## 4 Discussion
In addition, [PERSON] reported the significantly higher cyclic fatigue resistance (\(p<0.01\)) of 25.04 NiTi endodontic rotary files (ProFile, Maillefer, Baillagues, Switzerland) compared with 20.06 NiTi endodontic rotary files (ProFile, Maillefer, Baillagues, Switzerland) and 25.06 NiTi endodontic rotary files (ProFile, Maillefer, Baillagues, Switzerland). These results are in line with those of the present study and highlight the influence of the taper above the apical diameter. [PERSON] et al. also analyzed the cyclic fatigue resistance of rotary pathfinding instruments and reported that the 15.02 NiTi endodontic pathfinding rotary files (HyFlex GPF, Coltene-Whaledent, Allstetten, Switzerland) showed statistically higher cyclic fatigue resistance (\(p<0.05\)) compared with the 12.03 NiTi endodontic pathfinding rotary files (G files, MicroMega, Besancon Cedex, France), 16.04 NiTi endodontic pathfinding rotary files (ProGlider, Dentsply Maillefer, Ballaigues, Switzerland), 16.02 NiTi endodontic pathfinding rotary files (Pathfile, Dentsply Maillefer, Ballaigues, Switzerland), and 15.02 NiTi endodontic pathfinding rotary files (Scout Race, FKG Dentaine, La Chaux-de-Fonds, Switzerland) [38]. These results agreed with those of the present study, and [PERSON] et al. reported that the 25.06 NiTi endodontic reciprocating files (ProDesigner R, Easy, Belo Horizonte, Brazil) showed similar canal transportation and centering abilities after preparation of the second mesiobuccal canals compared with the 25.08 NiTi endodontic reciprocating files (Reciproc, VDW, Munich, Germany); however, the 25.06 NiTi endodontic rotary files (ProDesigner R, Easy, Belo Horizonte, Brazil) removed less volume of the root canal dentine and presented an absence of root canal perforation [39]. [PERSON] et al. also reported that the 35.06 NiTi endodontic reciprocating files (WaveOne Gold, Dentsply Sirona, Ballaigues, Switzerland) significantly increased (\(p<0.05\)) the percentage of root canal dentine removal compared to the 35.05 NiTi endodontic reciprocating files (ProDesigner R, Easy, Belo Horizonte, Brazil); however, no statistically significant differences (\(p>0.05\)) were observed between the apical transportation and percentage of untouched areas of the root canal systems using different apical diameters in curved canals [40]. These results can be summarized in that increasing the mass of the instrument based on an increase in the taper and/or the apical diameter negatively affected the resistance to cyclical fatigue of the instrument; influencing their flexibility and leading the instrumentsto cause excessive root canal dentine removal, apical transport, root perforations, and fractures [27; 41; 42]. The lengths of the fractured files were also measured to determine whether the fracture point would depend on the apical diameter or the taper of the NiTi endodontic rotary instruments, or if it were instead conditioned by the radius of the artificial root canal. No statistically significant differences were observed between the mean length of the fractured files regarding the apical diameter study groups (\(p\) = 0.344) and taper study groups (\(p\) = 0.344); therefore, the length of the fractured files may be associated with the radius of the artificial root canals rather than the apical diameter and taper of the NiTi endodontic rotary instruments. Unfortunately, the limitations of the study prevented the analysis of more tapers and apical diameters and, even with different NiTi alloys, the reciprocating movement and cross-section designs. The study was not developed in a clinical environment due to the difficulty in standardizing the sample.