Comparison of the mechanical properties and surface topography of as-received and as-retrieved Copper-Nickel-Titanium arch wires: An ex-vivo study

Abstract

The mechanical and surface characteristics of Copper NiTi wires following intraoral aging in an important topic. This ex-vivo study is designed to assessthe three most important mechanical properties; torsional stiffness, 3-point bending and surface hardness of the as-received Copper NiTi orthodontic archwires and compare them to the retrieved ones. In this study, 50 round CuNiTi (0.016 inch) and 50 rectangular (0.018×0.025 inch) CuNiTi orthodontic wires (American Orthodontics, Tanzo Copper Nickel Titanium, Sheboygan, WI) were tested. The groups were as follow: 25 as-received 0.016 inch round CuNiTi archwires (group 1), 25 as-retrieved 0.016 inch round CuNiTi archwires (group 2), 25 as-received 0.018×0.025 inch rectangular CuNiTi archwires (group 3), and 25 as-retrieved 0.018×0.025 inch rectangular CuNiTi archwires (group 4). The physical properties of all of the samples were examined using Vickers hardness, bending and torsional tests. The Kolmogorov-Smirnov test was applied to assess the normal distribution of data. An independent t-test was used to compare the variables between the groups. The results showed that the hardness does not significantly differ between the as-received and as-retrieved archwires in both 0.016 and 0.018×0.025 inch archwires (P< 0.05). The bending test of the round wires showed that the values of the activation forces in the as-received ones were significantly higher than those of the as-retrieved (P=0.00). The torsional and bending test results of rectangular wires showed that the amounts of forces exerted from the as-retrieved archwires were significantly higher than the new archwires (P=0.00). Round CuNiTi archwires could be retied in the succeeding visits. However, the bending activation that declines significantly should be took into consideration. On the other hand, since bending and torsion activation of CuNiTi rectangular archwires increased after intraoral use, these wires should be retied cautiously.