ProFile Vortex instruments after clinical use: a metallurgical properties study.

Introduction: The aim of the study was to analyze the incidence and mode of ProFile Vortex instrument (Dentsply Tulsa Dental Specialties, Tulsa, OK) defects during a predefined schedule of clinical use by the undergraduate 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 differential 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 clinical 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 microhardness was detected among these 3 instrument groups. X-ray diffraction results showed that NiTi files had austenite structure at room temperature.

Conclusions: 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.