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At least 685 records · Page 38Linked to original sources
PubMed1994

Hygroscopic expansion of resin based composites during 6 months of water storage.

Water absorption of composite materials causes an expansion (hygroscopic) which may result in an outward force being generated against the cavity walls. The purpose of this work was to investigate the relationship between this force and the water absorption of the material over a 6 month period of water storage. This investigation was performed by measuring the force required to displace specimens of the test materials from near cylindrical cavities. An outward force developed over a period of a few days of water storage for all test materials. The magnitude of the force was greatest for a microfilled composite, which also had the greatest water absorption. The smallest forces were observed for a hybrid composite. The magnitude of the force was independent of the Young's modulus of the test material. It would appear that expansion due to water absorption is able to rapidly compensate the effects of polymerisation shrinkage. In some cases the forces produced against the cavity walls give rise to some concern for the integrity of the restored tooth.

Absorption↗
PubMed2006

Thin and defect-free Pd-based composite membrane without any interlayer and substrate penetration by a combined organic and inorganic process.

A novel combined organic and inorganic process for preparing thin supported membrane was developed, using which a thin and defect-free Pd membrane with uniform thickness of 5 microm was directly coated onto porous alpha-Al2O3 hollow fiber without any interlayer and substrate penetration; at the same time, there existed a small interstice between membrane and substrate, which led to higher hydrogen permeance, infinite selectivity, and better membrane stability.

Journal Article↗
PubMed2000

Clinical evaluation of an urethane tetramethacrylate-based composite material as a prosthetic veneering agent.

The purpose of the current study was to evaluate the clinical performance of a hybrid composite material used as a prosthetic veneering agent after servicing for more than 4 years. A photo-curable composite material (Cesead) was selected as the veneering agent. Composite resin veneered restorations made with the composite and a noble metal alloy were inserted into 110 teeth of 40 patients. Modified United States Public Health Service (USPHS) criteria were used for direct evaluation of colour matching ability, veneer-metal interfacial staining, veneer surface texture, staining of the metal casting, and wear of the veneer-metal interface. After an average observation period of 5 years and 3 months, the rate of restorations considered to be clinically ideal (Alfa) was 75.5% for colour match, 93.6% for veneer-metal interfacial staining, 82.7% for veneer surface texture, 97.3% for staining of the metal casting, and 95.5% for wear. The restorations judged as clinically unacceptable (Charlie) consisted of only one case for colour match and three cases for veneer surface texture. Although the Alfa rate decreased with increasing length of service, the Cesead composite is considered to be a clinically reliable material as a prosthetic veneering agent.

Adult↗
PubMed1996

Microscopic DNA flexibility analysis. Probing the base composition and ion dependence of minor groove compression with an artificial dna bending agent.

We have used an artificial DNA bending agent to monitor the local flexibility of the DNA helix as a function of Mg2+ cation concentration, sequence, and temperature. A DNA bending agent was constructed from a pair of triple helix-forming oligonucleotides connected by a flexible polymeric linker, which, when the linker is short enough, causes a bend in a minor groove region separating the two sites of triple helix formation. The unique aspect of this system is that, since the bent region is not in direct contact with the linker or the triple helix-forming oligonucleotides, the free energy reflecting the bendability of the minor helix groove can be estimated from a comparison of binding affinity between the bent and unbent triple helices. A binding competition experiment and association and dissociation kinetic assays executed at 37 degrees C in the presence of 10 mM Mg2+ have revealed an extremely small difference in binding affinity between bent (50 degrees ) and straight triple helices, suggesting that DNA flexibility with respect to minor groove compression is extremely high and virtually independent of the sequence of the distorted duplex. This unexpectedly small difference in binding affinity was detected over the temperature range from 25 to 65 degrees C, and over a Mg2+ concentration range from 0.3 to 10 mM. Thus, these findings provide evidence that DNA bendability for minor groove compression is inherently high and independent of DNA sequence, temperature, or a 30-fold variation of Mg2+ ion concentration.

Binding, Competitive↗
PubMed2001

Development of porous clay-based composites for the sorption of lead from water.

Lead contamination of water is a major health hazard, as illustrated by the fact that exposure to this metal has been associated with death and disease in humans, birds, and animals. The present research was aimed at the development of a porous, solid-phase sorbent that can be used in the remediation of lead-contaminated water. A suitable sorbent was identified by screening various clays and other materials for their ability to effectively bind lead. The clay was adhered to a solid support using an aqueous solution of carboxymethyl cellulose. The binary composite was then tested for its ability to bind lead from solution, while providing void volume, increased surface area, and considerably enhanced hydraulic conductivity. The results suggested that a combination of sodium montmorillonite clay and carbon exhibited enhanced sorption of lead compared to carbon alone, and also supported the potential application of various combinations of sorbent materials. This value-added combination of clay, solid support, and adhesive will allow for the construction of column filtration systems that are multifunctional and capable of purifying large volumes of contaminated water.

Adsorption↗
PubMedDate not supplied

In vitro and in vivo degradation of mineralized collagen-based composite scaffold: nanohydroxyapatite/collagen/poly(L-lactide).

The objective of this article was to investigate the in vitro and in vivo biodegradation of a novel biomimetic bone scaffold composite, nanohydroxyapatite/collagen/poly(L-lactide), that could be used for bone tissue engineering. For evaluation of in vitro degradation specimens were immersed into 1% trypsin/phosphate-buffered saline solution at 37 degrees C. In vivo evaluation involved the implantation of samples into the posterolateral lumbar spine of rabbits, and the retrieved specimens were analyzed by Fourier transform-infrared spectroscopy. The results demonstrated that weight loss increased continuously in vitro with a reduction in mass of 19.6% after 4 weeks. During the experimental period in vitro, the relative rate of reduction of the three components in this material was shown to differ greatly: collagen decreased the fastest, from 40% by weight to 20% in the composite; hydroxyapatite content increased from 45 to 60%; and PLA changed little. The pore structure was maintained throughout the whole experimental period in vitro; however, the thickness of the walls of the pores decreased and the surface of the walls increased in roughness. In vivo, the ratio of collagen to hydroxyapatite appeared to be slightly higher near the transverse process than in the central part of the intertransverse process. This finding may have been due to new bone matrix formation extending from the transverse to the intertransverse process.

Animals↗
PubMed1985

Dermal effects of compositions based on the eutectic mixture of lignocaine and prilocaine (EMLA). Studies in volunteers.

The effects of the cutaneous application of EMLA cream (a eutectic mixture of lignocaine and prilocaine in their base form) were studied in volunteers. When tested by pin-prick, EMLA cream 2.5% and 5% produced analgesia of the area tested, the cream being most effective if left in contact with the skin for 60 min. The pain produced by the insertion of an i.v. cannula was successfully blocked by the application of this formulation, especially if applied to the antecubital area. Temporary blanching of the skin areas was frequently observed on removal of the occlusive tape bandages, but prolonged, or repeated, application of 5% EMLA cream did not produce local skin reactions. Tests for delayed hypersensitivity reactions were negative. Plasma concentrations of lignocaine and prilocaine were low after a standard application.

Administration, Topical↗