Mechanical properties of multi-force vs. conventional NiTi archwires

Mechanical properties along the length of latest generation "multi-force" archwires were measured and compare with commercially available thermally activated and non-thermally activated nickel-titanium (NiTi) archwires.

A modified deflection test was used to produce load/deflection curves for different positions along the lengths of a sample of 114 NiTi archwires composed by thermal NiTi, non-thermal NiTi, two types of multi-force NiTi and one type of multi-force copper archwires of various cross-sections (0.016 × 0.016 inch, 0.016 × 0.022 inch, 0.018 × 0.025 inch and 0.019 × 0.025 inch). The length, slope and mean force expressed were calculated from the resulting unloading plateaus, enabling comparison between types of archwire at different points along their lengths.

Among conventional thermal, conventional nonthermal and multiforce archwires, all parameters investigated were statistically different, whereby the performance of the latter was superior. Multi-force archwires displayed 27% and 31% lighter mean forces in the upper and lower arches, respectively, in addition to 62% and 40% reductions in unloading plateau slope and length, respectively, as compared to conventional CuNiTi wires. Comparison of the different types of multi-force wires tested revealed statistically significant differences in the three parameters, depending on the testing position but irrespective of their cross-section.

Although conventional archwires display identical behaviour along their lengths, as advertised the multi-force archwires do indeed exert a progressive force which differs between anterior, medial and posterior sections. The multi-force wires provide lighter, more prolonged and constant forces than conventional wires without cross-section-dependent variation.