João Manuel Domingos de Almeida Rollo

Effect of beryllium on the castability and resistance of ceramometal bonds in nickel-chromium alloys.

STATEMENT OF PROBLEM Castability and ceramometal bond resistance play an important role in accepting nickel-chromium alloys as a substitute for gold alloys in dentistry. PURPOSE This study was developed to verify the effect of beryllium on these factors in several compositions of nickel-based alloys by submitting them to castability and ceramometal bonding resistance tests. MATERIAL AND METHODS Three experimental compositions of Ni-Cr alloys with different amounts of beryllium were used. One beryllium-free alloy was used as the control. RESULTS Analysis of variance and Tukeys test showed significant differences (alpha = .001) for the castability test results and significant differences (alpha = .05) for ceramometal bond resistance between alloys. CONCLUSIONS Although the amounts of chromium, manganese, and niobium were maintained, the variations in the amounts of beryllium allowed the estimation that Be-containing alloys presented better castability than Be-free alloys. The 0.9% Be-containing alloy demonstrated higher resistance of the ceramometal bond than the Be-free alloy.

Correlation between metal-ceramic bond strength and coefficient of linear thermal expansion difference

The purpose of this study was to evaluate the metal-ceramic bond strength (MCBS) of 6 metal-ceramic pairs (2 Ni-Cr alloys and 1 Pd-Ag alloy with 2 dental ceramics) and correlate the MCBS values with the differences between the coefficients of linear thermal expansion (CTEs) of the metals and ceramics. Verabond (VB) Ni-Cr-Be alloy, Verabond II (VB2), Ni-Cr alloy, Pors-on 4 (P), Pd-Ag alloy, and IPS (I) and Duceram (D) ceramics were used for the MCBS test and dilatometric test. Forty-eight ceramic rings were built around metallic rods (3.0 mm in diameter and 70.0 mm in length) made from the evaluated alloys. The rods were subsequently embedded in gypsum cast in order to perform a tensile load test, which enabled calculating the CMBS. Five specimens (2.0 mm in diameter and 12.0 mm in length) of each material were made for the dilatometric test. The chromel-alumel thermocouple required for the test was welded into the metal test specimens and inserted into the ceramics. ANOVA and Tukeys test revealed significant differences (p=0.01) for the MCBS test results (MPa), with PI showing higher MCBS (67.72) than the other pairs, which did not present any significant differences. The CTE (10-6 °C-1) differences were: VBI (0.54), VBD (1.33), VB2I (-0.14), VB2D (0.63), PI (1.84) and PD (2.62). Pearsons correlation test (r=0.17) was performed to evaluate of correlation between MCBS and CTE differences. Within the limitations of this study and based on the obtained results, there was no correlation between MCBS and CTE differences for the evaluated metal-ceramic pairs.

Plastic behavior of medium carbon vanadium microalloyed steel at temperatures near gamma alpha transformation

Dilatometric techniques were used to build the continuous cooling transformation (CCT) diagram for a medium carbon microalloyed steel; the microstructure and hardness were determined at different cooling rates. The mechanical behavior of the steel in the austenite field and at temperatures approaching austenite to ferrite transformation was measured by means of hot torsion tests under isothermal and continuous cooling conditions. The no recrystallization temperatures, Tnr, and start of phase transformation, Ar3, were determined under continuous cooling condition using mean flow stress vs. inverse of absolute temperature diagrams. Interruption of static recrystallization within the interpass time in the austenite field indicated that the start of vanadium carbonitride precipitation occurred under 860 °C. Austenite transformation was found to start at around 710 °C, a temperature similar to that measured by dilatometry, suggesting that interphase precipitation delays the transformation of deformed austenite. Pearlite was observed at temperatures ranging from 650 °C to 600 °C, with the flow curves taking on a particular shape, i.e., stress rose sharply as strain was increased, reaching peak stress at low deformation, around 0.2, followed by an extensive softening region after peak stress.

Cartilage reconstruction using self-anchoring implant with functional gradient

This study presents an innovative and original biomaterial designed to substitute for articular cartilage and mimic its mechanical behavior, including elastic cushioning and the characteristics of fiber-reinforced gel. The material was composed of polyurethane and bioglass microfiber 45S5. It was designed to present a tribological surface to the cartilage of the tibial plateau, and to convert over a functional gradient to an osteointegrable region for self-anchorage to the subchondral bone. The biomaterial samples showed no toxicity and promoted cell spreading. Subsequent in vivo studies in rabbits demonstrated the formation of a rigid structure similar to bone trabeculae in the distal region of the tribological surface of the implant. The tribological surface of the proximal region showed a fibrocartilaginous tissue with highly vascularized chondrocytes, thus validating the proposed concept for the design of the implant incorporating a functional gradient and auto-stability.

Bone response to porous alumina implants coated with bioactive materials, observed using different characterization techniques

Background Implants or implantable devices should integrate into the host tissue faster than fibrous capsule formation, in which the design of the interface is one of the biggest challenges. Generally, bioactive materials are not viable for load-bearing applications, so inert biomaterials are proposed. However, the surface must be modified through techniques such as coating with bioactive materials, roughness and sized pores. The aim of this research was to validate an approach for the evaluation of the tissue growth on implants of porous alumina coated with bioactive materials. Methods Porous alumina implants were coated with 45S5 Bioglass® (BG) and hydroxyapatite (HA) and implanted in rat tibiae for a period of 28 days. Ex vivo resections were performed to analyze osseointegration, along with histological analysis, Scanning Electron Microscopy with Energy Dispersive X-Ray spectroscopy (SEM-EDX) line scanning, radiography and biomechanical testing. Results Given that the process of implant integration needs with the bone tissue to be accelerated, it was then seen that BG acted to start the rapid integration, and HA acted to sustaining the process. Conclusions Inert materials coated with bioglass and HA present a potential for application as bone substitutes, preferably with pores of diameters between 100 μm and 400 μm and, restrict for smaller than 100 μm, because it prevents pores without organized tissue formation or vacant. Designed as functional gradient material, stand out for applications in bone tissue under load, where, being the porous surface responsible for the osseointegration and the inner material to bear and to transmit the loads.

Potencialidade do elemento tóxico berílio, usado em prótese dentárias

In the present work, the effect of beryllium on microstructure, corrosion and melting temperatures in Ni-Cr-Mo-Co alloys was studied. The study consisted in obtaining several alloys through meltings under vacuum, followed by wrought in industrial conditions. After wrought, the alloys were thermally treated under several temperatures and cooled in water, air and furnace. The presence of beryllium in the Ni-Cr-Mo-Co alloys changes the microstructure, producing intermetallic phases. It was observed that in the studied alloys the presence of beryllium decreases melting temperatures and promotes pite corrosion

Study of Abrasive Cutting of Natural Quartz for Manufacturing Piezoelectric Power Generators

The present study is related with the dicing of natural quartz crystals as part of the process manufacturing of a power generator device. Power generation is important, mainly for wifi systems, which use of batteries is restrictive or impossible due short dimensions and difficult of maintenance. The manufacturing dicing process applied in micro electromechanical systems (MEMS) is the main reference for this study, which objective is explores different parameters of dicing process and the impact of it in the final performance of the generator. Failure impregnation and productivity were study in blade and band saw process with different parameters as speed and cutting force. The natural quartz was selected mainly because availability in Brazil and piezoelectric properties. It was obtained substrates AT cutting plan with thickness of 2.5mm and width of 3mm. The material was tested under compressive stress and the correspondent electric signal was obtained.

Microstructure by Thermal Attack under Vacuum of a Superduplex Stainless Steels and Electrochemical Behavior in H2S/CO2-Saturated Synthetic Seawater

Superduplex stainless steels (SSS) composed in both equal fraction ferritic-austenite phases, classically defined by ASTM A995M Gr.5A, in order to obtain a better relation of mechanical properties and corrosion properties, are applied as components for use in petrochemical industries in off-shore platforms. The corrosion resistance of stainless steels is due to the oxides formed on the surface, which is dependent on the temperature and environment in which they are exposed. This paper investigates a microstructure duplex during steps of thermal attack under vacuum at high temperatures through observation of the coloration and growth of oxide films. Some coloration was observed in the phases, austenite and ferrite, with the increase of the temperature to 1100 °C, which is indicative of the presence of chromium and iron oxides. In the cooling occurs the stability of oxides present in the films. Electrochemical tests were conducted in H2S/CO2-saturated in two different concentrations of chloride sodium electrolyte, simulating a seawater environment. Potentiodynamic polarization curves indicate that pitting corrosion resistance and repassivation process in media of 3.5 and 9.0% (wt.%) NaCl are not affected by the presence of H2S/CO2 (40/60 ppm) at room temperature (25 °C).

Axial compressive strength of human vertebrae trabecular bones classified as normal, osteopenic and osteoporotic by quantitative ultrasonometry of calcaneus

Abstract : Biomechanical assessment of trabecular bone microarchitecture contributes to the evaluation of Introductionfractures risk associated with osteoporosis and plays a crucial role in planning preventive strategies. One of the most widely clinical technics used for osteoporosis diagnosis by health professionals is bone dual-energy X-ray absorptiometry (DEXA). However, doubts about its accuracy motivate the introduction of congruent technical analysis such as calcaneal ultrasonometry (Quantitative Ultrasonometry - QUS). Methods: Correlations between Bone Quality Index (BQI), determined by calcaneal ultrasonometry of thirty (30) individuals classified as normal, osteopenic and osteoporotic, and elastic modulus (E) and ultimate compressive strength (UCS) from axial compression tests of ninety (90) proof bodies from human vertebrae trabecular bone, which were extracted from cadavers in the twelfth thoracic region (T 12 ), first and fourth lumbar (L 1 and L 4 ). Results: Analysis of variance (ANOVA) showed significant differences for E (p = 0.001), for UCS (p = 0.0001) and BQI. Spearman’s rank correlation coefficient (rho) between BQI and E (r = 0.499) and BQI and UCS (r = 0.508) were moderate.