Effect of Curvature Location on Fatigue Resistance of Five Nickel-titanium Files Determined at Body Temperature.

Abstract Introduction The purpose of this study was to evaluate the effect of five different curvature locations on the fatigue resistance of the thermomechanically treated nickel-titanium (NiTi) files and superelastic NiTi files at body temperature and to document the corresponding phase transformations. Methods EndoSequence (ES), EndoSequence CM (ESCM), K3, K3XF, and Vortex Blue (VB) NiTi files (size 25/.04) were subjected to fatigue tests inside customised artificial canals containing a curvature of 60° and a 3-mm radius. There were five different canals based on the location of initial curvature; these included groups where the distance between the canal orifice and the location of the curvature (DOC) was 5, 6, 8, 10, and 11 mm. The model canal was immersed in water at 37°C ± 1°C. The number of cycles to failure (Nf) was recorded, and the fracture surface of the fragments was examined by scanning electron microscopy. Two unused files of each brand were examined by differential scanning calorimetry. Results The Nf was highest in the 10 mm and 11 mm DOC groups and lowest with the 5 mm and 6 mm DOC groups (p Conclusion The location of the canal curvature had a significant effect on the fatigue resistance of both heat-treated and superelastic NiTi files. The fatigue life of files in the coronal curve was quite short.