title: Antimicrobial efficacy of different concentration of sodium hypochlorite on the biofilm ofEnterococcus faecalisat different stages of development.
abstract: BACKGROUND
  Persistent infection of the root canal due to the presence of resistance bacterial species, such asEnterococcus faecalis, has always been one of the most important reasons for endodontic treatment failure. This study investigated the antimicrobial efficacy of 1%, 2.5 % and 5% sodium hypochlorite in eliminatingE. faecalisbiofilms at different stages of development.
  
  
  METHODS
  In this study 4-, 6- and 10-week-oldE. faecalisbiofilms were subjected to one of the following approaches: phosphate-buffered saline solution (PBS) or 1%, 2.5% and 5% NaOCl. Dentin chip suspensions were used for colony forming unit (CFU) counting to estimate remainingE. faecaliscounts. Statistical comparison of the means was carried out with Kruskal-Wallis test, and pair-wise comparisons were made by Mann-Whitney U test, at a significance level ofP<0.05.
  
  
  RESULTS
  The results showed that 2.5% and 5% NaOCl completely eliminatedE. faecalisbiofilms in three stages of biofilm development, whereas 1% NaOCl resulted in 85.73%, 81.88% and 78.62% decreases in bacterial counts in 4-, 6- and 10-week-old biofilms, respectively, which was significantly more than those with PBS (p<0.05).
  
  
  CONCLUSIONS
  The bacteria in mature and old biofilms were more resistant to 1% NaOCl than were the bacteria in young biofilms. Overall survival rate and residual bacteria increased with biofilm aging.Key words:Antibacterial, biofilm, E. faecalis, sodium hypochlorite.
authors.affiliation: Associate Professor, Dental Faculty, Tabriz University (Medical Sciences), Tabriz, Iran.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Frough-Reyhani
authors.affiliation: Assistant Professor, Department of Endodontics, Dental and Periodontal Research Center, Dental Faculty, Tabriz University (Medical Sciences), Tabriz, Iran.
authors.forename: Negin
authors.initials: N
authors.lastname: Ghasemi
authors.affiliation: Assistant Professor, Department of Microbiology, Medical Faculty, Tabriz University (Medical Sciences), Tabriz, Iran.
authors.forename: Mohammadhosien
authors.initials: M
authors.lastname: Soroush-Barhaghi
authors.affiliation: Endodontist at private practice, Tabriz, Iran.
authors.forename: Mahsa
authors.initials: M
authors.lastname: Amini
authors.affiliation: Private practice, Tabriz, Iran.
authors.forename: Yousefreza
authors.initials: Y
authors.lastname: Gholizadeh