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. 2016 Jun;21(3):46-55.
doi: 10.1590/2177-6709.21.3.046-055.oar.

Superelasticity and force plateau of nickel-titanium springs: an in vitro study

Camila Ivini Viana Vieira  1 , Sergei Godeiro Fernandes Rabelo Caldas  2 , Lídia Parsekian Martins  3 , Renato Parsekian Martins  4
Affiliations

Superelasticity and force plateau of nickel-titanium springs: an in vitro study

Camila Ivini Viana Vieira et al. Dental Press J Orthod. 2016 Jun.

Abstract
in English, Portuguese

Objective: This paper analyzed whether nickel-titanium closed coil springs (NTCCS) have a different superelastic (SE) behavior according to activation and whether their force plateau corresponds to that informed by the manufacturer.

Methods: A total of 160 springs were divided into 16 subgroups according to their features and activated proportionally to the length of the extensible part (NiTi) of the spring (Y). The force values measured were analyzed to determine SE rates and force plateaus, which were mathematically calculated. These plateaus were compared to those informed by the manufacturer. Analysis of variance was accomplished followed by Tukey post-hoc test to detect and analyze differences between groups.

Results: All subgroups were SE at the activation of 400% of Y length, except for: subgroups 4B and 3A, which were SE at 300%; subgroups 4E and 4G, which were SE at 500%; and subgroup 3C, which was SE at 600%. Subgroup 3B did not show a SE behavior. Force plateaus depended on activation and, in some subgroups and some activations, were similar to the force informed.

Conclusions: Most of the springs showed SE behavior at 400% of activation. Force plateaus are difficult to compare due to lack of information provided by manufacturers.

Objetivo:: o presente artigo analisou se as molas helicoidais fechadas de níquel-titânio apresentam superelasticidade (SE), de acordo com a ativação, e se o platô de força medido corresponde ao informado pelo fabricante.

Material e Métodos:: 160 molas foram divididas em 16 subgrupos, de acordo com suas características, e foram ativadas proporcionalmente ao comprimento da parte extensível (NiTi) da mola (Y). Os valores de força obtidos foram analisados para determinar as taxas de SE e os platôs de força, os quais foram calculados matematicamente - sendo esses platôs comparados aos informados pelos fabricantes. Uma análise de variância foi realizada, seguida do teste post-hoc de Tukey, para detectar e analisar as diferenças entre os grupos.

Resultados:: todos os subgrupos apresentaram SE em ativação de 400% do comprimento Y, com exceção dos subgrupos 4B e 3A (que apresentaram SE a 300%), dos subgrupos 4E e 4G (com SE a 500%) e do subgrupo 3C (que apresentou SE na ativação de 600%). O subgrupo 3B não apresentou comportamento superelástico. Os platôs de força dependeram da ativação e em alguns subgrupos, em determinadas ativações, foram semelhantes à força informada pelo fabricante.

Conclusões:: a maioria das molas apresentou comportamento superelástico na ativação de 400%. Os platôs de força são difíceis de ser comparados, devido à falta de informações por parte dos fabricantes.

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Figures

Figure 1
Figure 1. Nickel-titanium coil spring, the X dimension corresponds to the total length of the spring (from eyelet to eyelet, made os stainless steel) and the Y dimension is the length of the extensible part (NiTi) of the spring.
Figure 2
Figure 2. General load/deflection graph of a superelastic (SE) alloy. Indication of the inflection points and SE plateau (± 20%) and the first and second derivative (dF1/dD1 and dF2/dD2, respectively). Source: adapted from Segner et al,13 1995.
Figure 3
Figure 3. Glass aquarium attached to the testing machine.
Figure 4
Figure 4. Load/deflection graph of one average spring of Group 1 (100 to 1000% of activation). On the axis of deflection, the amount of activation of the springs (mm) can be seen on the first line (A), the amount of activation corresponding to Y's percentage is on the second one (B), and the amount of activation of the springs added to its size is on the third line (C).
Figure 5
Figure 5. Load/deflection graph of one average spring of subgroup 2A (100 to 1000% of activation) and of subgroup 2B (100 to 900% of activation). On the axis of deflection, the amount of activation of the springs (mm) can be seen on the first line (A), the amount of activation corresponding to Y's percentage is on the second one (B), and the amount of activation of the springs added to its size is on the third line (C).
Figure 6
Figure 6. Load/deflection graph of one average spring of each of the subgroups of Group 3 (100 to 1000% of activation). On the axis of deflection, the amount of activation of the springs (mm) can be seen on the first line (A), the amount of activation corresponding to Y's percentage is on the second one (B), and the amount of activation of the springs added to its size is on the third line (C).
Figure 7
Figure 7. Load/deflection graph of one average spring of each of the subgroups of Group 4 (100 to 1000% of activation). On the axis of deflection, the amount of activation of the springs (mm) can be seen on the first line (A), the amount of activation corresponding to Y's percentage is on the second one (B), and the amount of activation of the springs added to its size is on the third line (C).
Figure 8
Figure 8. Graph of stress/temperature of SE alloys. Mf = martensitic final temperature, Ms = martensitic initial temperature, As = austenitic initial temperature, Af = austenitic final temperature, Md = temperature in which it is not possible for martensitic transformation to occur through stress
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