Introduction: Nickel-titanium (NiTi) rotary files were used widely in endodontics for preparing root canals. By using NiTi rotary files, the complications that are observed when using stainless steel files such as perforations, straightened root canals, ledges, zips, started to be seen less frequently. Nickle titanium files are flexible, have good elasticity and have more resistance to fracture. By the use of these files original canal anatomy was maintained. Materials and Methods: The custom made device and Hand piece of rotary Endodontic motor with file were stabilized in Universal Testing Machine (Instron). The instruments were rotated at 300 rpm by using an electric motor (Sybron Endo, Endotouch TC2) at maximum Torque. The instruments were aligned to a specific mark (to allow for repositioning the same location), and then the file were set to rotate, synchronized with timing by a stopwatch. The instruments were allowed to rotate freely until fracture. Timer was stopped as soon as fracture was detected visually or audibly. The time was then converted into number of revolutions to failure. Results: By applying Tukey-Kramer Multiple comparison test there is a significant difference between mean values of Time in seconds to Fracture and Number of rotations to failure in Neolix, One Shape and T Files compared together (p<0.001) Conclusions: Among all the groups, the group with Neolix files showed the highest resistance to cyclic fatigue when used in artificial simulated curved canals.
