Evaluation of Endodontic Irrigants Using Biofilms of Enterococcus faecalis

Objectives: To determine the efficacy of endodontic irrigants against biofilms of Enterococcus faecalis and compare this with the results from similar experiments using an extracted tooth model.

Methods: Biofilms of E. faecalis were grown on nitrocellulose filter membranes resting atop nutrient agar. After 48 hours aerobic growth at 37ºC, the biofilm laden membranes were immersed in 25ml of sodium hypochlorite (NaOCl) solution (0.01% to 1%) or phosphate-buffered saline control for 60 seconds. Following exposure, the membrane was transferred to 25ml sterile phosphate-buffered saline to immediately dilute any residual NaOCl before being placed into 10ml of a neutralising solution. The biofilm was dispersed by vortex mixing in the neutralising solution and the number of viable bacteria present on the membrane was determined by serial dilution in PBS and plating onto nutrient agar.

Results: Control biofilms yielded 3.54x10⁷ cfu following immersion in PBS. Immersion in 0.01% and 0.1% NaOCl delivered a log reduction below 1, however; a 3.67 log reduction in the number of viable bacteria was observed at a concentration of 0.2%, with no viable bacteria detectable after immersion in 1% NaOCl.

Conclusions: 1% NaOCl, as used in endodontic irrigation at the Liverpool University Dental Hospital, is an effective biocide against biofilms of E. faecalis. It is therefore assumed that the recalcitrance of this organism within the root is a result of mass transfer / mixing limitations between the root canal and lateral canals.