title: Minimum contact time and concentration of sodium hypochlorite required to eliminate Enterococcus faecalis.
abstract: BACKGROUND
  The purpose of this investigation was to determine the concentration of sodium hypochlorite and the irrigation time required to disinfect dentin cylinders infected with Enterococcus faecalis.
  
  
  METHODS
  Four hundred fifty dentin cylinders (5 mm in diameter and 4 mm in height) with a lumen (2-3 mm in width) were prepared from freshly extracted bovine incisors. The cementum and predentin were then removed. The tubules were opened by using a 4-minute application with 17% ethylenediaminetetraacetic acid and 5.25% NaOCl and then exposed to E. faecalis (ATCC 4082) for 3 weeks in brain-heart infusion broth. The cylinders were then divided into 3 groups, and a 1.3%, 2.5%, or 5.25% concentration of NaOCl was applied in 5-, 10-, 15-, 20-, 25-, 30-, 35-, and 40-minute intervals for a total of 30 subgroups including positive and negative controls. Each test sample was placed into a tube of 2 mL brain-heart infusion broth and incubated for 72 hours. Absence of turbidity demonstrated no bacterial growth, whereas turbidity indicated presence of remaining viable bacteria.
  
  
  RESULTS
  The most effective irrigation regimen was 5.25% at 40 minutes, whereas irrigation with 1.3% and 2.5% NaOCl for this same time interval was ineffective in removing E. faecalis from infected dentin cylinders.
  
  
  CONCLUSIONS
  High concentration and long exposure to NaOCl are needed for elimination of E. faecalis contaminated dentin.
authors.affiliation: Department of Endodontics, School of Dentistry, Loma Linda University, Loma Linda, California 92350, USA.
authors.forename: Bonnie
authors.initials: B
authors.lastname: Retamozo
authors.forename: Shahrokh
authors.initials: S
authors.lastname: Shabahang
authors.forename: Neal
authors.initials: N
authors.lastname: Johnson
authors.forename: Raydolfo M
authors.initials: RM
authors.lastname: Aprecio
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Torabinejad
mesh_terms: D000818:Animals; D002417:Cattle; D019551:Dental Disinfectants / Q000008:administration & dosage*; D003804:Dentin / Q000187:drug effects / Q000382:microbiology*; D004203:Disinfection / Q000379:methods*; D004305:Dose-Response Relationship, Drug; D013293:Enterococcus faecalis / Q000187:drug effects / Q000302:isolation & purification; D012388:Root Canal Irrigants / Q000737:chemistry / Q000627:therapeutic use*; D012973:Sodium Hypochlorite / Q000008:administration & dosage* / Q000737:chemistry; D007507:Therapeutic Irrigation / Q000379:methods; D013997:Time Factors
chemical_list: D019551:Dental Disinfectants; D012388:Root Canal Irrigants; D012973:Sodium Hypochlorite