The evaluation of cyclic fatigue of various nickel titanium instruments with different test methods

Nickel Titanium rotary systems are the most widely used procedures in root canal treatment. The major disadvantage of nickel titanium systems are seperation of files into the root canals due to mechanical properties. The aim of this study is to evaluate the cyclic fatigue resistance and fracture patterns of Reciproc, Waveone, Protaper Next, OneShape and TF Adaptive NiTi systems with three different test methods. Three different cyclic fatigue test methods with two different angle (45° and 60°) were used in this study. The test devices were stainless steel three-pin device, sloped stainless-steel block and metal block with groove device. Totally 300 files of five different brands (n=10) rotated until failure occurs at speed and torque settings recommended by their manufacturers. The time until the fracture recorded and converted to the number of rotations to failure by multiplying the time until the fracture by revolutions per minute. Representative samples were also examined 10x magnification with a stereomicroscope to determine fracture patterns and lenghts. There is a statistically significant difference between all instruments in each test method except stainless steel three-pin device 45°. Reciproc instruments have the highest number of cycles to fracture with each test method. This difference is statistically significant in metal block with groove device 45° and 60° (p<0.05). However, statistically significant differences were found between the test methods according to the instruments (p<0.05). The tested files have different results when different test methods were used. Therefore, cyclic fatigue test methods needs a standardization for comparable and safer results.