PSI - Issue 42

Guilherme Saldanha et al. / Procedia Structural Integrity 42 (2022) 631–638 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

633

3

2.1. Rotating bending tests The HyFlex EDM file system tested during this research consists of instruments of three different sizes, each designed to perform a specific function during endodontic treatment. This set consists of the rotary files OneFile 25/~, Glidepath 10/.05 and Orifice Opener 25/.12, as shown in Fig. 1a. The function of the Orifice Opener 25/.12 files is to create access to the root canals, and to operate, therefore, mainly in the coronal region of the canals. Considering this function, they present a smaller active length and a larger conicity than the others. Considering their dimensions, it was decided not to study their mechanical resistance to fatigue, as the experimental setup would have to be adapted, considering that it is designed to introduce a curvature in the apical region of the endodontic instruments. Besides, since its function is not to shape or clean the root canals, it is not expected that this type of file would be subject to the same level of induced stresses as the other files in the study. As suggested by the name, the function of Glidepath files is to clean, or in other words, remove tissue from the canals and not to shape them, unlike OneFile files. For this reason, they are thinner than the other two, with a tip diameter of 0.1 mm and a taper of 5%, operating predominantly in the intermediate region of the tooth. The OneFile files are larger than the previous ones, due to their function of shaping and widening the root canals in the apical area of the tooth (Fig. 1a). The notation " ~ " indicates a taper with a non-linear variation. This variation is a direct consequence of one of the defining characteristics, namely its cross-section, which has a variable geometry: at the top, it is almost triangular; it is trapezoidal in the middle section; and near the tip, it is rectangular. Its tip diameter is 0.25 mm (Fig. 1b). a b

Fig. 1. (a) HyFlex EDM endodontic files; (b) Dimensional characterization and cross section variation of the Hyflex EDM OneFile 25/~. Regarding experimental tests, it is convenient to evaluate the fatigue resistance of endodontic instruments under conditions with a high degree of adversity so that the results present a specific safety factor by themselves. To this end, the experimental setup designed by Fernandes (2013), and used in other studies, Martins et al. (2017) and Pereira et al. (2018), was used. This setup, shown in Figure 2, was designed to simulate the anatomy of a root canal with severe curvature, with a constant radius of 5 mm, applied along a 45° angle.

Fig. 2. Experimental apparatus simulating a root canal with a radius of curvature of 5 mm along 45º.