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Biomedical subjects

A Johnson

Publications and source records attributed to A Johnson.

At least 757 records · Page 42Linked to original sources
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The effect of surface treatments on the bond strength of a nonprecious alloy-ceramic interface.

PURPOSE: The purpose of this study was to compare the effect of seven different alloy surface treatments on the bond strength of the porcelain-metal interface. MATERIALS AND METHODS: Three layers of opaque porcelain and a measured thickness of dentin porcelain were applied to nickel-chromium alloy. A tensile bond strength test was used. RESULTS: The alloy surface treatment that exhibited the highest bond strength was sandblast + surface grinding + sandblast + de-gas, whereas the alloy surface treatment that exhibited the lowest bond strength was sandblast + surface grinding + sandblast + steam cleaning + de-gas. There was a significant difference between the two methods (P < 0.05). CONCLUSION: It was concluded that de-gassing the alloy prior to porcelain application increased the bond strength and excess surface grinding of the alloy reduced bond strength; steam cleaning the alloy surface prior to de-gassing and porcelain application also significantly reduced the bond strength.

Analysis of Variance↗
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The ADA at work.

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Persons with Disabilities↗
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The effect of five investing techniques on air bubble entrapment and casting nodules.

Five different investing techniques were used to invest lost-wax casting patterns. The use of an investing technique that subjects the invested casting ring to air pressure (40 lb per square inch) during setting was found to produce less air bubble/cast nodule incidence than did the other four techniques investigated. Not all cast nodules can be seen by the unaided eye; magnification is needed. More cast nodules than air bubbles were seen at the interface of pattern and investment, showing that there may be many air bubbles below the investment surface that are entered by the incoming alloy during casting. The effect of a surface-tension reducing (STR) agent on the air bubble incidence between pattern and investment depends on the investing technique used, although all techniques used showed a reduction in cast nodule incidence when an STR agent was used. Sprue direction was also found to influence the incidence of casting nodules.

Air↗
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Electron spectroscopy and microscopy applied to chemical and structural analysis of hair.

The application of surface specific x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) will be shown to be an effective means for the elucidation of hair fiber surface chemistry and structure. Example studies of bleaching and fiber conditioning treatments are discussed. The bleached fiber surface is found to become more hydrophilic due to the loss of the naturally occurring hydrocarbon overlayer and oxidation of surface functional groups as a result of bleaching. Comparison between generic bleaching regimens illustrates the importance of increased pH and the presence of surfactant for effective treatment. Adsorption of conditioning diester quat and dimethicone molecules reintroduces a hydrophobic like surface layer on the hair fiber. Spectroscopic data indicated a segregated adsorption structure of the chemically different conditioning molecules. Electron microscope images of the conditioned hair shows a smooth uniform surface.

Hair↗
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Influence of local anesthetics on ventilation.

Local anesthetics (lidocaine, mepivacaine or bupivacaine) were given as an intravenous infusion to 18 volunteers to study the influence of these drugs on resting ventilation (breathing air) and stimulated ventilation (hypercarbia- or hypoxemia-induced). Control measurements were made of resting ventilation and stimulated ventilation prior to the infusion. The ventilatory measurements were repeated during the latter half of the infusion, when plasma concentrations of these agents were considered to be near steady-state levels (mean plasma levels of lidocaine, mepivacaine and bupivacaine, 3.1 micrograms/ml, 2.7 micrograms/ml and 1.5 micrograms/ml, respectively) and within a range normally achieved clinically. None of the drugs tested affected resting ventilation or ventilation stimulated by hypercarbia. The drugs tested exerted a slight stimulatory effect on ventilation during hypoxemia.

Adult↗
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Comparative study of colorimetric DNA hybridization method and conventional culture procedure for detection of Salmonella in foods.

A second generation nucleic acid hybridization assay has been developed and evaluated against the conventional culture method for detection of salmonellae in foods. The assay involves a liquid hybridization with Salmonella-specific oligonucleotide probes, capture of probe:target hybrids onto a solid support (plastic dipstick), and a colorimetric end point detection. The assay can be completed in 2.5 h, following approximately 44 h of culture enrichment. One thousand samples representing 20 food types were analyzed in parallel by both methods. Samples included uninoculated test product, and product inoculated with Salmonella at 2 levels. Eighteen Salmonella serotypes were used as inocula. The data demonstrate that the colorimetric hybridization method and the conventional culture method are equivalent in their ability to detect Salmonella contamination of foods.

Animals↗
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Comparative studies of nucleic acid hybridization assay for Listeria in foods.

A nucleic acid hybridization assay has been developed for Listeria spp. in dairy foods and environmental samples. The assay is based on detection of unique Listeria 16S rRNA sequences by using a 32P-labeled synthetic DNA probe. Inclusivity and exclusivity of the probe were confirmed with 139 Listeria isolates representing all known species, and 73 non-Listeria bacterial strains. In this paper, we present results from our preliminary studies comparing the hybridization assay with conventional culture on a total of 575 specimens that represent a variety of inoculated and uninoculated foods and environmental samples. The assay, which is done in a filter manifold format after 2 days of cultural enrichment, requires a total assay time of less than 2.5 days. The false-negative rate for all sample groups tested using the GENE-TRAK hybridization assay was less than the rate for culture. Thus, the new assay allows rapid screening of the indicated product groups and provides reliable numerical results.

Dairy Products↗