In vitro antibacterial effect of 2% chlorhexidine against Enterococcus faecalis in dentin previously irrigated with 5% sodium hypochlorite. Int. J. Odontostomat., 9(1):25-29, 2015. ABSTRACT:The aim of this study was to observe whether the antibacterial effect of 2% chlorhexidine against Enterococcus faecalis in dentine is altered by previous irrigation with 5% sodium hypochlorite. Dentin discs were prepared with different irrigation protocols: group 1, immersed in 2% CHX for 25 min; group 2 immersed in 5% NaOCl for 25 minutes; group 3, immersed in 5% NaOCl, dried and irrigated with 3 ml of 2% CHX; group 4 and 5 immersed in 5% NaOCl, rinsed with 5 and 25 ml of distilled water respectively, dried and irrigated with 2% CHX. Group 6, immersed in 0.9% sodium chloride. Discs were then placed in agar plates in which E. faecalis was grown and the inhibition zone around each disc was measured after 24 hours of incubation at 37 ºC. All experimental groups showed E. faecalis growth inhibition. The most effective irrigant was 2% CHX (P<0.05). Groups in which both NaOCl and CHX were used displayed significantly smaller inhibition halos as compared with 2% CHX. Different volumes of water for rinsing did not cause significant improvement in growth inhibition. The antimicrobial effect of 2% chlorhexidine against E. faecalis was significantly reduced when dentin was previously irrigated with 5% sodium hypochlorite despite of rinsing with different volumes of water.