Role of polyethylene-graft-glycidyl methacrylate compatibilizer on the biodegradation of poly(epsilon-calprolactone)/cellulose acetate blends

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Barrier and Mechanical Properties of Clay-Reinforced Polymeric Nanocomposites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Influência de diferentes agentes de fixação na resistência de união, por tração, de ligas metálicas fixadas à dentina.

They were casted pieces using three kinds of alloy (Ni-Cr, Ag-Sn and Cu-Al) with circular and smooth surface. They were cemented to human teeth, on occlusal surface, grounded at dentin level, through three different materials kind (zinc polycarboxylate cement, glassionomer cement and composite). After 24 hours storing, the samples were subjected to the tensile test. The results showed that the samples cemented with composite and the casts made with Ag-Sn alloy had higher bond strength.

Estudo comaprativo da resistência da união esmalt/resina/metal. Efeito de resinas de fixação, artifícios retentivos e ligas metálicas.

The purpose of this study was to compare the enamel/resin/metal bond tensile strength by using human canines, in which castings were bonded. These castings were obtained by Co-Cr or Ni-Cr alloys and showed four types of mechanisms of retention: 50 micrograms aluminum oxide abrasive, electrochemical etch, acrylic beads metal mesh. The castings were bonded utilizing Comspan Opaque and Panavia Ex. The specimens were subjected to tensile forces after 24 hours in an Instron machine. The castings subjected to 50 micrograms aluminum oxide abrasive and bonded utilizing Panavia EX showed the biggest bond tensile strength.

Ação do diclofenaco de sódio, após a interrupção da peritonite estercorácea, no cólon de ratos. Estudo da resistência mecânica e do colágeno tecidual.

The objective of the present study was to investigate changes in colon wall in rats with fecal peritonitis (Per) associated with sodium diclofenac (SD) by studying breaking strength and tissue collagen concentration. The rats were divided into the following experimental groups: GROUP 1-SD: 60 animals injected intramuscularly with sodium diclofenac at the dose of 2 mg/kg body weight; GROUP 2-Per: 60 animals injected intraperitoneally with a suspension of human feces. Peritonitis was interrupted after six hours of evolution; GROUP 3-Per+SD: 60 animals injected intraperitoneally with a suspension of human feces and receiving SD according to the schedule used for Groups 1 and 2; CONTROL GROUP: 12 animals injected intramuscularly with physiological saline. The animals of Group 1, 2 and 3 were successively sacrificed 2, 4, 7, 14 and 21 days after interruption of peritonitis an/or the beginning of treatment. Under conditions of the experimental model and of the methods used, we conclude that sodium diclofenac, peritonitis and the peritonitis-sodium diclofenac association decrease the breaking strength and the concentration of tissue collagen in the colon segment.

Mechanical behaviour of strain aged dual phase steels

Dual phase steels, characterised by good formability and excellent surface finish, are suitable for applications where processing involves cold deformation. In this context an investigation has been conducted into the cold deformation aging susceptibility of carbon steel API-5L-B and microalloyed steel API-5L-X52, both with dual phase microstructures. Changes in mechanical properties such as phase microhardness, ultimate tensile strength, and yield strength in both types of steel were observed at aging temperatures of 25, 80, and 150°C. This aging is associated with dislocation structures formed on ferrite grains in the vicinity of ferrite/martensite interfaces during intercritical treatments, which become preferential sites for solute atom diffusion. © 1999 IoM Communications Ltd.

Effect of whitening agents on dentin bonding

Background: Several studies have shown a reduction in enamel bond strengths when the bonding procedure is carried out immediately after vital bleaching with peroxides. This reduction in bond strengths has become a concern in cosmetic dentistry with the introduction of new in-office and waiting-room bleaching techniques. The aim of this in vitro study was to evaluate the effect of three bleaching regimens: 35% hydrogen peroxide (HP), 35% carbamide peroxide (CP), and 10% CP, on dentin bond strengths. Materials and Methods: One hundred and twenty fresh bovine incisors were used in this study. The labial surface of each tooth was ground flat to expose dentin and was subsequently polished with 600-grit wet silicon carbide paper. The remaining dentin thickness was monitored and kept at an average of 2 mm. The teeth were randomly assigned to four bleaching regimens (n = 30): (A) control, no bleaching treatment; (B) 35% HP for 30 minutes; (C) 35% CP for 30 minutes; and (D) 10% CP for 6 hours. For each group, half of the specimens (n = 15) were bonded with Single Bond/Z100 immediately after the bleaching treatment, whereas the other half was bonded after the specimens were stored for 1 week in artificial saliva at 37°C. The specimens were fractured in shear using an Instron machine. Results: For the groups bonded immediately after bleaching, one-way analysis of variance (ANOVA) followed by the Duncan's post hoc test revealed a statistically significant reduction in bond strengths in a range from 71% to 76%. For the groups bonded at 1 week, one-way ANOVA showed that group B (35% HP for 30 min) resulted in the highest bond strengths, whereas 10% CP resulted in the lowest bond strengths. Student's t-test showed that delayed bonding resulted in a significant increase in bond strengths for groups B (35% HP) and C (35% CP); whereas the group bleached with 10% CP (group D) remained in the same range obtained for immediate bonding. Storage in artificial saliva also affected the control group, reducing its bond strengths to 53% of the original. ©2000 BC Decker Inc.

Unsaturated polyester based composites reinforced with curauá fiber - Preliminary studies

Curauá fiber processing characterization has been performed throughout the different processing steps. Unsaturated polyester has been used as matrix in the production of curauá reinforced composite samples. Compression molding process has been used to prepare the samples. Tensile strength, impact resistance, flexural strength, Young's modulus and elongation at break have been accessed for curauá composites in comparison with fiberglass composites. Mechanical properties were found not to attend the company's internal standards specification. However, the work has shown some alternatives to solve these problems such as the modification of equipment characteristics and resin formulation, the necessity of incorporation of a higher content of fiber and the possibility of using a new type of filler. Copyright © 2000 Society of Automotive Engineers, Inc.

Effect of diclofenac sodium on the healing process of end-to-end anastomosis in carotid arteries of rabbits. Histopathological and biomechanical studies

Aim. Diclofenac sodium is a non-steroidal anti-inflammatory drug commonly used to attenuate painful inflammatory reactions in surgery. However, it may delay healing in the skin and gastrointestinal tract. The aim of this study was to evaluate the influence of Diclofenac in vascular healing. Methods. Ninety rabbits had their carotid arteries sectioned and reconstructed by end-to-end anastomosis with interrupted sutures. The animals were randomly allocated into 3 groups of 30 each and treated by intramuscular route with saline (control), 5 mg/kg/day of diclofenac sodium (DS-5), and 10 mg/kg/day of diclofenac sodium (DS-10). Treatment began on the day of surgery and lasted 4 days. Angiography, biomechanical properties (failure load, failure elongation, yield point, yield point elongation, and stiffness were obtained from the load/elongation curve), macroscopic and histological examinations (hematoxylin-eosin, Masson, Calleja, Picrossirius-red), and scanning electron microscopy were studied in both arteries on the 3rd and 15th postoperative days. Results. No significant differences in biomechanical properties were observed either in the 3 groups or the experimental times. The carotid artery healing process was similar in the 3 groups. Conclusion. Diclofenac sodium did not cause alterations nor delayed carotid artery healing.

Otimização das propriedades mecânicas por meio de modificações microestruturais em aços de baixo carbono

This paper discusses the formation of microstructures with different volume fractions, as an outcome of a specific heat treatment, with the following phases: ferrite, martensite, bainite and retained austenite. For the microstructure characterization it is developed a chemical etching that allows to distinguish the phases by optical microscopy. The evaluation of the mechanical properties is done based on the results of tensile and fatigue tests. The experimental results show that appropriate heat treatments can contribute to a significant improvement in the mechanical properties of the steel. In this process it is essential to control the fraction volume, morphology of the phases, and grain size.

Behavior of the PMD coefficient of optical links under influence of mechanical and thermal effects

This papers presents results on the variation of the PMD coefficient of optical links under influence of mechanical tests, such as tensile strength, bending and compression, and also during the application of a thermal cycle. Results revealed that the link coefficient is more influenced by the application of a tension load and also suffers significant variation under strong temperature changes. Copyrigth © SBMO.

Effect of surface treatments on the resin bond to zirconium-based ceramic

Purpose: This study tested the hypothesis that the tribochemical silica coating on ceramic surfaces increases the bond strength of resin cement to a glass-infiltrated zirconium-based ceramic. Materials and Methods: Fifteen blocks of In-Ceram Zirconia from CEREC InLab (5 per group) and 15 composite blocks (Z-250) 5 mm x 5 mm x 4 mm were made. The ceramic surfaces were polished, and the blocks were divided into three groups: (1) airborne abrasion with 110-μm aluminum oxide particles; (2) Rocatec system, tribochemical silica coating; and (3) CoJet system, tribochemical silica coating. The ceramic blocks were cemented to the composite blocks using Panavia F according to the manufacturer's specifications. All samples were stored in 37°C distilled water for 7 days and later sectioned in two axes using a diamond disk under cooling to obtain specimens with a cross-sectional area of approximately 1 mm2 (n = 45). Each specimen was then attached with cyanoacrylate glue to an adapted device for the microtensile test, which was carried out on a universal testing machine. Results: The results were subjected to ANOVA and Tukey's test. Group 2 (23.0 ± 6.7 MPa) and group 3 (26.8 ± 7.4 MPa) showed greater bond strength than group 1 (15.1 ± 5.3 MPa). There was no significant difference between groups 2 and 3. All failures were in the adhesive zone. Conclusion: The hypothesis was confirmed - the tribochemical systems increased the bond strength between Panavia F and In-Ceram Zirconia.

The role of the oblique ligament in the mechanical behavior of the medial collateral ligament of the mongrel dog elbow joint - Some biomechanical aspects

This study investigated the oblique ligament mechanical contribution to the medial collateral ligament of the canine elbow joint. Fifteen dogs were used for the study of the failure load, displacement, and energy absorption of the medial collateral and oblique ligaments of the canine elbow joint, associate and separately in the joint. Medial collateral ligament failure load and energy absorption were significantly higher in relation to the isolated oblique ligament. When the ligaments were associated in the joint, they presented an increment in failure load, displacement and energy absorption in relation to the ligaments analyzed separately. It was concluded, therefore, that the oblique ligament could have an important paper in the stability of the canine elbow joint, as it favors the medial collateral ligament resistance to the tensile load, one of the main stabilizer of the elbow joint.

Avaliação ultraestrutural do colágeno do ligamento colateral medial associado ao ligamento oblíquo da articulaç ão do cotovelo de cão SRD após ensaio de tração

Ultrastructural evaluation of the collagen of the mongrel dog medial collateral ligament associated to the oblique ligament after strain. The present work aimed to observe the disposition of the collagen fibres of the medial collateral ligament of the elbow joint of the dog, when associated to the oblique ligament. Thus, 18 articulations were used, divided in three groups. A group had the medial collateral ligament collected and not stretched, other group had the collateral medial ligament stretched separately and the other group had both ligaments (medial collateral and oblique) stretched associately. The medial collateral ligament examined by scanning electron microscopy presented a wavy and reticular pattern of the collagen fibres when not submitted to strain, which was not totally destroyed when it was associated to the oblique ligament. When stretched separately, the medial collateral ligament after strain totally loses the reticular pattern, demonstrating the waste of the fibres to resist to the tension.

Relation between the compaction rate and physical and mechanical properties of particleboards

The compaction rate, the relation between the density of the wood panel and the density of the wood used for producing the particles, is an indicator of the product's densification. Among the various types of wood panels, particleboards are widely employed in the lumber industry, mainly for the furniture production. This paper presents a study of the relation between the compaction rate and the properties of tensile strength perpendicular to surface, Modulus of Rupture (MOR) and Modulus of Elasticity (MOE) obtained from a static bending test, thickness swelling and water absorption (2 and 24 hours). These properties were calculated according to the Brazilian ABNT, NBR 14810 standard. Particleboards were produced using the species Pinus elliotti and adhesive ureaformaldehyde. The relation was established by a multiple linear regression, and the most appropriate statistical models were determined. The estimated models indicate statistically significant effects of water absorption in 2 hours and MOR in the particleboards' compaction rate.