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

Aim To determine the relationships between the antibacterial activity of Na OC l and treatment time and biofilm age in early Enterococcus faecalis biofilms using a linear fitting procedure. Methodology Enterococcus faecalis biofilms were formed on hydroxyapatite discs. To investigate the relationship between the antibacterial activity of Na OC l and biofilm age, 22‐, 46‐, 70‐ and 94‐h‐old biofilms were exposed to Na OC l (0–3%) for 5 min. To investigate the relationship between the antibacterial activity of Na OC l and treatment time, 70‐h‐old biofilms were exposed to Na OC l (0–3%) for 1, 3, 5 and 7 min. After treatment, colony‐forming units ( CFU s) were counted. To determine the relationships between these variables, linear fitting was performed. Results The change in the minimum biofilm eradication concentration ( MBEC ) of Na OC l 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 Na OC l concentration ( R  ≤ −0.973, R 2  ≥ 0.948) in the 22‐, 46‐, 70‐ and 94‐h‐old biofilms implied that the antibacterial activity of Na OC l decreased as the biofilm age increased. The fitting lines for bacterial CFU count versus Na OC l concentration ( R  ≤ −0.970, R 2  ≥ 0.942) in the 1‐, 3‐, 5‐ and 7‐min treatments implied that the antibacterial activity of Na OC l increased with treatment time. Conclusions These results suggest that the antibacterial activity of Na OC l against early E. faecalis biofilms in root canals may follow a linear pattern depending on biofilm age or treatment time.