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Biomedical subjects

T C Shen

Publications and source records attributed to T C Shen.

At least 19 recordsLinked to original sources
PubMed1999

The use of different implant modalities in the atrophied ridge.

Many implant practitioners have been taught to use one implant system by a specific manufacturer. However, to successfully treat a patient, implant clinicians must learn to utilize the strengths of various systems when the patient's condition warrants it. The purpose of this paper is to illustrate how an edentulous patient with atrophied bone was treated with multiple-model implant procedures. Her treatment included different root form implants, bone spreading augmentations, endosseous submerged blades, tricortical support Diskimplants, and a custom-made ramus blade implant.

Alveolar Ridge Augmentation↗
PubMed1995

Transplanting teeth successfully: autografts and allografts that work.

This article suggests tooth transplantation as an alternative to other restorative options. The 10-year success rates for autografts--teeth moved from one location to another in a patient's mouth--range from 60 percent to 95 percent. Allografts, teeth moved from one person to another, are less successful. The authors report on one case of each type of transplant.

Adolescent↗
PubMed1994

In-situ polymerized PLOT columns III: divinylbenzene copolymers and dimethacrylate homopolymers.

Studies of divinylbenzene copolymers and dimethacrylate homopolymers indicate that the polymer pore size controls the separation of water and ammonia on porous-layer-open-tubular (PLOT) columns. To a lesser degree, the polarity of the polymers also affects the separation of a water-ammonia gas mixture. Our results demonstrate that the pore size can be regulated by controlling the cross-linking density or the chain length between the cross-linking functional groups. An optimum pore size will provide the best separation of water and ammonia.

Ammonia↗
PubMed1992

In-situ polymerization PLOT columns I: divinylbenzene.

A novel method for preparation of porous-layer open-tubular (PLOT) columns is described. The method involves a simple and reproducible, straight-forward in-situ polymerization of monomer directly on the metal tube.

Carbon Dioxide↗
PubMed1990

[A study of changes in the ratio of collagen types in skin after long-term treatment with topical glucocorticoids].

The topical glucocorticoids, widely used in the treatment of a variety of skin disorders, usually induce skin atrophy after long-term administration. In this study, the skin from a 30-year-old female patient was used, and the changes in the ratio of collagen types in atrophic skin derived from the treatment with glucocorticoid were investigated in comparison with that of normal human skin. By transmission electron microscopy, the collagen fibrils in the papillary dermis of normal skin were loose and fine, their diameters ranging from 30 to 40 nm; while those in the atrophic skin appeared tightly compact, their diameters increasing to 50-60 nm. The collagen chains, alpha 1 (I), alpha 2 and alpha 2 (III), from peptic digest of skin were separated by interrupted gel electrophoresis. The ratios of collagen type III to type I as calculated from the normal skins of a 21- and a 39-week fetus and a 36-year-old human were 49.45, 45.51 and 43.65%, respectively, while that of the atrophic skin was 12.89%. Therefore, the persistent treatment of skin with topical glucocorticoids results in a decrease in the ratio of collagen type III to type I.

Administration, Topical↗
PubMed1982

Effect of reduced pyridine nucleotides and tungstate on the in vitro insertion of molybdenum into demolybdo-nitrate reductase of Chlorella vulgaris.

Demolybdo-nitrate reductase (cytochrome c reductase) (NADH: acceptor oxidoreductase, EC 1.6.99.3) of Chlorella vulgaris can be activated in vitro to nitrate reductase by insertion of Mo from molybdate into the apoprotein. Evidence is here presented that reduction of the enzyme by reduced pyridine nucleotides inhibits the process of molybdenum insertion. This report also describes the effect of molybdate and tungstate concentration on the activation process. The activation is sigmoidally related to molybdate concentration with a calculated Hill coefficient of NH = 3. At suboptimal molybdate concentrations, tungstate stimulates enzyme activation by molybdate; but at saturating molybdate concentrations, tungstate is inhibitory. These facts are regarded as an indication that molybdate and tungstate are both positive effectors of molybdenum incorporation, but that they are competitors for the active Mo center.

Apoproteins↗
PubMed1982

Occurrence of nitrate reductase inhibitor in rice plants.

Nitrate reductase inhibitor is usually found in the roots of rice plants (Oryza sativa L. cv MR7), but it was also produced in the shoots of aging plants. The inhibitor was inducible in the shoot of rice seedlings by dark, minus-nitrate or plus-ammonium treatments. There appears to be a general involvement of the inhibitor in the control of nitrate assimilation in the plant.

Journal Article↗
PubMed1981

Molybdenum insertion in vitro in demolybdo nitrate reductase of Chlorella vulgaris.

Demolybdo nitrate reductase (also called cyt c reductase) of Chlorella vulgaris has been converted to active nitrate reductase by insertion of Mo from Na2MoO4 in vitro. A procedure is described which consistently gives about 0.3 unit of nitrate reductase from about 6 units of cyt c reductase, a yield of 30% of the maximum expected, if we calculate on a basis of a ratio of 6 to 1 for the cyt c reductase/nitrate reductase of purified normal enzyme. The demolybdoenzyme is incubated for 30 s at 31 degrees C with molybdate and reduced glutathione (GSH) at pH 4.8, and the pH is then raised to 7, and the incubation continued for 20 min. At the acid pH, there must be a partial denaturation or unfolding which permits Mo insertion, with a refolding to active enzyme at the higher pH. The GSH is not essential for activation, but in its absence the yield of active enzyme was about 50% lower. Experiments with labeled GSH showed that no GSH was incorporated into the protein during the activation procedure. Although the enzyme activity measurements suggested that only 30% of the enzyme was activated, measurements with 99Mo showed that there was one Mo incorporated per subunit weight of 90,000. The Km for nitrate of the activated nitrate reductase was identical with the Km for nitrate of the normal enzyme. On gradient centrifugation, activated nitrate reductase, cyt c reductase, and normal nitrate reductase all behaved identically.

Chlorella↗
PubMed1980

Nitrate reductase inhibitor of rice plants.

Two fractions of nitrate reductase inhibitor activities were found in extracts of primary and regenerated roots of nitrate-grown rice seedlings. The inhibitor was proteinaceous in nature and specific to nitrate reductase. The main site of action of the inhibitor was the NADH: cytochrome c reductase component of nitrate reductase. NADH was able to protect the NADH:nitrate reductase against the inhibitor.

Chromatography, Gel↗
PubMed1976

NADH- and NAD(P)H-Nitrate Reductases in Rice Seedlings.

By use of affinity chromatography on blue dextran-Sepharose, two nitrate reductases from rice (Oryza sativa L.) seedlings, specifically, NADH:nitrate oxidoreductase (EC 1.6.6.1) and NAD(P)-H:nitrate oxidoreductase (EC 1.6.6.2), have been partially separated. Nitrate-induced seedlings contained more NADH-nitrate reductase than NAD(P)H-nitrate reductase, whereas chloramphenicol-induced seedlings contained primarily NAD(P)H-nitrate reductase. NAD(P)H-nitrate reductase was shown to utilize NADPH directly as reductant. This enzyme has a preference for NADPH, but reacts about half as well with NADH.

Journal Article↗