INFLUENCE OF THE PHASE TRANSFORMATION BEHAVIOR OF R-PHASE NICKEL-TITANIUM INSTRUMENT ON ITS CYCLIC FATIGUE RESISTANCE AND SHAPING ABILITY

抄録

The purpose of this study was to investigate the influence of phase transformation behavior of R-phase Ni-Ti file on its cyclic fatigue resistance and the root canal shaping ability.

The pre-treated NRT (NRT-N) and NRT files (MANI, Tochigi, Japan) were examined. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were performed to analyze the phase- transformation behavior. The numbers of rotations until fracture for the 06/#25 and 06/#40 files were determined by performing cyclic fatigue resistance tests. A curved root canal model was apically enlarged using the 06/#25, 06/#30, 06/#35, and 06/#40 files. Next, pre- and post-operative images of the model were superimposed. The increases in the outer and inner canal widths of the curvature were measured at 0, 1, 2, 3, 4, and 5 mm from the apex, in order to determine the canal centering abilities of the files.

The XRD patterns showed that the predominant phases in NRT-N and NRT at room temperature were the austenite phase and the R-phase, respectively. The DSC results showed that the reverse transformation finish temperature from the R-phase to the austenite phase in the case of NRT was 40.45±2.63℃, while it was 23.20±3.33℃ for NRT-N. The NRT files exhibited superior cyclic fatigue resistance regardless of the instrument size. When the #40 files were used for apical enlargement, the increase in the outer canal width at 0 mm in the case of the NRT file was smaller than that in the case of the NRT-N file (p < 0.05). When the #30 and #35 files were used, the NRT file exhibited a higher centering ability at 0 mm than did the NRT-N file variety (p < 0.05).

Thus, it was concluded that Ni-Ti file exhibited R-phase had better cyclic fatigue resistance and shaping ability than Ni-Ti files exhibit austenite phase at clinical temperature.