title: Uncontrolled Removal of Dentin during In Vitro Ultrasonic Irrigant Activation in Curved Root Canals.
abstract: BACKGROUND
  The aim of this study was to examine the effect of file type and activation time on the uncontrolled removal of dentin during in vitro ultrasonic irrigant activation in prepared curved root canals.
  
  
  METHODS
  Seventy-two curved mesial root canals of human mandibular molars were prepared to size 35/.04 taper. The specimens were randomly allocated to 4 groups (n = 18). Two milliliters of 2% sodium hypochlorite were delivered 3 times to each root canal, and the irrigant was ultrasonically activated every time for 10 seconds at 35% power either by a ultrasonic K-file (group A), an Irrisafe file (Acteon Satelec, Merignac, France) (group B), or a smooth wire (group C). The same specimens also received further activation continuously for another 30 seconds. No activation took place in group D. Specimens were scanned by micro-computed tomographic imaging before and after preparation and after the first and second activation period. Scans were coregistered and segmented, and the amount of dentin removed during activation was quantified by morphological operations. Results were analyzed by nonparametric statistical tests (α = 0.05).
  
  
  RESULTS
  Defects with a maximum depth of 0.18 mm were identified. Both the type of file and activation time affected the removal of dentin (P ≤ .002 and P ≤ .031, respectively). K-files removed more dentin than Irrisafe files and smooth wires in the coronal and middle third. All files removed comparable amounts in the apical third.
  
  
  CONCLUSIONS
  All 3 types of files may result in uncontrolled removal of dentin. A longer activation time may increase this effect.
authors.affiliation: Department of Endodontology, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands.
authors.forename: Anastasios
authors.initials: A
authors.lastname: Retsas
authors.affiliation: Department of Endodontology, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands.
authors.forename: Anastasios
authors.initials: A
authors.lastname: Koursoumis
authors.affiliation: Department of Endodontology, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands.
authors.forename: Nestor
authors.initials: N
authors.lastname: Tzimpoulas
authors.affiliation: Department of Endodontology, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands. Electronic address: c.boutsioukis@acta.nl.
authors.forename: Christos
authors.initials: C
authors.lastname: Boutsioukis
mesh_terms: D003762:Dental Instruments; D003786:Dental Pulp Cavity; D003804:Dentin / Q000033:anatomy & histology* / Q000473:pathology; D006801:Humans; D008963:Molar / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D012388:Root Canal Irrigants / Q000008:administration & dosage / Q000009:adverse effects*; D018915:Root Canal Preparation / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D012973:Sodium Hypochlorite / Q000494:pharmacology; D007507:Therapeutic Irrigation / Q000379:methods; D014464:Ultrasonic Therapy / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods
chemical_list: D012388:Root Canal Irrigants; D012973:Sodium Hypochlorite
keywords: Dentin; Irrisafe; K-file; micro–computed tomography; smooth wire; ultrasonic activation