Browsing by Author "Branco, A. C."
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- Development of Composites of PLA Filled with Different Amounts of Rice Husk Fibers for Fused Deposition ModelingPublication . Pereira, Daniel F.; Branco, A. C.; Cláudio, R.; Marques, Ana C.; Figueiredo-Pina, CélioPolylactic acid (PLA) has been used as a matrix material to produce compo- sites with natural fibers, which present several advantages, being one of them the addition of value to agricultural waste. Thus, this study aims to develop a PLA 3D filament with the incorporation of a waste agriculture product (rice husk (RH)). For that, RH fibers were prepared, and PLA was loaded up to 20% RH. The filaments were obtained by extrusion. Finally, samples were produced by fused deposition modeling (FDM). The fibers and filaments’ density and thermal stability (TGA) were determined, and their chemical structure changes due to alkali treatment were accessed by Fourier Transform Infrared Spectroscopy (FTIR). Printability tests were performed, and printed samples were characterized in terms of density, water absorp- tion, and mechanical behavior (compression, tensile, and flexural tests). The results showed that the alkali treatment changed the chemical structure of RH fibers and TGA showed that the filaments did not degrade significantly until 250ºC. The best printability was achieved with 5% of HR content and was the one that showed the lowest mechanical properties reduction. Overall, the present work showed that RH fibers can be successfully used as a filler in PLA filaments for FDM.
- Effect of albumin, urea, lysozyme and mucin on the triboactivity of Ti6Al4V/zirconia pair used in dental implantsPublication . Teixeira, H.; Branco, A. C.; Rodrigues, I.; Silva, D.; Cardoso, S.; Colaço, R.; Serro, A. P.; Figueiredo-Pina, CélioThe titanium implant/zirconia abutment interface can suffer failure upon mechanical and biological issues, ul- timately leading to the loss of the artificial tooth. The study of the effect of the organic compounds present in saliva on the tribological behavior of these systems is of utmost importance to understand the failure mechanisms and better mimic the in vivo conditions. The aim of the present work is to evaluate the effect of the addition of albumin, urea, lysozyme and mucin to artificial saliva, on the triboactivity of Ti6Al4V/zirconia pair commonly used in dental implants and then, compare the results with those obtained with human saliva. The solutions’ viscosity was measured and the adsorption of the different biomolecules to both Ti6Al4V and zirconia was accessed. Tribological tests were performed using Ti6Al4V balls sliding on zirconia plates inside of a corrosion cell. Friction and wear coefficients were determined, and the open circuit potential (OCP) was monitored during the tests. Also, the wear mechanisms were identified. The presence of mucin in the artificial lubricant led to the lowest wear coefficients. The main wear mechanism was abrasion, independently of the used lubricant. Adhesive wear was observed for the systems without mucin. Tribocorrosion activity and wear coefficient were lower in the presence of mucin. None of the studied artificial lubricants mimicked the effect of human saliva (HS) on the tribological behavior of the studied pair since this lubricant led to the lowest friction coefficient and highest corrosion activity.
- Effect of pH of H2O2 solutions on the morphology and wear resistance of human dental enamel: an AFM studyPublication . Branco, A. C.; Polido, M.; Colaço, R.; Figueiredo-Pina, C. G.; Serro, A. P.
- Suitability of 3D printed pieces of nanocrystalline zirconia for dental applicationsPublication . Branco, A. C.; Silva, R.; Santos, T.; Jorge, H.; Rodrigues, A. R.; Fernandes, R.; Bandarra, S.; Barahona, I.; Matos, A. P. A.; Lorenz, K.; Polido, M.; Colaço, R.; Serro, A. P.; Figueiredo-Pina, C. G.Objectives: The main goal of this work is to evaluate the suitability of nanostructured zirconia pieces obtained by robocasting additive manufacturing (AM), for dental applications. Methods: The density, crystalline structure, morphology/porosity, surface roughness, hardness, toughness, wettability and biocompatibility of the produced samples were compared with those of samples obtained by conventional subtractive manufacturing (SM) of a similar commercial zirconia material. Chewing simulation studies were carried out against dental human cusps in artificial saliva. The wear of the material was quantified and the wear mechanisms investigated, as well as the influence of glaze coating. Results: AM samples, that revealed to be biocompatible, are slightly less dense and more porous than SM samples, showing lower hardness, toughness and wettability than SM samples. After chewing tests, no wear was found both on AM and SM samples. However, the dental wear was significantly lower when AM samples were used as counterbody. Concerning the glazed samples, both coated surfaces and dental cusps suffered wear, being the cusps’ wear higher than that found for unglazed samples. More, cusps tested against AM coated samples suffered less wear comparatively to those opposed to SM coated samples. Significance. Overall, the results presented in this paper show that AM processed nanostructured zirconia can be used in dental restorations, with important advantages from the point of view of processing and tribological performance. Moreover, the option for glaze finishing should be carefully considered both in SM and AM processed specimens.
- Tribological behavior of restorative dental microcomposites after exposure to mouth acidsPublication . Branco, A. C.; Brito, J.; Codorniz, M.; Steinhausen, M.; Martins, F.; Reis, J.; Maurício, P.; Colaço, R.; Serro, A. P.In this work, the effect of the exposure to acids that are usually present in the mouth environment on the tribological behavior of restorative dental microcomposites is evaluated. A commercial microcomposite widely used in dentistry (Filtek Z250) and a strong and a week acid that are part of the mouth environment (hydrochloric and lactic acid, respectively) were chosen for the study. Samples of the microcomposite were exposed to each acid for two different periods: 1 day and 7 days, respectively. It was observed that the exposure to both acids lead to an increase of the surface roughness, especially in the samples that contacted for the shorter period with hydrochloric acid, and the same trend was observed in what concerns the coefficient of friction. Concomitantly, the resins’ microhardness suffered a small decreased after exposure to both acids. However, it was observed that the wear resistance of the microcomposite is only affected in a statistically significant manner after the exposition to the hydrochloric acid solution. Atomic force microscopy observation of the worn regions enables to attribute the decrease of the wear resistance of the material after the exposure to the strong acid to the detachment of the resin’s filler microparticles of silica and zirconia caused by the corrosive action of the strong acid. The results strongly suggest that the exposure to acids affects the dental resins’ tribomechanical performance which may compromise the restorations’ lifetime, especially in the case of exposure to the strong acids, such as hydrochloric.
- Tribological performance of the pair human teeth vs 3D printed zirconia : an in vitro chewing simulation studyPublication . Branco, A. C.; Silva, R.; Jorge, H.; Santos, T.; Lorenz, K.; Polido, M.; Colaço, R.; Serro, A. P.; Figueiredo-Pina, C. G.This study aims to evaluate the tribological performance of the pair human teeth/robocasted zirconia, with a special focus on the enamel wear mechanisms. Zirconia pieces produced by robocasting (RC) and unidirectional compression (UC) were compared in terms of crystalline structure, density, porosity, hardness and toughness. Chewing simulation tests were performed against human dental cusps. The cusps wear was quantified and the wear mechanisms identified. Although most of the properties of UC and RC samples are similar, differences were observed for surface roughness and porosity. Although the samples did not suffer wear, the antagonist cusps worn in a similar way. In conclusion, robocasting seems a promising technique to produce customized zirconia dental pieces, namely in what concerns the overall tribological behaviour.
- Wear of zirconia/leucite glass-ceramics composites: A chewing simulator studyPublication . Branco, A. C.; Santos, T.; Polido, M.; Colaço, R.; Serro, A. P.; Figueiredo-Pina, CélioLeucite and zirconia are commonly used in the production of prosthetic dental materials. Leucite presents attractive optical properties but low toughness and wear resistance, which limits its use. Zirconia has much higher toughness, but due to aesthetic reasons and ageing issues, needs to be glass veneered. Chipping of such veneer is usually responsible for the abnormal wear induced on the antagonist teeth. Leucite reinforced with 25% of nano-zirconia is a promising alternative to overcome these issues, allowing the production of dental resto- rations without veneer. This study aims to investigate if leucite-zirconia composites have suitable optical, me- chanical and tribological properties to be used in dental restoration. Samples with different compositions of leucite and/or nano-zirconia were produced by unidirectional compression and characterized concerning den- sity, surface morphology, roughness, hardness, toughness, and translucency. Wear tests were performed in a chewing simulator using human cusps as counterbodies. Tests were also performed in glazed zirconia for com- parison. 25% ZrO2 leads to the lowest wear of the tribological pair among the studied systems, except 100% ZrO2. This can be attributed to the toughening effect of zirconia and reduced size of third body particles. Abrasion was the main wear mechanism observed in this pair. In addition, this was the composite that presented the highest translucency.