Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 8 2 2011 06 15 48 54 S. Vahabi Assistant Professor, Department of Periodontics, Dental School, Shahid Beheshti University of Medica R. Fekrazad Assistant Professor, Dental Department, AJA University of Medical Sciences- Laser Research Center of S. Ayremlou Research fellow, Department of Microbiology, Medical School, Shahid Beheshti University of Medical S S. Taheri Research Fellow, Dental School, Qazvin University of Medical Sciences, Tehran, Iran N. Zangeneh Research Fellow, Dental School, Qazvin University of Medical Sciences, Tehran, Iran 2015 10 03 Objectives: Dental caries and periodontal diseases are caused by infection of teeth and supporting tissues due to complex aggregate of bacteria known as biofilm, firstly colonized by streptococci. The main purpose of this in vitro study was to evaluate the antimicrobial effects of toluidine blue O (TBO) and Radachlorin® in combination with a diode laser on the viability of Streptococcus mutans. Materials and Methods: Bacterial suspensions of Streptococcus mutans were exposed to either 0.1% TBO associated with (20 mW, 633 nm diode laser, continuous mode, 150 s) or 0.1% Radachlorin® and laser irradiation (100 mW, 662 nm diode laser, continuous mode, 120 s). Those in control groups were subjected to laser irradiation alone or TBO/Radachlorin® alone or received neither TBO/Radachlorin® nor laser exposure. The suspensions were then spread over specific agar plates and incubated aerobically at 37°C. Finally, the bactericidal effects were evaluated based on colony formation. Results: Potential bacterial cell killing was only observed following photosensitization with TBO and 3 j/cm2 laser exposure (p<0.05), whereas Radachlorin® showed significant reduction in dark condition compared to laser exposure (p<0.05). Conclusion: TBO-mediated photodynamic therapy seems to be more efficient than Radachlorin ® in significantly reducing the viability of Streptococcus mutans in vitro. https://fid.tums.ac.ir/index.php/fid/article/view/242 https://fid.tums.ac.ir/index.php/fid/article/download/242/242