title: Bending properties of rotary nickel-titanium instruments.
abstract: OBJECTIVE
  We sought to compare the bending properties of different rotary nickel-titanium instruments and to investigate the correlation between their bending moments and their cross-sectional surface areas.
  
  
  METHODS
  Resistance to bending was determined according to International Standards Organization publication 3630-1. The sample size was 10 files for each type, taper, and size. The cross-sectional surface area of all instruments was determined by using scanning electron microscope photographs of the cross section. The images were scanned and the area was calculated by using special software. Data were analyzed by using analysis of variance and the Student t test and the Newman-Keuls test for all pairwise comparisons. The strength of the correlation between the bending moment and the cross-sectional area was determined by computing the Pearson product moment correlation.
  
  
  RESULTS
  Bending moments were significantly lower for ProFile and RaCe files than for all other files (P <.05). K3 files were significantly less flexible than all other instruments (P <.05). The correlation between stiffness and cross-sectional area was highly significant (r = 0.928; P <.0001).
  
  
  CONCLUSIONS
  Nickel-titanium files with tapers greater than.04 should not be used for apical enlargement of curved canals because these files are considerably stiffer than are those with.02 or.04 tapers.
authors.affiliation: Poliklinik für Zahnerhaltung, Westfälische Wilhelms-Universität, Münster, Germany. eschaef@uni-muenster.de
authors.forename: Edgar
authors.initials: E
authors.lastname: Schäfer
authors.forename: Anita
authors.initials: A
authors.lastname: Dzepina
authors.forename: Gholamreza
authors.initials: G
authors.lastname: Danesh
mesh_terms: D000704:Analysis of Variance; D003722:Dental Alloys / Q000737:chemistry; D004548:Elasticity; D004867:Equipment Design; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016555:Matched-Pair Analysis; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium