title: A comparison of instrument-centering ability within the root canal for three contemporary instrumentation techniques.
abstract: OBJECTIVE
  To study and compare Great Taper (GT) hand files using a reversed balanced force technique, nickel-titanium (NiTi)flex files with a balanced force technique and stainless steel (SS) K-type files using a step-back technique.
  
  
  METHODS
  Forty-eight extracted mandibular premolar teeth with single root canals having curvatures between 15 and 45 degrees were prepared using a modified Bramante model and randomly divided into three groups. The teeth were cross-sectioned at 2, 6 and 10 mm from the working length. Preoperative images of canals at three levels were captured at 20x magnification using a stereomicroscope. Canals in each group were, respectively, prepared to an apical size.10 GT file with 0.2 mm tip diameter, size 30 NiTiflex file and size 30 SS K-file. The GT file was used in a reversed balanced force technique, the NiTiflex file was used in a balanced force technique, and the SS K-file was used in a step-back technique. Postoperative canals were imaged under the conditions same as those for the preoperative canals. The postoperative images were superimposed over the preoperative images using software photoshop 6.0. The ability to maintain the instrument in the central axis of the canal and the deviation from the central canal axis were determined and compared by statistical analysis, along with the assessment of the amount of dentine removed.
  
  
  RESULTS
  At apical level, the centering ratio, the distance of transportation and the dentine removed in GT and NiTiflex groups were significantly less than those in SS group (P < 0.01), but no statistical differences were found between the two NiTi groups. At other levels, there were no substantial differences amongst the groups.
  
  
  CONCLUSIONS
  Compared with SS K-files, GT hand files and NiTiflex files remain better centered and produce significantly less transportation in curved canals.
authors.affiliation: Department of Endodontics, School and Hospital of Stomatology, Wuhan University, Ministry of Education, Wuhan, China.
authors.forename: Y L
authors.initials: YL
authors.lastname: Song
authors.forename: Z
authors.initials: Z
authors.lastname: Bian
authors.forename: B
authors.initials: B
authors.lastname: Fan
authors.forename: M W
authors.initials: MW
authors.lastname: Fan
authors.forename: J L
authors.initials: JL
authors.lastname: Gutmann
authors.forename: B
authors.initials: B
authors.lastname: Peng
mesh_terms: D001641:Bicuspid; D003722:Dental Alloys; D003762:Dental Instruments; D003786:Dental Pulp Cavity / Q000033:anatomy & histology; D003799:Dental Stress Analysis; D006801:Humans; D007091:Image Processing, Computer-Assisted; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013193:Stainless Steel; D014025:Titanium
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D013193:Stainless Steel; D009532:Nickel; D014025:Titanium