Objective: To test the hypothesis that treatment time, debris/biofilm, and oral pH have an influence on the physical-chemical properties of orthodontic brackets and arch wires. Materials and Methods: One hundred twenty metal brackets were evaluated. They were divided into four groups (n 5 30) according to treatment time: group C (control) and groups T12, T24, and T36 (brackets recovered after 12, 24, and 36 months of treatment, respectively). Rectangular stainless-steel arch wires that remained in the oral cavity for 12 to 24 months were also analyzed. Dimensional stability, surface morphology, composition of brackets, resistance to sliding of the bracket-wire set, surface roughness of wires, and oral pH were analyzed. One-way analysis of variance, followed by a Tukey multiple comparisons test, was used for statistical analysis (P , .05).Results: Carbon and oxygen were shown to be elements that increased expressively and in direct proportion to time, and there was a progressive increase in the coefficient of friction and roughness of wires as a function of time of clinical use after 36 months. Oral pH showed a significant difference between group T36 and its control (P 5 .014). Conclusions: The hypothesis was partially accepted: treatment time and biofilm and debris accumulation in bracket slots were shown to have more influence on the degradation process and frictional force of these devices than did oral pH. (Angle Orthod. 2015;85:298-304.)
This study evaluates the margin of a nanofill, a nanohybrid, and a conventional microhybrid composite in restorations in occlusal cavities of posterior teeth after 12 months. Forty-one patients, each with three molars affected by primary caries or the need to replace restorations, participated in this research. The teeth were restored with a nanofill (Filtek Z350), a nanohybrid (Esthet-X), and a microhybrid as a control (Filtek Z250). Ten patients were selected randomly, and the three restorations were molded with a low-viscosity polyvinyl siloxane material. The molds were poured with epoxy resin, gold-sputter coated, observed by scanning electron microscopy, and classified as: "perfect margin," "marginal irregularity," "marginal gap," "marginal fracture," or "artifact." For statistical analysis, the Wilcoxon and Friedman nonparametric tests and paired-samples t-test were used (significance level of 5%). The performance of the three materials was compared after 1 week and 12 months. No statistically significant differences were detected for all criteria (P > 0.05). When each composite was compared over time, statistically significant differences were found for the criterion, perfect margins (Esthet-X and Filtek Z350, P < 0.05). The materials performed satisfactorily over the 12-month-observation period, but all composites under investigation showed a certain amount of deterioration relating to marginal quality over time.
The use of quasicrystalline alloys as reinforcement material is due to the fact that they posses high hardness and low coefficient of friction. For this purpose was used compaction/extrusion equipment with which it was possible to observe a tendency toward increase in the mechanical strength from 72MPa (0% reinforcement) to 129Mpa (6% reinforcement).
Eu-doped semiconductor matrix of ZnO at concentrations of 0.05 and 0.10 mols was synthesized by combustion reaction, using zinc nitrate, europium nitrate, and urea as fuel. In order to analyze the effect of europium concentration and sintering on the structure, band gap, magnetic and morphological properties of ZnO, the samples were sintered at 1100 °C for 30 min and analyzed before and after sintering via X-ray diffraction, ultraviolet and visible spectroscopy, vibrant sample magnetometry, and scanning electron microscopy. From the results obtained, it was found that there was the formation of the semiconductor phase ZnO and also a second-phase (Eu2O3). It was observed that the samples before and after sintering presented band gap values within the semiconductor range and ferromagnetism at room temperature.
The geopolymer although being a recently discovered material, it is already present in many industrial sectors. This range of applications is due to the commitment of the scientific community to understand and manipulate the material, seeking a contribution in this regard, it has produced geopolymer matrix composites with quasicrystalline and reinforcement, Al62,2Cu25,5Fe12,3 in the proportion of 10%, 20% and 30% by volume. These composites were obtained by manual production and heat treated at 400 º C for two hours. The characterization was made with the aid of scanning electron microscopy (SEM) and x-ray diffraction (XRD). Diffractograms of composites without heat treatment showed characteristic peaks of the phases present in the matrix and reinforcement. For the composites with heat-treated, it was observed that besides the phases mentioned above the presence of diffraction peaks possibly associated phase silica sodium aluminate. The composite showed good interface quasicrystal / geopolymer, showing the existence of a phase with lamellar morphology in the treated material.
The formation of brittle microstructures around the fusion line in dissimilar welds has required a deeper microstructural analysis in this region. The study becomes more relevant when these welds are used in environments that facilitate hydrogen embrittlement. The present work aims to characterize the microstructure and hardness at the diluted zone interface in joints welded with dissimilar materials. Aiming for a better efficacy in the microstructural characterization of this zone, samples of both normal cross-section (NCS) and section with slope were used, according to the low-angle microsectioning (LAMS) technique, which allows a greater amplification of partially mixed zones (PMZs). The results indicated the diffusion of carbon from the heat-affected zone (HAZ) towards the fusion line which, in combination with other alloying elements, form highly brittle carbides. In turn, the hardness of the base metal and the HAZ was reduced after post weld heat treatment, whereas in the weld metal an opposite behavior was observed. The dissimilar interface was promising for applications in environments facilitating hydrogen embrittlement, especially regarding the characteristics of zone Φ.
A 182 F22 steel, used in components subsea for oil extraction, are previously buttered with ductile metal such as Inconel 625, before being welded to steel pipes similar to ASTM A36 steels. The thermal buttering weld cycle provides the formation of high hardness micro-phases and carbides at the interface between F22 steel and the buttering with Inconel, which when in contact with hydrogen, originating from the cathodic protection applied to these equipment, can lead to the embrittlement of this region, causing fragile fractures. In this work, ASTM A 182 F22 steel, buttered with Inconel 625 and welded to A36 steel, submitted to post-weld heat treatment without hydrogenation and subjected to cathodic protection for hydrogen permeation were submitted to fracture toughness test. The welds and buttering were done using GMAW process with AWS ERNiCrMo-3 wire as filler and buttering metal and a mixture of Ar and He as shield gas. The results indicated a 56% of area reduction, and 15% in the elongation values in the tensile tests, in addition to a 13.3% reduction in the CTOD value, for welded joints subjected to hydrogen permeation, which showed a quasi-cleavage fracture mechanism.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.