Effectiveness of Endodontic Disinfecting Solutions against Young and Old Enterococcus faecalis Biofilms in Dentin Canals

IntroductionEnterococcus faecalis is a species commonly isolated from persistent root canal infections. The purpose of this study was to compare the antibacterial effects of different disinfecting solutions on young and old E. faecalis biofilms in dentin canals using a novel dentin infection model and confocal laser scanning microscopy (CLSM).MethodsThe bacteria were introduced into the dentinal tubules by centrifugation. After 1 day and 3 weeks of incubation, 40 infected dentin specimens were subjected to 1 and 3 minutes of exposure to disinfecting solutions, which included 2% sodium hypochlorite (NaOCl) (EMD Chemicals Inc, Darmstadt, Germany), 6% NaOCl, 2% chlorhexidine (CHX) (Sigma Chemical Co, St Louis, MO), and QMiX (Dentsply Tulsa Dental, Tulsa, OK). The proportions of dead and live bacteria inside the dentinal tubules after exposure to these disinfectants were assessed by CLSM using a LIVE/DEAD bacterial viability stain.ResultsSignificantly fewer bacteria were killed in the 3-week-old dentin biofilm than in the 1-day-old biofilm. Three minutes of exposure resulted in more dead bacteria than 1 minute of exposure for both biofilms in all experimental groups (P < .05). Six percent NaOCl and QMiX were the most effective disinfecting solutions against the young biofilm, whereas against the 3-week-old biofilm, 6% NaOCl was the most effective followed by QMiX. Two percent NaOCl was equally effective as 2% CHX. All the disinfecting agents killed significantly more bacteria than the sterile water used as a negative control (P < .05).ConclusionsWithin dentin canals, bacteria in established biofilms are less easily killed by endodontic medicaments than bacteria in young biofilms.