Influence of Anatomical Root Factors on Cyclic Fatigue Resistance of Heat Treated NiTi Instrument: A Review

Endodontic treatments have been improved over the last decade by the use of nickel titanium (NiTi) alloys. NiTi instrument had shape memory and superelastic properties which made the instrument more flexible, so the treatment quality was enhanced by eliminating the procedural errors. Although the numerous benefits of the NiTi instruments, the fracture was the most frequent failure that may be happened during its use due to flexural (cyclic) or torsional fatigue. Various thermo-mechanical heat treatments have been applied to NiTi instruments to improve fracture resistance and clinical performance. Several parameters influenced the fatigue resistance of NiTi files, and the most important factor that affected the likelihood of NiTi instrument fatigue was the root canal shape. Data collected of 100 papers from the Goggle scholar and Scien ceDirect database. After excluding 60 unrelated papers, thi s review of 40 included related studies aims to evaluate an overview of the anatomical root-related factors affecting t he cyclic fatigue of heat-treated NiTi instruments. Concl uded that the separation rates of file increased when the radius of curvature decreases and when the angle of curvature increased. Canals with the double curvatures increase the risk of cyclic fatigue. Also, the resistance to cyclic fatigue of NiTi files was affected by the canal curvature posit ion, with a short failure life coronally. So even in the improve ment of wire metallurgy and designs of instrument, the anatomy of canal still impact on the cyclic fatigue and should be considered during preparation especially with th e new concept of minimally invasive endodontic treatmen t.