Navegando por Autor "Carvalho, Oscar"

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Effect of laser surface texturing on primary stability and surface properties of zirconia implants
(Elsevier, 2017-12-01) Nascimento, Rubens Maribondo do; Moura, Filipe Samuel; Pereira, Rafael Santiago Floriani; Buciumeanu, Mihaela; Carvalho, Oscar; Bartolomeu, Flávio; Silva, Filipe Samuel
The aim of this study was to investigate the influence of different laser surface texturing parameters on static and dynamic coefficient of friction values of Yttria-tetragonal zirconia polycrystals (3Y-TZP) against bone to assess the primary stability of implants. The ability of the textures to promote osseointegration, as measured by wettability, and eventual changes in roughness, due to possible aging during sterilization, were also assessed. 3Y-TZP disks were divided into four groups: as sintered sample, sandblasting and etching treatment, laser irradiation using two output power of 0.9 and 1.8 W. The friction tests were carried out by using a pin-on-plate configuration, being the pins the 3Y-TZP disks and the plates the bone. The surfaces were inspected by SEM/ EDS and by surface roughness profilometer. Wettability characteristics were also evaluated by drop contact angle, and aging was assessed, after laser treatments, by XRD analysis. Results demonstrate that with laser surface texturing of zirconia it is possible to combine better wettability, better aging performance, and better primary stability, as compared to traditional - Sand blasting and Etching treatments. Thus, it is shown that the laser irradiation technique is a promising alternative to conventional sandblasting and etching procedures
Effect of zirconia and alumina fillers on the microstructure and mechanical strength of dental glass ionomer cements
(Bentham Open, 2016-03) Martinelli, Antonio Eduardo; Souza, Júlio C. M.; Silva, Joel B.; Aladim, Andrea; Carvalho, Oscar; Nascimento, Rubens M.; Silva, Filipe S.; Henriques, Bruno
Background: Glass-ionomer cements perform a protective effect on the dentin-pulp complex considering the F ions release and chemical bonding to the dental structures. On the other hand, those materials have poor physic-mechanical properties in comparison with the restorative resin composite. The main aim of this work was to evaluate the influence of zirconia and/or alumina fillers on the microstructure and strength of a resin modified glass-ionomer cement after thermal cycling. Methods: An in vitro experimental study was carried out on 9 groups (n = 10) of cylindrical samples (6 x 4 mm) made from resin modified glass-ionomer (Vitremer, 3M, USA) with different contents of alumina and/or zirconia fillers. A nano-hybrid resin composite was tested as a control group. Samples were mechanically characterized by axial compressive tests and electron scanning microscopy (SEM) coupled to energy dispersive X-ray spectrophotometry (EDS), before and after thermal cycling. Thermal cycling procedures were performed at 3000, 6000 and 10000 cycles in Fusayama´s artificial saliva at 5 and 60 oC. Results: An improvement of compressive strength was noticed on glass-ionomer reinforced with alumina fillers in comparison with the commercial glass ionomer. SEM images revealed the morphology and distribution of alumina or zirconia in the microstructure of glass-ionomers. Also, defects such as cracks and pores were detected on the glass-ionomer cements. The materials tested were not affected by thermal cycling in artificial saliva. Conclusion: Addition of inorganic particles at nano-scale such as alumina can increase the mechanical properties of glass-ionomer cements. However, the presence of cracks and pores present in glass-ionomer can negatively affect the mechanical properties of the material because they are areas of stress concentration
Laser printing of micro-electronic communication systems for smart implants applications
(Elsevier, 2020-08) Nascimento, Rubens Maribondo do; Moura, Caroline Gomes; Magalhães, Vitor H.; Pereira, Rafael Santiago Floriani; Carvalho, Oscar; Cerqueira, Maria de Fátima; Gonçalves, Luis Miguel V.; Silva, Filipe Samuel
Endow the implant with intrinsic communication system between sensors and actuators or between implant and patient is a key factor for its long-term success. The capacity of early diagnosis of failures and the ability to remedy them are necessary to minimize expensive complications and reducing revision procedures. Ti6Al4V is the most used titanium alloy for implant’s fabrication. In this sense, this work presents a promising approach to print communication systems by using laser technology, aiming integrate the smart components on titanium implants. Laser has been employed as a versatile tool to modify the surface in different ways, such as texturing, oxidizing and sintering. Silver wires have been printed on Ti6Al4V surface in order to conduct electrical current. To minimize current loss for the substrate, titanium oxide layer has been produced by different methods (laser and anodization). Laser sintering (LS) has been also compared to a conventional method (Hot-pressing- HP) to consolidate the silver powder into the cavities. In comparison to the conventional techniques, laser demonstrated to be a competitive approach to oxidizing the surface and also for consolidating the micro-wires on Ti6Al4V surface. Consequently, the micro-wires printed by laser approach presented satisfactory results in terms of electrical resistance, actuating as the conductor path for electrical current, with values of 0.0131 Ω, which is similar to the resistance of the wire printed in an insulator substrate
Laser surface texturing of Ti-6Al-4V by nanosecond laser: surface characterization, Ti-oxide layer analysis and its electrical insulation performance
(Elsevier, 2019-11) Nascimento, Rubens Maribondo do; Moura, Caroline Gomes; Carvalho, Oscar; Gonçalves, Luis Miguel V.; Cerqueira, Maria de Fátima; Silva, Filipe Samuel
The development of smart biomedical implants with intrinsic communication system between sensors and actuators, or between implant and patient, remains a challenge for scientific community. Titanium and its alloys, especially Ti6Al4V, are the most used materials in the implant's fabrication. The present work is concerned with implant internal communication printing process and presents a detailed study o titanium alloy (Ti6Al4V) surface texturing and their characterization (morphological and chemical) produced by a Nd: YAG laser, aiming to create localized electrical insulation zones, necessary to accommodate electrical communication systems. The characterization of the textured surface was carried out by scanning electron microscopy and the heat affected zone was analyzed by X-ray diffraction. The results showed the formation of α-Ti, Ti6O and Ti2O phases on the textured surface. Through simulations in TINA software, the outer oxide layer formed during laser texturing had efficiency above 90% as insulator when an electrical current was applied
Shear bond strength of veneering porcelain to zirconia: Effect of surface treatment by CNC-milling and composite layer deposition on zirconia
(Elsevier, 2016-07) Nascimento, Rubens Maribondo do; Santos, Rafaela Luiz Pereira; Silva, Filipe Samuel; Souza, Júlio César Matias de; Motta, Fabiana Villela da; Carvalho, Oscar; Henriques, Bruno
Objectives: The purpose of this study was to evaluate the shear bond strength of veneering feldspathic porcelain to zirconia substrates modified by CNC-milling process or by coating zirconia with a composite interlayer. Methods: Four types of zirconia–porcelain interface configurations were tested: RZ – porcelain bonded to rough zirconia substrate (n1⁄416); PZ – porcelain bonded to zirconia substrate with surface holes (n1⁄416); RZI – application of a composite interlayer between the veneering porcelain and the rough zirconia substrate (n1⁄416); PZI – application of a composite interlayer between the porcelain and the zirconia substrate treated by CNC-milling (n1⁄416). The composite interlayer was composed of zirconia particles reinforced porcelain (30%, vol%). The mechanical properties of the ceramic composite have been determined. The shear bond strength test was performed at 0.5 mm/min using a universal testing machine. The interfaces of fractured and untested specimens were examined by FEG-SEM/EDS. Data was analyzed with Shapiro–Wilk test to test the assumption of normality. The one-way ANOVA followed by Tukey HSD multiple comparison test was used to compare shear bond strength results (α1⁄40.05). Results: The shear bond strength of PZ (100715 MPa) and RZI (96711 MPa) specimens were higher than that recorded for RZ (control group) specimens (89715 MPa), although not significantly (p40.05). The highest shear bond strength values were recorded for PZI specimens (138719 MPa), yielding a significant improvement of 55% relative to RZ specimens (po0.05)
Tribological behaviour of glass-ceramics reinforced by Yttria Stabilized Zirconia
(Elsevier, 2016) Santos, Rafaela Luiz Pereira; Buciumeanu, Mihaela; Silva, Filipe Samuel; Souza, Júlio César Matias de; Nascimento, Rubens Maribondo do; Motta, Fabiana Villela da; Carvalho, Oscar; Henriques, Bruno
The aim of this study was to evaluate the tribological behaviour of a dental glass-ceramic (GC) reinforced by 20% (vol.) Yttria-Stabilized Zirconia. Two types of particles were tested: zirconia agglomerates (ZA) and pre-sintered zirconia particles (ZP). The wear tests were carried out using a ball-on-plate configuration. The wear mechanisms were characterized by field emission guns scanning electron microscope. Results revealed an improvement of wear behaviour for GC reinforced by ZP. The improvement on wear resistance was attributed to the effect of reinforcement, by the action of the uniformly distributed ZP that allowed the load transfer reinforcing mechanism through the matrix and reinforcement phase. Dental glass-ceramic reinforced by ZP can constitute a promising alternative to conventional glass-ceramics to produce prosthetic restorations

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Navegando por Autor "Carvalho, Oscar"