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Biomedical subjects

R W Bryant

Publications and source records attributed to R W Bryant.

89 records · Page 5Linked to original sources
PubMed1979

Isolation of a new lipoxygenase metabolite of arachidonic acid, 8. 11, 12-trihydroxy-5,9,14-eicosatrienoic acid from human platelets.

Washed human platelets incubated with 1-14C-arachidonic acid (1mM) produced a new metabolite which migrated on thin layer chromatography close to thromboxane B2, but which was identified by mass spectrometry as a trihydroxy fatty acid. The mass spectrum was consistent with the assigned structure, 8,11,12-trihydroxy-5,9,14-eicosatrienoic acid (THETE). Platelet THETE synthesis from arachidonate was not inhibited by preincubation with asprin or indomethacin but was blocked by 5,8,11,14-eicosatetraynoic acid. Therefore, THETE appears to arise via the platelet lipoxygenase pathway rather than via the prostaglandin cyclooxygenase. Two proposed structures, including a novel dihydro-hydroxy-pyran cyclic intermediate, which could give rise to THETE are presented.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1979

The strength of fifteen amalgam alloys.

The compressive and tensile (by diametral compression) strengths of amalgams prepared from fifteen conventional and higher copper alloys are compared and the rate at which these amalgams develop strength is investigated. Alloys of the single melt high copper type generally possess the greatest strength at all times of testing. The amalgams tend to achieve maximum tensile strength more rapidly than maximum compressive strength. The major increase in strength takes place between one hour and one day.

Chemical Phenomena↗
PubMed1977

Differential separation of thromboxanes from prostaglandins by one and two-dimensional thin layer chromatography.

[14C]-labelled thromboxane B2 and hydroxy fatty acids were isolated using thin layer and gas chromatographic procedures from human platelets incubated with [1-14C]-arachidonic acid. A number of TLC solvent systems were evaluated for differential separation of thromboxanes and hydroxy fatty acids from prostaglandins E2, A2, D2 and F2alpha. Chromatographic properities in nine different solvent systems are tabulated. Two dimensional TLC procedures suitable for complete resolution of mixtures of these compounds on a single plate were developed. The systems were used to demonstrate conversion of [1-14C]-arachidonic acid to thromboxane B2 and prostaglandin E2 by human lung fibroblasts in tissue culture.

Arachidonic Acids↗
PubMed1976

Menaquinone biosynthesis: conversion of o-succinylbenzoic acid to 1,4-dihydroxy-2-naphthoic acid and menaquinones by Escherichia coli extracts.

Two intermediates in the biosynthetic pathway to bacterial menaquinones are o-succinylbenzoic acid and 1,4-dihydroxy-2-naphthoic acid. Cell-free extracts have been prepared from Escherichia coli which catalyze the conversion of labeled o-succinylbenzoic acid to the naphthoic acid and also to menaquinones. The naphthoate synthetase has been partially purified and found to require coenzyme A and ATP. The synthetase has an approximate molecular weight of 45 000. The conversion of o-succinylbenzoic acid to menaquinones is stimulated by the presence of farnesyl pyrophosphate. The major menaquinone produced is then MK-3 with the farnesyl side chain.

Benzoates↗
PubMed1976

A simulated clinical appraisal of base materials for amalgam restorations.

Eight materials were placed as bases on the pulpal surface of cavities prepared in extracted teeth. Seven minutes after mixing of the material commenced, amalgam was condensed on to the lined cavity. The restored teeth were sectioned subsequently for microscopic examination. The results suggested that all uniformly mixed, carefully placed base forming materials that have reached the state of "clinical set" are able to withstand loads applied during amalgam condensation irrespective of their strength.

Calcium Hydroxide↗
PubMed1976

The rate of development of strength in base forming materials for dental amalgam.

Eleven base forming materials used under amalgam restorations were examined for the rate of development of their compressive and tensile strengths. Materials from three categories were compared. Under in vitro conditions of testing, it was found that, immediately after a state of clinical set had been reached, the quick-setting zinc oxide-eugenol materials possessed strengths significantly greater than the calcium hydroxide cements but significantly weaker than the zinc phosphate cements. Calcium hydroxide cements possessed the lowest compressive strength to tensile strength ratio and modified zinc oxide-eugenol materials the highest.

Calcium Hydroxide↗
PubMed1976

The effects of manipulative variables on base forming materials for amalgam restorations.

The influence of several manipulative variables on the compressive and tensile strengths of eight base forming materials has been investigated. The most important manipulative variable from the point of view of influencing the development of strength was found to be the powder-liquid ratio. In particular, thicker mixes produced greater early strengths. The setting time of each material was found to be influenced more by the temperature during setting than the ambient temperature or presence of moisture.

Dental Amalgam↗
PubMed1975

Bases for gold inlays and crown restorations.

Modified zinc oxide-eugenol and calcium hydroxide cements are frequently used as bases beneath restorations. Investigation reveals that the bond strength between different types of dement may be less than that between different consistencies of the same type of dental cement. In some clinical situations, the choice of the type of cement as a base forming material beneath inlays and crowns should be made bearing in mind the type of luting material to be used.

Calcium Hydroxide↗
PubMedDate not supplied

Occlusal margin defects around different types of composite resin restorations in posterior teeth.

Using stone replicas of individual restorations from a clinical study investigating three types of posterior composite resins, four types of defects were identified on the occlusal margins. It was observed that particular types of defects were commonly associated with each type of composite resin. The microfilled composite usually exhibited crevice formation (marginal fracture), the small-particle hybrid showed evidence of both wear and crevice formation, and a coarse composite resin most noticeably exhibited wear. Fracture of excess composite was associated with the fine-textured composites.

Acrylic Resins↗