# Torsional Fracture Resistance of Niti Rotary Glide Path Files under Flexural Stress
## 3 Results
### Torsional Fracture Resistance  
Ultimate strengths (N cm) were significantly higher (\(p<0.001\)) under flexural stress than in straight mode for RaCe Evo and HyFlex EDM (Table 2). Distortion angles increased significantly (\(p<0.001\)) under flexural stress for RaCe Evo, HyFlex EDM, TruNatomy Glider, and V Taper 2H but were not significantly different than in straight mode for PathFile and RaCe (Table 2).  
When comparing between files, V Taper 2H showed the highest ultimate strength, and PathFile had the lowest in both test modes (Table 2). The ultimate strength of TruNatomy Glider was higher than those of PathFile and RaCe and lower than that of V Taper 2H.  
The distortion angle was highest for V Taper 2H, followed by RaCe Evo and TruNatomy Glider in both test modes (Table 3). RaCe showed the lowest distortion angle in both test modes.  
Graphs of the torque and distortion angle were plotted for representative samples in each group (Figure 4). As soon as the file was rotated, the torque increased in proportion to the distortion angle, which is regarded as elastic deformation, and the elastic limit of each file is marked in the graph. After that, the torque was found to increase unevenly, the decrease and increase were repeated, and the deformation between the elastic limit and failure point was regarded as plastic deformation. The amount of plastic deformation increased with the flexural stress (Figure 4).  
SEM images of the lateral surface of the fractured files showed a typical ductile fracture pattern for the tested instruments (Figure 5). Circular abrasion marks were observed in the central area of the fractured surfaces for all the samples (Figure 6). There was no difference in the fractographic patterns in the microscopic images according to the test mode.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **PathFile** & **RaCe** & **RaCe Evo** & \begin{tabular}{c} **HyFlex** \\ **EDM** \\ \end{tabular} & \
\begin{tabular}{c} **TruNatomy** \\ **Glider** \\ \end{tabular} &
\begin{tabular}{c} **V Taper** \\ **2H** \\ \end{tabular} \\ \hline \multirow{2}{*}{**Straight**} & 0.213 & 0.225 & 0.250 & 0.293 & 0.285 & 0.404 \\  & (0.030) \({}^{\text{a}}\) & (0.039) \({}^{\text{a}}\) & (0.060) \({}^{\text{a,b}}\) & (0.051) \({}^{\text{b}}\) & (0.063) \({}^{\text{b}}\) & (0.079) \({}^{\text{c}}\) \\ \hline \multirow{2}{*}{**Flexural**} & 0.227 & 0.233 & 0.348 & 0.348 & 0.307 & 0.397 \\  & (0.024) \({}^{\text{a}}\) & (0.056) \({}^{\text{a}}\) & (0.055) \({}^{\text{b,c,*}}\) & (0.019) \({}^{\text{b,c,*}}\) & (0.061) \({}^{\text{b}}\) & (0.081) \({}^{\text{c}}\)Figure 4: Representative torque (N cm)-angle (degrees) curves from the torsional resistance test. The curves of each file brand were depicted in both straight mode and flexural mode. (**A**) PathFile; (**B**) RaCe; (**C**) RaCe Evo; (**D**) HyFlex EDM; (**E**) TruNatomy Glider; (**F**) V Taper 2H. An arrow indicates elastic limit in each test mode.  
Figure 5: SEM images of the fractured instruments. Lateral surfaces of PathFile (**A**), RaCe (**B**), RaCe Evo (**C**), HyFlex EDM (**D**), TruNatomy Glider (**E**), and V Taper 2H (**F**), which fractured in straight mode. Lateral surfaces of PathFile (**G**), RaCe (**H**), RaCe Evo (**I**), HyFlex EDM (**J**), TruNatomy Glider (**K**), and V Taper 2H (**L**), which fractured in flexural mode. Plastic deformation included unwinding and overwinding of instruments (original magnification \(\times\)100).  
Figure 6: SEM images of the fractured surfaces of instruments. The left two images in each row show fractured surface of instrument in straight mode and its magnified view of the central area; the right two images are fractured surface of instrument in flexural mode and its magnified view. **(A)** PathFile; **(B)** RaCe; **(C)** RaCe Evo; **(D)** HyFlex EDM; **(E)** TruNatomy Glider; **(F)** V Taper 2H (original magnification \(\times\)1000, \(\times\)5000).