Journal Article

Load–deflection characteristics of superelastic and thermal nickel–titanium wires

Elda Gatto, Giovanni Matarese, Guido Di Bella, Riccardo Nucera, Chiara Borsellino and Giancarlo Cordasco

in The European Journal of Orthodontics

Published on behalf of European Orthodontics Society

Volume 35, issue 1, pages 115-123
Published in print February 2013 | ISSN: 0141-5387
Published online October 2011 | e-ISSN: 1460-2210 | DOI: http://dx.doi.org/10.1093/ejo/cjr103
Load–deflection characteristics of superelastic and thermal nickel–titanium wires

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The aim of this study was to investigate the mechanical properties of superelastic and thermal nickel–titanium (NiTi) archwires for correct selection of orthodontic wires. Seven different NiTi wires of two different sizes (0.014 and 0.016 inches), commonly used during the alignment phase, were tested. A three-point bending test was carried out to evaluate the load–deflection characteristics. The archwires were subjected to bending at a constant temperature of 37°C and deflections of 2 and 4 mm.

Analysis of variance showed that thermal NiTi wires exerted significantly lower working forces than superelastic wires of the same size in all experimental tests (P < 0.05). Wire size had a significant effect on the forces produced: with an increase in archwire dimension, the released strength increased for both thermal and superelastic wires. Superelastic wires showed, at a deflection of 2 mm, narrow and steep hysteresis curves in comparison with the corresponding thermal wires, which presented a wide interval between loading and unloading forces. During unloading at 4 mm of deflection, all wires showed curves with a wider plateau when compared with 2 mm deflection. Such a difference for the superelastic wires was caused by the martensite stress induced at higher deformation levels.

A comprehensive understanding of mechanical characteristics of orthodontic wires is essential and selection should be undertaken in accordance with the behaviour of the different wires. It is also necessary to take into account the biomechanics used. In low-friction mechanics, thermal NiTi wires are to be preferred to superelastic wires, during the alignment phase due to their lower working forces. In conventional straightwire mechanics, a low force archwire would be unable to overcome the resistance to sliding.

Journal Article.  4142 words.  Illustrated.

Subjects: Restorative Dentistry and Orthodontics

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