摘要： Background: Sterilization of the root canal system is of prime importance for a successful root canal therapy. Lasers and photodynamic therapy (PDT) have become the latest choice to eradicate microorganisms in the root canal. Objective(s): To evaluate and compare the antimicrobial activity of diode laser, photodynamic therapy, and sodium hypochlorite along with their combinations on endodontic pathogens: Enterococcus faecalis and Streptococcus mutans. Methods: A total of 120 uniradicular teeth were stored in 5.2% NaOCl solution to remove organic residues and the crowns were sectioned at the cemento-enamel junction (CEJ) to obtain root canal length of 15 mm. Canals were shaped using step-back technique up to #40 K-file and were autoclaved. The selected teeth (specimen) were randomly divided into two equal groups with sixty root canals inoculated with E. faecalis (Group E) and remaining sixty teeth with S. mutans (Group S). Further, the groups were subdivided according to the disinfection technique used. Ten teeth from each subgroup were disinfected with a diode laser, photo activated disinfection (PAD), sodium hypochlorite, a combination of sodium hypochlorite and diode laser, a combination of sodium hypochlorite and PAD respectively. Ten teeth in each group served as control without any disinfection. The treated specimens were transferred to test tubes containing 5ml sterile Luria Bertani broth, incubated and the bacterial count, optical density in each root specimen was calculated and compared. The pairwise comparison of colonies across the subgroups was done by the Kruskal-Wallis test and within the subgroups was carried out using the Mann-Whitney U test. The statistical implication was tested at 5% and the study was performed using SPSS 18.0 ver. (SPSS Inc.). Results: A significant reduction (98%) in the E. faecalis count was observed when the NaOCl was used in combination with the diode laser or PAD. PAD along with 3% NaOCl presents the advantage of utilizing a lower wavelength laser beam. Hence, PAD in combination with NaOCl can be an alternative and better option for root canal disinfection for both the endodontic pathogens, E. faecalis and S. mutans.