Mechanical Properties of Commercial NiTi Orthodontic Archwires

The use of NiTi wires as an initial wire in the first stage in orthodontics treatment has been greatly favored by the low modulus of elasticity, high springback, and wide force-delivery range demonstrated by the alloys. During the early leveling stages of treatment, more physiologically bone response and acceptable tooth movement can be achieved if light, continuous forces and these forces can be provided by low-stiffness archwires. Minor differences in the production process may contribute to the variation in the behavior of these wires. Objective: The objective of the present work is to investigate the flexural behavior of superelastic NiTi orthodontic wires under a three-point bending test of different commercially available lots from the same manufacturer. Materials and methods: Thirty six specimens of NiTi archwire of three brands (3M/Unitek - USA; Morelli - Brazil and Orthosource - USA) represented by three different lots were divided in 9 group of 6 specimens. The wires were submitted bending test according to ISO 15841 standard. One-way ANOVA and Tukey multiple comparison test was used. Results: The results suggest that significant differences were present between 3M/Unitek lots. Although no differences were expected once lots of the same manufacturer were representative of the same NiTi wire, differences were statistically revealed by Tukey post-hoc test between groups 3M and Morelli. A possible explanation of this result could be changes in composition and mechanical manufacturing process. Although this difference between 3M lots, the loading and unloading plateaus indicate patterns of constant forces which are suitable for most clinical applications. Conclusions: This method is effective to disclose differences between different commercially available superelastic NiTi archwires. The differences showed between three lots could be result of a minimal production process alteration. All groups showed flexural properties which are suitable for most clinical applications.