Cyclic fatigue behavior of nickel-titanium dental rotary files in clinical simulated root canals

J Formos Med Assoc. 2017 Apr;116(4):306-312. doi: 10.1016/j.jfma.2016.06.002. Epub 2016 Jun 30.

Abstract

Background/purpose: Dental rotary instruments can be applied in multiple conditions of canals, but unpredictable fatigue fracture may happen. This study evaluated the fatigue lives of two batches of nickel-titanium (NiTi) dental rotary files operating in clinically simulated root canals.

Methods: Single-step cyclic fatigue tests were carried out to assess the performance of two batches of NiTi files (ProTaper and ProFile) in nine combinations of simulated canals (cylinder radii 5 mm, 7.5 mm, and 10 mm, and insertion angles 20°, 40°, and 60°). Two-step cyclic fatigue tests were carried out in simulated root canals with the same radius by using the following two sets of insertion angles: (20°, 40°), (20°, 60°), (40°, 20°), and (60°, 20°). Fracture surfaces were observed by scanning electron microscopy.

Results: The single-step cyclic fatigue results showed that cyclic fatigue lives of the files decreased with increasing insertion angles or decreasing cylinder radius. The ProFile #25 .04 file was more fatigue resistant than the ProTaper F2 file. In two-step cyclic fatigue tests, the total fatigue lives were usually more than 100% when the files operated at a lower strain and then at a higher strain. By scanning electron microscopy, a larger area of fatigue striation corresponded to a longer fatigue life.

Conclusion: Cyclic fatigue life can be influenced by the strains and geometries of files. The fatigue life was prolonged when the files operated at a lower strain and then at a higher strain. However, the fatigue life was shortened if the loading sequence was reversed.

Keywords: cyclic fatigue life; nickel–titanium endodontic instrument; two-step fatigue test.

Publication types

  • Comparative Study

MeSH terms

  • Dental Stress Analysis
  • Equipment Design
  • Equipment Failure
  • Humans
  • Materials Testing / instrumentation
  • Materials Testing / methods*
  • Microscopy, Electron, Scanning
  • Nickel*
  • Root Canal Preparation / instrumentation*
  • Rotation
  • Stress, Mechanical
  • Titanium*

Substances

  • titanium nickelide
  • Nickel
  • Titanium