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Biomedical subjects

W D Cook

Publications and source records attributed to W D Cook.

At least 55 records · Page 3Linked to original sources
PubMed1982

Rheological studies of the polymerization of elastomeric impression materials. I. Network structure of the set state.

As part of a detailed study of the curing of a range of dental elastomeric impression materials, their chemistry was investigated. This information, the dependence of the stress relaxation modulus of the set material on the catalyst/base ratios, and the level of diluent were used to elucidate the network structure. Such information is required before the rheological behavior during cure can be understood. The clinical significance of the recommended catalyst/base ratio is discussed.

Chemical Phenomena↗
PubMed1982

Rheological studies of the polymerization of elastomeric impression materials. II. viscosity measurements.

As part of a detailed study of the curing of a range of dental elastomeric impression materials, a cone and plate rheometer was used to measure the variation in viscosity due to chain growth. The dependence of this behavior on the catalyst/base ratio, retarding and accelerating agents, and alternative initiators was studied and rationalized in terms of the polymerization chemistry investigated previously. Limited success was achieved with the quantitative interpretation of this data in terms of the polymerization kinetics. Of clinical relevance, only the viscosity behavior of the imine-terminated polyether and one of the thiol-terminated polysulfides approached that of an ideal impression material.

Chemical Phenomena↗
PubMed1982

Rheological studies of the polymerization of elastomeric impression materials. III. Dynamic stress relaxation modulus.

As part of a detailed study of the curing of a range of dental elastomeric impression materials, the 10-s stress relaxation modulus was measured as a function of the curing time. The influence of the catalyst/base ratio was also investigated and compared with the pregel viscosity previously studied. Using the theory of network formation and an understanding of the chemistry of these materials, the modulus data were interpreted in terms of the polymerization kinetics. The addition silicones exhibited the most abrupt transition between the gel and final set stage, which is close the ideal response. The clinical significant of the results is discussed.

Chemical Phenomena↗
PubMed1982

Dental polyelectrolyte cements. I. Chemistry of the early stages of the setting reaction.

As part of an investigation of the setting of dental polyelectrolyte cements, the chemistry of a selection of glass ionomer and zinc polycarboxylate cements was studied by pH, conductivity and I.R. measurements. The zinc polycarboxylate cements were found to react at a greater rate than the glass ionomer cements. The effect of reducing the powder/liquid (P/L) ratio is to decrease the surface area available to attack and hence the reaction rate. The basic form of the kinetics appears to be unaffected except for low P/L ratios where there is a deficiency of available metal cations.

Chemical Phenomena↗
PubMed1982

Somatic mutation in a cultured mouse myeloma cell affects antigen binding.

The S107 mouse myeloma cell line synthesizes an IgA antibody that binds the hapten phosphocholine and is similar if not identical in its heavy and light chain variable region sequence to the predominant antibody produced by BALB/c mice in response to immunization with phosphocholine. This cell line frequently and spontaneously generates somatic variants producing immunoglobulins with decreased ability to bind antigen. One such variant, S 107.U1, is described here. This variant has a decreased ability to bind phosphocholine when it is attached to a carrier, although its affinity for free hapten is the same as that of the parent. This decrease in antigen binding is associated with a single amino acid substitution at the fifth residue in the JH segment.

Amino Acid Sequence↗
PubMed1982

Single amino acid substitution altering antigen-binding specificity.

S107, a phosphocholine-binding myeloma protein, has been cloned in soft agar, and an antigen-binding variant has been isolated and characterized. The variant does not bind phosphocholine attached to carrier or as free hapten in solution but does retain antigenic determinants (idiotypes) of the parent. Chain recombination experiments suggest that the defect in binding is entirely in the heavy chain. Amino acid sequence analysis showed a single substitution--glutamic acid to alanine at position 35--in the first hypervariable or complementarity-determining region. In terms of the three-dimensional model of the phosphocholine-binding site, glutamic acid-35 provides a hydrogen bond to tyrosine-94 of the light chain that appears to be critical for stability of this portion of the binding site. The removal of this bond and the presence of the smaller alanine side chain is thus consistent with the loss in binding activity. These results suggest that small numbers of substitutions in antibodies, such as those presumably introduced by somatic mutation, may in some situations be effective in altering antigen-binding specificity.

Amino Acid Sequence↗
PubMed1982

Rapid thymomas induced by Abelson murine leukemia virus.

Abelson murine leukemia virus (A-MuLV) is derived from the thymotropic Moloney leukemia virus. However, injection of mice with A-MuLV by conventional routes results in rapidly arising peripheral and bone marrow lymphomas, not thymomas or T cell tumors. In this study thymomas have been induced by intrathymic injection of A-MuLV into BALB/c and C57BL/Ka mice. In both strains thymomas arose with short latent periods, comparable with the latencies of nonthymic tumors induced by intraperitoneal injection of A-MuLV and significantly shorter than those of thymomas induced by intrathymic injection of Moloney leukemia virus. Cells of the BALB/c thymomas were predominantly Thy-1-; those of C57BL/Ka thymomas were predominantly Thy-1+. Tissue culture lines were established and cloned. Some of these expressed low amounts of Thy-1 and one also expressed Lyt-1. Virus from cloned lines transformed 3T3 cells in vitro and induced Abelson disease in vivo when injected intraperitoneally into neonates. The A-MuLV p120 protein has been precipitated from metabolically labeled cell lysates of one cloned Thy-1+ line. These results show that A-MuLV can transform cells in the T lymphocyte lineage.

Abelson murine leukemia virus↗
PubMed1981

Somatically generated mouse myeloma variants synthesizing IgA half-molecules.

Whereas mouse myelomas that secrete IgA half-molecules have been shown to arise in vivo, their origin has not been definitely established. We show that somatic variants secreting phenotypically similar molecules can arise directly from the normal IgA-secreting myelomas S107 and W3082. In addition to being improperly assembled, the variant proteins have distinct carboxy-terminal deletions and an aberrant heavy-light chain disulfide bond. For at least one of the variants, variable region serology and affinity for hapten are both unaffected by these changes. Southern and Northern blot analyses indicate normal size DNA restriction fragments and mRNA, suggesting premature termination as the mechanism of deletion. These results are discussed in relation to possible mutational hot spots and long-range interdomain interactions.

Animals↗
PubMed1981

Permanent set and stress relaxation in elastomeric impression materials.

The permanent set of a range of elastomeric impression materials, used in dentistry, was investigated as a function of the materials' age and the duration and level of the deformation. The permanent set appears to be primarily controlled by the rate of polymerization at the time of deformation. However, stress relaxation experiments revealed that, for condensation silicone and in particular polysulfide elastomers, bond interchange reactions produce additional permanent set. The rate of recovery of the elastomers from deformation was very rapid and was consistent with the influence of entanglement in the network.

Dental Impression Materials↗
PubMed1981

An investigation of the radiopacity of composite restorative materials.

The radiopacity of 33 commercially available composite materials was measured in terms of their equivalent thickness of an aluminum alloy per unit thickness of material. The theoretical significance of this definition was discussed. The radiopacities were found to vary by more than an order of magnitude. Although nearly 30 percent of the materials have radiopacities less than dentine, all materials claimed to be radiopaque were more so than dentine. The influence of operating potential, specimen thickness, X-ray generator type, film type, filtration and X-ray dose were investigated. The former two factors were found to have a large influence on the radiopacity.

Absorptiometry, Photon↗
PubMed1981

An investigation of methods proposed for the analysis of the various forms of fluoride in toothpaste.

Analytical methods for the determination of soluble fluoride, soluble fluorine and total fluorine derivatives in toothpaste were investigated. Potentiometric determinations of soluble fluoride in TISAB-toothpaste slurries were shown to be inaccurate. Based on recovery measurements, analyses for soluble fluoride and soluble fluorine derivatives in the supernatant liquid were found to be reliable provided the slurrying time was standardized. A gas chromatography method for the analysis of total fluorine, using the silane derivative fluoride, was compared with methods involving ashing and distillation prior to colorimetric or potentiometric analysis.

Chromatography, Gas↗
PubMed1980

The oscillating rheometer--what does it measure?

The motion involved in the operation of an oscillating rheometer was analyzed, and revealed that the instrument measured a complex mixture of an instrument-dependent parameter, the spring constant, and two material-dependent parameters--the dynamic viscosity and the shear storage modulus. The significance of the working and setting time parameters measured by the rheometer are discussed.

Chemical Phenomena↗
PubMed1980

Factors affecting the depth of cure of UV-polymerized composites.

Knoop hardness measurements of UV-polymerized dental composites showed that, at a certain depth below the surface, the degree of cure rapidly decreases. The depth of cure was found to be critically dependent on the UV source and exposure time used. A theoretical model was derived which was in quantitative accord with the results.

Absorption↗
PubMed1977

Antigen-binding mutants of mouse myeloma cells.

A cultured mouse myeloma cell line, S107, that secretes an IgA phosphocholine-binding immunoglobulin has been cloned in soft agar and overlaid with phosphocholine-hemocyanin. Spontaneous mutants that secrete immunoglobulin with a decreased ability to precipitate antigen were detected with this plate assay and occur at a very high frequency. From one such mutant, phenotypic revertants arise spontaneously with a frequency of 0.28-2.8%. This mutant and one of its revertants were studied, and they were found to differ from the parent and from each other serologically and in antigen binding. While it is not yet clear whether these findings bear any relationship to the normal generation of antibody diversity, they do indicate that it is possible to generate antigen binding diversity in somatic cells.

Antibody Specificity↗