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

Abstract Introduction Enterococcus 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). Methods The 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. Results Significantly 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