title: Influence of the oscillation direction of an ultrasonic file on the cleaning efficacy of passive ultrasonic irrigation.
abstract: BACKGROUND
  The cleaning mechanisms and characteristics of passive ultrasonic irrigation (PUI) are not yet completely understood. The aim of this study was to investigate whether the oscillatory direction of the ultrasonically driven file had an influence on dentin debris removal from artificially made grooves in standardized root canals.
  
  
  METHODS
  Each of 20 ex vivo root canal models with a standard groove in the apical portion of one canal wall filled with dentin debris received PUI repeatedly, either with file oscillation toward the groove or with file oscillation perpendicular to the groove. After each irrigation procedure, the amount of dentin debris in the groove was evaluated by photographs of the groove and by scoring. The oscillations of the ultrasonic file were also visualized in vitro by using high-speed imaging at a time scale relevant to the cleaning process, order 10 microseconds.
  
  
  RESULTS
  A nonparametric analysis showed significantly more dentin debris reduction when the file oscillated toward the groove (P = .002). High-speed imaging showed that the oscillation of the file is in a single plane, resulting in high-velocity jets emanating from the file tip in the direction of the oscillations.
  
  
  CONCLUSIONS
  Oscillation of the ultrasonically driven file toward the groove is more effective in removing dentin debris from the groove than oscillation perpendicular to the groove, which can be related to the fact that there is a high-velocity jet from the file tip in a single direction following the file oscillation and a relatively slow inflow in the perpendicular direction.
authors.affiliation: Department of Endodontology, Academic Centre of Dentistry Amsterdam (ACTA), University of Amsterdam and VU University, 1066EA Amsterdam, The Netherlands. l.jiang@acta.nl
authors.forename: Lei-Meng
authors.initials: LM
authors.lastname: Jiang
authors.forename: Bram
authors.initials: B
authors.lastname: Verhaagen
authors.forename: Michel
authors.initials: M
authors.lastname: Versluis
authors.forename: Lucas W M
authors.initials: LW
authors.lastname: van der Sluis
mesh_terms: D003786:Dental Pulp Cavity / Q000648:ultrastructure; D003804:Dentin / Q000648:ultrastructure; D006801:Humans; D008422:Materials Testing; D010781:Photography; D012212:Rheology; D012388:Root Canal Irrigants / Q000008:administration & dosage; D018915:Root Canal Preparation / Q000295:instrumentation* / Q000379:methods; D012973:Sodium Hypochlorite / Q000008:administration & dosage; D013010:Sonication / Q000295:instrumentation / Q000379:methods; D013594:Syringes; D007507:Therapeutic Irrigation / Q000295:instrumentation / Q000379:methods; D013997:Time Factors; D014465:Ultrasonics
chemical_list: D012388:Root Canal Irrigants; D012973:Sodium Hypochlorite