Introduction: This study compared the angular deflection at failure, maximum torque, and toughness of two nickel-titanium (NiTi) instruments under torsional stress: Reciproc (VDW, Munich, Germany) and WaveOne (Dentsply Maillefer, Ballaigues, Switzerland). Two NiTi instruments: Mtwo (VDW) and ProTaper (Dentsply Maillefer) served as controls. Methods: The instruments were subjected to torsional assays to evaluate the maximum torque and angular deflection at failure. A stress-strain (N × mm) curve was plotted using specific software and toughness was calculated as the integral of the area under the curve. Data obtained were statistically evaluated by ANOVA and Student-Newman-Keuls (SNK) test for multiple comparisons, with the significance level set at 5%. Results: Significant difference was observed in the angular deflection at failure for pairwise comparisons between ProTaper and the other instruments (P 0.05). No significant differences were observed in the comparisons between the other instruments (P > 0.05). The maximum torque was ranked as follows: ProTaper > Reciproc > WaveOne > Mtwo; significant differences were observed between all instruments (P 0.05). Differences in toughness were also detected between all instruments tested (P 0.05), except for Reciproc versus WaveOne. Conclusion: The findings from this study revealed that Reciproc and WaveOne displayed similar mechanical behaviour in terms of angular deflection and toughness, typical of ductile metallic materials under torsion. This suggests that both instruments absorb comparable amounts of energy until fracture. Regarding torque, Reciproc exhibited the best results in comparison with WaveOne. Keywords: angular deflection, endodontic instruments, maximum torque, torsional fracture, toughness