Avaliação da resistência à deformação plástica dos fios redondos de níquel-titânio / Evaluation of plastic deformation resistance of nickeltitanium round wires

Resumo As ligas de níquel-titânio (NiTi) possuem elasticidade elevada sem sofrer deformações plásticas permanentes, sendo amplamente indicadas nas primeiras fases do tratamento ortodôntico. O Objetivo deste estudo é avaliar a resistência de fios ortodônticos de NiTi termoativados em relação à deformação plástica. Foram avaliados fios de 6 marcas comerciais (GAC®, Morelli®, American Orthodontics®, Infinity®e 3M®). Primeiramente a partir de modelos prototipados foi simulada a relação entre deformação plástica e deflexão pela distância interbráquetes em 4 níveis de força a 37°C por 30 dias. Um segundo experimento foi realizado através da análise de fotografias padronizadas com diagramas observando o antes e depois de aplicada uma deformação ao fio a diferentes temperaturas. Os resultados do primeiro teste mostraram que todas as marcas comerciais testadas retornaram a sua forma original após sofrer deflexão por 30 dias. O segundo experimento mostrou que os fios da marca GAC® e American Orthodontics® não apresentaram diferenças estatisticamente significativas comparando as medidas do fio antes da deformação, deformado e após aquecimento (fio aquecido). Já os fios das marcas 3M®, Orthometric® e Infinity®, Morelli apresentaram diferenças significantes entre os fios novos e os fios deformados, e entre os fios deformados e os fios aquecidos, porém, não houve diferenças significantes entre os fios novos e aquecidos. Concluiu-se que nenhum fio, em nenhuma magnitude de deflexão aplicada, sofreu deformação plástica (permanente). Assim, todos os fios das marcas comerciais testadas foram considerados satisfatórios para a prática clínica da Ortodontia no que diz respeito à resistência a deformação plástica. (AU)

Abstract Nickel-titanium (NiTi) alloys have high elasticity without suffering permanent plastic deformations, widely indicated in the early stages of orthodontic treatment. This study aims to evaluate the heat-activated NiTi orthodontic wires' resistance to plastic deformation. The wire from 6 commercial brands (GAC®, Morelli®, American Orthodontics®, Infinity®, and 3M®) was evaluated first from prototype models, simulating the relationship between plastic deformation and deflection by the inter bracket distance at four levels of force at 37° C for 30 days. A second experiment was carried out by analyzing standardized photographs with diagrams observing the before and after deformation was applied to the wire at different temperatures. The first test showed that all tested trademarks returned to their original shape after deflecting for 30 days. The second experiment showed that GAC® and American Orthodontics® wires did not present statistically significant differences comparing the wire measurements before deformed deformation and after heating (heated wire). On the other hand, 3M®, Orthometric® and Infinity®, Morelli wires showed significant differences between new and deformed wires and between twisted and heated wires; however, there were no significant differences between new and heated wires. It was concluded that no wire, at any magnitude of applied deflection, suffered plastic (permanent) deformation. Thus, all wires of the commercial brands tested were considered satisfactory for the clinical practice of Orthodontics in terms of resistance to plastic deformation.(AU)

Influence of heat treatment on the mechanical properties of CrNi stainless steel orthodontic wires.

INTRODUCTION: The heat treatment of stainless steel wires is a routine clinical procedure adopted by many dentists in order to relieve the stress caused after performing bends in the archwire. OBJECTIVE: This study aimed to evaluate the influence of heat treatment of stainless steel archwires with a rectangular section of 0.016 x 0.022'-in. METHODS: For analysis of the dimensional stability, the anterior and posterior dimensions of forty 0.016 x 0.022-in stainless steel orthodontic archwires without heat treatment and 30 days after heat treatment were evaluated. For analysis of the mechanical properties, 12 stainless steel wire segments with the same rectangular section without heat treatment and 30 days after heat treatment were tested through tensile strength and strain tests. To evaluate if there were differences between the anterior and posterior dimensions, the results were analyzed by the Student's t-test. To compare the tensile strength and strain between the groups, the ANOVA test was used. The level of significance adopted was 95% (p< 0.05). RESULTS: The heat treatment did not stop the expansion of archwires 30 days after their preparation, and there was no statistical difference in the tensile strength and strain tests with and without heat treatment. CONCLUSION: From the findings of this study, it can be conclude that the mechanical behavior of heat-treated stainless steel archwires is similar to that of archwires not subjected to heat treatment.

Influence of heat treatment on the mechanical properties of CrNi stainless steel orthodontic wires

ABSTRACT Introduction: The heat treatment of stainless steel wires is a routine clinical procedure adopted by many dentists in order to relieve the stress caused after performing bends in the archwire. Objective: This study aimed to evaluate the influence of heat treatment of stainless steel archwires with a rectangular section of 0.016 x 0.022'-in. Methods: For analysis of the dimensional stability, the anterior and posterior dimensions of forty 0.016 x 0.022-in stainless steel orthodontic archwires without heat treatment and 30 days after heat treatment were evaluated. For analysis of the mechanical properties, 12 stainless steel wire segments with the same rectangular section without heat treatment and 30 days after heat treatment were tested through tensile strength and strain tests. To evaluate if there were differences between the anterior and posterior dimensions, the results were analyzed by the Student's t-test. To compare the tensile strength and strain between the groups, the ANOVA test was used. The level of significance adopted was 95% (p< 0.05). Results: The heat treatment did not stop the expansion of archwires 30 days after their preparation, and there was no statistical difference in the tensile strength and strain tests with and without heat treatment. Conclusion: From the findings of this study, it can be conclude that the mechanical behavior of heat-treated stainless steel archwires is similar to that of archwires not subjected to heat treatment.

RESUMO Introdução: o tratamento térmico de fios de aço inoxidável é um procedimento clínico rotineiro adotado por muitos cirurgiões-dentistas para aliviar o estresse causado após a confecção de dobras no fio. O presente estudo avaliou a influência do tratamento térmico em fios de aço inoxidável com secção retangular de 0,016'' x 0,022''. Métodos: para análise da estabilidade dimensional, foram avaliadas as dimensões anteriores e posteriores de 40 arcos ortodônticos de aço inoxidável de 0,016'' x 0,022'' sem tratamento térmico e 30 dias após o tratamento térmico. Para análise das propriedades mecânicas, 12 segmentos de fio de aço inoxidável com a mesma secção retangular sem tratamento térmico e 30 dias após o tratamento térmico foram analisadas por testes de resistência à tração e tensão. Para verificar se houve diferenças entre as dimensões anteriores e posteriores, os resultados foram analisados pelo teste t de Student. Para comparar a resistência à tração e tensão entre os grupos, foi utilizado o teste ANOVA. O nível de significância adotado foi 95% (p< 0,05). Resultados: o tratamento térmico não interrompeu a expansão dos fios 30 dias após seu preparo, e não houve diferença estatística nos testes de resistência à tração e tensão com e sem o tratamento térmico. Conclusão: pelos achados desse estudo, conclui-se que o comportamento mecânico de fios submetidos a tratamento térmico é semelhante ao de fios de aço não submetidos ao tratamento térmico.

Effects of R-Phase on Mechanical Responses of a Nickel-Titanium Endodontic Instrument: Structural Characterization and Finite Element Analysis.

The effects of the presence of the R-phase in a near-equiatomic NiTi alloy on the mechanical responses of an endodontic instrument were studied by using finite element analysis. The input data for the constitutive model in the simulation were obtained by tensile testing of three NiTi wires: superelastic austenite NiTi, austenite + R-phase NiTi, and fully R-phased NiTi. The wires were also characterized by X-ray diffraction and differential scanning calorimetry. A commercially available endodontic instrument was scanned using microcomputed tomography, and the resulting images were used to build the geometrical model. The numerical analyses were performed in ABAQUS using load and boundary conditions based on the ISO 3630-1 specification for the bending and torsion of endodontic instruments. The modeled instrument containing only R-phase demanded the lowest moment to be bent, followed by the one with mixed austenite + R-phase. The superelastic instrument, containing essentially austenite, required the highest bending moment. During bending, the fully R-phased instrument reached the lowest stress values; however, it also experienced the highest angular deflection when subjected to torsion. In summary, this simulation showed that NiTi endodontic instruments containing only R-phase in their microstructure would show higher flexibility without compromising their performance under torsion.

Comparison of the mechanical behavior between controlled memory and superelastic nickel-titanium files via finite element analysis.

INTRODUCTION: The aim of this study was to evaluate the flexibility and torsional stiffness of a controlled memory (CM) nickel-titanium (NiTi) file and compare its mechanical responses with those of a superelastic NiTi file with the same geometry using finite element simulation. METHODS: A commercially available instrument with a tip size of 30 and a 0.06 taper was selected for this study. The geometric model for finite element analysis was generated by micro-computed tomographic scanning, and the data for the constitutive model of controlled memory NiTi were obtained from the literature. The numeric analysis was performed in ABAQUS (SIMULIA, Providence, RI) with boundary conditions that were based on the ISO 3630-1 specification. RESULTS: The CM NiTi file exhibited the least bending moment and maximum stress value (523 MPa) under 45° bending simulation. However, the least torsional stiffness was calculated for this same instrument. CONCLUSIONS: The higher flexibility and potential fatigue resistance of the CM NiTi files were confirmed, indicating that this new technology represents an improvement in the mechanical behavior of the rotary NiTi files.