Analysis of the Hardness, Nano Indentation and Nano Roughness of NiTi Orthodontic Arch wires

Objective: The aim was to observe the modification of NiTi arch wires mechanical characteristics before and after their use and to highlight that when shape memory and super elasticity are stressed, hardness and roughness are also altered. Materials and methods: Samples of used and new 0.016-0.022- and 0.016-inch archwires made by American Orthodontics (AO), AZDent and Ortho Classic (OC) were retrieved from 192 patients. They were analyzed using an Atomic Force Microscope, a hardness tester and SEM. The arches were classified into various categories: the qualitative factors that include manufacturers, type, usage, age, gender, size and location. The quantitative factors include roughness (nm) and hardness (Vickers). The analysis was divided into three parts, comparison of new arches for all three companies, comparison of used arches between all three and comparison between new and used arches company by company. Results: As expected, the acquired results revealed a decrease in the hardness value (ΔHV~50 Vickers) of the retrieved samples after 4–6-week oral installation compared to the control samples, as well as increased surface roughness and porosity. AZDent brand bows have the smallest drop in hardness. The AO brand arches proved to be the roughest while those manufactured by AZDent were the smoothest. It should also be noted that 0.016-0.022 arches showed the most degradation. Conclusion: We was able to demonstrate that the mechanical properties of NiTi arches (shape memory and super-elasticity) appear to differ significantly before and after intra-oral usage. That mean the old arch wires have fewer mechanical properties than the new one and, in this situation, we need to find a solution to avoid this problem.