Objectives: To evaluate the effect of intraoral use of three brands of nickel titanium archwires on their mechanical properties and crowding relief ability. Methods: Three groups (n=39) of 0.016” round NiTi archwires: Dentaurum (A), American Orthodontics (B) and IMD Orthodontics (C) were subdivided according to the intervention (n=13) into: As-received, no intervention (subgroup 1), in-vivo (subgroup 2), and in-vitro (subgroup 3). Plateau slope, resilience, and elastic modulus of all wires were tested using a universal testing machine. The relief of crowding following intraoral use for 8 weeks was assessed using Little’s irregularity index. Results were significant at p ≤ 0.05. Results: For all NiTi brands, the highest plateau slope value; among the subgroups, was recorded following the intraoral use (in-vivo). For the in-vivo wires (subgroup 2), the Dentaurum wires revealed the lowest plateau slope value (0.258 N/mm ±0.032) while the IMD wires revealed the lowest resilience values (36.24 J.mm-3 ±0.6). There was no significant difference in the modulus of elasticity of wires between all 3 subgroups. The Little’s irregularity index decreased over time, and the difference between the groups was not significant. No significant difference was found between the groups in terms of inter-canine width.