A NiTi rotary instrument manufactured by twisting: morphology and mechanical properties

Abstract

Objectives: The surface morphology of TF ® endodontic instruments was studied using stereomicroscopy and scanning electron microscopy (SEM). Mechanical tests were done for flexibility and microhardness. Methods: Four tapers of TF ® files were used (0.04; 0.06; 0.08 and 0.10 mm/mm). The stereomicroscopy associated with the AxioVision ® program was used to measure the tip angle, the helical angle, the taper and the tip diameter of the instruments. SEM was used to identify surface defects due to machining and finishing. The flexibility and the microhardness were measured with bending and microhardness Vickers tests, respectively. Results and Conclusion: The analysis showed that the manufacturer complied with the values recommended by the ANSI/ADA standard number 28. The SEM results showed many surface defects and a distortion of the instrument helix. It was observed that the instrument flexibility changes with its taper. The forces to induce the phase transformation by stress on instruments with taper 0.04; 0.06 and 0.08 mm/mm were 100 gf, 150 gf and 250 gf, respectively. The values of Vickers microhardness of the instruments are compatible with rotary instruments manufactured by the machining process.