Objective: This study investigated the effect of endogenous erosion on the microhardness of dentine and a nanofilled composite resin. Procedures for preventing erosion were also studied. Materials and Methods: 90 bovine dentine specimens were divided into three groups in accordance with the method for preventing: negative control, topical application of fluoride and resin-modified glass ionomer varnish. 120 composite resin specimens were distributed into four groups, which also included a resin sealant, among the preventive procedures. Specimens were then randomly divided into three subgroups according to the exposure to simulate gastric acid solution and subsequent remineralization: negative control, 9 and 18 cycles. Surface analysis was carried out by measuring the Knoop hardness. The data obtained were statistically analyzed using 2-way ANOVA and Tukey test. Result: The mean hardness of dentine and of the composite specimens resin exhibited lower hardness after 18 cycles. However, the resin-modified glass ionomer varnish resulted in greater values compared to the other preventive procedures. Conclusion: A resin-modified glass ionomer varnish seems to be a promising method for minimizing the damage caused by endogenous acid, but its protection can be reduced depending on the intensity of the erosive challenge.
OBJECTIvE: This study evaluated the surface roughness of a nanofilled composite resin submitted to different degrees of erosion and methods of control. METHODS: 120 cylindrical composite specimens (6×1.5 mm) were randomly divided into four groups, according to the surface protection against the erosive challenge [negative control, topical application of fluoride, glass-ionomer sealant, resin sealant]. After the application of the respective method, specimens were divided into three subgroups (n=10): a) absence of erosive challenge; b) 9 cycles of DES-RE; c) 18 cycles of DES-RE. Surface roughness (Ra, μm) was recorded and statistically analyzed (2-way Anova/Tukey). RESULTS: The glass-ionomer sealant exhibited less rough surfaces under all the conditions. However, the average roughness was significantly higher after 18 DES-RE cycles. CONCLUSION: Despite the potential shown by glass-ionomer sealant, it was concluded that no material prevented an increase in surface roughness of the nanofilled composite after an intense erosive challenge.Key words: Tooth wear; Fluorine compounds; Definitive dental restoration Efeito da erosão e de métodos para seu controle sobre a rugosidade superficial da resina composta RESUMO OBJETIvO: Este estudo avaliou a rugosidade superficial de uma resina composta nanoparticulada submetida a diferentes graus de erosão e a métodos para seu controle. MÉTODOS: 120 corpos de prova cilíndricos (6×1.5 mm) em resina composta foram aleatoriamente divididos em quatro grupos experimentais, de acordo com o método de proteção superficial [controle negativo, aplicação tópica de flúor, selante ionomérico, selante resinoso]. Após a aplicação dos respectivos métodos, os corpos de prova foram divididos em três subgrupos (n=10): a) ausência de exposição à solução simulada de ácido gástrico; b) 9 ciclos de DES-RE; c) 18 ciclos de DES-RE. valores da rugosidade superficial (Ra, μm) foram registrados e analisados estatisticamente (Anova 2-critérios/Tukey). RESULTADOS: O selante ionomérico promoveu superfícies menos rugosas, em todas as condições experimentais testadas. Porém, todas as médias de rugosidade ficaram significativamente mais altas após 18 ciclos de DES-RE. CONCLUSÃO: Apesar do potencial demonstrado pelo selante ionomérico, conclui-se que nenhum material foi capaz de evitar o aumento de rugosidade superficial da resina composta nanoparticuladas após a maior intensidade de desafio erosivo.
The dentin exposed to erosive challenges is often superficially protected to prevent progression of the lesion. This study investigated the marginal and internal adaptation of composite resin restorations made on surfaces that had first been treated with different methods for controlling erosion. Cavities with margins in dentin were prepared in bovine incisors (n=360) and were divided into three groups according to the method for controlling the erosive challenge: negative control, topical application of fluoride and resin-modified glass ionomer varnish. The specimens were then randomly divided into three sub-groups according to the exposure to simulated gastric acid solution (DES) (5% HCl, pH=2.2) and subsequent remineralization (RE): negative control, 9 and 18 cycles of DES-RE. Finally, teeth were divided into four groups, depending on the bonding agent used for composite resin restoration (n=10): conventional etch-and-rinse adhesive system (2 and 3 steps) and self-etching (1 and 2 steps). Front and internal images of the interface tooth/restoration were recorded in stereoscopic microscope (15x) to quantify the percentage of adhesive failures. Despite the promising results of the resin-modified glass ionomer varnish after 9 cycles; no protective material prevented increased internal defects after 18 erosive cycles. More continuous internal margins were noted with etch-and-rinse acid systems after more intense erosion. The maintenance of internal margins in eroded substrates was positively influenced by the resin-modified glass ionomer varnish and, under the most aggressive challenge, by the use of etch-and-rinse adhesives systems. Keywords: Tooth Erosion. Dentin. Acid Gastric. ResumoA dentina exposta a desafios erosivos é muitas vezes superficialmente protegida para prevenir a progressão da lesão. Este estudo investigou a adaptação marginal e interna de restaurações de resina composta realizadas em superfícies que foram previamente tratadas com diferentes métodos para controlar a erosão. Cavidades com margens em dentina foram preparadas em dentes incisivos bovinos (n=360) e divididas em três grupos de acordo com o método de controle do desafio erosivo: controle negativo, aplicação tópica de flúor e verniz de ionômero de vidro modificado por resina. Os espécimes foram então divididos aleatoriamente em três subgrupos de acordo com a exposição à solução de ácido gástrico simulada (DES) (HCl a 5%, pH = 2,2) e posterior remineralização (RE): controle negativo, 9 e 18 ciclos de DES-RE. Por fim, os dentes foram divididos em quatro grupos, de acordo com o agente de união utilizado para a restauração da resina composta (n=10): sistema adesivo convencional (2 e 3 passos) e autocondicionante (1 e 2 passos). Imagens frontais e internas da interface dente/restauração foram registradas em microscópio estereoscópico (15x) para quantificar a porcentagem de falhas adesivas. Apesar dos resultados promissores do verniz de ionômero de vidro modificado por resina após 9 ciclos; nenhum material de proteção impediu o aumento de defeitos internos após 18 ciclos erosivos. Margens internas mais contínuas foram observadas com sistemas adesivos convencionais após erosão mais intensa. A manutenção das margens internas em substratos erodidos foi influenciada positivamente pelo verniz de ionômero de vidro modificado por resina e, sob o desafio mais agressivo, pelo uso de sistemas de adesivos convencionais. Palavras-chave: Erosão Dentária. Dentina. Ácido Gástrico.
Strained silicon engineering has proven to be a successful technology to keep Moore's law and presents a great potential for its use in even smaller and highly stressed technological nodes in microelectronics in the future. Such a task demands the use of stress characterization techniques for semiconductor research and development.One potential characterization tool which makes possible quantitative stress measurement of silicon is the Raman spectroscopy. This characterization method is a wellestablished non-destructive technique that permits stress characterization with a spatial resolution of below 1 μm and does not require complex sample preparation procedure.However, studies on Raman shift behavior of highly stressed structures (stress greater than 2 GPa) with the critical dimension smaller than 100 nm are scarce in the literature, being a bottleneck for the systematic use of Raman measurements in future technological devices.Here, it was investigated the Raman shift-stress behavior from the (001) silicon surface of highly strained ultra-thin (15 nm-thick) suspended nanowires with stresses in the range of 0 -6.3 GPa along the [110] direction. The use of ultrathin nanowires as a platform of study, along the [110] crystallographic direction, allowed the systematic investigation of one essential block that might be present in future nMOS transistors channels. Furthermore, this suspended platform reached ultra-high stress values (up to 6.3 GPa) without external actuators, allowing for the first time the systematic study of the Raman stress behavior of highly stressed nanowires.The stresses were evaluated by finite element method (FEM) simulations to achieve great accuracy in the stress characterization. Then, experimental Raman measurements were performed, followed by a thermal correction protocol to extract the corrected Raman peak free of thermal effects.The extracted stress shift coefficient (SSC), for lower stresses (below 4.5 GPa), was in good agreement with some of the SSC values in literature. For higher stresses (greater than 4.5 GPa), it was demonstrated, for the first time, that the linear shift Raman -stress relation does not hold, thus requiring an empirical model correction proposed in this work.The results demonstrate the feasibility of the Raman technique for the stress characterization of ultra-thin silicon nanowires, which should be useful to characterize strained silicon nanodevices for technological nodes below 100 nm under a wide range of stresses, contributing to such an important topic in the semiconductor industry.
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