title: Structural analysis of cyclic-loaded nickel-titanium rotary instruments by using resonance frequency as a parameter.
abstract: BACKGROUND
  The aim of this study was to investigate the relationship between fatigue life and resonance frequency (RF) of various types of nickel-titanium (NiTi) rotary instruments. In addition, the influence of NiTi instruments with different manufacturing methods on cyclic loading was evaluated by using RF as a parameter.
  
  
  METHODS
  Twenty-eight ProFile instruments and 10 Twisted File instruments were subjected to cyclic fatigue-loading until fracture by repeated preparation with simulated root canals made of clear resin. The RF of each sample was recorded immediately after the simulated canal block was prepared. For each sample, the microscopic images on the fracture surface, change in lengthening deformation, number of canal blocks prepared, and corresponding RF changes were recorded.
  
  
  RESULTS
  For all the tested instruments, RF values decreased gradually before breakdown when the fatigue failure of the instruments was associated with plastic deformation. In addition, there was a linear relationship between the RF change and the corresponding deformation of the failed instruments.
  
  
  CONCLUSIONS
  These results demonstrate that the RF analysis has potential as a tool for structural analysis in NiTi instruments.
authors.affiliation: School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: Haw-Ming
authors.initials: HM
authors.lastname: Huang
authors.forename: Wei-Jen
authors.initials: WJ
authors.lastname: Chang
authors.forename: Nai-Chia
authors.initials: NC
authors.lastname: Teng
authors.forename: Hung-Lung
authors.initials: HL
authors.lastname: Lin
authors.forename: Sung-Chih
authors.initials: SC
authors.lastname: Hsieh
mesh_terms: D003722:Dental Alloys; D003762:Dental Instruments; D003799:Dental Stress Analysis / Q000379:methods*; D004867:Equipment Design; D004868:Equipment Failure; D008422:Materials Testing / Q000379:methods*; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D014025:Titanium
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium