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

abstract 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

Influence of the cranial base flexion on Class I, II and III malocclusions: a systematic review

ABSTRACT Objective: The aim of this study was to perform a systematic review on the morphological characteristics of the skull base (flexion, anterior length and posterior length) and the concomitant development of malocclusions, by comparing differences in dimorphism, ethnicity and age. Methods: The articles were selected by means of electronic search on BBO, MEDLINE and LILACS databases from 1966 to 2016. A qualitative evaluation of the methodologies used on the articles was also performed. Results: Although the literature on this topic is abundant, only 16 articles were selected for the present systematic review. The cranial base angle itself does not seem to play a significant role in the development of malocclusions. In fact, the cranial base angle is relatively stable at the ages of 5 to 15 years. Conclusions: A more obtuse angle at the skull base, in association or not with a greater anterior length of the cranial base, can contribute to the development of Class II division 1 malocclusions. On the other hand, a more acute angle at the skull base can contribute to a more anterior positioning of the mandible and to the development of Class III malocclusions

Degradação de forças dos elasticos intermaxilares ortodônticos sintéticos

This study aimed to evaluate the force degradation of synthetic elastics over time using dynamic biomechanical tests in order to find clinical parameters of what size of elastic and frequency of exchange should be used in orthodontic therapy. It was used 240 elastics of Dental Morelli, sizes 1/8", 3/16", 1/4 "and 5/16", medium force, divided in four groups. In each group was measured forces at different times, from immediate to 72 hours after immersion in water at 37°C and incubated stretched to 600% of its initial inner diameter. Tensile tests were performed on a universal testing machine EMIC DL2000 submerged in distilled water maintained at 37°C. Data were analyzed using SPSS version 16.0, by the Analysis of Variance (One-Way) with Tukey´s post test. There was a greater increase in pattern of force decay of immediate measurement until 24 hours in all sizes of synthetic elastics, from which it was observed a decrease in force progressively smaller, with the exception of 5/16´´ elastic with a maximum force decay occurred at 12h. It was concluded that: the elastic synthetic Dental Morelli suffered significant force degradation over time, with reduction of approximately 70% of the initial force during 24 hours of stretching, followed by a progressively smaller decrease; the amount of stretch for a ideal force in intermaxillary therapies depends on the distance between the points of attachment of elastic, being necessary to consult the tables to choose the size, force and frequency of replacement.O objetivo do estudo foi avaliar a degradação de força dos elásticos sintéticos ao longo do tempo por meio de ensaios biomecânicos dinâmicos, a fim de buscar parâmetros clínicos de qual tamanho de elástico e frequência de troca devemos utilizar nas terapias ortodônticas. Utilizaram-se 240 elásticos da Dental Morelli, tamanho 1/8", 3/16", 1/4" e 5/16" de força média, divididos em quatro grupos. A cada grupo foram mensuradas forças em tempos diferentes, de imediato a 72 horas após imersão em água destilada a 37°C mantidas em estufa e distendidos em 600% do seu diâmetro interno inicial. Os ensaios de tração foram realizados em máquina de ensaios universal Emic DL2000, imersos em água destilada mantida a 37°C. Os dados foram analisados por meio de software SPSS versão 16.0, através da Análise de Variância a um critério (One-Way) com pós-teste de Tukey. Verificou-se um padrão de degradação de força maior da mensuração imediata até 24 horas em todos os tamanhos de elásticos sintéticos, a partir da qual se observa uma diminuição da força progressivamente menor, com exceção do elástico 5/16'', cuja maior redução de força ocorreu em 12 horas. Concluiu-se que: os elásticos sintéticos Dental Morelli sofreram significativa degradação de força ao longo do tempo, com redução de aproximadamente 70% da força inicial em 24 horas de estiramento, seguida de uma diminuição progressivamente menor; a quantidade de estiramento para uma força ideal em terapias intermaxilares depende da distância entre os pontos de fixação do elástico, sendo necessária a consulta nas tabelas para escolha de tamanho, força e frequência de substituição