title: Influence of Cyclic Flexural Deformation on the Torsional Resistance of Controlled Memory and Conventional Nickel-titanium Instruments.
abstract: BACKGROUND
  The aim of this study was to evaluate the influence of cyclic deformation on the torsional resistance of controlled memory (CM) nickel-titanium files in comparison with superelastic (SE) instruments with similar geometric and dimensional characteristics.
  
  
  METHODS
  New 30/.06 HyFlex (HF; Coltene/Whaledent, Inc, Cuyahoga Falls, OH), Typhoon (Clinician's Choice Dental Products, New Milford, CT), RaCe (FKG, La-Chaux De Fonds, Switzerland), and ProTaper Universal F2 instruments (F2; Dentsply Maillefer, Ballaigues, Switzerland) were assessed. The diameter and pitch length were measured along the active part of the instruments. The number of cycles to failure (Nf) in flexural fatigue and the torsional resistance were evaluated for new files (n = 10). Ten new instruments of each type were fatigued to 3/4 of their fatigue life and then submitted to torsion until rupture. Data were analyzed using 1-way analysis of variance (α = .05).
  
  
  RESULTS
  New CM files had a significantly higher Nf when compared with SE instruments; HF exhibited the highest value (P = .001). The mean torque value for F2 was the highest (P = .001). CM files precycled to 3/4 Nf had a significantly lower torque than the new files (HF: P = .003, Typhoon: P = .001), whereas the SE instruments displayed no significant differences (F2: P = .059, RaCe: P = .079).
  
  
  CONCLUSIONS
  Cyclic flexural loading significantly reduced the torsional resistance of CM instruments.
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Eufemia Carolina Peláez
authors.initials: EC
authors.lastname: Acosta
authors.affiliation: Department of Metallurgical and Materials Engineering, School of Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Pedro Damas
authors.initials: PD
authors.lastname: Resende
authors.affiliation: Department of Metallurgical and Materials Engineering, School of Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Isabella Faria da Cunha
authors.initials: IF
authors.lastname: Peixoto
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal da Bahia, Salvador, Bahia, Brazil.
authors.forename: Érika Sales Joviano
authors.initials: ÉS
authors.lastname: Pereira
authors.affiliation: Department of Metallurgical and Materials Engineering, School of Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil. Electronic address: vbuono@demet.ufmg.br.
authors.forename: Vicente Tadeu Lopes
authors.initials: VT
authors.lastname: Buono
authors.affiliation: Department of Restorative Dentistry, Faculty of Dentistry, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Maria Guiomar de Azevedo
authors.initials: MG
authors.lastname: Bahia
mesh_terms: D000497:Alloys; D004708:Endodontics / Q000295:instrumentation*; D004868:Equipment Failure; D019544:Equipment Failure Analysis; D006801:Humans; D009532:Nickel; D014025:Titanium; D054159:Torsion, Mechanical
chemical_list: D000497:Alloys; C040654:titanium nickelide; C013616:nitinol; D009532:Nickel; D014025:Titanium
keywords: Controlled memory; fatigue resistance; nickel-titanium; rotary endodontic instruments; torsional resistance