Search PubMed⌕ Search

Biomedical subjects

W J O'Brien

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

At least 73 records · Page 4Linked to original sources
PubMed1989

Performance assessment of colorimetric devices on dental porcelains.

The selection of an appropriate material that duplicates the appearance of natural tooth structure is very important in restorative dentistry. Photometric and colorimetric analysis techniques offer great potential as a tool for aiding in the duplication process. The degree to which these techniques will be useful depends on the accuracy and precision with which they can be applied to translucent as well as opaque surfaces. The purpose of this investigation was to evaluate the performance of three currently-available photometric devices. The performance capabilities of the instruments were tested on various shades of opaque and translucent dental porcelain surfaces. The performance tests were designed for evaluation of the accuracy and precision of the instrument relative to a well-studied reference instrument. CIELAB color difference metrics were used for the performance analysis. The results revealed that each of the photometric instruments evaluated was capable of producing color measurements with precision. However, the degree of accuracy with which the color measurements were made varied depending on the instrument used and the type of material surface being measured. A photo-electric tristimulus colorimeter showed the best overall performance on the porcelain surfaces, supporting its use as a valuable tool for evaluating color in dentistry.

Analysis of Variance↗
PubMed1989

Patterns of antigen expression in hepatoblastoma and hepatocellular carcinoma in childhood.

Two hepatocellular carcinomas and six hepatoblastomas were examined for the presence of 13 antigens using immunoperoxidase, avidin-biotin, staining techniques. Primary antibodies were directed against alpha-fetoprotein (AFP), alpha-1-antitrypsin (AAT), lysozyme (LYS), carcinoembryonic antigen (CEA), human chorionic gonadotropin (HCG), glial fibrillary acidic protein (GFAP), neuron specific enolase (NSE), epithelial membrane antigen (EMA), hepatitis B surface antigen (HbSA), lactoferrin (LF), desmin (DES), vimentin (VIM), and keratin (KER). Except for HbSA, the antigen staining pattern was unable to differentiate between hepatoblastoma and hepatocellular carcinoma. Both neoplasms where positive for AFP, AAT, CEA, EMA, and KER; however, neither stained for GFAP, NSE, LYS, LF, HCG, or DES. Vimentin was weakly positive in those hepatoblastomas where mesenchymal tissue was present in the tumor. Only the tissue adjacent to hepatocellular carcinomas stained positively for HbSA and correlated with the elevated serum levels of HbSA.

Adolescent↗
PubMed1989

Synergistic antiherpes virus activity of acyclovir and interferon in human corneal stromal cells.

Synergistic anti-herpes simplex virus type 1 (HSV-1) activity between acyclovir (ACV) and recombinant human interferon alpha A2 (IFN) was detected in cell cultures derived from human corneas. This activity was demonstrated when cells were infected at high multipicities of infection (5 pfu/cell) in both cytopathic effect reduction and yield reduction assays as well as in plaque reduction assays at low multiplicities. The synergistic effects occurred over a 30-fold range of concentrations of IFN (6-200 IU/ml) and ACV (0.15-5 microM) at various ratios of the drugs. The augmentation of antiviral activity was greatest when cells were treated with IFN prior to infection and ACV following infection. The addition of IFN after infection, with simultaneous ACV treatment, also resulted in enhanced anti-HSV-1 activity. The combination of IFN with ACV did not increase the cytotoxicity of ACV. The synergistic antiviral activity in corneal cells may account for the previously reported enhanced efficacy of combined treatment with IFNs and nucleoside analogs for therapy of herpetic keratitis.

Acyclovir↗
PubMed1989

The isolation of herpes simplex virus from rabbit corneas during latency.

Herpes simplex virus type 1 (HSV-1) latency, as operationally defined, is a state in which cell-free infectious virus cannot be demonstrated in tissue at the time of sacrifice, but infectious virus can be isolated from the same tissue after prolonged cultivation. Latent HSV has been routinely detected in sensory ganglia of the infected dermatome. We have isolated HSV-1 (RE) from the corneas of 11% of infected rabbits which harbored virus in a latent state in trigeminal ganglia. HSV-1 (RE) was isolated from 10 of 88 cultures of corneal cells established following collagenase digestion of individual corneas taken from asymptomatic animals 118 days after infection. Virus was recovered only after prolonged primary culture and in some cases serial passage of corneal cells (range 5 to 26 days to initial cytopathic effect, n = 10). Virus was isolated from 68 of 68 trigeminal ganglia from the same rabbits by cocultivation of ganglion pieces with Vero cells (range 9 to 20 days to initial cytopathic effect, n = 68) while no cell-free virus was isolated from ganglia at the time of sacrifice. Virus isolation from corneas during the latent period occurred in a manner independent of prior antiviral or antiviral plus immunosuppressive therapy. Clinical evaluation of the corneas throughout the course of acute disease, stromal disease, and at the time of sacrifice provided no evidence that could be used to predict which corneas would yield virus. These data suggest that HSV-1 can remain in a nonreplicative state characteristic of latency in cells of rabbit corneas for long periods after infection and therapy of herpetic eye disease.

Animals↗
PubMed1988

Fraunhofer diffraction of light by human enamel.

Fraunhofer diffraction patterns of human enamel samples were photographed with a helium-neon laser beam (lambda = 633 nm). The first-order diffraction angle was in reasonable agreement with a prediction based upon enamel prisms acting as a two-dimensional grating. These results support the hypothesis that enamel diffracts light because of the periodic structure of enamel prisms with interprismatic spaces, which act as slits.

Chemical Phenomena↗
PubMed1988

Inhibition of leukemic HL60 cell growth by transferrin-gallium: effects on ribonucleotide reductase and demonstration of drug synergy with hydroxyurea.

Cellular requirements for iron during DNA synthesis are related to the increased activity of the iron-containing M2 subunit of ribonucleotide reductase, the enzyme responsible for the reduction of ribonucleotides to deoxyribonucleotides. We have previously shown that transferrin-gallium (Tf-Ga) inhibits cellular iron incorporation. In the present study, Tf-Ga-induced inhibition of HL60 cell growth and upregulation of Tf receptor density was reversed with hemin. Cells exposed to 2 mumol/L Tf-Ga for six hours or longer displayed a diminution in the electron spin resonance (ESR) spectroscopy signal of the tyrosyl radical of the M2 subunit of ribonucleotide reductase. The effect of Tf-Ga on the ESR signal was reversed by hemin. Tf-Ga decreased the incorporation of 14C-adenosine into DNA and decreased intracellular deoxyribonucleotide pools, with the maximum diminution seen in deoxyadenosine triphosphate (dATP) and deoxycytidine triphosphate (dCTP) pools. Exposure of cells to combinations of Tf-Ga and hydroxyurea (a known inhibitor of ribonucleotide reductase) resulted in a marked inhibition of cell growth that was consistent with drug synergy. Our studies suggest that Tf-Ga inhibits DNA synthesis through action on the M2 subunit of ribonucleotide reductase and that combinations of Ga and hydroxyurea should be further evaluated in in vivo tumor models.

Cell Division↗
PubMed1987

Adenosine deaminase in herpes simplex virus induced corneal stromal disease.

The development of herpes simplex virus (HSV)-induced disciform stromal disease produced by the intrastromal injection of the RE strain of HSV-1 is characterized by concurrent increases in adenosine deaminase (ADA) activity and corneal thickness. ADA activity increased from 8.6 units/cornea in normal corneas to about 14.1 units and 31.1 units in mock-infected controls and HSV-infected corneas respectively by 15 days postinjection. The molecular weight species of ADA in the corneas of HSV-infected rabbits appeared altered relative to that present in corneas which were not infected. A single topical dose with as low as 0.1% 2'-deoxycoformycin (dCF), an ADA inhibitor possessing immunosuppressive activity, was capable of totally inhibiting the corneal ADA activity. Titration of the free dCF in the cornea following a single topical dose of 0.25% dCF indicated that enough dCF remained in the cornea 24 hrs after instillation to totally inhibit all corneal ADA plus 66 units of additional enzyme. These data suggest that ADA may be a suitable target for immunosuppressive therapy during HSV-induced disciform stromal disease.

Adenosine Deaminase↗
PubMed1987

The antiherpesvirus activity and cytotoxicity of sangivamycin.

Sangivamycin, 4-amino-5-carboxamido-7-(beta-D-ribofuranosyl)-pyrrolo[2,3-d]-pyrimidine is a structural analog of adenosine belonging to a group of nucleosides classified as pyrrolopyrimidines. Sangivamycin, an adenosine deaminase resistant analog, was found to inhibit the replication of three strains of herpes simplex virus type 1 (HSV-1) by 50% (ED50) at a concentration approximately equal to the concentration which inhibits cell growth by 50% (LD50). Both Vero cells and rabbit corneal stromal cells in exponential growth were about 10-fold more sensitive to the drug than quiescent cells. The selectivity indices of sangivamycin indicated that the drug was not a highly selective antiviral agent and, therefore, would offer no advantage over drugs currently available for the treatment of herpetic keratitis.

Animals↗
PubMed1987

Interferon production in inbred mice during herpetic eye disease.

Low levels (less than 5 units/eye) of interferon (IFN) were detected in the eyes of BALB/c and C57BL/6 mice one to five days after instillation of 10(7) pfu/eye of herpes simplex virus type 1 (HSV) onto scarified corneas. This dose of virus produced herpetic keratitis characterized by dendritic epithelial lesions one day post infection in both strains of mice. The disease progressed to severe necrotizing stromal keratitis in the eyes of all BALB/c mice, but only three of 10 eyes of C57BL/6 mice by 21 days after infection. Footpad immunization 30 days prior to ocular infection protected both strains from stromal disease, but did not enhance IFN production in the eye. At lower inoculating doses of virus (less than or equal to 10(5) pfu/eye), C57BL/6 mice showed greater resistance to stromal disease and produced less virus over a shorter period of time than BALB/c mice. No IFN was detected at any time after infection with doses of virus less than 10(7) pfu/eye, nor was IFN detected in plasma of any infected mice. The failure to detect high levels of IFN in homogenates of eyes did not reflect an inability of ocular tissues to produce IFN since IFN-beta was detected as early as two hours after topical treatment with the potent IFN inducer, carboxymethylacridanone (CMA). The two mouse strains produced similar levels of IFN in the eye in response to CMA. These data indicated that the relative resistance of mice to HSV eye infection was not related to the rapid local production of IFN, nor was resistance related to systemic IFN production in plasma or spleen.

Animals↗
PubMed1987

Herpetic keratitis in experimental vitamin A deficiency.

Herpes simplex virus type I (KOS) was instilled onto the eyes of rabbits with experimentally induced xerophthalmia (vitamin A deficient) and control animals fed a vitamin A supplemented diet. The severity of the herpes virus-induced corneal disease, assessed by biomicroscopic examination and by counting the number of corneal lesions as well as by determining the virus titers, was significantly less in vitamin A deficient animals than in controls. Infection of the corneas of the vitamin A deficient rabbits with herpes simplex virus did not precipitate keratomalacia. The few lesions present on the corneas of the vitamin A deficient animals were in the corneal periphery, which was less keratinized than the central cornea. Electron microscopy suggested that virus was capable of replicating in the basal and wing cells in the peripheral corneal lesions in the vitamin A deficient animals. These studies indicate that vitamin A deficiency alone may not predispose the host to more severe ocular herpesvirus infections.

Acute Disease↗
PubMed1986

Spectrophotometric analysis of color differences between porcelain systems.

Spectrophotometric measuring techniques were used to determine the color of four corresponding shades of three brands of metal-fusing porcelain systems. The color was expressed in terms of CIE L*a*b* color coordinates. The relationship of these values to the more commonly used attributes of Hue, lightness (Value), and saturation (Chroma) respectively were discussed. The location of the porcelain shades in the color space and the direction of the color differences found between the different brands of porcelain were evaluated. Color differences for each paired comparison within each shade group were determined from the color data. These values represent the magnitude of color differences found between brands and have a direct relationship to visual perceptibility. For the brands and shades measured, the following conclusions can be made: The CIELAB color system provides an objective technique for evaluating the color of dental porcelains. Corresponding shades of different brands of porcelain can produce perceivably different colors. The perceived color differences between the brands were mostly a result of differences in all three color directions. Greater color differences were found to exist between the corresponding opaque porcelains than between the corresponding layered samples. The addition of 1 mm of body porcelain to the opaque compensated to a large extent for the greater color differences found between the corresponding opaques. The results of this study have significant clinical ramifications. Variations in optical characteristics of porcelains produced by different manufacturers add to the problem of color control in ceramic crown fabrication.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1986

Light scattering and gloss of an experimental quartz-filled composite.

For samples of polymethylmethacrylate with and without quartz filler, the inverse of the contrast-gloss ratio is shown to be related to surface roughness and to the optical scattering coefficient. This finding adds to the importance of optical scattering, which has been widely studied because of its relation to color and translucency of materials. Furthermore, optical scattering by composite fillers is shown to be linearly related to the concentration of the filler material within the range of concentrations studied. Quartz fillers were incorporated at concentrations from 5 to 20 weight percent and were short fibers or granular powder, with the granular particles ranging in median equivalent spherical diameter from 15 to 3.3 micron. The efficiency of optical scattering for the granular quartz filler increased as the size of the filler decreased.

Color↗
PubMed1986

Therapy with 9-beta-D-arabinofuranosyladenine (ARA-A) and 2'-deoxycoformycin increases the ARA-A content of ocular tissues.

The amount of 9-beta-D-arabinofuranosyladenine (ARA-A) and 9-beta-D-arabinofuranosylhypoxanthine (ARA-Hx) present in ocular tissues of rabbits was determined following therapy with ARA-A alone and when ARA-A was used in combination with 2'-deoxycoformycin (dCF). Topical therapy was initiated three days after infection of the corneas of rabbits with herpes simplex virus type 1. Ocular tissues were harvested after two days of therapy and analyzed by high performance liquid chromatography. Combination topical therapy with ARA-A and dCF significantly increased the tissue content of ARA-A in all tissues examined except retina, as compared to therapy with ARA-A alone. The ARA-A content of the two ocular tissues most often subject to acute herpes infections, the conjunctiva and cornea, was increased from 29.9 +/- 11.7 to 144.0 +/- 53.3 pmoles/mg dry weight and from 15.4 +/- 6.1 to 231.8 +/- 30.8 pmoles/mg dry weight, respectively. Except for the aqueous humor, the total arabinoside content of each tissue was not significantly altered by combination therapy, merely the ratio of ARA-A to ARA-Hx was changed. These studies demonstrate that combination topical therapy with ARA-A and an inhibitor of ARA-A catabolism, dCF, can effectively result in elevated amounts of ARA-A in ocular tissues.

Animals↗
PubMed1985

Clearance of triamcinolone from vitreous.

The clearance of intravitreally injected triamcinolone acetonide was monitored by both indirect ophthalmoscopy and high-performance liquid chromatography (HPLC) and found to be more rapid than previously reported by others. Twenty-four rabbits were intravitreally injected in each eye with 0.4 mg of triamcinolone acetonide. Three rabbits each were sacrificed at intervals ranging from one hour to 46 days. The vitreous was then harvested and processed for HPLC analysis. Triamcinolone and the internal standard prednisolone were identified and quantitated by the use of HPLC, which was found to be both sensitive and specific for the steroids. The half-life as determined by HPLC was 1.6 days, the level at 13 days postinjection was 66 +/- 19 micrograms, and no drug was detectable by HPLC analysis at 21 days in five of six eyes. The intravitreal masses thought to be triamcinolone were clinically observable to an average of 23.3 days. The chromatographically determined clearance rate did not correlate well with clinical impressions based on indirect ophthalmoscopy.

Animals↗
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↗