ProFile Vortex Instruments after Clinical Use: A Metallurgical Properties Study Ya Shen, DDS, PhD,* Jeffrey M. Coil, DMD, MSD, PhD,* Hui-min Zhou, DDS, PhD, † Esther Tam, DDS,* Yu-feng Zheng, PhD, ‡ and Markus Haapasalo, DDS, PhD* Abstract Introduction: The aim of the study was to analyze the incidence and mode of ProFile Vortex instrument (Dents- ply Tulsa Dental Specialties, Tulsa, OK) defects during a predefined schedule of clinical use by the undergrad- uate students in a dental school setting and to examine the metallurgical characteristics of unused and clinically used Vortex instruments. Methods: A total of 2,203 ProFile Vortex instruments discarded after single use from the undergraduate students program over 24 months were collected and examined for defects using a stereomicrosocpe at 10 magnification. The incidence and type of instrument defects or separation were analyzed. The lateral surfaces of part of the defected instruments and fracture surfaces of fractured files were examined using scanning electron microscopy. Unused and clinically used files were examined by differ- ential scanning calorimetry and X-ray diffraction. Vickers hardness of the files was measured with a 200-g load. Results: Only 1 of the 2,203 files fractured during clin- ical use. The cause of fracture was shear stress, and the file also showed unwinding of the helix structure. None of the remaining 2,202 files exhibited unwinding after clinical use. Blunt apicals were detected in 86 used files (3.9%). Austenite-finish temperatures were very similar for as-received, used files with defects and used files without defects, all exceeding 50  C. No difference in mi- crohardness was detected among these 3 instrument groups. X-ray diffraction results showed that NiTi files had austenite structure at room temperature. Conclu- sions: The risk of ProFile Vortex fracture is very low when files are used 1 time by undergraduate students. Unwinding of the files was not detected except for the fractured file. Clinical single use had no detectable effect on austenite-martensite phase transformation of the files. Unused and clinical single-use files contain a similar phase structure at body temperature. (J Endod 2012;38:1613–1617) Key Words Defect, differential scanning calorimetry, endodontic instrument, M-Wire, nickel- titanium instrument, ProFile Vortex, x-ray diffraction T he introduction of nickel-titanium (NiTi) to endodontics over 2 decades ago has dramatically changed the way root canal preparation is performed in both experi- enced and inexperienced operators’ practices. Instruments made of the NiTi alloy, which consists of nickel and titanium in a nearly equal atomic ratio, not only have high resis- tance to corrosion and excellent biocompatibility but also a special mechanical property known as ‘‘superelasticity’’ (1). Superelasticity is associated with the occurrence of a phase transformation of the alloy upon application of stress above a critical level, which takes place when the ambient temperature is above the so-called austenite-finish (A f ) temperature of the material. This stress-induced martensitic transformation reverses spontaneously upon release of the stress; the material then returns to its original shape and size (2). This special property manifests as an enhanced elasticity of the NiTi alloy, allowing the material to recover after large strains. Thus, NiTi instruments are highly flex- ible and elastic; hence, there is the possibility to use them in a continuous rotary fashion and in a curved canal. Many studies have shown that NiTi rotary systems are able to prepare root canals with desired taper, less canal transportation, and at a much faster rate than hand files (3–5). Despite the advantages, there is concern about the incidence of instrument fractures during root canal preparation (6, 7). Two mechanisms that may lead to NiTi rotary fracture, cyclic fatigue, and torsional overloading have been described (8, 9). The separation of a rotary instrument in the root canal caused by fatigue in particular has been identified as a primary concern in endodontics especially for root canals with severe curvatures (9, 10). Improvements in metallurgy, surface treatment, design, and quality control and the introduction of hands-on training have reduced the extent of file fracture. Recently, thermal treatment of NiTi alloys (eg, controlled memory wire [CM Wire; DS Dental, Johnson City, TN], M-Wire [Dentsply Tulsa Dental Specialities, Tulsa, OK], and R-phase wire [SybronEndo, Orange, CA]) have been used to modify the mechanical properties. Thermomechanical processing is a frequently used method to optimize the microstruc- ture and transformation behavior of NiTi alloys, which in turn has great influence on the reliability and mechanical properties of NiTi files (11–14). In 2009, ProFile Vortex (Dentsply Tulsa Dental, Johnson City, TN), the ‘‘next generation’’ in the ProFile instrument series was introduced. Vortex files are manufactured from M-Wire; they have a triangular cross-section without radial lands and a helical angle. A number of studies have examined the failed NiTi instruments collected after clinical use (6, 7, 10, 15–20). Several general observations have been made, which From the *Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, Canada; † Center for Biomedical Materials and Engineering, College of Material Science and Chemical Engineering, Harbin Engineering University, Harbin, China; and ‡ State Key Laboratory for Turbulence and Complex Systems and Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing, China. Address requests for reprints to Dr Markus Haapasalo, Division of Endodontics, Department of Oral Biological and Medical Sciences, UBC Faculty of Dentistry, 2199 Wesbrook Mall, Vancouver, BC, Canada V6T 1Z3. E-mail address: markush@dentistry.ubc.ca 0099-2399/$ - see front matter Copyright ª 2012 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2012.09.018 Basic Research—Technology JOE — Volume 38, Number 12, December 2012 ProFile Vortex Instruments 1613