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Biomedical subjects

W J O'Brien

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

At least 55 records · Page 3Linked to original sources
PubMed1993

The strengthening mechanism of a magnesia core ceramic.

A high-expansion core material containing magnesia and forsterite may be used to make all-ceramic dental crowns with porcelain-fused-to-metal body porcelains. The purpose of this study was to investigate the strengthening mechanism for the magnesia core material. Six batches of the magnesia core material were made by reacting magnesia with a silica glass with holding times ranging from 17 to 120 min. The flexural strength was measured using three-point loading according to the ISO specification for dental ceramics. The forsterite content was measured using quantitative x-ray diffraction. A statistically significant correlation was found between the forsterite content and flexural strength. The proposed mechanism for strengthening is the precipitation of fine forsterite crystals in the glass matrix surrounding unreacted magnesia. Longer reaction times produced more dissolution of magnesia and subsequent precipitation of forsterite. This method results in a new strengthening mechanism for dental ceramics which have previously relied on the incorporation of alumina, leucite or ceramic whiskers.

Analysis of Variance↗
PubMed1992

Infection with a plasmid-free variant Chlamydia related to Chlamydia trachomatis identified by using multiple assays for nucleic acid detection.

Clinical samples in transport media from 40 patients exhibiting pathologies potentially caused by Chlamydia trachomatis infection were analyzed for chlamydial nucleic acid, and the results were compared with those of culture. Chlamydial culture was performed by a shell vial centrifugation method with HeLa 229 host cells. Polymerase chain reaction (PCR) assays were used to detect either regions on a 7.5-kb plasmid characteristic of C. trachomatis (plasmid-PCR) or a segment of the 16S rRNA genes (rRNA-PCR). All PCR results were confirmed by hybridization with probes for the specific amplified products in either a Southern or a dot blot format. An RNase protection (RNP) assay was used to detect genus-specific chlamydial 16S rRNA directly from the clinical samples. The PCR assays detected C. trachomatis but not other bacteria, including Chlamydia spp. C. trachomatis was isolated from six samples which were positive by the rDNA-PCR and plasmid-PCR assays. Five of the culture-positive specimens were positive by the RNP assay. Twenty-two samples were negative by all criteria. Surprisingly, nine samples were positive by rRNA-PCR and RNP assays only. Nucleic acid sequencing of the rRNA-PCR-amplified products indicated a close relationship between the variants and C. trachomatis. The data may indicate an unrecognized process in C. trachomatis infection or that these patients were infected by a variant strain of C. trachomatis which lacks the C. trachomatis-specific plasmid.

Animals↗
PubMed1992

Persistence of herpes simplex virus DNA in rabbit corneal cells.

Corneal cell cultures were established from the corneas of rabbits killed during a period of latency 118 d after ocular infection with the RE strain of herpes simplex virus (HSV). DNA was isolated from frozen cell pellets of 42 cell cultures that did not develop viral cytopathic effects during 44 d in culture. Using the polymerase chain reaction (PCR) to amplify HSV thymidine kinase (TK) gene sequences, HSV-specific DNA was detected in 15 of 42 culture-negative cell cultures. Subsequent reamplification, using nested primers that were complementary to HSV TK sequences internal to the orginal primers, resulted in eight additional culture-negative samples showing positive hybridization for HSV TK DNA. Twenty three of the 42 virus culture-negative corneal cell cultures tested by PCR were found to contain HSV genetic material. Detailed examination of the clinical histories of the eyes from which the corneal cultures were obtained showed no correlation between increased frequency or severity of epithelial disease, stromal disease, or virus shedding and more frequent isolation of virus or detection of HSV-specific DNA. These studies document that HSV DNA residues in the corneas of HSV-infected rabbits up to 118 d post-infection. About 10% of the eyes contained virus that could be reactivated in culture, whereas an additional 55% of the eyes contained DNA sequences homologous to a portion of the HSV TK gene.

Animals↗
PubMed1991

Inhibition of ribonucleotide reductase by gallium in murine leukemic L1210 cells.

Our previous studies of the mechanism of cell growth inhibition by gallium have suggested that the block in cellular iron uptake induced by transferrin-gallium results in an inhibition of the iron-dependent M2 subunit of ribonucleotide reductase. However, it is not known whether the inhibitory effect of gallium on ribonucleotide reductase is solely the result of limiting iron availability for enzyme activity or whether a direct effect of intracellular gallium on the enzyme is also involved. In the present study, utilizing a cell-free assay, we show that gallium nitrate directly inhibits CDP and ADP reductase activity. Inhibition of DNA synthesis by gallium nitrate thus appears to be due to a combination of a block in iron availability to ribonucleotide reductase and a direct inhibition of the enzyme by gallium.

Animals↗
PubMed1991

Sources of color variation on firing porcelain.

The final color matching of porcelain crowns depends upon the accuracy of the original shade matching by the dentist and variables introduced during processing. Possible sources of processing variables include thickness and color of the opaque, thickness, color, and translucency of the body and enamel layers, firing temperature, and number of firings (Miller, 1987). These processing variables can lead to an error in shade match. The purpose of this study was to quantify, in CIE delta E units: (1) the shade variations when the same batches are fired, (2) the shade variations between different batches, and (3) the differences in color produced by the multiple firing. Three lots of six shades of four commercial brands were included in this study. The color variation of the opaque samples (mean delta E was 0.46) was generally lower than that of the body/opaque samples (mean delta E was 0.86). The average color variation for three different batches of the body/opaque samples was 1.44. The average color difference produced as a result of multiple firings was 1.00 after six firings, compared with the color after three firings.

Analysis of Variance↗
PubMed1991

The development of corneal edema in herpes simplex virus type 1-infected rabbits following termination of therapy for corneal stromal disease.

One complication of combined antiviral/corticosteroid therapy for herpetic stromal disease in patients is rebound of disease upon termination of therapy. To develop a model of steroid rebound, rabbits were injected intrastromally with 10(3) pfu of HSV-1 (RE strain). Therapy with 1% trifluorothymidine (F3TdR) alone or in combination with immunosuppressive agents was initiated 7 days post-infection, at a time when epithelial disease had reached its peak and corneal thickness had begun to increase. Therapy was continued 5 times daily through day 18 post-infection. Following cessation of therapy 13 of 16 eyes receiving both 1% F3TdR and 0.125% prednisolone acetate experienced rebound of disease characterized by an increase in corneal thickness from 514 +/- 106 microns to 743 +/- 189 microns, reaching a maximum at 27 +/- 3 days post-infection. Rabbits receiving therapy with either phosphate buffered saline or F3TdR alone displayed rebound in 2 and 3 of 12 eyes, respectively. Rabbits receiving F3TdR combined with either cyclosporine or deoxycoformycin experienced rebound of disease in 9 of 20 and 6 of 16 eyes, respectively. Cultures of eye washings taken from eyes at the time of rebound were negative in all cases. The data indicate that only steroids significantly increased the proportion of eyes with rebounding stromal disease and corneal edema. These studies document steroid rebound of stromal disease in an animal model.

Animals↗
PubMed1991

Combined anti-herpes virus activity of nucleoside analogs and interferon.

Addition of interferon (IFN) to nucleoside analog therapy for herpetic keratitis has been shown to significantly increase the efficacy of therapy compared to nucleoside alone. We have analysed several nucleoside analogs and recombinant IFN-alpha 2 to determine which combinations have increased anti-herpes simplex virus type 1 (HSV) activity. Synergistic anti-HSV activity between IFN-alpha 2 and the acyclic guanosine analogs, acyclovir (ACV) and ganciclovir (DHPG), was demonstrated in cytopathic effect reduction assay in human corneal cell cultures as well as in Vero cells. In this assay system IFN-alpha 2 alone had little detectable antiviral activity at titers of greater than or equal to 2,000 IU/ml, however, treatment of cells with about 100 IU/ml of IFN-alpha 2 for 24 hrs prior to infection decreased the ED50 of ACV approximately 2- to 3-fold and of DHPG approximately 5- to 6-fold in Vero cells. Combinations of IFN-alpha 2 with bromovinyldeoxyuridine (BVdU) in Vero cells or human corneal stromal cells did not increase the antiviral activity of BVdU. Combinations of IFN-alpha 2 with trifluorothymidine (TFT) also did not increase the effective antiviral activity of this nucleoside and resulted in decreased uptake of TFT from the medium. These studies document that combinations of acyclic nucleoside analogs, ACV and DHPG, with IFN-alpha 2 resulted in synergistic anti-HSV activities in both Vero and human corneal stromal cells, while the pyrimidine analogs, TFT and BVdU, were not synergistic with IFN-alpha 2. IFN-alpha 2 treatment of cells induced modifications of nucleoside (e.g., thymidine and TFT), but not nucleobase (e.g., ACV) uptake. These studies suggest that selective inhibition of nucleoside versus nucleobase uptake may contribute to the mechanism of IFN/nucleobase synergy in the inhibition of HSV replication.

Animals↗
PubMed1991

Therapeutic response of herpes simplex virus-induced corneal edema to trifluridine in combination with immunosuppressive agents.

Herpetic stromal disease often is treated with combinations of antiviral agents and corticosteroids. The addition of steroids to the antiviral treatment regimen frequently increases the efficacy of therapy in patients; however, many complications may arise as a result of corticosteroid therapy. Using a rabbit model, the effects of trifluridine (F3TdR) on corneal edema and stromal disease were examined when combined with each of three immunosuppressive agents. The therapeutic response was evaluated by classifying eyes as either responsive or unresponsive based on the maximum corneal thickness attained during therapy. The data indicate that about 56% of the eyes responded to therapy with 1% F3TdR alone even when therapy was initiated after signs of stromal inflammation had begun to appear and epithelial disease was resolving. Combination of F3TdR with 0.125% prednisolone acetate significantly increased the proportion of responsive eyes to about 78%. Therapy with F3TdR combined with topical 5% cyclosporine A was no better than F3TdR alone, and combination with 0.2% deoxycoformycin and 0.4% 2'-deoxyadenosine significantly decreased the proportion of responsive eyes. These data further document that the responses of stromal disease to therapy must be evaluated on an eye-by-eye basis because the distribution of the data may not be Gaussian in nature. Eyes with corneal edema and stromal disease induced by herpes simplex viral (HSV) infection may respond to therapy with antiviral agents alone, but others require steroid. Still others do not respond to combined therapy. Combining the responses of all eyes in a given treatment group to obtain a "population mean" may be misleading.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Nucleoside metabolism in herpes simplex virus-infected cells following treatment with interferon and acyclovir, a possible mechanism of synergistic antiviral activity.

Alpha interferon (IFN-alpha) and nucleoside analogs have been shown to have synergistic antiherpesvirus activity in cultured cells. The mechanisms responsible for this synergistic activity are not known, but we hypothesize that IFN-alpha-induced alterations of nucleoside metabolism in virus-infected cells may play an important role. Infection of cells with herpes simplex virus type 1 (HSV-1) led to an increase in uptake of thymidine into cells. Treatment of infected cells with recombinant IFN-alpha for 24 h prior to infection resulted in a significant reduction in the uptake of exogenous thymidine but did not reduce the apparent incorporation of exogenous thymidine into DNA. The amount of exogenous thymidine phosphorylated relative to the amount taken up was the same in IFN-alpha-treated and control cultures. IFN-alpha treatment of HSV-1-infected cells also resulted in a reduction in the pool sizes of endogenous deoxyribonucleoside-5'-triphosphates relative to those of untreated HSV-1-infected cultures. Although IFN-alpha affected the metabolism of natural nucleosides in HSV-1-infected cells, it did not significantly reduce the uptake of the antiviral guanosine analog acyclovir into HSV-1-infected cells or the amount of acyclovir-5'-triphosphate accumulated. Therefore, in IFN-alpha-treated cells the concentration of a natural nucleoside, thymidine, was reduced, as were the pools of all deoxyribonucleoside-5'-triphosphates. No decrease in acyclovir or acyclovir-5'-triphosphate concentration was observed, however, when acyclovir-treated cells were exposed to IFN-alpha. These data suggest that IFN-alpha-induced alterations in nucleoside metabolism may be one mechanism whereby IFN-alpha and acyclovir express synergistic antiherpes-virus activity.

Acyclovir↗
PubMed1990

Pathogenesis of corneal oedema associated with herpetic eye disease.

Corneal oedema and stromal disease, induced in rabbits by intrastromal injection of herpes simplex virus, type 1, strain RE (HSV-1, RE), reached a peak of 12-15 days after infection. Corneal oedema as measured by ultrasonic pachymetry, and stromal disease as measured by a subjective scoring system, were closely related for 30 days after infection. Morphometric analysis of wide field specular micrographs showed that no immediate endothelial cell damage occurred in either control or HSV-1 infected corneas. Alizarin red S staining of corneas taken during the period of most severe oedema indicated no significant endothelial cell loss; however, visual inspection indicated numerous staining abnormalities. Scanning and transmission electron microscopy provided evidence of an intact endothelial layer possessing integrated infiltrating cells. Virus antigen could not be detected on endothelial cells by immunoperoxidase staining at any time during development of corneal oedema. The results indicate that corneal oedema associated with HSV-1 induced disease can occur in the absence of detectable virus replication and cytolysis of corneal endothelial cells.

Animals↗
PubMed1990

Correlation between histological and behavioral measures of visual acuity in a zooplanktivorous fish, the white crappie (Pomoxis annularis).

Estimates of visual acuity in a pelagic freshwater zooplanktivorous fish, the white crappie (Pomoxis annularis, Centrarchidae), were made using a behavioral measure, the maximum observed prey pursuit distance (MxPD), and a histological measure, the density of cone cells in the retina. The greatest number of pursuits occurs in the 0-30 degrees wedge of the visual field; 87% of all pursuits occur in the first 40 degrees. The longest pursuits (200 mm) also occur in this area and generally get shorter from 0 to 180 degrees (from forward-directed) in the visual field. Consistent with the behavioral results, the largest number of cone photoreceptors (13,000/mm2) is found in the far temporal retina along the eye's horizontal meridian. Cone cell densities in the corresponding region of the nasal retina are approximately half this value. The number of cones decreases dorsally and ventrally from the horizontal meridian. Although the absolute values of visual acuity calculated from cone cell topography (i.e. MxPDs of 500 mm) are 2-3 times greater than those observed behaviorally (i.e. MxPDs of 200 mm), the trends in visual acuity across the visual field obtained from both measures are consistent. We suggest that overestimates of visual acuity obtained from cone cell counts alone result from this measure's not accounting for, among other properties of the nervous system, cone cell convergence onto ganglion cells and higher brain centers. Behavioral measures of visual acuity are, therefore, likely to yield a more accurate estimate of an animal's visual abilities.

Animals↗
PubMed1990

A new, small-color-difference equation for dental shades.

Traditionally, dental-shade-guide standards are designated in terms of Munsell hue (H), value (V), and chroma (C). However, delta E color differences proposed as ADA tolerances for shade guides are in the CIE L*a*b* system. The purpose of this study was to evaluate a new color-difference equation, delta EM = C delta H/5 + 7 delta V + 4 delta C for estimation of small color differences by Munsell parameters. The published values of the Bioform shade-guide tooth colors determined with a Beckman spectrophotometer were used. Color differences among 276 combinations of the 24 Bioform shade-guide colors were calculated with Eq. 1, with use of the Munsell notation, and also with the CIE L*a*b* equation for delta E. An estimate of the accuracy of Eq. 1 was 0.41 delta E units when delta E CIE was below 4.0. The Vita shade-guide colors were determined with a Beckman spectrophotometer. This data set contained 16 samples, and 120 combinations were used for calculation of color difference. An estimate of the accuracy for this set of data was 0.35 delta E units when delta E CIE was less than 4.0. The new color-difference equation provides a means for estimation of delta E CIE L*a*b* color difference between dental shades with Munsell notation. This equation will be useful for estimation of small delta E CIE L*a*b* values for shade-guide teeth that are designated in terms of Munsell notation.

Color↗
PubMed1990

Loss of stromal glycosaminoglycans during corneal edema.

This study tried to determine if glycosaminoglycans (GAGs) are released from the rabbit stroma during corneal edema. The GAGs of rabbit corneas were labeled in situ using anterior-chamber injections of 35S-sulfate and 3H-glucosamine. Labeled corneal pairs were excised and the endothelium perfused in vitro in the specular microscope. Edema was induced in one cornea by perfusion with a calcium-free balanced salt solution; the control cornea was perfused with glutathione bicarbonate Ringer's (GBR). Corneal thickness was measured every 15 minutes during the 3-hour perfusion period, and perfusate fractions were collected from each cornea and analyzed for the presence of GAGs. Edematous corneas swelled from 438 +/- 14.8 microns to 688 +/- 10.6 microns compared with control corneas (427 +/- 4.7 microns to 454 +/- 7.2 microns). Total 3H-glucosamine (4.00 +/- 0.68%) and 35S-sulfate (10.36 +/- 0.92%) released from the edematous corneas during perfusion exceeded that lost by control corneas (1.92 +/- 0.18% for 3H-glucosamine; 3.23 +/- 0.52% for 35S-sulfate). Enzymatic digestion studies showed the presence of keratan sulfate in the edematous perfusates. The results suggest that increased loss of radiolabeled components from edematous corneas represent a loss of stromal GAGs and possibly GAG fragments. Therefore, corneal edema involves loss of GAGs and water uptake.

Animals↗
PubMed1989

One-dimensional color order system for dental shade guides.

The purpose of this study was to re-arrange the master Bioform shade guide into a long-range one-dimensional color system based upon color difference. Although most shade guides may show local order when arranged according to hue, long-range order has not been established. However, shade guide arrangement according to a logical color order would be an advantage to the user. The first step in determining the color order was to measure the color of the shade guide teeth. A methodology was developed for measuring the color by use of a reflectance spectrophotometer. The precision of measurement was determined to be equal to CIE L*a*b* delta E of 0.5. Spectra were obtained and converted into CIE L*a*b* and Munsell notation. The measured colors of the Bioform shades ranged from a Munsell hue of 0.9 Y to 3.5 Y; a value of 6.6 to 7.8; and a chroma of 1.9 to 4.1. The teeth were then arranged visually from light to dark. The correlation coefficient between the visual ranking and color difference was 0.95. There was an inverse correlation between visual ranking and Munsell value, with a correlation coefficient of 0.90. Therefore, the sequence according to color difference provided the better agreement with visual perception.

Color↗
PubMed1989

The detection of incipient caries with tracer dyes.

The purpose of this study was to determine the increase in color contrast produced by the use of a tracer dye in detection of incipient caries lesions with transillumination. Twenty-four caries-free first premolars were immersed in an acid gelatin for production of artificial incipient caries lesions. After the lesions had developed, these teeth were photographed by transillumination. Two photographs were taken of each tooth. The first photograph showed the lesion without dye. A blue tracer dye was then added and absorbed by the lesion, and a second photograph was taken. The data on the color difference were obtained by use of a reflectance colorimeter and showed a four-fold increase between the lesion and surrounding area with the dye. A two-way analysis of variance was used for the statistical interpretation. The color difference between the lesion without the dye and then with the dye was significant. The use of the blue tracer dye, therefore, significantly increased the contrast in the images of the artificial incipient lesions.

Benzenesulfonates↗
PubMed1989

The colors of mixtures of dental opaque porcelains.

The colors of mixtures of dental opaque porcelains and modifiers were measured with use of the CIE L*a*b* uniform color space. Mixtures of dental porcelains were tested to duplicate the range of human tooth colors. Vertical movements in the yellow and blue directions were obtained. Horizontal movements in the red and green directions were achieved. Reflectance measurements were made with use of a spectrophotometer with an integrating sphere. Spectrophotometer measurements were converted to absolute reflectance and then used to calculate CIE a*b* values for a 2 degrees standard observer and for illuminant C. Movements in the yellow, red, blue, and green directions for adequate simulation of the tooth color range can be demonstrated with use of dental opaque and modifier porcelains.

Color↗
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↗