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Effect of fatigue on torsional failure of nickel-titanium controlled memory instruments Campbell, Les


Abstract Introduction: This study was undertaken to understand how fatigue affects the torsional properties of both traditional nickel-titanium (NiTi) and nickel-titanium controlled memory (CM) files. Methods: Typhoon (TYP) 25.04 and 40.04 rotary files, in both NiTi and CM, were tested using a three-point bending apparatus to obtain the mean number of cycles to failure (mNCF). New files were precycled to four conditions (i.e., 0%, 25%, 50%, and 75% of the mNCF) before torsional resistance tests were performed. Each file was exposed to torsional stress until failure, and at that point the torque and distortion angles were measured. The fracture surface of each fragment was examined with a scanning electron microscope. Results: The TYP CM files yielded a seven-fold improvement in mNCF over the TYP NiTi files (P ≤ 0.05). In both file sizes there was no difference in torque between the CM files and the conventional Ni-Ti files (P > 0.05). The torque of the size 40.04 files was significantly higher than the torque of the size 25/.04 files (P ≤ 0.05). In the 40.04 TYP files group, the 75% precycling group had a significantly lower torque to failure than the no precycling group (P ≤ 0.05). The CM files of both sizes had significantly higher distortion angles than the Ni-Ti files of both sizes (P ≤ 0.05). The 40.04 TYP CM files that were not precycled showed a significantly higher distortion angle than the precycled groups. The fractured files in the precycling groups showed the typical pattern of torsional failure. Conclusions: Cyclic fatigue has an effect on torsional fracture resistance of TYP and TYP CM files on size 40.04. TYP CM files displayed a similar torque value to TYP files but rotated a greater angle before fracture in both preloading and no preloading groups.

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