## 4 Discussion  
In the present literature, the evaluation of torsional behavior of NTR is mostly assessed with torsional resistance test [30; 31]. This test could only evaluate the resistance to torsional stresses concentrated in a given point of the instrument under static condition. Therefore, in recent years, many studies tried to investigate the role of torsional stresses dynamically, in order to reproduce the real application of NTR during intracranial instrumentation. Recently, the concept of operative torque was introduced in the literature [10; 29]. The operative torque test ensures a precise recording of the multitude of torsional stresses along all the surfaces of the whole tested instrument. Moreover, this test evaluates the instrument dynamically, taking into account the stresses developed during intracranial instrumentation, from the orifice towards the apex. On the other hand, this real-time measurement is constantly influenced by the time needed and technique used to reach the working length. In the literature, several studies indicate that the anatomy of the root canal can influence the RCTs [32]. During intracranial instrumentation, calcifications, zips, perforations, and resorption significantly lengthen the operating time. In these cases, the mean operative torque (MOT) test could not be the correct evaluation method, as an increase in operating times with low torque values reached could reduce the mean amount of torque to reach the apex [33]. The MOT test evaluation process usually includes a graph that shows all the torque values reached during the RCT (Figure 2). Indeed, as showed in Figure 2, numerous areas with high peaks are noted in the graph. Each peak is the torque records related to one pecking motion. This correspondence between torque recorded and file motion could be described as a rising area, corresponding to the inward action of the file; an apex corresponding to the maximum torque reached by the pecking action; a descend area corresponding to the backward action. It is clear that, evaluating these areas, while the values that rise to reach the peak are gradual, the values that descend from the peak are decreasing in a very short time. These characteristics depend on the technique used. Indeed, while the inward motion is gradually performed due to dental wall resistance to the cutting action of the file, the outward motion of the file is faster and safer. Up to date, the interpretation of this graph has only taken into account the mean operative torque. This calculation takes into account all the torque values reached during instrumentation and is obtained by adding up these values [34]. Besides, since \"the apex of the peak\" is already a sum of all the previous values, this interpretation could be misleading. For this reason, in the present study, a new concept based on the above-mentioned premises has been proposed--the average peak torque value. This numerical value is the mean obtained from the apex value of each peak shown in the graph. Since \"the apex of the peak\" value could be considered as the resultant of all the values preceding it, the APT is the mean of each significant value recorded during root-canal instrumentation (Figure 3). Therefore, the proposed concept could be a more representative record of clinical motion of the files, since it is not influenced by the time needed to perform the treatment and is not influenced by a less torque-consuming outward brushing motion. Moreover, it could be considered a good representation of the real difficulties of the root-canal treatment performed and of the amount of stress accumulated by