Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 6 1 2014 02 15 26 30 EN Kazem Ashofteh Endodontic Department, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. Khosrow Sohrabi Laser Research Center of Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. Kaveh Iranparvar Laser Research Center of Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. Nasim Chiniforush Laser Research Center of Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. 2015 10 16 Introduction: Bacteria are the primary etiology of pulpal and periradicular pathosis. In endodontically treated teeth with persistent infections only one or a few bacterial species are present of which the most important is Enterococcus faecalis. The aim of this study was to compare antibacterial efficacy of canal disinfectants including 5.25% sodium hypochlorite, 2% chlorhexidine, MTAD (a mixture of doxycycline, citric acid and a detergent (Tween 80) and 830 nm diode laser. Methods and Materials: The canals of 135 extracted single rooted human teeth were prepared using rotary instruments. The canals were contaminated with Enterococcus faecalis for 4 weeks and then were divided into 4 groups of 30 teeth in each, a positive control group containing 10 teeth and a negative control group of 5 teeth. After using the disinfectants, samples obtained from canals by paper points and also shaving the canal walls were cultured. The Kruskal-Wallis test was used to analyze the results. Results: The results showed the bacterial reduction as follows: 99.97 ± 0.14 for sodium hypochlorite, 99.65 ± 1.13 for chlorhexidine, 97.56 ± 6.36 for laser and 96.91 ± 5.60 for MTAD. The count of CFU obtained from dentin shavings was:16/96 ± 91/23 for sodium hypochlorite, 82/73 ± 186/63 for chlorhexidine, 47/26 ± 112/21 for laser and 341/34 ± 1139/83 for MTAD. Conclusion: According to the results, sodium hypochlorite was the most effective agent against Enterococcus faecalis. https://ijm.tums.ac.ir/index.php/ijm/article/view/468 https://ijm.tums.ac.ir/index.php/ijm/article/download/468/244