Research Article The Effect of Hydrofluoric Acid Surface Treatment on the Cyclic Fatigue Resistance of K3 NiTi Instruments Kee-Yeon Kum 1 and Seok Woo Chang 2 1 Department of Conservative Dentistry, Seoul National University Dental Hospital, Seoul Dental Hospital for Disabled, Dental Research Institute, Seoul National University School of Dentistry, Seoul, Republic of Korea 2 Department of Conservative Dentistry, School of Dentistry, Kyung Hee University, Seoul, Republic of Korea Correspondence should be addressed to Seok Woo Chang; swc2007smc@gmail.com Received 19 October 2016; Revised 19 March 2017; Accepted 11 April 2017; Published 2 May 2017 Academic Editor: Ian S. Butler Copyright © 2017 Kee-Yeon Kum and Seok Woo Chang. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te aim of this study was to investigate the efect of 50% hydrofuoric acid (HF) surface treatment on the cyclic fatigue resistance (CFR) of K3 NiTi instruments. Twenty as-received and twenty HF-treated K3 NiTi instruments were compared in CFR. Te surface texture and fracture surface of two instrument groups were examined with a scanning electron microscope (SEM). Additionally, any change of Ni and Ti composition from both instrument groups was investigated using energy dispersive spectrometry. Te results were analyzed with -test. Te HF-treated K3 group showed statistically higher cyclic fatigue resistance than as-received K3 group ( < 0.05). HF-treated K3 instruments showed smoother and rounded surface compared to as-received K3 under SEM observation. Te fracture surfaces of both groups showed typical patterns of cyclic fatigue fracture. Tere was no diference in surface Ni and Ti composition between two groups. HF treatment of K3 instruments smoothed the fle surface and increased the cyclic fatigue resistance, while it had no efect on surface ion composition and the fle fracture pattern. 1. Introduction In modern endodontics, many clinicians use engine driven nickel-titanium (NiTi) rotary instruments, which makes root canal preparation more fast and efective [1]. However, acci- dental instrument separation is a concern for every clinician who uses NiTi rotary instruments in their practice. Te two main fracture mechanisms of NiTi rotary instrument are cyclic fatigue fracture and torsional fracture [2]. Cyclic fatigue fracture has been reported to be afected by many factors such as manufacturing process [2], root canal geometry [3], instrumentation motion [4], cross-sectional confguration, rotational speed [5], and surface treatment method [6]. It is recently focused that surface defects such as microcracks and machining grooves, which were induced in machining process during manufacturing, are the stress concentration point where the initiation of fle fracture begins to propagate [5, 7–9]. Te grinding procedure across the grains of NiTi wire has been also suggested to deteriorate the mechanical strength of the instrument owing to the machining defects on instrument surface and the residual stress within the internal structure [10–12]. Previous studies supported this postulation in that the ground fle showed much lower cyclic fatigue resistance than twisted fles [5]. Terefore, various surface treatment methods such as electropolishing [13], ion implan- tation [14], and chemical and physical vapor deposition [15, 16] have been tried for improving mechanical properties and reducing surface defects of ground NiTi rotary instruments. Tese methods were reported to be efective in improving the mechanical properties of NiTi rotary instruments, but there have not been frmly established consensus about the efectiveness of such treatment for improving cyclic fatigue resistance of NiTi rotary instruments, yet. Acid treatment is widely used method during manufac- turing process to chemically polish the surface of ground NiTi instruments. Hydrofuoric acid (HF), which is the ingredients of Kroll’s reagent, is used for chemical polishing of ground NiTi alloy [17]. In spite of the surface treatment during manufacturing, previous studies clearly showed that the as- received ground NiTi rotary instruments have rough surface Hindawi Bioinorganic Chemistry and Applications Volume 2017, Article ID 3189729, 6 pages https://doi.org/10.1155/2017/3189729