Are endodontic nickel–titanium instruments indefectible? A fractographic analysis of a compound core manufacturing defect

The aim of this study is to present a compound core manufacturing defect identified in a nickel-titanium (NiTi) instrument via fractographic analysis during additional retrospective analysis after dynamic cyclic fatigue resistance testing. This study raises awareness of core manufacturing defects and fosters the development of high-quality NiTi instruments without defects for clinical application. A scanning electron microscope with an acceleration voltage of 5 kV was used for fractographic analysis after cyclic fatigue testing. The fractographic analysis identified a compound core manufacturing defect, involving unmelted powder, and two interconnected failures. To the best of our knowledge, this is the first study to identify such compound core manufacturing defect in a NiTi instrument during fractographic analysis via scanning electron microscopy. The study underscores the need for detection and rectification of manufacturing defects, with methods such as X-ray computed tomography and hot isostatic pressing. The presence of core manufacturing defects in the NiTi instruments elevates the likelihood of premature clinical fracture, which may add to their inherent susceptibility to fracture in root canals due to cyclic fatigue and/or torsional stress.