Evaluation of Mechanical Properties of Austenite-phase and R-phase Ni-Ti Files

Objectives: The purpose of this study was to compare the bending properties, resintance to torsional stress and cyclic fatigue of austenite-phase and R-phase Ni-Ti files with the same file (cross sectional) design.
Methods: K3 (austenite-phase) and K3XF (R-phase) files with sizes of #25/.04 taper, #30/.04 taper, #35/.04 taper, #40/.04 taper and #25/.06 taper, #30/.06 taper, #35/.06 taper, #40/.06 taper were selected for the study (n=10/each files). The bending property of K3 and K3XF files was measured by bending torque test. To evaluate the torsional resistance, the file was twisted until fractured, and then the fracture angle and maximum torque were measured. The number of cycles to failure for each instrument was determined to evaluate the cyclic fatigue resistance. Data was analyzed by Student’s t-test at the significance level of 5%.
Results: On bending torque test, K3XF files showed lower values than K3 files except #40/.06. Torsional bending tests showed K3 files had the larger fracture torque than K3XF except #40/.06, and K3 files had the larger fracture angle than K3XF at #35/.04. K3XF showed superior cyclic fatigue resistance to K3 except #25/.06.
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Conclusions: The results of this experiment indicate K3XF files of R-phase Ni-Ti improved their flexibility and cyclic fatigue resistance compared with K3 files. It supposes that R-phase Ni-Ti files are less torsional strength than austenite-phase in the same file design.