The effects of sodium hypochlorite and chlorhexidine irrigants on the antibacterial activities of alkaline media against Enterococcus faecalis

• E. faecalis survival decreased in CHX or 5.25% NaOCl and next alkaline challenge.
• E. faecalis biofilm survival rates were reduced in CHX and next alkaline challenge.
• E. faecalis biofilm survival increased in NaOCl and next alkaline challenge.
• CHX might be more effective in improving the alkaline than NaOCl.

ObjectiveSodium hypochlorite (NaOCl), chlorhexidine (CHX) and calcium hydroxide are common intracanal medicaments. The present study aimed to evaluate the effects of NaOCl and CHX on the antibacterial activities of alkaline media against Enterococcus faecalis.DesignsThe survival rates of planktonic and biofilm E. faecalis were evaluated by plate counts after 1 min of pretreatment with NaOCl and CHX, and time-kill assays were then used to assess subsequent pH alkaline challenges. Dead and living cells in the E. faecalis biofilm were assessed with SYTO 9 and PI staining in combination with confocal laser scanning microscopy following exposure to NaOCl or CHX and subsequent alkaline challenges by common root canal irrigation and dressing procedures.ResultsOne minute of pretreatment with 2% CHX, 0.2% CHX, or 5.25% NaOCl in combination with a subsequent alkaline challenge significantly decreased planktonic E. faecalis survival rates, but pretreatment with 1% NaOCl did not. The E. faecalis biofilm survival rates were reduced in the subsequent alkaline challenge following CHX pretreatment but gradually increased following NaOCl pretreatment. Similarly, CLSM analysis revealed that the greatest proportions of dead E. faecalis cells in the biofilms were presented in the CHX and alkaline treatment group.ConclusionCHX might be more effective in improving the antibacterial activities of alkaline root canal medicaments against E. faecalis than NaOCl during routine root canal therapy procedures.