The purpose of this study was to compare the antibacterial effectiveness of 2.5 % Sodium hypochlorite and 2 % Chlorhexidine on Enterococcus faecalis (ATCC 29212). Sixty-five extracted human single-rooted teeth were used. These teeth were divided into 4 experimental groups (n=15), a positive control group (n=4) and a negative control group (n=1). The crown of each tooth was sectioned to obtain the root of 12 mm long and sterilized. The 64 sectioned roots (the experimental and the positive control group) were infected with Enterococcus faecalis incubating in Todd-Hewitt broth for 2 weeks. Canals were instrumented using
stepback technique until master apical file was size 40. Group 1, canals were irrigated with 2.5 % NaOCl 20 ml with smear layer removed using 17 % EDTA 10 ml and 5.25 % NaOCl 10 ml. Group 2, canals were irrigated using 2.5 % NaOCl 20 ml and 0.9 % normal saline 20 ml. Group 3, canals were irrigated with 2 % Chlorhexidine 20 ml and 0.9 % normal saline 20 ml. Group 4, canals were irrigated with 2.5 % NaOCl 10 ml and 2 % Chlorhexidine 10 ml and 0.9 % normal saline 20 ml. In the positive control group, canals were irrigated with 0.9 % normal saline 40 ml. In the negative control group, canal was not infected, no instrumentation and no irrigation. The dentin chips from a sterilized round bur size ISO 012 were cultured for 24 hr to determine the presence of the colonies of Enterococcus faecalis. The colony was confirmed using the biochemistry method. The results of Chi-square test indicated no statistically significant differences (p >.05) between the experimental groups. However, the irrigating solutions from all experimental groups can eradicate microorganisms better than a positive control group (p <.05). Smear layer has no statistical
significant difference (p >.05) in eradicating microorganisms whether it was removed or intact.