Original Articles
Characteristics of cyclic fatigue fracture of nickel-titanium files in continuous rotary or reciprocating motion
2016 Volume 37 Issue 3 Pages 150-155
Details
2016 Volume 37 Issue 3 Pages 150-155
Abstract : Purpose : The aim of this study was to evaluate and compare the cyclic fatigue resistance of nickel-titanium rotary files in continuous rotation and reciprocating motion in artificial metal canals.
Methods : A total of 44 new rotary BioRaCe files (ISO size=25, taper=0.06, length=25 mm) were selected and randomly divided into four groups (n=11 each) : CR (BioRaCe NiTi files in continuous rotation with up-and-down), C (BioRace NiTi files in continuous rotation without up-and-down), Re (BioRace NiTi files in reciprocating motion with up-and-down), and Re-C (BioRace NiTi files in reciprocating motion without up-and-down). A cyclic fatigue testing device was fabricated with a 45° angle of curvature in artificial metal blocks.
A continuous up-and-down (4 mm in each direction at 0.5 second) pecking movement was incorporated to simulate the pecking motion in a real clinical situation. All instruments were rotated or reciprocated until fracture occurred. The time taken for each instrument to fracture and the lengths of the broken fragments were recorded. All the fractured files were analyzed under a scanning electron microscope to detect the mode of fracture. Data were analyzed by one-way analysis of variance, followed by a Tukey-Kramer multiple comparison test.
Results : The time taken for the instruments of the Re groups to fail under cyclic loading was significantly longer compared with the CR groups. The Re groups showed a significant difference in the time of cyclic fatigue fracture compared with the Re-C and C groups (p<0.01). The lengths of the fractured segments were between 3 and 5 mm, which was not statistically significant among the experimental groups. Scanning electron microscope observations showed craterlike formations along with numerous dimples and micro-bubbles.
Conclusion : Reciprocating motion showed a significantly higher cyclic fatigue resistance than continuous rotation.
