Ação do fluor na microdureza do esmalte humano submetido a dois tipos de agentes clareadores

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise da superfície de cerâmicas de dissilicato de lítio após imersão em soluções ácidas e a base de flúor

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo da dureza e da resistência à compressão de resinas compostas para dentes posteriores após a imersão em água destilada. Efeito da aplicação de selante superficial

Novos compósitos têm surgido no mercado especificamente destinados à confecção de restaurações estéticas posteriores. Entretanto, embora tais materiais apresentem resultados iniciais animadores, há a necessidade de comprovações adicionais para que possam ser utilizados com segurança. Resinas compostas posteriores são submetidas a estresses complexos de compressão e abrasão durante a mastigação e a aplicação de selantes superficiais tem sido relatada como forma de aumentar a resistência ao desgaste destes materiais. O presente trabalho teve como propósito avaliar a dureza e a resistência à compressão das resinas compostas Alert (Jeneric/Pentron), Ariston (Vivadent), Definite (Degussa), P60 (3M), Solitarie (Kulzer), Surefil (Dentsply) e Z100 (3M) após 90 dias de imersão em água destilada, recobertas com selante Protect It (Jeneric/Pentron) e submetidas à ciclagem mecânica (10.000 ciclos, 600N, 5Hz). Os ensaios de dureza (n=8) foram realizados em aparelho Wolpert, com diamante Vickers e peso de 50gf aplicado por 30 segundos, antes e após períodos de imersão de 30, 60 e 90 dias. Os ensaios de resistência à compressão (n=8) foram realizados somente após 90 dias, em corpos-de-prova cilíndricos medindo 8mm de altura por 4mm de diâmetro. Apenas os espécimes destinados à compressão foram ciclados mecanicamente. Os ensaios foram realizados em máquina MTS 810, equipada com célula de carga de 10kN (ciclagem) e 100kN (compressão) e velocidade de 0,5mm/min. Após análise de variância (p<0,05), os resultados mostraram, previamente à imersão, maiores valores de dureza para os materiais Z100 (74,253VHN) e Ariston (71,308VHN). A seguir, com valor semelhante à resina Ariston, mas inferior à resina Z100, apresentou-se o material Surefil (69,969VHN)...(Resumo completo, clicar acesso eletrônico abaixo)

Análise de corrosão, dureza e fratura de conjuntos implantes / componentes protético de Titânio c.p., após serem submetidos a ciclos de fadiga em um meio fluoretado com diferentes PH

Atualmente o titânio é empregado como biomaterial devido à sua biocompatibilidade e resistência à corrosão. Entretanto, íons fluoretos, freqüentemente empregados em dentifrícios bucais, podem interferir no processo de corrosão. O objetivo deste estudo foi analisar a influência de um meio fluoretado com diferentes pH nas propriedades mecânicas e na resistência à corrosão dos conjuntos implantes/componentes protéticos à base de Ti c.p., a partir dos testes de fadiga, microscopia eletrônica de varredura (MEV) e dureza. Foram simulados cinco anos de uso regular de meios de higiene oral com conteúdo de 1500 ppm de NaF, com dois diferentes pH, 7,4 e 5,3, mediante imersão das amostras nesses meios durante 184 horas e também em água destilada, grupo controle. As amostras foram testadas num durômetro Micromet 2001 (500gf/30s). Os dados dos testes de dureza foram analisados pelo teste de Wilcoxon, demonstrando que as amostras sofreram influência negativa na dureza após a ação dos íons fluoreto. Entretanto, essa influência não ocorreu nos testes de fadiga realizados em uma máquina de ensaios mecânicos MTS-810, fixada a 100.000 ciclos, 15Hz e programada com força de fadiga a 150 N. Pela análise de MEV foram constatadas evidências de corrosão na superfície das amostras após ação de íons fluoretos, entretanto pelo EDS não se verificou incorporação de íons fluoretos sobre a superfície dos conjuntos. Concluiu-se que a concentração de flúor e o pH das soluções não exerceram influência nas propriedades mecânicas.

Estudo do comportamento em fadiga de uma chapa de aço microligado, grau API 5L X70

In engineering, for correct designing the structural components required for cyclical stresses, it is necessary to determine a limit of resistance to fatigue, which is the maximum amplitude of the applied tension under which the fatigue failure does not occurs after a certain number cycles. The marine environment is hostile, not only by the high pressure, corrosion, but also by low temperatures. Petrol Production units, composed of the risers (pipelines connecting the oil well to the ship), are dimensioned to remain installed for periods of 20 up to 30 years, and must therefore be prepared to support various efforts, such as tidal, wind currents and everything that is related. This paper focuses on a study on the fatigue behavior of microalloyed steel, API 5L Grade X70, used to transport oil and gas by pipelines. For analysis, we obtained the curves S-N (stress vs. number of cycles) using laboratory data collected from cylindrical longitudinal and transverse specimens used in axial fatigue test in accordance with ASTM E466. The tensile tests and microhardness were performed to characterize the mechanical properties of the samples, and it was found that the values meet the specifications of the standard API 5L. To characterize microstructurally the material, it was also made a metallographic analysis of the steel under study, and the origin of the fatigue crack was investigated with the support of a scanning electron microscope (SEM).

Avaliação do comportamento mecânico sob deformação da liga Ti- 30Ta visando aplicações biomédicas

Titanium and its alloys have been used for biomedical applications due their excellent properties such as high corrosion resistance, biocompatibility and mechanical properites. In this study, microstructural and mechanical properties of Ti-30Ta alloy was evaluated during its processing. Ti-30Ta alloy ingots were produced from sheets of commercially pure titanium (99.9%) and tantalum (99.9%). Its melting was realized in arc melting furnace in an argon atmosphere. After homogenizing at 1200ºC, ingots were cold worked by swaging. Samples with 13 mm in diameter were obtained. They were forging at the reduction ratios of 15%. After deformation, microstructure was evaluated by optical microscopy in each condition. Also, Vickers microhardness of samples was measured and phase constitution was evaluated using XRD analysis

Propriedades físicas de vidros Sb2O3-P2O5

This work presents experimental results of some physical properties of antimony phosphate glasses with compositions (x) Sb2O3 - (1-x) P2O5 (x = 0.75, 0.85, 0.90). Mechanical, thermal, optical and electrical properties were investigated: density, elastic moduli (Young's moduli and Poisson's ratio), Vickers microhardness, coefficient of thermal expansion, glass transition temperature, refractive index and electrical conductivity (for x = 0.75). There was no evidence of electronic conductivity by bipolaron hopping. Measurements of energy dispersive spectroscopy (EDS) showed that volatilization of Sb2O3 takes place during the glass melting

Estudo em fadiga no aço API 5L X80 soldado pelo processo HF/ERW

The technological advancement in order to improve the methods of obtaining energy sources such as oil and natural gas is mainly motivated by the recent discovery of oil reserves. So, increasingly , there is a need for a thorough knowledge of the materials used in the manufacture of pipelines for transportation and exploration of oil and natural gas. The steels which follow the API standard (American Petroleum Institute), also known as high strenght low alloy (hsla), are used in the manufacture of these pipes, as they have, with their welded joints, mechanical properties to withstand the working conditions to which these ducts will be submitted . The objective of this study is to evaluate the fatigue behavior in microalloyed steel grade API 5L X80 welded by process HF / ERW . For this, axial fatigue tests to obtain S-N curve (stress vs. number of cycles ) were conducted. To complement the study, it was performed metallographic , fractographic , Vickers hardness tests and tensile tests to characterize the mechanical properties of the steel and check whether the values satisfy the specifications of the API 5L standard . From the fatigue tests , it was concluded that the surface finish influences directly on the fatigue life of the material

Estudo de cerâmicas avançadas para fins de blindagem balística

The research involving new materials has always been considered as a differential in the development of a technology company. This occurred naturally since ancient times, often motivated by reasons of a certain age, where the most common material used was also the name of your time and may be cited as an example the Bronze Age, and later was the Iron. Currently, the use of firearms are they used in resolving conflicts between countries, or a more equivocal, as an instrument of social banditry make innovations in the area of shielding welcome, whether for personal use, in the form of vests or vehicle such as cars, tanks and even aircraft. In this context, is a Silicon Carbide Ceramic, with low density and high hardness. Thus, the aim of this study is the evaluation and comparison of these materials, seeking to improve their properties by means of additives such as boron and silicon metal and amorphous YAG. For this work, the specimens were pre-shaped by means of uniaxial later to be referred for isostatic pressing and sintering. The maximum percentage for each additive was 5%, except for the YAG whose percentage was 8.2% (mass percentage). All compositions were subjected to the same tests (x-ray diffraction, apparent density, optical microscopy, Vickers hardness, scanning electron Microscopita), so that one could draw a comparison between the materials under study, samples that showed better mechanical properties and micro structural, related here by hardness testing and microscopy (optical and SEM) were the silicon carbide doped with YAG and alumina samples, demonstrating the potential of these materials for ballistic protection. Other compositions have high porosity, which is highly undesirable, since in order to harmful influences on the mechanical properties discussed below

Caracterização de cerâmicas a base de nitreto de silício para aplicações estruturais

The need for development of new materials is a natural process in the companies’ technological point of view, seeking improvements in materials and processes. Specifically, among the materials, ceramic exhibit valuable properties, especially the covalent ceramics which have excellent properties for applications which requires the abrasion resistance, hardness, high temperatures, resistence, etc. being a material that has applications in several areas. Most studies are related to improvement of properties, specially fracture toughness that allows the expansion of its application. Among the most promising ceramic materials are silicon nitride (Si3N4) which has excellent properties. The goal of this work was the development and caracterization of Si3N4-based ceramics, doped with yttrium oxide (Y2O3), rar earth concentrate (CTR2O3) and cerium oxide (CeO2) in the same proportion for the evaluation of properties. The powders' mixtures were homogenized, dried and compressed under pressure uniaxial and isostatic. Sintering was carried out in 1850 ⁰C under pressure of 0,1MPa N2 for 1 h with a heating rate of 25 ⁰C / min and cooling in the furnace inertia. The characterizations were performed using Archimedes principle to relative density, weight loss by measuring before and after sintering, phase analysis by X-ray diffraction, microstructure by scanning electron microscope (SEM), hardness and fracture toughness by the method Vickers indentation. The results obtained showed relative density of 97-98%, Vickers hardness 17 to 19 GPa, fracture toughness 5.6 to 6.8 MPa.m1/2, with phases varying from α-SiAlON and β-Si3N4 depending the types of additives used. The results are promising for tribological applications and can be defined according to the types of additives to be used

Dureza e rugosidade superficial de cimentos de ionômero de vidro após ensaio de escovação

To evaluate the surface roughness and Vickers hardness of glass ionomer cements Ketac Molar® and Ketac Molar Easy Mix® (ESPE Dental AG) after brushing. Methods – After roughness and hardness tests of 14 specimens of each material, they were submitted to 30,000 brushing cycles and new analysis of roughness and hardness. Statistical analysis showed that there was no significant difference between the materials in relation to the initial roughness. Results – However, after brushing there was higher surface roughness for Ketac Molar Easy Mix®. For both materials, there was increase of hardness after brushing and the highest values were presented by Ketac Molar Easy Mix®. Conclusion – It can be concluded that, when choosing a glass ionomer cement for restoration it should be preferred to Ketac Molar, because it showed hardness similar to Ketac Molar Easy Mix, but it was less rough.

Influence of heat treatment and mechanical cycling on hardness and fracture analysis of Ti35Nb5Zr casting alloy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Efeito de fontes de luz na microdureza de resinas compostas

This study assessed the surface microhardness of compound resins cured by different light sources. Methods Three micro hybrid (Vit-l-escence, Amelogen Plus, Opallis) and one nanoparticle (Filtek Z350, 3M ESPETM Dental Products, St. Paul, USA) compound resins were selected. The resins were polymerized by a halogen light unit (Ultralux, Dabi Atlante, Ribeirão Preto, Brasil) with two tips, one semi-guided made of glass and another of painted acrylic and a LED-based source (UltraLume 2, Ultradent®, South Jordan, USA). Specimens constructed from a circular aluminum matrix were photopolymerized for 40 second after they received the compound resin and stored dry for 24 hours. After this period, a Vickers surface microhardness assay was performed, measuring the top (hardness 1) and base (hardness 2) surfaces four times each. Variance analyses were complemented by Newman-Keuls method, with significance set at 5%. Results The Opallis (FGM, Santa Catarina, Brasil) resin subjected to UltraLume 2 (Ultradent®, South Jordan, USA) obtained the lowest mean hardness values for the top surface. The Vit-l-escence (Ultradent®, South Jordan, USA) compound cured by Led UltraLume 2 (Ultradent®, South Jordan, USA) and by Ultralux PCP (Dabi Atlante, Ribeirão Preto, Brasil) halogen light obtained the highest mean hardness, followed by the Filtek Z350 (3M ESPETM Dental Products, St. Paul, USA) resin subjected to UltraLume 2 (Ultradent® South Jordan, USA). The Opallis (FGM, Santa Catarina, Brasil) resin cured by LED UltraLume 2 (Ultradent®, South Jordan, USA) also obtained the lowest mean hardness for the base surface and the Vit-L-Escence (Ultradent®, South Jordan, USA) resin obtained the highest value, followed by Amelogen Plus, when cured by Ultralux (Dabi Atlante, Ribeirão Preto, Brasil) using the semi-guided tip. Conclusion The polymerization and, consequently, the microhardness achieved by the LED unit was equivalent to those achieved by conventional halogen units for three of the four composites tested.

Effect of different light-curing techniques on hardness of a microhybrid dental composite resin

Coordenação de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)

Long-term surface hardness and monomer conversion of a nonofilled and a microhybrid composite resin

Objective: This study aims to evaluate the degree of conversion (DC) and hydrolytic degradation through the Vickers hardness test (HV) of a nanofilled (Filtek™ Z-250, 3M) and a microhybrid (Filtek™Supreme-XT, 3M) composite resin. Materials and methods: Eight disk-shaped specimens (4 mm diameter × 2 mm thick, ISO 4049) of each material were prepared for each test. Composites were inserted into single increment in a metallic matrix and light-cured for 40 seconds. VH readings were performed for each specimen at predetermined intervals: immediately after polymerization (control), 1, 2, 3, 7, 14, 21, 30 and 180 days. After curing, initial hardness measurements were performed and the specimens were immersed in artificial saliva at 37°C. For DC (%), specimens were ground, pressed with KBr and analyzed by FT-IR spectrophotometer. Results: Student t-test showed that there was no difference between the resins for DC (p = 0.252). ANOVA analysis revealed that Z-250 VH means were all greater than S-XT, for both top and bottom surfaces, whatever the storage-period in artificial saliva (p < 0.001). After 180 days of storage, the hardness obtained for S-XT was similar with that at the baseline, for both top and bottom surfaces. While for Z-250 hardness was not significantly different from baseline only for top surface, but there was a significant decrease observed in hardness for bottom surface. Conclusion: The materials tested showed no evidence of hydrolytic degradation in a significant way, in a 6-month storagetime in artificial saliva. Nanofilled resin presents a monomer conversion comparable to the conventional microhybrid.