptococcus cricetus, Streptococcus sanguis, Lactobacillus casei, Lactobacillus acidophilus, and Candida albicans were exposed to a gallium-aluminium-arsenide laser light (660 nm) with a light energy dose of 28.8 J/cm² in presence of the photosensitizer toluidine blue O (0.1 mg/ml). In addition, samples of stimulated saliva collected from ten healthy subjects were mixed and exposed to photosensitizer and/or laser irradiation. Besides, nine adult volunteers wore an acrylic resin appliance containing two human dental enamel blocks, on which 20% sucrose solution was dripped 8 times/day. After 14 days, the bacterial plaque accumulated on the blocks was dispersed, its suspension was submitted to the same treatment and plated on specific agar medium. For all experiments, the viable microorganisms were incubated on ideal conditions and counted on agar plates. Results: A decrease in the number of viable microorganisms was only verified when they were exposed to both the laser light and the dye at the same time. A total inhibition of growth was found for S. mutans, S. sobrinus, S. cricetus, L. acidophilus, L. casei. Reduction in the viable count of microorganisms was observed for S. sanguis (2,0x10⁹ to 6,60x10⁴), C. albicans (1,9x10⁷ to 7,8x10⁶) and Streptococci from saliva (1,3x10⁹ to 4,4x10⁴). Conclusion: Bacteria can be killed by low-power laser light in the presence of the photosensitizer under mentioned conditions. Supported by FAPESP (00/04945-0) and FAEP (0991/00).