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Este estudo objetivou determinar o efeito do armazenamento em longo prazo nas características mecânicas dos elásticos intermaxilares e o período apropriado para substituição no uso clínico. 270 elásticos (135 látex e 135 sintéticos), 3/16" médio, foram submetidos a testes de tração uniaxial com estiramento de 200% até 600% dos seus diâmetros internos. Os elásticos foram divididos nos grupos "Como Recebidos" (CR, n = 15); armazenados em refrigerador por 3 anos (n = 60), e armazenados à temperatura ambiente por 3 anos (n = 60). Os grupos de elásticos armazenados foram subdivididos em 4 subgrupos (n = 15 cada): sem estiramento prévio (SEP); estiramento prévio simulando o ambiente intraoral por 24 horas (EP24h), 48 horas (EP48h) e 72 horas (EP72h). Quanto aos elásticos de látex, as forças expressadas pelo grupo SEP, independente da temperatura de armazenamento, permaneceram similares às forças do grupo CR. Elásticos armazenados em temperatura ambiente de SEP até EP72h perderam aproximadamente 25 gF (p = 0.001), enquanto os refrigerados perderam em média 10 gF (p = 0.05). Sobre os elásticos sintéticos, o grupo SEP, independente da temperatura de armazenamento, ganhou, em média, 50 gF (p = 0.001) em comparação ao grupo CR. Os armazenados em temperatura ambiente, desde SEP até EP72h, perderam em média 30 gF (p = 0.001), enquanto os refrigerados perderam aproximadamente 50 gF (p = 0.001). Concluiu-se que os elásticos ortodônticos armazenados em longo prazo em suas embalagens originais expressam forças maiores do que os elásticos novos, e ao usar clinicamente elásticos armazenados a longo prazo, as substituições podem ser feitas a cada 72 horas sem perda da eficiência mecânica (AU)

This paper aimed to determine the effect of long-term storage on latex and non-latex intermaxillary elastics, and the proper time between substitutions. 270 elastics (135 latex and 135 non-latex elastics), medium force and standard size of 3/16", underwent uniaxial tensile tests with increase from 200% to 600% of their inner diameter. Each type was divided into groups of as received elastics (AR - n = 15), 3 years stored under refrigeration (n=60), and e years stored at room temperature (n=60). The stored groups were divided into 4 subgroups (n = 15): no previous stretching (NPS), pre-stretched si mulating the intraoral environment during 24 hours (PS24h), 48 hours (PS48h), and 72 hours (PS72h). About the elastics of latex, the forces expressed by the NPS at room temperature remained equal to the AR, while the forces of the refrigerated NPS had increased ±70 gF on average (p = 0.001). PS24h to PS72h at room temperature showed loss of ±20 gF (p = 0.001) when compared to the NPS or to AR. Non-latex - NPS, regardless of the temperature of storage, increased forces ± 70gF (p = 0.001) when compared to the AR. Starting at PS24h to PS72h, it was seen an average loss of ± 40gF (p = 0.001) when compared to the NPS. All 3 years stored non-latex elastics forces increased ± 30gF (p = 0.01) when compared to the AR. It was concluded that orthodontic elastics long-term stored in their original packages shows higher average forces than new elastics, and the replacement, when using long-term stored could be every 72 hours (AU)

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INTRODUCTION: The objective of this investigation was to evaluate the effects of high-intensity light-emitting diode (LED) light from a curing device on the retinas of Wistar rats. METHODS: Six male Wistar rats were used, and their ocular structures were the focus of this study. During the photostimulation of each animal, the right eye of the animal, considered the control sample, was covered with a removable polyvinyl chloride cap, and the contralateral eye, the experimental sample, was exposed to high-intensity LED light, 3200 mW/cm2 (VALO Ortho; Ultradent Products, South Jordan, Utah) for 144 seconds from a distance of 30 cm. The animals were exposed to the LED light 3 times on the same day to investigate if any acute inflammatory changes in the retina occurred. Seven days after the photostimulation sessions, the animals were anesthetized and perfused with paraformaldehyde solution. After which, the eyes were resected and processed histologically. The histologic sections were analyzed stereologically and histomorphometrically to measure the parameters of the retina under investigation. RESULTS: There was a statistically significant increase in total retinal volume in the experimental group because of the increased volume of the ganglion cell layers, inner plexiform layers, outer nuclear layers, and the cone and rod extensions. There was no statistically significant difference in terms of density. However, there was a statistically significant increase in the nuclear area of the cells in all the studied layers in the group exposed to high-intensity LED light. In addition, hyperchromatic cells that are suggestive of pyknosis were observed. CONCLUSIONS: An acute but short protocol of exposure of high-intensity LED light to the eye caused morphometric alterations in the retinal structures, specifically in the nuclear area of the photosensitive cells.

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Introdução: A evolução dos fotopolimerizadores quanto à sua potência e consequente redução do tempo clínico tem se mostrado de grande valia para a otimização da rotina de colagem de bráquetes ortodônticos. Contudo, existe uma carência na literatura do efeito desses aparelhos sobre a retina do profissional e/ou do paciente, uma vez que ambos podem receber indiretamente parte da luz refletida durante os procedimentos clínicos. Objetivo: Avaliar os efeitos do uso de um aparelho fotopolimerizador LED de alta potência nas retinas de ratos Wistar. Material e métodos: Seis ratos Wistar foram utilizados na pesquisa e suas estruturas oculares foram os objetos de estudo. Durante a fotoestimulação de cada animal, o olho direito do animal, considerado a amostra controle, foi coberto com um tampão removível em PVC, enquanto que o olho contralateral, a amostra experimental, foi exposto à luz do LED de alta potência, 3200mW/cm2 (Valo Ortho - Ultradent), por 144 segundos à distância de 30cm. Os animais foram expostos ao LED três vezes durante um dia, com o objetivo de induzir possíveis alterações inflamatórias agudas na retina. Decorrido o período de sete dias após a fotoestimulação, os animais foram anestesiados, procedido à eutanásia, removidos os olhos e processados histologicamente. Em seguida, as lâminas foram digitalizadas utilizando-se uma câmera acoplada a um microscópio óptico e suas imagens analisadas estereologicamente e histomorfometricamente para aferição de parâmetros estudados da retina. Resultados: Houve um aumento estatisticamente significativo no volume total da retina e no volume das camadas de células ganglionares (CCG), camada plexiforme interna (CPI), camada nuclear externa (CNE) e os prolongamentos de cones e bastonetes (PCB) no grupo experimental. Em relação à densidade, não houve diferença estatisticamente significativa. Entretanto, observou-se um aumento estatisticamente significativo da área nuclear das células em todas as camadas estudadas no grupo exposto à luz LED de alta potência. Além disso, observou-se células hipercromadas que são sugestivas de picnose. Conclusões: Mesmo com um protocolo agudo e curto de exposição do olho à luz LED de alta potência, houve uma alteração nas estruturas retinianas, especialmente da atividade metabólica das células fotossensíveis e neuronais, o que ressalta a necessidade de proteção durante a utilização desses aparelhos fotoativadores (AU).

Introduction: The evolution of light curing units (LCU) in terms of potency and consequent reduction of clinical time have been shown to be of great value to orthodontists, regarding the routine of brackets bonding. However, there is a lack in the literature regarding the effect of these devices on the operator and/or patient retina, as both may receive indirect reflected light during procedures. Aims: Evaluate the effect of the use of a high potency light emitting diodebased device (LED) in the retina of Wistar rats. Material and Methods: Six Wistar rats were used and their ocular structures considered objects of the study. During the photostimulation of each animal, the right eye, established as the control sample, was covered with a removable PVC tampon, as the contralateral eye - experimental sample - was exposed to high potency LED light, 3200mW/cm2 (Valo Ortho - Ultradent) for 144 seconds, at the distance of 30cm. Animals were exposed to LED light three times per day, aiming to induce possible acute inflammatory alterations in retina. Seven days after the first photostimulation, all rats were anesthetized and then euthanized for posterior eye removal and histological processing. The histological slides were scanned using a camera connected to an optical microscope and their images analyzed for the measurement of histomorphological and stereological parameters of the retina. Results: A statistically significant raise was found in the total volume of retina and in the following layers: ganglion cells layer (GCL), outer nuclear layer (ONL), inner nuclear layer (INL) and extension of cone and rods (ECR) in the experimental group. Regarding density, no statistically significant difference was observed. However, the nuclear area of the cells raised significantly in all layers analyzed after high potency LED exposure. Besides that, hyperchromic cells suggestive of pyknosis were found. Conclusions: Despite the short and acute protocol of eye exposure to high potency LED, a significant alteration was found, especially in the metabolic activity of photosensitive and neuronal cells. These results emphasize the importance of using eye protection during the use of these devices (AU).

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ABSTRACT Objective: Evaluate changes in the force system of T-Loop Springs (TLS) preactivated by curvature, due to stress relaxation. Methods: Ninety TLSs measuring 6 x 10 mm, produced out with 0.017 x 0.025-in TMA® wire and preactived by gradual curvature, were randomly distributed into nine groups according to time point of evaluation. Group 1 was tested immediately after spring preactivation and stress relief, by trial activation. The other eight groups were tested after 24, 48 and 72 hours, 1, 2, 4, 8 and 12 weeks, respectively. Using a moment transducer coupled to a digital extensometer indicator adapted to a universal testing machine, the amount of horizontal force, moment and moment-to-force ratios were recorded at every 0.5 mm of deactivation from 5 mm of the initial activation, in an interbracket distance of 23 mm. Results: The horizontal forces decreased gradually among the groups (p< 0.001) and the moments showed a significant and slow decrease over time among the groups (p< 0.001). All groups produced similar M/F ratios (p= 0.532), with no influence of time. Conclusions: The TLSs preactivated by curvature suffered a gradual deformation over time, which affected the force system, specifically the moments, which affected the horizontal forces produced.

RESUMO Objetivo: avaliar as mudanças no sistema de forças das molas T pré-ativadas por curvatura, devido ao alívio de tensão estrutural. Métodos: noventa molas em forma de "T", medindo 6 mm x 10 mm, confeccionadas com fio de beta-titânio TMA® de 0,017" x 0,025" e pré-ativadas por curvatura gradual, foram distribuídas aleatoriamente em nove grupos, de acordo com o momento de avaliação. O Grupo 1 foi testado imediatamente após a pré-ativação da mola e liberação do estresse, por meio de simulação da ativação. Os outros oito grupos foram divididos conforme o intervalo de tempo testado: após 24, 48 e 72 horas; 1, 2, 4, 8 e 12 semanas. Usando um transdutor de momentos acoplado a um indicador digital para extensometria e adaptado a uma máquina universal de ensaios, as magnitudes da força horizontal, do momento e da proporção momento/força (M/F) foram registradas a cada 0,5 mm de desativação a partir da ativação inicial de 5 mm, utilizando-se uma distância interbraquetes de 23 mm. Resultados: as forças horizontais reduziram-se gradualmente nos grupos (p< 0,001) e o momento apresentou uma queda lenta e significativa ao longo do tempo (p< 0,001). Todos os grupos tiveram proporções M/F semelhantes (p= 0,532), não influenciadas pelo período de tempo. Conclusões: as molas pré-ativadas por curvatura gradual sofreram deformação progressiva ao longo do tempo, o que afetou o sistema de forças - especificamente o momento -, alterando as forças horizontais produzidas.

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OBJECTIVE: Evaluate changes in the force system of T-Loop Springs (TLS) preactivated by curvature, due to stress relaxation. METHODS: Ninety TLSs measuring 6 x 10 mm, produced out with 0.017 x 0.025-in TMA® wire and preactived by gradual curvature, were randomly distributed into nine groups according to time point of evaluation. Group 1 was tested immediately after spring preactivation and stress relief, by trial activation. The other eight groups were tested after 24, 48 and 72 hours, 1, 2, 4, 8 and 12 weeks, respectively. Using a moment transducer coupled to a digital extensometer indicator adapted to a universal testing machine, the amount of horizontal force, moment and moment-to-force ratios were recorded at every 0.5 mm of deactivation from 5 mm of the initial activation, in an interbracket distance of 23 mm. RESULTS: The horizontal forces decreased gradually among the groups (p< 0.001) and the moments showed a significant and slow decrease over time among the groups (p< 0.001). All groups produced similar M/F ratios (p= 0.532), with no influence of time. CONCLUSIONS: The TLSs preactivated by curvature suffered a gradual deformation over time, which affected the force system, specifically the moments, which affected the horizontal forces produced.

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