Contents lists available at ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal Progressive structural deterioration of an endodontic instrument – A preliminary micro-computed tomography study Igor Bastos Barbosa a , Pantaleo Scelza a , André Maues Brabo Pereira b , Fabiano Guerra Ferreira a , Rodrigo Bagueira c , Caroline Sousa Ribeiro Adeodato a , Miriam Zaccaro Scelza a, ⁎ a Department of Endodontics, Fluminense Federal University (UFF), Rua Mario Santos Braga, 30, Niteroi, RJ 24020-140, Brazil b School of Engineering, Fluminense Federal University (UFF), Rua Passo da Pátria, 156, Niterói, RJ 24210 240, Brazil c Institute of Chemistry, Fluminense Federal University (UFF), Rua Outeiro de São João Batista, s/n, Niterói, RJ 24020-141, Brazil ARTICLE INFO Keywords: Endodontic instrument Fatigue failure Microanalysis Non-destructive inspection X-ray analysis ABSTRACT The aim of this study was to investigate the methodological potential of a new application of micro-computed tomography in providing an external and internal assessment of the structural integrity of an endodontic test file, and its progressive structural deterioration after repeated use in simulated root canals (resin blocks), until fracture. The progressive deterioration of the in- strument was observed, and the external and internal defects were described. Radiolucent images suggestive of micro-cavities were observed in the instrument's core prior to its first use, and the formation and subsequent propagation of cracks in an apparently non-linear manner were ob- served after consecutive uses, until the final collapse of the whole structure. This novel assess- ment method allowed the visualization the external surface and the core of the same instrument at different time points in the instrumentation process, thus enabling researchers to identify where the cracks started and their progression during the course of instrument use. 1. Introduction Mechanized endodontic instruments are subjected to repeated loads and cyclic stresses during the instrumentation process. This mechanical challenge causes physical damage, which builds up during its continuous use, resulting in cracks and other macroscopic defects that can propagate and lead to instrument fracture [1–4]. This process of damage and failure due to cyclic loading is called fatigue [4]. In 2008, Yared [5] used a kinematic called reciprocation, defined as the alternation between the clockwise and counterclockwise directions of the rotational motion of the instrument, aiming at preventing the buildup of mechanical stress in the instrument, providing a reduction in the phenomena of cyclic fatigue and taper lock of the instrument inside the canal, and thus preventing instrument fracture [6–8]. Although the manufacturers of the most commonly used single-file systems—namely Reciproc (VDW GmbH, Munich, Germany) and WaveOne (Dentsply Maillefer, Ballaigues, Switzerland)—recommend disposing of the instrument after using it for only one https://doi.org/10.1016/j.engfailanal.2019.05.029 Received 13 April 2018; Received in revised form 10 May 2019; Accepted 29 May 2019 Abbreviations: AFM, atomic force microscopy; DET, detector; Micro-CT, micro-computed tomography; SPE, specimen; SEM, scanning eletron microscopy; XRS, x-ray source ⁎ Corresponding author. E-mail address: scelza@terra.com.br (M. Zaccaro Scelza). Engineering Failure Analysis 104 (2019) 105–111 Available online 31 May 2019 1350-6307/ © 2019 Published by Elsevier Ltd. T