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Biomedical subjects

W J O'Brien

Publications and source records attributed to W J O'Brien.

At least 91 records · Page 5Linked to original sources
PubMed1985

Thermal stress failure of porcelain bonded to a palladium-silver alloy.

Cracking or rupturing, due to thermal stress, of porcelain bonded to a palladium-silver alloy indicated that porcelain-metal thermal compatibility was dependent on: the difference in thermal expansion coefficients of the porcelain and metal; the geometry and dimensions of the samples; and the porcelain-metal thickness ratio. A spherical configuration was more sensitive to thermal expansion coefficient differences than was a disc configuration. A higher incidence of cracking resulted from an increase in both specimen size and porcelain-metal thickness ratio.

Chemical Phenomena↗
PubMed1985

Double-layer color effects in porcelain systems.

The color of an unshaded body porcelain was determined at three thicknesses on white, gray, and three chromatic backings. Spectral absorption and scattering coefficients of the porcelain were determined from the diffuse reflectance at one thickness on the white and gray backings. These optical coefficients, when utilized with the Kubelka-Munk reflectance theory, accurately predicted the color of the other sample configurations studied. The scattering of the body porcelain was found to decrease with increasing wavelength within the visible spectrum, in accordance with scattering theory for particles not substantially less than the wavelength of the scattered light. For the filtering effects of a translucent material in optical contact with a backing, the Kubelka-Munk reflectance theory described the interaction between the optical absorption and scattering within the translucent material and the reflectance of the backing.

Chemical Phenomena↗
PubMed1985

Interferon production and sensitivity of rabbit corneal epithelial and stromal cells.

The induction of interferon and the ability of interferon to induce the antiviral state were studied using rabbit corneal epithelial and stromal cells which were cultured for fewer than five passages. Interferon titers in the range of 7000 units/ml were induced in epithelial cell cultures and 76,000 units/ml in stromal cell cultures treated with UV-inactivated bluetongue virus. The interferon induced was stable to pH 2.0 treatment and heating to 56 degrees C for 16 hr. Infection of epithelial and stromal cell cultures with various strains of herpes simplex virus type 1 showed that all strains tested replicated to equivalent titers in the respective cell types, and that no detectable interferon was induced in stromal cells and only trace amounts in epithelial cells. Exogenously supplied rabbit interferon induced the antiviral state in cultures of both cell types restricting the replication of not only encephalomyocarditis virus but also herpes simplex virus. Sixty to ninety units of rabbit interferon reduced HSV-1 virus replication by 50%. Human interferons had less than 27% of the antiviral activity in rabbit cells than they had in a human cell line. The data indicate that exogenously supplied interferon may act to reduce the severity of herpetic keratitis by directly inducing the antiviral state in corneal epithelial and stromal cells. However, interferon endogenously produced by rabbit corneal cells in response to HSV-1 infection probably plays a minor role in the pathogenesis of ocular HSV-1 infections.

Animals↗
PubMed1985

Double layer effect and other optical phenomena related to esthetics.

A number of optical phenomena have been applied to an understanding of the appearance of dental porcelain restorations. Chromatic adaptation by observers has been identified as a major source of error in taking shades under artificial light. The measurement of tooth color by means of an instrument appears to be a long range solution, but is not yet practical. Surface gloss interferes with the correct identification of tooth and porcelain color due to specular reflection. Diffuse illumination is recommended for color matching. The color of teeth and porcelain crowns is determined by the "double layer effect." This means that the apparent color is the result of diffuse reflectance from the inner dentin or opaque porcelain layer through the outer translucent layer. Therefore, changes in the translucency of dental enamel due to illumination or desiccation alters the overall color of the tooth. Chromatic adaptation, translucency changes, and the double layer effect appear to be the major effects rather than metamerism. An understanding of these effects is needed to improve the esthetics of dental restorations.

Color↗
PubMed1985

Magnesia ceramic jacket crowns.

A high-extension core material based upon magnesia has been developed. This material may be used in the construction of all ceramic jacket crowns with the same body and enamel porcelains used for porcelain fused to metal crowns. Jacket crowns may be constructed using a modified platinum foil technique with greater accuracy and higher strength. The main advantage is a stronger jacket crown with exceptional esthetics without the need for special equipment or long processes.

Ceramics↗
PubMed1984

The determination of effective antiviral doses using a computer program for sigmoid dose-response curves.

A computer program was designed to construct best fit sigmoid dose-response curves for determination of the dose required to reduce the yield of virus by 50%, effective antiviral dose (ED50). A single antiviral agent, 9-beta-D-arabinofuranosyladenine, was examined for effectiveness against four strains of herpes simplex virus type 1. The resulting ED50 values were compared with those obtained by probit analysis. The statistical parameters obtained from sigmoid curve fit program were utilized to evaluate statistical differences between ED50 values for resistant and sensitive virus strains and to evaluate the goodness-of-fit of the regression line to the data. In addition, using this analytical method, it was shown that a change in one experimental variable, i.e., multiplicity of infection, in the yield reduction assay significantly affected the apparent ED50 value. The computer program was easily utilized for analysis of data obtained from both plaque reduction and yield reduction assays and generated the parameters necessary for statistical comparison of relative antiviral activity of any antiviral agent.

Animals↗
PubMed1984

Effect of transcutaneous electrical nerve stimulation on human blood beta-endorphin levels.

We randomly assigned 42 subjects for treatment with transcutaneous electrical nerve stimulation (TENS) to one of three groups: conventional TENS--80 Hz; low frequency TENS--2 Hz; and a control group--TENS without batteries. Pain threshold measurements and blood beta-endorphin levels were obtained at regular intervals before, during, and for 17 hours after TENS application. We found no significant difference in blood beta-endorphin levels between the groups before, during, or immediately after TENS application. The differences in pain threshold and beta-endorphin levels appeared to be a function of the patient-selection process and not the application of TENS. The results indicated that TENS, with the stimulation characteristics used in this study, did not significantly change the measured plasma levels of beta-endorphin. The blind administration of naloxone hydrochloride, an opiate antagonist, did not significantly alter the perceived experimental pain of these subjects. We could find no evidence that TENS altered experimental pain threshold or plasma beta-endorphin levels.

Analysis of Variance↗
PubMed1984

Pulsing electromagnetic field therapy in nerve regeneration: an experimental study in the cat.

A multidisciplinary approach to the study of peripheral nerve regeneration in the cat has been presented. The purpose of this work has been to determine if pulsing electromagnetic field (PEMF) therapy can enhance peripheral nerve regeneration after injury. In equal groups of animals, two types of pulsing electromagnetic field treatment were compared with untreated controls. All animals underwent quantitative electrophysiologic and morphologic assessment at the area of injury. In addition, muscle fiber sizing in the periphery and retrograde labeling of anterior horn motoneurons with horseradish peroxidase were studied. Results have shown no statistical differences between the groups in electrophysiologic or morphologic parameters. However, in animals treated with a pulse-burst electromagnetic field there was a statistically significant improvement in the labeling and localization of anterior horn cells in the central nervous system. These results indicate that pulse-burst electromagnetic radiation can increase the numbers of motor neurons that reestablish appropriate connections to the periphery after nerve injury. It remains to be seen if this improved spinal cord organization can translate to improved peripheral functional return.

Animals↗
PubMed1984

The surface roughness and gloss of composites.

The contrast gloss and the average roughness were measured for four commercial composite filling materials. Using a factorial design, each material was subjected to four available finishing methods. A significant difference was found in the contrast gloss among finishing methods, and a significant linear regression is given which relates the inverse of the contrast gloss to the average roughness. Surface gloss is proposed as playing a major role in the esthetic appearance of composite restorations.

Composite Resins↗
PubMed1984

Masking power of dental opaque porcelains.

A technique was developed to qualify the masking power of undiluted opaque dental porcelain by dilution of opaque powder with a clear glaze powder and by extrapolation of quantitative data gathered by reflectance spectrophotometry. Quantification of reflectance data was made on dilute opaque porcelains using the scattering and absorption coefficients in the Kubelka-Munk equation. Qualitative comparisons of undiluted opaque porcelains were made from quantitative data gathered from diluted opaque porcelains.

Chemical Phenomena↗
PubMed1984

The effects of retinoids on the replication of herpes simplex virus type 1.

Topical treatment of primary herpetic keratitis with 0.25% retinoic acid was effective in significantly diminishing the severity of epithelial lesions in rabbits. Antiviral activity against herpes simplex virus type 1 was also demonstrated in cell culture. Retinoic acid treatment of virus particles for 24 hours had no effect on the infectivity of the virus. At effective antiviral concentrations in cell culture, retinoic acid had toxic action on two different cell lines as detected by an increase in cellular generation time or inhibition of DNA synthesis. Topical instillation of retinoic acid into the eyes of rabbits at the effective antiviral dose (0.25%) had no inhibitory effect on corneal wound closure but did reduce the rate of incorporation of thymidine into DNA by 27%. These studies suggest that although retinoic acid may inhibit the replication of herpes simplex virus type 1, it is difficult to distinguish antiviral effects from anticellular effects.

Animals↗
PubMed1984

Pharmacokinetics of topical ocular phenylephrine HCl.

The rates of corneal penetration and efflux of phenylephrine (PE) and its metabolites were found to be limited by the epithelium. The rate constant for corneal penetration as measured in a lucite block perfusion system was 1.06 X 10(-3) hr-1 when the epithelium was present and 1.25 X 10(-2) hr-1 when the epithelium was denuded. Epithelial removal reduced the half-time (t1/2) for corneal efflux of PE from 24 min to 6 min. Ocular absorption of topically applied 0.1% PE (three 30-microliters instillations at five-minute intervals) was increased when the corneal epithelium was removed prior to application. Corneal concentrations of PE increased threefold, aqueous humor concentrations increased ten to 13-fold and iris/ciliary body concentrations increased sixfold upon epithelial removal. HPLC analysis suggested that the corneal epithelium was responsible for the metabolic degradation of PE, which occurred following topical instillation of PE.

Absorption↗
PubMed1983

Prostacyclin and thromboxane A2 derivatives in rhegmatogenous subretinal fluid.

Aberrations in prostacyclin and thromboxane A2 metabolism have been implicated in a wide spectrum of systemic disease. To our knowledge, derivatives of prostacyclin and thromboxane A2 have not been demonstrated previously in the subretinal fluid of rhegmatogenous detachments. Radioimmunoassays to determine levels of stable derivatives of prostacyclin and thromboxane A2, 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane B2, in rhegmatogenous subretinal fluid samples from ten patients showed the following: 6-keto-PGF1 alpha level, less than 100 to 1,268 pg/mL; thromboxane B2 level, less than 100 to 3,619 pg/mL. The fact that some of these concentrations are higher than the circulating plasma concentrations of 6-keto-PGF1 alpha and thromboxane B2 suggests endogenous ocular production. Our findings establish the presence of prostacyclin and thromboxane A2 derivatives in the rhegmatogenous subretinal fluid.

6-Ketoprostaglandin F1 alpha↗
PubMed1983

Liquid-chromatographic quantification of piracetam.

Piracetam, an analog of gamma-aminobutyric acid, absorbs maximally at 197 nm. Its molar absorptivity at 208 nm and pH 4.5 is 3576 (SD 251) L . mol-1 cm-1, approximately 45% of its absorptivity at 197 nm. Direct quantification of piracetam at 197 nm in biological extracts is complicated by the fact that many other compounds absorb between 190 and 220 nm due to carbon-nitrogen bonding. Chromatography of methanol extracts of serum and aqueous humor on a reversed-phase C-18 column developed isocratically with KH2PO4 (0.1 mol/L, pH 4.8) allows detection and quantification of 0.2 mmol of piracetam per liter. Under these conditions the retention time of piracetam is about 5 min. The detector response is linear for quantities between 5 and 15 nmol. The method is rapid, inexpensive, and convenient for the clinical laboratory.

Animals↗
PubMed1983

Secondary aqueous humor stimulates the proliferation of cultured bovine corneal endothelial cells.

Secondary aqueous humor (2 degrees AH) is known to contain elevated levels of serum macromolecules and has been shown to stimulate the proliferation of lens epithelial cells both in vivo and in vitro as well as corneal endothelial cells in vitro. The purpose of this study was to characterize the response of bovine corneal endothelial cells to 2 degrees AH from rabbits and to compare the effect when the cells were grown on plastic dishes covered with an extracellular matrix or on plastic alone. The addition of varying amounts of 2 degrees AH protein (0.1 to 10 mg/ml) to bovine corneal endothelial cells (cultured in MEM plus 1% serum) resulted in a dose dependent proliferative response as measured by the incorporation of 3H-thymidine into DNA. Except for a 2-hr lag phase, the proliferative response increased with increasing time of exposure (6-18 hrs) of the cells to 2 degrees AH containing a constant amount (2.0 mg/ml) of protein. The generation time and final density of the cells, but not the plating efficiency, was significantly greater when the cells were grown in the presence of 2 degrees AH protein on an extracellular matrix rather than plastic alone. Selective adsorption of prostaglandins and aromatic compounds from 2 degrees AH reduced its ability to produce a proliferative response to control levels. These results indicate that 2 degrees AH can alter or regulate events in the cell cycle of corneal endothelial cells. The responsible factor(s) could be involved in control of cellular regeneration in the eye following injury.

Animals↗