Wear analysis and cyclic fatigue resistance of electro discharge machined NiTi rotary instruments

Aim: To evaluate the wear of new rotary instruments produced via electro discharge machining and to test their fatigue resistance. Methodology: Twenty-one HyFlex EDM (Colte`ne/Whaledent, Switzerland) files were used for laboratory instrumentation of curved root canals of extracted teeth. Superficial characteristics were analyzed pre- and postoperatively by scanning electron microscopy (SEM) (JSM-5200, JEOL, Tokyo, Japan) at same points and with same angulations to identify the wear features. Number of fractures, microcracks blunt/disruption of cutting edge and tip deformations were reported. Twenty HyFlex EDM and 20 HyFlex CM (Colte`ne/Whaledent, Switzerland) were subjected to cyclic fatigue test in a 708 artificial metal canal. Results were statistically analyzed using Mann—Whitney tests. Results: Nofractureswereregisteredduringlaboratorycanalinstrumentation.Nowearandno degradation of the 25.12 and 25.08 files were reported. Slight plastic deformations were only observed in three 10.05 files. The cyclic fatigue test revealed a significant increase of fatigue resistance of EDM files compared to CM ( p = 0.0001). Conclusions: The typical irregular surface of HyFlex EDM remained unaffected after multiple uses, confirming a high wear resistance. The new manufacturing process of electrical discharge machining had a substantial impact on fatigue lifetime of EDM files when compared with HyFlex CM. Within limitations of the present in vitro results, EDM files appeared suitable in shaping severely curved canals. ß 2016 Societ`a Italiana di Endodonzia. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc- nd/4.0/).