Relationships between the antibacterial activity of sodium hypochlorite and treatment time and biofilm age in early Enterococcus faecalis biofilms

AimTo determine the relationships between the antibacterial activity of NaOCl and treatment time and biofilm age in early Enterococcus faecalis biofilms using a linear fitting procedure. MethodologyEnterococcus faecalis biofilms were formed on hydroxyapatite discs. To investigate the relationship between the antibacterial activity of NaOCl and biofilm age, 22-, 46-, 70- and 94-h-old biofilms were exposed to NaOCl (0-3%) for 5min. To investigate the relationship between the antibacterial activity of NaOCl and treatment time, 70-h-old biofilms were exposed to NaOCl (0-3%) for 1, 3, 5 and 7min. After treatment, colony-forming units (CFUs) were counted. To determine the relationships between these variables, linear fitting was performed. ResultsThe change in the minimum biofilm eradication concentration (MBEC) of NaOCl followed a linear pattern of biofilm age (R=0.941, R-2=0.886) or treatment time dependence (R=-0.948, R-2=0.898). Below the MBEC, the fitting lines for bacterial CFU count versus NaOCl concentration (R-0.973, R(2)0.948) in the 22-, 46-, 70- and 94-h-old biofilms implied that the antibacterial activity of NaOCl decreased as the biofilm age increased. The fitting lines for bacterial CFU count versus NaOCl concentration (R-0.970, R(2)0.942) in the 1-, 3-, 5- and 7-min treatments implied that the antibacterial activity of NaOCl increased with treatment time. ConclusionsThese results suggest that the antibacterial activity of NaOCl against early E.faecalis biofilms in root canals may follow a linear pattern depending on biofilm age or treatment time.