@article{Pedullà_Lo Savio_Plotino_Grande_Rapisarda_Gambarini_La Rosa_2015, title={Effect of cyclic torsional preloading on cyclic fatigue resistance of ProTaper Next and Mtwo nickel—titanium instruments}, volume={29}, url={https://giornaleitalianoendodonzia.it/gie/article/view/56}, DOI={10.32067/gie.2015.29.01.03}, abstractNote={<p>Aim: To evaluate the influence of different torsional preloads on cyclic fatigue resistance of endodontic rotary instruments made by conventional nickel—titanium (NiTi) or M-Wire. Methods: Eighty new Mtwo (#25/0.06) (Sweden & Martina, Due Carrare, Padova, Italy) and ProTaper Next X2 (Dentsply Maillefer, Ballaigues, Switzerland) were used. The Torque and distortion angles at failure of new instruments (n = 10) were measured and 0% (n = 10), 25%, 50%, and 75% (n = 20) of the mean ultimate torsional strength as preloading condition were applied according to ISO 3630-1 for each brand. The twenty files tested for every extent of preload were subjected to 25 or 50 torsional cycles (n = 10). After torsional preloading, the number of cycles to failure was evaluated in a simulated canal with 608 angle of curvature and 5 mm of radius of curvature. Data were analyzed using 2-way analysis of variance. Scanning electron microscope (SEM) was performed to evaluate the fracture surface of each fragment. Results: ProTaper Next X2 reduced their cyclic fatigue after 25 or 50 cycles of every torsional preloading (25%, 50%, and 75%) (P < 0.01). Cyclic fatigue of Mtwo was reduced by 50 cycles of every torsional preloading and only after the 75% of preload for 25 cycles (P < 0.01). Conclusions: Torsional preloads reduced the cyclic fatigue resistance of M-wire and conventional (as ProTaper Next and Mtwo) NiTi rotary instruments except for Mtwo with 25% or 50% of torsional preloading.</p>}, number={1}, journal={Giornale Italiano di Endodonzia}, author={Pedullà, Eugenio and Lo Savio, Fabio and Plotino, Gianluca and Grande, Nicola Maria and Rapisarda, Silvia and Gambarini, Gianluca and La Rosa, Guido}, year={2015}, month={Jun.}, pages={3–8} }