Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 11 1 2014 02 15 30 7 Behnam Bolhari Assistant Professor, Dental Research Center Dentistry Research Institute, Department of Endodontics, Dental school, Tehran University of Medical Sciences, Tehran, Iran. Abbas Bahador Assistant Professor, Department of Medical Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Hadi Assadian Assistant Professor, Department of Endodontics, Dental school, sShahed University, Tehran, Iran. Somayyeh Dehghan Postgraduate Student, Department of Endodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. 2015 10 16 To eliminate microorganisms that are responsible for pulpal and periapical infections and to prevent reinfection of the root canal system an effective chemomechanical preparation by irrigants with sustained antimicrobial activity is beneficial. Hereby, we evaluated the residual antibacterial activity of MTAD after canal obturation at different time intervals.A total of 120 human single-canalled anterior teeth were selected. The root canals were instrumented to a standardized apical size. Among all, 90 teeth received final irrigation with MTAD and were divided into three groups according to their obturation materials; i.e. gutta-percha/AH26, Resilon/RealSeal SE and positive controls. All these groups were divided into three 1-, 3- and 6-week time interval subgroups. Thirty teeth as negative control had no final irrigation with MTAD, but were obturated with gutta-percha/AH26 or Resilon/RealSealSE. Dentin powder was prepared after 1, 3 and 6 weeks. Dentin powder was exposed to Enterococcus faecalis for 24h and then cultured. Colony Forming Unit (CFU) was counted.Residual antimicrobial activity of MTAD in the teeth obturated with guttapercha/AH26 was significantly higher than the teeth obturated with Resilon/RealSeal SE (p https://fid.tums.ac.ir/index.php/fid/article/view/564 https://fid.tums.ac.ir/index.php/fid/article/download/564/539