title: Assessment of the mechanical properties of ProTaper Next Nickel-titanium rotary files.
abstract: BACKGROUND
  The purpose of this study was to compare the torsional resistance, flexibility, and surface microhardness of ProTaper Next files (PTN) with Twisted Files (TF) and RaCe (RC).
  
  
  METHODS
  A metal block with a cubical hole was used to evaluate the torsional resistance. Five millimeters of the tip of each file was securely held in place by filling the mold with a resin composite, and the files were driven clockwise at 300 rpm. The number of load applications before fracture was recorded for each file. A scanning electron microscope was used to characterize the topographic features of the fracture surfaces of the broken files. The files were tested for bending resistance by using cantilever-bending test. Vickers microhardness was measured on the cross section of instruments with 300-g load and 15-second dwell time. Torsional resistance data were analyzed by using the nonparametric Kruskal-Wallis and Mann-Whitney U tests. Bending resistance and microhardness data were analyzed by using analysis of variance and Tukey tests.
  
  
  RESULTS
  PTN showed the highest torsional resistance and microhardness, followed by RC (P < .05). The fracture cross sections of all brands showed dimpling near the center of fracture surface. The ranking in the bending resistance values was as follows: RC > PTN > TF.
  
  
  CONCLUSIONS
  PTN improved its resistance to torsional stresses and wear compared with TF and RC. TF showed improved flexibility compared with other tested brands.
authors.affiliation: Department of Conservative Dentistry and Endodontics, Faculty of Dentistry, Mansoura University, Mansoura, Egypt. Electronic address: aelnaghy@mans.edu.eg.
authors.forename: Amr M
authors.initials: AM
authors.lastname: Elnaghy
authors.affiliation: Department of Dental Biomaterials, Faculty of Dentistry, Mansoura University, Mansoura, Egypt.
authors.forename: Shaymaa E
authors.initials: SE
authors.lastname: Elsaka
mesh_terms: D003722:Dental Alloys / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D004548:Elasticity; D004867:Equipment Design; D004868:Equipment Failure; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D055595:Mechanical Phenomena; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000737:chemistry*; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*; D054159:Torsion, Mechanical
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: Flexibility; ProTaper Next; microhardness; nickel-titanium files; torsional resistance