Novel Cyclic Fatigue Testing Machine for Endodontic Files
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RESEARCH PAPER
Novel Cyclic Fatigue Testing Machine for Endodontic Files F. Lo Savio 1 & G. La Rosa 1 & M. Bonfanti 1 & D. Alizzio 2 & E. Rapisarda 3 & E. Pedullà 3 Received: 10 February 2020 / Accepted: 13 June 2020 # The Society for Experimental Mechanics, Inc 2020
Abstract 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. Keywords Nickel-titanium rotary files . Cyclic fatigue . Bending testing machine . Predictive thermographic tests
Introduction Endodontic therapy is a generally complex treatment, due to the large anatomical variability of the dental elements, whose ultimate aim is the conservation of the natural tooth in a functional and asymptomatic way over time. In endodontics, nickel-titanium alloy (NiTi) rotary files are widely used in the field of root canal processing. This is due to Highlights • A cyclic fatigue-bending machine, able to test endodontic instruments, is proposed. • Contact points, to change the file configuration, rotate freely minimizing friction. • The device is able to monitor thermal changes on endodontic files while testing. • The device allows the real-time bending force measure on the file up to the breakage. • The device is able to reproduce any anatomical geometry that the root canal can take. * F. Lo Savio [email protected] 1
Department of Civil Engineering and Architecture, University of Catania, Via S. Sofia, 54-95100 Catania, Italy
2
Department of Engineering, University of Messina, Cont.da Di Dio, 98166 Messina, Italy
3
Department of Gen. Surgery and Surgical-Medical Specialties, University of Catania, Via Plebiscito, 628-95100 Catania, Italy
the characteristics of superelasticity and shape-memory of the NiTi, which allow maintaining flexibility and resistance during rotation within curved canals [1]. The main properties of NiTi alloys derive from a reversible phase transformation at the solid state between the austenitic and martensitic structures, known as “thermoplastic martensitic transformation”. This transformation makes it possible to recover high deformations
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