title: Available chlorine consumption from NaOCl solutions passively placed in instrumented human root canals.
abstract: OBJECTIVE
  To monitor chlorine consumption from nonagitated aqueous sodium hypochlorite (NaOCl) solutions in human root canals using a recently developed assay, which can determine the order of magnitude of available chlorine in small volumes of liquid.
  
  
  METHODS
  The root canals of 80 extracted single-rooted human teeth were instrumented to ProTaper Universal F4 and irrigated using 1% NaOCl. Subsequently, canals were irrigated with copious amounts of deionized water to rinse out the residual chlorine. Subsequently, the teeth were sealed externally and placed in a water bath of 37 °C. Root canals were filled with NaOCl of 1%, 2.75%, 5.5%, or distilled water for 1, 10, 100 or 1000 min (n = 5 teeth per solution and time). Consumption of chlorine was measured using paper points pre-impregnated with 15% potassium iodide. Colour change of the paper points was determined photo-electronically, assessing their red value after absorbing solutions from root canals. Measurements were compared to a standard series of NaOCl down to 0.001% (n = 5 paper points per concentration).
  
  
  RESULTS
  Red values of the paper points inserted into the root canal were affected by initial NaOCl concentration and time (two-way anova, P < 0.05). If NaOCl concentrations above 0.1% are considered to be clinically relevant, then 5.5% NaOCl retained its activity in the root canal for more than 100 min, whereas 1% NaOCl lost its activity between 10 and 100 min.
  
  
  CONCLUSIONS
  Nonagitated NaOCl solutions can remain biologically active in human root canals for extended time periods.
authors.affiliation: Clinic of Preventive Dentistry, Periodontology and Cariology, Center of Dental Medicine, University of Zürich, Zürich, Switzerland.
authors.forename: K T
authors.initials: KT
authors.lastname: Ragnarsson
authors.forename: D K
authors.initials: DK
authors.lastname: Rechenberg
authors.forename: T
authors.initials: T
authors.lastname: Attin
authors.forename: M
authors.initials: M
authors.lastname: Zehnder
mesh_terms: D002713:Chlorine / Q000032:analysis*; D003786:Dental Pulp Cavity / Q000737:chemistry*; D006801:Humans; D066298:In Vitro Techniques; D012388:Root Canal Irrigants / Q000008:administration & dosage / Q000032:analysis*; D012973:Sodium Hypochlorite / Q000008:administration & dosage / Q000032:analysis*
chemical_list: D012388:Root Canal Irrigants; D002713:Chlorine; D012973:Sodium Hypochlorite
keywords: NaOCl; hypochlorite; paper point; root canal