Efficacy of sodium hypochlorite combined with chlorhexidine against Enterococcus faecalis in vitro Morgana E. Vianna, DDS, MS, PhD, a,b and Brenda P. F. A. Gomes, DDS, MS, PhD, a Piracicaba, Brazil; and London, United Kingdom UNIVERSITY OF CAMPINAS AND UNIVERSITY COLLEGE LONDON The aim of this study was to investigate in vitro the efficacy of the combination of sodium hypochlorite (NaOCl) and chlorhexidine (CHX) in different concentrations against Enterococcus faecalis compard with the antimicrobial activity of the same irrigating substances when applied alone. The substances tested were 2.0% CHX gel, 2.0% CHX liquid, 1% NaOCl, 2.5% NaOCl, 5.25% NaOCl, and combinations of them in the same proportions. Two methods were used: the agar diffusion test and the broth dilution test. The largest mean microbial growth zone was obtained by 2.0% CHX gel, and the smallest zones were obtained by 1% and 2.5% NaOCl (P  .05). 2.0% CHX (gel and liquid formulation), 5.25% NaOCl, and the combination of 2.0% CHX liquid and 5.25% NaOCl, all of which needed 1 min to eliminate E. faecalis. The association of NaOCl and CHX did not improve the antimicrobial activity of CHX alone. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;107:585-589) The bacterial microflora in the root canal system ini- tiates and maintains periapical inflammatory lesions. 1 Thereby, the root canal treatment aims to eliminate bacteria from the infected root canal and prevent rein- fection. Although cleaning, shaping, and irrigating the canal greatly reduce the number of bacteria, it is im- possible to obtain complete disinfection in all cases. 2,4 Several substances have been used as endodontic irrigants to enhance the microbial reduction; the most common irrigant solution is sodium hypochlorite (NaOCl), which has been used for decades. 3 Another option of antimicrobial substance to be used during root canal preparation is chlorhexidine (CHX). 2 The com- bination of NaOCl and CHX has been advocated to enhance their antimicrobial properties. Kuruvilla and Kamath 5 suggested the antimicrobial effect of 2.5% NaOCl and 0.2% CHX used in combination was better than that of either component alone. Zehnder 6 reviewed the literature and proposed an irrigation regimen in which NaOCl would be used throughout instrumenta- tion, followed by EDTA, and CHX would be used as a final irrigant. However, if NaOCl is still present in the canal, a precipitate was observed 6 ; this precipitate would be a result of possible chemical interactions between the irrigants 7 and possibly interferes in the antimicrobial property. The aim of the present study was to investigate in vitro the efficacy of the combination of NaOCl and CHX in different concentrations against Enterococcus faecalis compared with the antimicrobial activity of the same irrigating substances when applied alone. MATERIALS AND METHODS The methodology used in this study was the same used in one of our previous works. 8 The substances tested were: 1% NaOCl, 2.5% NaOCl, 5.25% NaOCl, 2.0% CHX liquid, 2.0% CHX gel, 2.0% CHX gel + 1% NaOCl, 2.0% CHX gel + 2.5% NaOCl, 2.0% CHX gel + 5.25% NaOCl, 2.0% CHX liquid + 1% NaOCl, 2.0% CHX liquid + 2.5% NaOCl, and 2.0% CHX liquid + 5.25% NaOCl. The 2.0% CHX gluconate (gel and liquid) and 0.5%, 1%, 2.5%, 4%, and 5.25% NaOCl were prepared by the same manufacturer (Proderma Farmácia de Manipu- lação, Piracicaba, SP, Brazil). The manufacturer diluted NaOCl and CHX liquid at different concentrations in sterile water without preservatives. The solutions were prepared 24 h before the beginning of the experiment, always in small portions. The CHX gel consisted of gel base (1% natrosol) and CHX gluconate. Sterile saline (0.89%) and natrosol (1%) were used as controls. The solution combinations were made at the time of the test in a 1:1 proportion. Supported by the Brazilian agencies CAPES (PRODOC 0118/05-2), FAPESP (05/55695-7; 07/58518-4), and CNPq (305437/2006-2; 470820/2006-3). a Endodontic Division, Department of Restorative Dentistry, Piraci- caba Dental School, University of Campinas. b Unit of Endodontology, UCL-Eastman Dental Institute, University College London. Received for publication Aug 12, 2008; returned for revision Oct 29, 2008; accepted for publication Oct 31, 2008. 1079-2104/$ - see front matter © 2009 Published by Mosby, Inc. doi:10.1016/j.tripleo.2008.10.023 585