Novel Cyclic Fatigue Testing Machine for Endodontic Files

The characteristics of superelasticity and shape-memory of the NiTi make endodontic rotary files suitably flexible and resistant while operating within curved canals. However, continuous rotation within accentuated curvatures causes stresses that can lead to intraoperative fracture by torsional shear or flexural cyclic fatigue. The aim of this paper is to design and build a rotary bending testing machine able to estimate reproducibly the fatigue life of endodontic instruments. The main innovation of this apparatus consists in ensuring that the file rotates freely, not being forced within a suitable shaped housing, and this provides both advantages of reducing the influence of the friction phenomena and maintaining unchanged geometric parameters. A further element of novelty is the real-time measurement of the bending force during the test up to the failure. Moreover, such a machine makes it possible to perform predictive thermographic tests of the file fatigue life and to monitor the energetic trend of the static and rotary bending while testing.