## 4 Discussion  
The instrumentation phase of root canals is considered to be one of the most important steps in endodontics [32] because it facilitates the passage of irrigants along its entire length and geometrically configures the canal for a correct, three-dimensional obturation [33]. In recent decades, to perform instrumentation, numerous rotary systems have emerged, which advocate simplifying the task for clinicians, minimizing errors during instrumentation [23] and preserving root-canal anatomy during preparation [34]. The alloys and geometry of the instruments have evolved over the years to give them more flexibility, cutting ability, and resistance to fracture [35]. The incorporation of rotary instrumentation leads to faster treatment times and lower complication rates [36; 37]. Previous studies have shown that the introduction of rotary endodontics provides students with greater confidence and safety when performing treatments [38]. With the aim of better preparing students to perform endodontic treatments on real patients, the Universidad Europea de Madrid advocates the introduction of rotary instrumentation in preclinical practice in order to minimize procedural errors on the one hand, and on the other hand, to allow for a greater number of canals to be performed in the same preclinical practice time, thus reducing the learning-curve time [39]. The starting point was those students who had never prepared canals with rotary instrumentation. These inexperienced students were chosen because they had no acquired vices from previous rotary endodontic training, so they could strictly follow the manufacturer's instructions. It was assumed that procedural errors could occur (ledges, apical transportations, blockages, etc.). The objective was to test the files in an unfavorable situation and to verify if they were able to instrument the canals in an adequate way. Therefore, we wanted to evaluate whether improvements in alloys would enable any \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Mann–Whitney** & **Wilcoxon W** & **Z** & **Sig.** \\  & **U** & & & \\ \hline
0 mm inner & 589.000 & 1450.000 & \(-1.555\) & 0.120 \\
0 mm outer & 489.000 & 1155.000 & \(-2.542\) & 0.011 \({}^{\text{-P}}\) \\
1 mm inner & 760.500 & 1621.500 & \(-0.378\) & 0.705 \\
1 mm outer & 441.500 & 1221.500 & \(-3.446\) & 0.001 \({}^{\text{-P}}\) \\
2 mm inner & 807.500 & 1668.500 & \(-0.118\) & 0.906 \\
2 mm outer & 490.500 & 1310.500 & \(-3.114\) & 0.002 \({}^{\text{-P}}\) \\
3 mm inner & 786.000 & 1647.000 & \(-0.321\) & 0.748 \\
3 mm outer & 495.500 & 1315.500 & \(-3.066\) & 0.002 \({}^{\text{-P}}\) \\
4 mm inner & 650.000 & 1511.000 & \(-1.607\) & 0.108 \\
4 mm outer & 541.500 & 1361.500 & \(-2.632\) & 0.008 \({}^{\text{-P}}\) \\
5 mm inner & 506.500 & 1367.500 & \(-2.966\) & 0.003 \({}^{\text{-B}}\) \\
5 mm outer & 436.000 & 1256.000 & \(-3.631\) & 0.000 \({}^{\text{-P}}\) \\
6 mm inner & 396.000 & 1257.000 & \(-4.041\) & 0.000 \({}^{\text{-B}}\) \\
6 mm outer & 296.000 & 1116.000 & \(-4.954\) & 0.000 \({}^{\text{-P}}\) \\
7 mm inner & 438.500 & 1299.500 & \(-3.652\) & 0.000 \({}^{\text{-B}}\) \\
7 mm outer & 263.500 & 1083.500 & \(-5.260\) & 0.000 \({}^{\text{-B}}\) \\
8 mm inner & 631.000 & 1492.000 & \(-1.796\) & 0.073 \\
8 mm outer & 407.500 & 1227.500 & \(-3.898\) & 0.000 \({}^{\text{-P}}\) \\
9 mm inner & 550.500 & 1370.500 & \(-2.553\) & 0.011 \({}^{\text{-P}}\) \\
9 mm outer & 648.500 & 1468.500 & \(-1.621\) & 0.105 \\ \hline \hline \end{tabular} \({}^{\star}\)_p_-value \(<\) 0.05—statistically significant, \({}^{\text{-P}}\)\(p\)-value \(<\) 0.001—highly statistically significant. \({}^{\text{-P}}\) = PTG \(>\) BS, \({}^{\text{B}}\) = BS \(>\) PTG.  
\end{table} 
Table 2: Amounts of resin removed per system. practitioner with no experience in rotary endodontics to perform the instrumentation of simulated canals without altering the anatomy of the artificial canal. Thus, this study was carried out with files of the same section but manufactured with different alloys.