Influência do grau de ativação na deformação plástica de elasticos ortodônticos em cadeia / Influence of the degree of activation on the plastic deformation of orthodontic elastic chain

Objetivo: Avaliar a influência do grau de ativação na deformação plástica de elásticos ortodônticos em cadeia em função do tempo que permaneceram estirados. Método: Foram testadas 72 amostras de cadeia elástica da marca Morelli, tamanho médio cristal, que foram mantidas em um jig confeccionado, especialmente, para este fim, com diferentes graus de ativação, 30%, 50% e 70% dos seus comprimentos iniciais, sendo avaliadas 24 cadeias elásticas para cada grau de ativação. Os elásticos foram mantidos em suas embalagens plásticas originais, como recomendado pelo fabricante, até serem testados. O jig com os elásticos foram conservados em um recipiente plástico contendo saliva artificial e mantidos em uma estufa artesanal com temperatura controlada de 37ºC ± 1ºC por todo o tempo do experimento, sendo removidos deste ambiente somente ao final de 3 semanas de ativação. As medidas dos comprimentos iniciais e finais de seis elos de cada cadeia elástica foram realizadas utilizando-se um paquímetro digital de precisão e o percentual de deformação plástica foi calculado em relação ao comprimento inicial. A comparação entre os valores médios de deformação plástica sofrida pelos elásticos nos diferentes graus de ativação foi realizada estatisticamente com o auxílio do programa SPSS (Statistical Package for Social Sciences), versão 15.0. Resultados: Os valores médios encontrados, 13,89%, 20,66% e 30,68% de deformação plástica, para os diferentes graus de ativação, respectivamente, foram submetidos a teste estatístico análise de variância (ANOVA) com nível de significância de 5%, tendo sido encontrada significância estatística entre os mesmos. Conclusão: O grau de ativação influenciou de forma significativa a deformação plástica sofrida pelos elásticos testados.

Objective: To evaluate the influence of the degree of activation on the plastic deformation of orthodontic elastic chains according to the stretching duration. Methods: Seventy-two samples of medium size crystal orthodontic elastic chains from the commercial brand Morelli were maintained in a custom-made jig with different degrees of activation (30%, 50% and 70%) of their initial lengths, being 24 elastic chains for each degree of activation. The elastics were maintained in their original plastic packages, as recommended by the manufacturer, until the moment of testing. The jig with the elastics were kept in a plastic recipient containing artificial saliva and stored in an artisanal stove with controlled temperature of 37§C ñ 1§C during the whole experiment, being removed only after 3 weeks of activation. The initial and final lengths of 6 rings of each elastic chain were measured using a precision digital caliper and the percentage of plastic deformation in relation to the initial length was calculated. Comparison among the mean values of plastic deformation suffered by the elastics with the different degrees of activation was performed using the SPSS (Statistical Package for Social Sciences) software, version 15.0. Data were analyzed statistically by ANOVA with significance level of 5%. Results: The mean values of plastic deformation for the 30%, 50% and 70% degrees of activation were 13.89%, 20.66% and 30.68%, respectively, with statistically significant difference (p<0.05) among them. Conclusion: The degree of activation influenced significantly the plastic deformation suffered by the elastics evaluated in this study.

Load-deflection characteristics and plastic deformation of NiTi closed coil springs / 대한치과교정학회지

OBJECTIVE: NiTi closed coil springs were reported to have relatively constant unloading forces. However, the characteristics of NiTi closed coil springs from various manufacturers have not been elucidated. The purpose of this study was to compare load-deflection characteristics of various NiTi closed coil springs and to find out the optimal range of extension. METHODS: Seven kinds of NiTi closed coil springs from five manufacturers were tested. Load deflection curves were obtained at extension ranges from 2 mm to 30 mm. Also, springs were kept extended during a 4 week period, and then load deflection curves were obtained again. RESULTS: Sentalloy (Tomy) and Jinsung blue (Jinsung) showed superelasticity in every extension ranges tested and showed plastic deformation of less than 1 mm. Ni-Ti (Ormco) showed superelasticity only after the springs were extended at or more than 10 mm, thereby meaning that clinicians should extend these springs at or more than 10 mm to utilize the superelasticity. Orthonol (RMO) and Nitanium (Ortho Organizers) did not show superelasticity. After 4 weeks of extension, all springs showed plastic deformation less than 1 mm when the extension was at or under 25 mm. CONCLUSIONS: The superelastic behavior of NiTi closed springs were different among various NiTi spring products, and some NiTi closed springs failed to show superelasticity.

Plastic deformation of both forearm bones

A case of acute traumatic bowing or plastic deformation of both forearm bones was described. A discussion of the mechanism of injury, management, and orthopedic implications of traumatic bowing was given