## 4 Discussion  
The results of this study reject the null hypothesis (H\({}_{0}\)) that the length of CM Gold wire and CM Blue wire NiTi alloy endodontic rotary files has no effect on their dynamic cyclic fatigue resistance. The results derived from the present study indicated that the rotary file length negatively impacts the resistance to fracture of NiTi alloy endodontic rotary files. It is, therefore, recommended that clinicians properly select the instrument length in relation to the root canal system length, paying closer attention to those cases that require long NiTi alloy \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Study Group** & \(n\) & **Mean** & **SD** & **Minimum** & **Maximum** \\ \hline
31 mm & 10 & 358.33  & 38.21 & 302.50 & 412.60 \\
25 mm & 10 & 420.78  & 5.83 & 413.00 & 431.10 \\
21 mm & 10 & 485.12  & 43.43 & 399.10 & 538.10 \\
17 mm & 10 & 577.39  & 40.26 & 502.70 & 632.60 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Descriptive analysis of time to failure (seconds). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Study** & \multicolumn{3}{c}{**Weibull Shape (\(\beta\))**} & \multicolumn{3}{c}{**Weibull Scale (\(\eta\))**} \\ \cline{2-9}
**Group** & **Estimate** & **St Error** & **Lower** & **Upper** & **Estimate** & **St Error** & **Lower** & **Upper** \\ \hline
31 mm & 11.2531 & 2.8108 & 6.8970 & 18.3606 & 374.8087 & 11.1397 & 353.5990 & 397.2905 \\
25 mm & 76.9101 & 18.0821 & 48.5131 & 121.9290 & 423.5920 & 1.8497 & 419.9820 & 427.2329 \\
21 mm & 15.8995 & 4.1752 & 9.5030 & 26.6016 & 502.6726 & 10.4693 & 482.5664 & 523.6165 \\
17 mm & 18.7645 & 4.7630 & 11.4097 & 30.8603 & 594.4943 & 10.5473 & 574.1773 & 615.5303 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Weibull statistics of the time to failure for each study group. endodontic rotary files as there is more surface in contact and stress and, therefore, the concentration of cumulative stress is greater. The fracture mechanisms of NiTi alloy endodontic rotary files are of clinical interest because instrument failure can jeopardize good clinical outcomes of root canal treatment [25]. The rates of failure of the NiTi alloy endodontic rotary files can be influenced by a combination of different variables that converge during the root canal shaping procedure. Therefore, while challenging, isolating each variable individually is essential to assess their respective influence on cyclical fatigue. Experimental studies provide a controlled environment in which a clinical setting is reproduced, enabling unique or a reduced number of variables to be analyzed. In addition, further clinical studies are needed to replicate clinical conditions and extrapolate the cyclic fatigue results to a clinical setting. However, it is difficult to homogenize the radius, curvature angle, apical diameter, hardness, and cross-section of the root canals, which can bias the study by introducing additional variables [26]. As a result, custom-made dynamic cyclic fatigue devices can be used to individually analyze the influence of the specific variable under study. Regrettably, there are normative regulations for the characteristics of the custom-made cyclic fatigue devices, nor is there an international standard for testing the behavior of NiTi endodontic rotary instruments with a taper greater than 2% in response to cyclic fatigue [27]. We selected CM Gold wire and CM Blue wire NiTi alloy endodontic rotary files with 6% taper, according to previous studies [21; 22; 23]; moreover, all CM Gold wire and CM Blue wire NiTi alloy endodontic rotary files presented the same taper to avoid including another variable. In addition, a 60\({}^{\circ}\) curvature angle was selected for the custom artificial root canals, according to previous studies [21; 22; 23]. Previous studies highlighted the effect mechanical and performance qualities of NiTi alloy endodontic rotary files have on their cyclic fatigue resistance [28].