## 3 Results  
### Mechanical Tests  
K3 XF displayed the highest bending resistance (1.5 \(\pm\) 0.2 N cm), followed by ProFile (1.3 \(\pm\) 0.2 N cm) and ProTaper Gold (1.3 \(\pm\) 0.1 N cm), with V Taper 2H exhibiting the lowest value (0.7 \(\pm\) 0.04 N cm) (Figure 2A, Table 2). ProFile exhibited the highest buckling resistance (8 \(\pm\) 0.8 N), whereas K3 XF (3.7 \(\pm\) 0.4 N) and V Taper 2H (3.6 \(\pm\) 0.4 N) (Figure 2B, Table 2) had the lowest. HyFlex CM (784 \(\pm\) 65) exhibited the highest NCF, followed by ProfaTaper Gold (686 \(\pm\) 64) and V Taper 2H (602 \(\pm\) 41) (Figure 2C, Table 2). K3 XF exhibited the lowest NCF value (319 \(\pm\) 33). Moreover, V Taper 2H (745 \(\pm\) 56 degrees) and ProFile (686 \(\pm\) 42 degrees) had the highest ARF, whereas ProTaper Gold showed the lowest (396 \(\pm\) 39 degrees) (Figure 2D, Table 2). ProTaper Gold (15.6 \(\pm\) 1.3 N mm) possessed the highest UTS, whereas HyFlex CM had the lowest (8.5 \(\pm\) 0.7 N mm) (Figure 2E, Table 2). Furthermore, K3 XF displayed the highest stiffness (0.16 \(\pm\) 0.02 N mm/degrees), whereas HyFlex CM had the lowest (0.03 \(\pm\) 0.004 N mm/degrees) (Figure 2F, Table 2). Figure 3 depicts representative curves of torque versus rotation angle plotted using data from the torsional resistance test.  
Figure 2: Mechanical test results. (**A**) Bending resistance, (**B**) buckling resistance, (**C**) number of cycles to failure, (**D**) angle of rotation to fracture, (**E**) ultimate torsional strength, and (**F**) stiffness. Groups under the same name bar have no significant difference.  
The fractured surfaces of the files reveal microcracks in the peripheral region and multiple striations near the microcracks as a result of cyclic fatigue resistance testing (Figure 4). The magnified images of the cross-sections show mixed zones comprising fatigue striations and dimple clusters (Figure 4(A2-G2)). The lateral surfaces of the fractured NiTi files display brittle fractures with cracks (Figure 4). Plastic deformation patterns, such as flute unwinding, were not visible in the fractured files.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **ProFile** & **ProTaper Gold** & **ProfaTaper Gold** & **HyFlex CM** & **2 Shape** & **V Taper 2H** & **K3 XF** \\ \hline \
\begin{tabular}{c} Bending \\ resistance (N cm) \\ \end{tabular} & \(1.3\pm 0.2\)  & \(1\pm 0.1\)  & \(0.9\pm 0.1\)  & \(1.5\pm 0.2\)  & \(6.3\pm 0.9\)  & \(4.8\pm 0.5\)  & \(3.6\pm 0.4\)  \\ \hline
\begin{tabular}{c} Number of cycles \\ to failure \\ \end{tabular} & \(424\pm 45\) [FOOTNOThe fractured surfaces after the torsional resistance tests exhibit multiple circular abrasion marks at the center of the cross-section (Figure 5(A2-G2). The lateral surfaces of the fractured NiTi files display ductile fractures with plastic deformation (Figure 5).  
Figure 4: SEM images after cyclic fatigue resistance testing of (**A**) ProFile, (**B**) ProTaper Gold, (**C**) ProfaTaper Gold, (**D**) HyFlex CM, (**E**) V Taper 2H, (**F**) 2 Shape, and (**G**) K3 XF. (**A1–G1**) Fractured surfaces (\(\times\)200); (**A2–G2**) magnified (\(\times\)1000) images of the fractured surfaces at the arrow regions in (**A1–G1**), showing fatigue striations; (**A3–G3**) lateral surfaces (\(\times\)250); (**A4–G4**) magnified (\(\times\)1000) views of fractured surfaces at the arrow regions in (**A3–G3**), showing cracks.