title: Evidence for Reduced Fatigue Resistance of Contemporary Rotary Instruments Exposed to Body Temperature.
abstract: BACKGROUND
  The purpose of this study was to evaluate the effect of 2 different temperatures (20°C and 37°C) on the cyclic fatigue life of rotary instruments and correlate the results with martensitic transformation temperatures.
  
  
  METHODS
  Contemporary nickel-titanium rotary instruments (n = 20 each and tip size #25, including Hyflex CM [Coltene, Cuyahoga Falls, OH], TRUShape [Dentsply Tulsa Dental Specialties, Tulsa, OK], Vortex Blue [Dentsply Tulsa Dental Specialties], and ProTaper Universal [Dentsply Tulsa Dental Specialties]) were tested for cyclic fatigue at room temperature (20°C ± 1°C) and at body temperature (37°C ± 1°C). Instruments were rotated until fracture occurred in a simulated canal with an angle curvature of about 60° and a radius curvature of 3 mm; the center of the curvature was 4.5 mm from the instrument tip. The number of cycles to fracture was measured. Phase transformation temperatures for 2 instruments of each brand were analyzed by differential scanning calorimetry. Data were analyzed using the t test and 1-way analysis of variance with the significance level set at 0.05.
  
  
  RESULTS
  For the tested size and at 20°C, Hyflex CM showed the highest resistance to fracture; no significant difference was found between TRUShape and Vortex Blue, whereas ProTaper Universal showed the lowest resistance to fracture. At 37°C, resistance to fatigue fracture was significantly reduced, up to 85%, for the tested instruments (P < .001); at that temperature, Hyflex CM and Vortex Blue had similar and higher fatigue resistance compared with TRUShape and ProTaper Universal.
  
  
  CONCLUSIONS
  Under the conditions of this study, using a novel testing design, immersion in water at simulated body temperature was associated with a marked decrease in the fatigue life of all rotary instruments tested.
authors.affiliation: Department of Endodontics, University of the Pacific, Arthur A. Dugoni School of Dentistry, San Francisco, California; Department of Restorative Dentistry, Sao Jose dos Campos School of Dentistry, Institute of Science and Technology, Sao Jose dos Campos, São Paulo, Brazil.
authors.forename: Rafaela Andrade
authors.initials: RA
authors.lastname: de Vasconcelos
authors.affiliation: Department of Endodontics, University of the Pacific, Arthur A. Dugoni School of Dentistry, San Francisco, California.
authors.forename: Sarah
authors.initials: S
authors.lastname: Murphy
authors.affiliation: Department of Restorative Dentistry, Sao Jose dos Campos School of Dentistry, Institute of Science and Technology, Sao Jose dos Campos, São Paulo, Brazil.
authors.forename: Claudio Antonio Talge
authors.initials: CA
authors.lastname: Carvalho
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley, California.
authors.forename: Rajiv G
authors.initials: RG
authors.lastname: Govindjee
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley, California.
authors.forename: Sanjay
authors.initials: S
authors.lastname: Govindjee
authors.affiliation: Department of Endodontics, University of the Pacific, Arthur A. Dugoni School of Dentistry, San Francisco, California. Electronic address: opeters@pacific.edu.
authors.forename: Ove A
authors.initials: OA
authors.lastname: Peters
mesh_terms: D000704:Analysis of Variance; D001831:Body Temperature; D002152:Calorimetry, Differential Scanning; D003722:Dental Alloys / Q000737:chemistry; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D014025:Titanium / Q000737:chemistry; D019415:Torque; D054159:Torsion, Mechanical; D044366:Transition Temperature
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; C093824:Martensite; D009532:Nickel; D014025:Titanium
keywords: Body temperature; cyclic fatigue; martensitic transformation