Effectiveness of chlorhexidine and sodium hypochlorite to reduce Enterococcus faecalis biofilm biomass

Bacteria present in biofilm show an increased resistance to antimicrobial activity of endodontic irrigants, and the persistence of these microorganisms after chemomechanical preparation may lead to endodontic treatment failure. Thus, the aim of this study was to evaluate the effectiveness of sodium hypochlorite (NaOCl) and chlorhexidine (CHX) to reduce Enterococcus faecalis biofilm biomass. Biofilms built by E. faecalis ATCC 29212 in polystyrene 96-microtiter plate wells were exposed to different concentrations of NaOCl (1, 2.5 and 6%) and CHX (0.12, 0.2 and 2%) for three different time periods (1, 3 and 10 min). The reduction of the biofilm biomass was evaluated by measuring the optical density with a microplate absorbance reader. All the NaOCl solutions were significantly more effective than any of the CHX solutions tested, regardless of the time of exposure (P 0.05); by contrast, after 10 min of exposure to the NaOCl the biofilm was not significantly different from the positive control without biofilm (P > 0.05). Moreover, considering the period of times used in this study (1 to 10 min), no significant differences were observed among different concentrations for each desinfectant. In conclusion, none of the tested concentrations of CHX showed an ability to decrease the biofilm biomass. On the other hand, even the most diluted NaOCl solution (1%) reduced the biofilm biomass to a level that was compatible with the complete disruption of the biomass structure.