In vitro assessment of the immediate and prolonged antimicrobial action of chlorhexidine gel as an endodontic irrigant against Enterococcus faecalis

Objective. The aim of this study was to assess in vitro the antimicrobial activity of 2% chlorhexidine gel against Enterococcus faecalis, comparing it to other endodontic irrigants (2% chlorhexidine liquid and 5.25% sodium hypochlorite). Study design. Eighty roots of human mandibular premolars were prepared by serial instrumentation technique, autoclaved, and contaminated for 7 days with E faecalis monocultures. The roots were then divided into 5 groups according to the irrigant substance used during the standardized biomechanical preparation. In order to evaluate the antimicrobial action of the irrigant substances, 3 microbial samples were taken: initial (before the biomechanical preparation); post-treatment (immediately after the biomechanical preparation), and final (7 days after the biomechanical preparation). The microbiological samples were plated to count the colony-forming units (CFU). Results. The 2% chlorhexidine gel and 2% chlorhexidine liquid significantly reduced the E faecalis CFU in the post-treatment and final microbiological samples. The 5.25% sodium hypochlorite also reduced the E faecalis CFU immediately after the root canal instrumentation, but it was not able to keep the root canal free of detectable E faecalis in the final sample. Conclusions. The 2% chlorhexidine gluconate (gel and liquid) antimicrobial ability was more effective than 5.25% sodium hypochlorite in keeping low CFU of E faecalis for 7 days after the biomechanical preparation.