title: Relationship between flexibility and physical, chemical, and geometric characteristics of rotary nickel-titanium instruments.
abstract: OBJECTIVE
  The purpose of this study was to assess the influence of both the metallurgic and the geometric characteristics of nickel-titanium endodontic instruments on their flexibility.
  
  
  METHODS
  ProTaper Universal (PTU), K3, and EndoSequence (ES) instruments were evaluated. Their chemical composition and phase constitution were characterized by conventional analytical techniques. Instrument diameter and cross-sectional area were evaluated by image analysis. Flexibility was evaluated in bending tests according to the ISO 3630-1.
  
  
  RESULTS
  K3 presented the highest average bending moment (M(B)), followed by PTU and ES. A linear relationship was found between M(B) and the instrument's diameter and cross-sectional area at 3 mm from the tip. Alloy chemical compositions were similar among the files, but transformation temperatures were lower for K3 instruments, which presented only austenite as a constituent phase.
  
  
  CONCLUSIONS
  Nickel-titanium instruments from different manufacturers have unequal behavior related to their flexibility properties. Manufacturing processes changed the phase constitution and transformation temperatures of the instruments investigated and may also have influenced their flexibility.
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Ana Cecília Diniz
authors.initials: AC
authors.lastname: Viana
authors.forename: Marta
authors.initials: M
authors.lastname: Chaves Craveiro de Melo
authors.forename: Maria
authors.initials: M
authors.lastname: Guiomar de Azevedo Bahia
authors.forename: Vicente Tadeu
authors.initials: VT
authors.lastname: Lopes Buono
mesh_terms: D002152:Calorimetry, Differential Scanning; D003722:Dental Alloys / Q000737:chemistry; D003762:Dental Instruments; D003799:Dental Stress Analysis; D004867:Equipment Design; D007091:Image Processing, Computer-Assisted; D009532:Nickel / Q000737:chemistry; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D013052:Spectrometry, X-Ray Emission; D014025:Titanium / Q000737:chemistry; D044366:Transition Temperature; D014961:X-Ray Diffraction
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium