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. 2017 Feb;22(1):38-46.
doi: 10.1590/2177-6709.22.1.038-046.oar.

Deformation of nickel-titanium closed coil springs: an in vitro study

Camilla Ivini Viana Vieira  1 , José Maurício Dos Santos Nunes Reis  2 , Luiz Geraldo Vaz  2 , Lídia Parsekian Martins  1 , Renato Parsekian Martins  1
Affiliations

Deformation of nickel-titanium closed coil springs: an in vitro study

Camilla Ivini Viana Vieira et al. Dental Press J Orthod. 2017 Feb.

Abstract
in English, Portuguese

Objective: The aim of this paper was to determine the amount of deformation in four commercial brands of nickel-titanium closed springs.

Methods: A total of 130 springs were divided into 13 subgroups, according to their features and manufacturers (Morelli, Orthometric, Ormco and GAC) and activated from 100% to 1000% of the effective length of the nickel-titanium portion present at the spring, at 37 °C. Deactivation data were plotted and deformation was found graphically. The values were compared by analysis of variance and Tukey's post-hoc test.

Results: Springs manufactured by Morelli had the same amount of deformation when they were activated up to 700% of Y activation; springs by Orthometric had the same amount of deformation up to 600-700% of Y; springs by Ormco had the same amount of deformation up to 700-800% of Y; and finally, the majority of springs by GAC had similar deformation up to 800%-1000% of activation. All springs tested could be activated up to 700% without rupture.

Conclusions: Most subgroups were similarly deformed up to 700% of activation, without rupture of springs. Subgroups 4B, 4C, 4D and 4E showed the same amount of deformation up to 1000% of activation without any rupture at all.

Objetivo:: o objetivo desse trabalho foi determinar a deformação em molas fechadas de níquel-titânio de quatro marcas comerciais.

Métodos:: cento e trinta molas foram divididas em treze subgrupos, de acordo com suas características e fabricantes (Morelli, Orthometric, Ormco e GAC), com ativação entre 100% e 1.000% do comprimento efetivo de níquel-titânio presente na mola (Y), a 37 °C. Dados de desativação foram coletados e a deformação foi obtida de forma gráfica. Os valores foram comparados por meio de análise de variância e teste post-hoc de Tukey.

Resultados:: as molas da Morelli apresentaram a mesma quantidade de deformação considerando-se 700% de ativação de Y; as molas da Orthometric tiveram a mesma quantidade de deformação até 600-700% de Y; as molas da Ormco tiveram a mesma quantidade de deformação até 700-800% de Y; e, por fim, a maioria das molas da GAC apresentou deformação semelhante até 800-1.000% de ativação. Todas as molas testadas puderam ser ativadas até 700% sem ruptura.

Conclusões:: a maioria dos subgrupos se deformou de maneira semelhante até 700% de ativação, sem ruptura das molas. Os subgrupos 4B, 4C, 4D e 4E demonstraram a mesma quantidade de deformação até 1.000% de ativação, sem nenhuma ruptura.

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Conflict of interest statement

" The authors report no commercial, proprietary or financial interest in the products or companies described in this article.

Figures

Figure 1
Figure 1. Nickel-titanium closed coil spring, the X dimension corresponds to the total length of the spring and the Y dimension corresponds to the length of the nickel-titanium portion.
Figure 2
Figure 2. Nickel-titanium closed coil spring, before activation (B) and after 900% of activation (A). After heating it above a certain temperature (Af), the martensitic deformation will resume due to the shape memory effect.
Figure 3
Figure 3. Space closure after extraction of first premolars where a nickel titanium spring was attached to a hook from the first molar to a hook distal to the canine (23 mm distance), remaining active even after space closure (minus 7 mm of pre-molar space).
Figure 4
Figure 4. A) Load/deflection graph for the springs of the subgroup 1A activated at 900% of Y (20.7 mm of activation or 29.3 mm if the size of the spring is accounted). The blue box corresponds to the distance between the hook of the first molar and a hook distal to the upper canine (minus size of the spring), as in Figure 3 (23 mm minus X). Note that to take full advantage of the springs' SE properties, an increase of approximately 3 mm in the eyelets (not in nickel titanium portion) would be required in order to maintain the force in the SE plateau. That would shift the blue box to the left the same 3 mm. B) Same situation on the subgroup 1B, however, full SE capability would not be achieved in last 2 mm or so of space closure, since the force would start to decrease due to lack of stress.
Figure 5
Figure 5. A 15- mm long nickel-titanium spring (nickel-titanium portion with 9.8 mm), activated 9.8mm. A spam of activation from the hook of a first molar to the canine, from 23 mm to 16 mm (similar to Figure 3), is shown by the blue arrow. In this case, due to the springs length, that activation would account 8 mm, deactivating to 1 mm after space closure. Note that no superelasticity will not exist in this spring at this activation.
Figure 6
Figure 6. A 7 -mm long nickel-titanium spring (2.3 mm of nickel-titanium portion) activated approximately 16 mm, which would result in an activation of 23 mm. It can be observed that due to the shape of the load-deflection graph, the pseudo-plateau area, or the near-to-constant force, of the spring would not be used during a 7 mm space closure.
Figure 7
Figure 7. A 9- mm long nickel-titanium spring (3.9 mm of nickel-titanium portion) activated 23.4 mm, or 600% the length of its SE material. A spam of activation from 14 mm to 7 mm is shown by the blue arrow. Note that a pseudo-plateau can be used in this situation only if the spring is overactivated 10 mm beyond its affixation. The amount of overactivation will depend on the spring's total length, the length of nickel-titanium portion, and the interbracket distance.
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