Navegando por Autor "Silva, F.S."
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Artigo Mechanical and thermal properties of hot pressedCoCrMo–porcelain composites developed forprosthetic dentistry(Elsevier, 2014-02) Henriques, B.; Gasik, M.; Souza, J.C.M.; Nascimento, Rubens Maribondo do; Soares, D.; Silva, F.S.In this study, mechanical and thermal properties of CoCrMo–porcelain composites fordental restorations have been evaluated. These metal–ceramic composites were producedby powder metallurgy and hot pressing techniques from the mixtures of metal and ceramicpowders with different volume fractions. Young's moduli and the coefficient of thermalexpansion of materials were evaluated by dynamic mechanical analysis (DMA) anddilatometry (DIL) tests, respectively. The strength inflexion and shear was measured witha universal test machine and hardness with a respective tester. The microstructures andfracture surfaces were inspected by the means of optical microscopy and ScanningElectron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS).Shear strength, Flexural strength and Young' moduli of ceramic and metal-matrixcomposites were found to increase with higher metal particles content. The DMA testsperformed at different frequencies showed no frequency-dependent features of thematerials studied, indicating no viscoelastic behavior. The fracture surfaces analysissuggests the load-transfer mechanism be possibly responsible for this behavior, as thedifferences in CTE are low enough to cause significant thermal stresses in these materials.The results might be included in a materials properties database for further use for designand optimization of dental restorations.Artigo Mechanical properties of hot pressed CoCrMo alloy compacts for biomedical applications(Elsevier, 2015) Henriques, Bruno; Bagheri, A.; Gasik, M.; Souza, J.C.M.; Carvalho, O.; Silva, F.S.; Nascimento, Rubens Maribondo doThis study aimed at investigating the influence of the processing conditions on the mechanical properties of hot pressed compacts of a CoCrMo biomedical alloy. Several hot pressed CoCrMo compacts were processed in vacuum (102 mbar), at a pressure of 60 MPa with different temperatures (900 C, 1000 C and 1100 C) and different times (10 min, 30 min and 60 min). Compacts were examined by SEM/EDS. The transverse rupture strength, Young’s Moduli and hardness were determined. The fracture surface of compacts were also examined. The compacts hot pressed at 900 C exhibited lower TRS than those processed at 1000 C and 1100 C, which showed similar strength values, regardless the sintering time. The 900 C compacts showed also lower YM and higher porosity. Lower hardness values were registered for 900 C compacts while 1000 C compacts exhibited the highest values. The fracture surface analyses revealed fragile fracture for 900 C compacts (10 min and 30 min) and 1000 C (10 min). The remaining compacts exhibited ductile fracture. A full characterization of the mechanical properties of hot pressed CoCrMo compacts has been made and the selection of the processing parameters according to the desired mechanical properties is now possible.Artigo Relation between Dental Implant Joint Surfaces and Biofilm Formation(Dentistry, 2015) Pereira, J.; Tavares, F.P.; Lima, K.C.; Carreiro, A.F.P.; Henriques, B.; Silva, F.S.; Nascimento, Rubens Maribondo do; Lopez-Lopez, J.; Souza, J.C.M.Objective: The main aim of this work was to evaluate the multi-species biofilm formation in vitro on surfaces of dental abutment and implants. Methods: Five commercial implant-abutment assemblies (Titamax CM; Neodent®, Curitiba; Brazil) were assessed in this study. Also, commercially pure (cp) titanium grade IV square samples (10×10×1 mm) were used to prepare surfaces similar to those of titanium implant and abutments (n=10). Titanium square samples and implant-abutmentassemblies were placed into 24 well-plates containing diluted human saliva at 37°C under microaerophilic conditions (5% CO2). After 24, 48, 72 and 96 hours of incubation, biofilms were analyzed by scanning electron microscopy (SEM) and microbiological analyses. Results: The multi-species biofilm formed at retentive areas of commercial abutments and implants like scratches,micro-gaps and defects revealed a high biofilm agglomeration, as shown by SEM analysis. The biofilm density and thecolony-forming unit number were significant higher (p<0.05) on titanium rough surfaces than that of polished titanium surfaces along the growth time. Conclusions: Biofilm analyses revealed a higher biomass density and cell viability on SLA rough surfaces than on polished ones. Abutment and implants revealed the presence of several rough areas promoted by the surface treatment that increase the biofilm accumulation at peri-implant areas.