title: Apical extent of rotary canal instrumentation with an apex-locating handpiece in vitro.
abstract: OBJECTIVE
  The Tri Auto ZX (J. Morita Co., Kyoto, Japan) is a cordless endodontic handpiece with a built-in apex locator that is programmed to reverse the direction of rotation when the file reaches a predetermined apical level or when torque becomes excessive.
  
  
  OBJECTIVE
  The purpose of this investigation was to examine the apical extent of rotary canal instrumentation and the ability to maintain apical constriction with the Tri Auto ZX at different automated settings.
  
  
  METHODS
  In 60 extracted teeth, canals were measured to the apical constriction, first visually and then electronically with the Tri Auto ZX; then they were instrumented with nickel titanium rotary files. For the instrumentation, the automatic apical reverse mechanism of the handpiece was set to 1, 1.5, or 2; these settings correspond to different distances from the apical foramen. Instrumentation was carried out apically until rotation was reversed by the automatic apical reverse function; the instrumented length was then measured, and the canal was filled with gutta-percha and sealer. The integrity of the apical constriction was assessed by exposing the apical 4 mm of the canal and observing the dentin-cementum junction. Paired t-tests were used to compare the visually measured length, the electronically measured length, and the instrumented length for each tooth.
  
  
  RESULTS
  On average, the electronically measured length was 0.54 mm shorter than the visually measured length (p < 0.05). When the automatic apical reverse mechanism's setting was 1, the instrumented length was 0.1 mm shorter than the electronically measured length; when the setting was 1.5, the instrumented length was 0.36 mm shorter than the electronically measured length (p < 0.01). Results were inconsistent when the setting was 2.
  
  
  CONCLUSIONS
  Instrumentation with the automatic apical reverse feature set at 1 consistently approximated the apical constriction; however, the constriction was frequently enlarged.
authors.affiliation: Department of Endodontics, Faculty of Dentistry, University of Toronto, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Campbell
authors.forename: S
authors.initials: S
authors.lastname: Friedman
authors.forename: H Q
authors.initials: HQ
authors.lastname: Nguyen
authors.forename: A
authors.initials: A
authors.lastname: Kaufman
authors.forename: S
authors.initials: S
authors.lastname: Keila
mesh_terms: D003722:Dental Alloys; D003739:Dental Cementum / Q000033:anatomy & histology; D003786:Dental Pulp Cavity / Q000033:anatomy & histology*; D003804:Dentin / Q000033:anatomy & histology; D004582:Electronics, Medical / Q000295:instrumentation; D004867:Equipment Design; D006171:Gutta-Percha; D006801:Humans; D009532:Nickel; D011670:Pulpectomy / Q000295:instrumentation*; D012387:Root Canal Filling Materials; D012399:Rotation; D013499:Surface Properties; D014025:Titanium; D019227:Tooth Apex / Q000033:anatomy & histology*; D019415:Torque
chemical_list: D003722:Dental Alloys; D012387:Root Canal Filling Materials; C040654:titanium nickelide; D009532:Nickel; D006171:Gutta-Percha; D014025:Titanium