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Biomedical subjects

C Shen

Publications and source records attributed to C Shen.

At least 127 records · Page 7Linked to original sources
PubMed1989

The effect of glutaraldehyde base disinfectants on denture base resins.

The effect of two alkaline glutaraldehyde base disinfectants on a heat-cured denture base resin was evaluated by the flexural strength, the repair flexural strength, and the surface morphology of the material that had been immersed up to 12 hours in the disinfecting solutions. The flexural strength of the material was not significantly affected by either disinfectant. The disinfectant with phenolic buffer caused surface pitting of the material after 10 minutes of immersion, and softening and swelling of the surface after 2 hours of immersion. No apparent surface change was observed with the regular alkaline formulation, however. Between the two repair resins, the autopolymerized resin yielded greater repair flexural strength than the light-cured repair resin. However, the repair flexural strength of autopolymerized resin seemed to be influenced by either disinfecting solution whereas the light-cured repair resin was not affected.

Acrylic Resins↗
PubMed1987

Prebiotic synthesis of imidazole-4-acetaldehyde and histidine.

The prebiotic synthesis of imidazole-4-acetaldehyde and imidazole-4-glycol from erythrose and formamidine has been demonstrated as well as the prebiotic synthesis of imidazole-4-ethanol and imidazole-4-glycol from erythrose, formaldehyde and ammonia. The products were identified by TLC, HPLC, and LC-MS by comparison with authentic samples. The maximum yields of imidazole-4-acetaldehyde, imidazole-4-ethanol, and imidazole-4-glycol obtained in these reactions are 1.6, 5.4, 6.8% respectively, based on the erythrose. Imidazole-4-acetaldehyde would have been converted to histidine on the primitive earth by a Strecker synthesis, and several prebiotic reactions would convert imidazole-4-glycol and imidazole-4-ethanol to imidazole-4-acetaldehyde.

Aldehydes↗
PubMed1986

Assessment of microleakage of restorative materials by a diffusion model.

The time-dependent microleakage behaviour of two types of restorative materials, a microfilled composite resin and a glass ionomer, was studied. A dentine bonding agent was also included. This study was based on a diffusion model of microleakage. It was found that the initial gap sizes of the restorations increased progressively for restorations microfilled with bonding agent, microfilled alone, and glass ionomers, in that order. Analysis of microleakage over some periods suggests that the gap size of the restorations by microfilled with bonding agent may increase with time, and that while restorations by glass ionomer and microfilled composite resin decrease in gap sizes with time, glass ionomer restorations show a faster rate of decrease.

Adhesives↗
PubMed1985

Controlled release of fluoride in connection with dental composite resins.

A delivery system of F- in connection with dental restorations was tested. The system utilized the gap space which often exists between the restorative material and the tooth structure. A known quantity of fluoride compound was placed at a site within prepared plastic cavity blocks prior to restoring with composite resins. It was found that each specimen exhibited a unique steady-state release of F- during a certain period of the experiment. The rate and duration of the steady-state release of fluoride were independent of the types of composites used. This phenomenon was explained in terms of the gap size which could have been influenced by the manipulation and the nature of the materials. The benefit of this delivery system in dental application is its ability to maintain a high concentration of F- within the gap.

Composite Resins↗
PubMed1985

Interactive effect of stress and temperature on creep of PFM alloys.

The creep rates of six alloys for porcelain-fused-to-metal (PFM) restorations were determined as a function of flexural stress and temperature. Although two Pd-Cu alloys demonstrated excellent resistance to creep at low-stress, high-temperature conditions, they were especially susceptible to deformation at high stresses and temperatures near the glass transition temperature of dental porcelains. In comparison, a Ni-Cr alloy and a Pd-Co alloy demonstrated superior creep resistance at high-stress, low-temperature conditions. This indicates a relatively low potential for deformation due to stresses which may result from a thermal contraction differential between these two alloys and incompatible dental porcelains.

Chemical Phenomena↗
PubMed1984

The prebiotic synthesis and catalytic role of imidazoles and other condensing agents.

In the past decade significant advances have been made in the synthesis of oligonucleotides and other polymers by means of imidazoles and other condensing agents. In spite of the current knowledge of the chemistry of imidazoles and their importance as prebiotic catalysts, their formation under primitive earth conditions has not been properly demonstrated. We have now been able to synthesize imidazole as well as its 2-methyl and 4-methyl derivatives under plausible prebiotic conditions. One method utilizes an aldehyde (formaldehyde or acetaldehyde), glyoxal and ammonia as the starting materials for the formation of imidazole and 2-methylimidazole. The other method uses a carbohydrate and ammonia as the key reagents for the synthesis of 4-methylimidazole. The importance of imidazole and related compounds (e.g., cyanamide) in the synthesis of oligonucleotides has been studied by us as well as others. Apparently the charge relay group (-N-C-N-) present in imidazoles, carbodiimides, cyanamide, or the histidine and arginine of enzyme active centers is essential for the synthesis of phosphodiester and pyrophosphate bonds.

Acetaldehyde↗
PubMed1984

Effects of canal lubrication on retention of cemented posts.

The effect of lubricating the canal space prior to making a custom acrylic post pattern was studied in regard to the retention of cast posts cemented with zinc phosphate. Ways of removing the lubricant before cementation were also evaluated.

Acrylic Resins↗
PubMed1982

Antibodies from patients with connective tissue diseases bind specific subsets of cellular RNA-protein particles.

We characterized the RNA-containing antigens precipitated by sera from 260 patients with positive antinuclear antibodies. 49 individuals, most of whom had systemic lupus erythematosus or Sjögren's syndrome, possessed antibodies that precipitated the previously identified RNP, Sm, Ro, and La antigens either singly or in combinations. These antigens, which are located on discrete sets of small nuclear or cytoplasmic RNA-protein particles, exhibited a number of antigenic interrelationships. One patient's serum recognized a new particle containing a small RNA which we have called Th; it also precipitated the Ro complexes. Other patients with systemic lupus erythematosus, hepatitis B virus infection, juvenile rheumatoid arthritis, myositis, and rheumatoid arthritis had antibodies that precipitated specific subsets of ribosomal RNA and transfer RNA. One patient's serum contained a monoclonal immunoglobulin G that precipitated ribosomes. Most of these antibodies identified antigenic determinants constituted at least in part of protein. The specificity of the proteins bound to particular cellular RNA, probably explains the exquisite precision with which antibodies from rheumatic disease patients discriminate among RNA subsets. Such sera should be useful probes for investigating specific roles that different RNA and RNA-protein complexes play in cellular metabolism.

Antibodies, Antinuclear↗