title: An in vitro assessment of the physical properties of novel Hyflex nickel-titanium rotary instruments.
abstract: OBJECTIVE
  To determine several properties including torsional and fatigue limits, as well as torque during canal preparation, of Hyflex, a rotary instrument manufactured from so-called controlled memory nickel-titanium alloy.
  
  
  METHODS
  The instruments were tested in vitro using a special torque bench that permits both stationary torque tests according to ISO3630-1 and fatigue limit determination, as well as measurement of torque (in Ncm) and apical force (in N) during canal preparation. Fatigue limit (in numbers of cycles to failure) was determined in a 90°, 5 mm radius block-and-rod assembly. Simulated canals in plastic blocks were prepared using both a manufacturer-recommended single-length technique as well as a generic crown-down approach. anova with Bonferroni post hoc procedures was used for statistical analysis.
  
  
  RESULTS
  Torque at failure ranged from 0.47 to 1.38 Ncm, with significant differences between instrument sizes (P < 0.0001). Fatigue life ranged from 260 to 2565, with the shortest and longest lifespan for instruments size 20, .04 taper and size 25, .08 taper, respectively. Torque during canal preparation was significantly higher for small instruments used in the single-length technique but lower for the size 40, .04 taper, compared to a crown-down approach. No instrument fractured; 82% of the instruments used were plastically deformed; however, only 37% of these remained deformed after a sterilization cycle.
  
  
  CONCLUSIONS
  Hyflex rotary instruments are bendable and flexible and have similar torsional resistance compared to instruments made of conventional NiTi. Fatigue resistance is much higher, and torque during preparation is less, compared to other rotary instruments tested previously under similar conditions.
authors.affiliation: Department of Endodontics, Arthur A. Dugoni School of Dentistry, University of the Pacific, San Francisco, CA 94941, USA. opeters@pacific.edu
authors.forename: O A
authors.initials: OA
authors.lastname: Peters
authors.forename: A K
authors.initials: AK
authors.lastname: Gluskin
authors.forename: R A
authors.initials: RA
authors.lastname: Weiss
authors.forename: J T
authors.initials: JT
authors.lastname: Han
mesh_terms: D000704:Analysis of Variance; D003722:Dental Alloys; D003762:Dental Instruments; D003799:Dental Stress Analysis; D008422:Materials Testing / Q000295:instrumentation; D009532:Nickel; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D018709:Statistics, Nonparametric; D014025:Titanium; D019415:Torque
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium