Efeito do armazenamento em longo prazo sobre as características mecânicas dos elásticos de látex e sintéticos / Effect of long-term storage on the mechanical characteristics of latex and synthetic elastics

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)

Retinal damage related to high-intensity light-emitting diode exposure: An in vivo study.

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.

Physical-Mechanical Properties and Micromorphology of Calcium Cements Exposed to Polyacrylic and Phosphoric Acids.

OBJECTIVE: To evaluate if physical and mechanical properties of self-curing calcium hydroxide cements were affected by contact with polyacrylic and phosphoric acids. MATERIALS AND METHODS: Resin-containing (Life (LF)) and resin-free (Hydro C (HyC)) materials were subjected to polyacrylic acid conditioning and rinsing (POL); phosphoric acid conditioning and rinsing (PHO); rinsing only; and no treatment (n = 10). Water sorption/solubility, release of hydroxyl ions (pH), roughness (Ra), and impact resistance were evaluated. Additional samples (n = 1) were prepared for scanning electron microscopy (SEM) analysis of the surface morphology. Data were analyzed by two-way ANOVA and Tukey post hoc test (P < 0.05). RESULTS: Water sorption was significantly higher for LF when in contact with PHO and lower for POL (P < 0.05). The mean solubility was higher with POL for both cements (P < 0.05). PHO increased the mean surface roughness for HyC (P < 0.01); a significant decrease was noted for LF after contact with both acids (P < 0.01). PHO promoted lower release of hydroxyl ions on both cements (P < 0.05). For LF, rinsing, PHO, and POL presented similar morphology, differing from the control group. For HyC, PHO and POL presented similar morphology, differing from the control group. CONCLUSIONS: PHO had a negative effect on the physical properties of the cements tested, except for the solubility test. POL affected roughness and solubility of HyC cement. CLINICAL RELEVANCE: Clinical procedures that require polyacrylic and phosphoric acid conditioning must be done carefully on self-curing calcium hydroxide cements in order to avoid negative impact on their properties.