Porphyromonas gingivalis is a major pathogen associated with initiation and progression of periodontitis.  Aim and Objective The aim of the study is to compare effect of lowlevel laser of wavelength 650nm on viability of porphyromonas gingivalis with and without photosensitisers.  Methods Thirty samples of bacterial suspensions (200µl) were prepared and divided into six groups .Group 1- laser group (low level laser with wavelength of 650nm, and irradiation time of 30 s), Group 2- Methylene blue + laser group (after pre-irradiation time of 10 min, laser was irradiated), and Group 3- Toluidine blue O + laser group (after pre irradiation time of 10 min, LED was irradiated), Group 4 -Methylene blue Group 5 - Toluidine blue O (TBO) and Group 6- Control group (no treatment), Then, 20 μL of each sample was cultured in blood agar plates and incubated for 72 hours in microaerophilic atmosphere for colony counting.  Result The concentration of P. gingivalis was significantly reduced after using the Methylene blue + laser and the Toluidine blue O + laser group. (P values < 0.005)  Conclusion Within the constraints of this investigation, it can be deduced that photodynamic inactivation applying a laser and photosensitizers like Methylene blue and toluidine blue was more efficient than photosensitizers and laser irradiation alone in eliminating P. gingivalis.

Keywords : Porphyromonas Gingivalis , Low Level Laser , Methylene Blue , Toluidine Blue O.