title: Cyclic fatigue resistance tests of Nickel-Titanium rotary files using simulated canal and weight loading conditions.
abstract: OBJECTIVE
  This study compared the cyclic fatigue resistance of nickel-titanium (NiTi) files obtained in a conventional test using a simulated canal with a newly developed method that allows the application of constant fatigue load conditions.
  
  
  METHODS
  ProFile and K3 files of #25/.06, #30/.06, and #40/.04 were selected. Two types of testing devices were built to test their fatigue performance. The first (conventional) device prescribed curvature inside a simulated canal (C-test), the second new device exerted a constant load (L-test) whilst allowing any resulting curvature. Ten new instruments of each size and brand were tested with each device. The files were rotated until fracture and the number of cycles to failure (NCF) was determined. The NCF were subjected to one-way ANOVA and Duncan's post-hoc test for each method. Spearman's rank correlation coefficient was computed to examine any association between methods.
  
  
  RESULTS
  Spearman's rank correlation coefficient (ρ = -0.905) showed a significant negative correlation between methods. Groups with significant difference after the L-test divided into 4 clusters, whilst the C-test gave just 2 clusters. From the L-test, considering the negative correlation of NCF, K3 gave a significantly lower fatigue resistance than ProFile as in the C-test. K3 #30/.06 showed a lower fatigue resistance than K3 #25/.06, which was not found by the C-test. Variation in fatigue test methodology resulted in different cyclic fatigue resistance rankings for various NiTi files.
  
  
  CONCLUSIONS
  The new methodology standardized the load during fatigue testing, allowing determination fatigue behavior under constant load conditions.
authors.affiliation: Department of Conservative Dentistry, Pusan National University School of Dentistry, Yangsan, Korea.
authors.forename: Ok-In
authors.initials: OI
authors.lastname: Cho
authors.forename: Antheunis
authors.initials: A
authors.lastname: Versluis
authors.forename: Gary Sp
authors.initials: GS
authors.lastname: Cheung
authors.forename: Jung-Hong
authors.initials: JH
authors.lastname: Ha
authors.forename: Bock
authors.initials: B
authors.lastname: Hur
authors.forename: Hyeon-Cheol
authors.initials: HC
authors.lastname: Kim
keywords: Constant angle; Constant load; Cyclic fatigue fracture; Nickel-titanium rotary file; Simulated canal