title: Effects of raw material and rotational speed on the cyclic fatigue of ProFile Vortex rotary instruments.
abstract: BACKGROUND
  This in vitro study compared the cyclic fatigue resistance of ProFile Vortex rotary instruments (DENTSPLY Tulsa Dental, Tulsa, OK) made of two different raw materials: M-Wire and regular superelastic wire (SE-wire) at two different rotational speeds. Two rotary-based Profile Vortex instruments with taper 0.04 and 0.06 (25 mm in length and #30 in size) were compared.
  
  
  METHODS
  Cyclic fatigue testing was performed by rotating instruments in an artificially constructed stainless steel canal with a 5-mm radius and a 90 degrees angle of curvature at two different test frequencies: 300 and 500 rpm. The time to failure was recorded, and the total number of cycles to failure was calculated and compared for a total of 160 samples. Statistical analysis was performed with one-way analysis of variance and the Tukey test for individual comparisons (confidence level of p < 0.05). Fracture surfaces of broken instruments were also observed under scanning electron microscopy. Over 50% of broken files made of SE-wire exhibited multiple crack initiation sites compared with the single crack initiation on files made of M-Wire.
  
  
  RESULTS
  Overall, there were significant differences in rotary instruments made of different materials (p < 0.001). However, for rotary instruments made from the same material (either M-Wire or SE-wire), there was no significant difference (p > 0.05) of cyclic fatigue life under different rotational speeds (300 and 500 rpm).
  
  
  CONCLUSIONS
  ProFile Vortex files made of M-Wire exhibited superior cyclic fatigue resistance (approximately 150% longer in fatigue life) compared with those made of regular SE-wire at two test frequencies (300 and 500 rpm).
authors.affiliation: DENTSPLY Tulsa Dental Specialties, Tulsa, OK 74135, USA. yong.gao@dentsply.com
authors.forename: Yong
authors.initials: Y
authors.lastname: Gao
authors.forename: Vincent
authors.initials: V
authors.lastname: Shotton
authors.forename: Kevin
authors.initials: K
authors.lastname: Wilkinson
authors.forename: Greg
authors.initials: G
authors.lastname: Phillips
authors.forename: William Ben
authors.initials: WB
authors.lastname: Johnson
mesh_terms: D003722:Dental Alloys / Q000737:chemistry*; D055119:Elastic Modulus; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000737:chemistry*; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium