Methods: The Ti-Nb-Al alloy wire or an orthodontic superelastic wire (Ni-Ti alloy wire) was set in the mouth of male Wistar-strain rats at 6 weeks of age, and orthodontic lingual movement of maxillary first molars was performed with an initial load of 15 gf as described by Saito et al. (1997). Impressions of each rat's maxilla were taken at 0, 1, 3, 7, 10, 14, 17, 21 days after application of the orthodontic force. Precise models were made form the impressions, and then the amount of the tooth movement was measured. The morphological changes in alveolar bone were also observed by microfocus X-ray computed tomography (SMX-225 CT, Shimazu Corp., Kyoto).
Results: There was no significant difference in the amount of movement between the Ti-Nb-Al alloy group and the Ni-Ti alloy group. Microfocus X-ray CT observation did not reveal any difference in morphological changes between two groups, either. The Ti-Nb-Al alloy used in this study have mechanical properties which are equivalent to those of a Ni-Ti alloy such as 5.8% maximum recovery strain and 100% shape recovery rate. Our results indicate that the Ti-Nb-Al alloy wire can be a comparable orthodontic wire to Ni-Ti alloy wires.
Conclusion: The newly developed Ni-free Ti-Nb-Al SMA, which has higher biocompatibility, could be a useful orthodontic material.