Biomedical subjects

R P O'Connor

Publications and source records attributed to R P O'Connor.

At least 19 recordsLinked to original sources

PubMed2001

Geophysical variables and behavior: CIII. Days with sudden infant deaths and cardiac arrhythmias in adults share a factor with PC1 geomagnetic pulsations: implications for pursuing mechanism.

If geomagnetic-mediated stimuli trigger many sudden infant deaths, then the days in which they and hospital admissions for cardiac arrhythmias for adults occur should share a similar source of variance. Factor analyses of the days in which a sudden infant death occurred in Ontario or adults were admitted for one of eight categories of cardiac crisis in the Sudbury (Ontario) Region for the year 1984 supported the hypothesis. This factor, with which infant deaths and adult cardiac arrhythmias each shared about 40% of their variance, also shared about 40% of the variance with a factor with which about 35% of the variance in daily occurrence of geomagnetic pulsations (0.2 Hz to 5 Hz) was associated. These results are consistent with the important role of geomagnetic variables in the occurrence of transient electrical anomalies in brain function rather than cardiac blood flow.

Adult↗

PubMed2001

Geophysical variables and behavior: CIV. Power-frequency magnetic field transients (5 microtesla) and reports of haunt experiences within an electronically dense house.

Magnetic field measurements for power frequencies were measured continuously over two 24-hr. periods for a small house in which two adults who exhibited above normal occurrences of complex partial epileptic-like experiences had reported "waves of fear", tactile sensations, nightmares, apparitions, and a sensed presence. The experiences occurred within an area in which irregular amplitude modulations between 1 microT and 5 microT (50 mG) from 60-Hz sources, with durations of a few seconds to several tens of seconds, were measured. This case suggests that transient, complex temporal patterns of power-frequency magnetic fields generated by less than optimal grounding in dwellings and telluric currents may be sufficient to evoke experiences in the brains of sensitive individuals. Cultural labels, applied by the experients, then affect the explanations and expectancies for these experiences.

Behavior↗

PubMed2001

Normal spatial memory following postseizure treatment with ketamine: selective damage attenuates memory deficits in brain-damaged rodents.

Within 30 min after the initiation of status epilepticus (SE) by lithium and pilocarpine, rats were injected with either acepromazine or ketamine. Compared to the rats that had received the acepromazine, the group that had received the ketamine displayed more accurate spatial memory. Their scores did not differ significantly from normal (non-seized) controls. Although the ketamine treatment did not significantly change the amount of neuronal loss within about 100 Paxinos and Watson structures, it was neuroprotective for several structures within the thalamus and portions of the temporal and parietal cortices. Ketamine-treated rats, however, displayed markedly more damage within the entorhinal cortices and amygdalohippocampal area.

Acepromazine↗

PubMed1999

Innovative uses for hypodermic needles in endodontics.

Hypodermic needles have sharp cutting edges along their bevels. These can be used to enlarge canal openings and to cut around a broken instrument or other object to be removed. Means of attaching the needle to such foreign objects for removal are discussed.

Dental Instruments↗

PubMed1999

Geophysical variables and behavior: LXXXV. Sudden infant death, bands of geomagnetic activity, and pc1 (0.2 to 5 HZ) geomagnetic micropulsations.

Pc1s (continuous pulsations) within the geomagnetic field, whose durations are about 30 minutes but which can reoccur several times nightly, are observed during periods when global geomagnetic activity is very low (less than 10 nT). The hypothesis that these 0.2 to 5 Hz synchronized micropulsations or hydromagnetic emissions might stimulate physical chemical cascades within the brain that precipitate the sudden death in infants was tested by correlational analysis for a two-year period (1960-1961) for Ontario. Results were consistent with the hypothesis that the monthly incidences of these unexpected deaths, pcl micropulsations and geomagnetic activity less than 10 nT displayed a shared source of variance. Implications are discussed.

California↗

PubMed1999

A linear relationship between postnatal geomagnetic activity and self-reports of epileptic seizures in young adults.

To test the hypothesis of a linear relationship between the intensity of geomagnetic activity during the first two days after birth and the development of epilepsy, the responses of the item "I have had an epileptic seizure" was obtained from the Personal Philosophy Inventories of 1,453 students who had been enrolled in first-year psychology courses over a 13-yr. period. The only statistically significant effect was linear and was between the successive 10 nT (nanoTesla) increments of the intensity of geomagnetic activity during the two days after birth and the percentage of students who reported epileptic seizures. The percentage of subjects reporting a history of seizures ranged from 1% for those born when the activity was less than 10 nT to 4% for those born when this activity exceeded 40 nT.

Adolescent↗

PubMed1997

Geophysical variables and behavior: LXXXII. A strong association between sudden infant death syndrome and increments of global geomagnetic activity--possible support for the melatonin hypothesis.

A significant subpopulation of young infants who die suddenly (SIDS) often exhibit anomalies consistent with disruptions within the pineal-limbic system. We have hypothesized that sudden decreases in nocturnal melatonin by a specific range of geomagnetic activity would precipitate sudden infant death. A correlation of .90 was found between the numbers of cases of Sudden Infant Death Syndrome per month during the years 1960 and 1961 in Ontario and an increase (primarily) in numbers of days per month with average geomagnetic activity between 11 and 20 nT and 31 through 40 nT but a decrease in the numbers of days with values between 21 and 30 nT. This nonlinear sensitivity, presumably associated with specific ripple frequencies within the geomagnetic field, may explain the failure by other researchers to detect linear associations between the numbers of these types of deaths and gross, scalar indicators of geomagnetic activity.

Brain Chemistry↗

PubMed1996

Castability, opaque masking, and porcelain bonding of 17 porcelain-fused-to-metal alloys.

Seventeen porcelain-fused-to-metal alloys, which represented a cross section of the various alloy types available, were evaluated for castability, opaque masking, and porcelain bond strength. The base metal alloys generally cast more completely than the noble alloys, with the presence of beryllium as an important factor for greater castability among the base metal alloys. Statistically significant differences were observed in the ability of an opaque porcelain to mask the different alloy substrates but no systematic effect of alloy type was observed. Porcelain bond testing revealed that nickel-chromium-beryllium alloys produced significantly better porcelain-metal bonds than nickel-chromium alloys without beryllium. In addition, it was found that palladium-copper alloys produced significantly better bonds with porcelain than palladium-cobalt alloys.

Analysis of Variance↗

PubMed1996

Increases in geomagnetic activity are associated with increases in thyroxine levels in a single patient: implications for melatonin levels.

Blood levels of free T4 (thyroxine), cortisol and prolactin over 19 successive days from a single limbic epileptic patient were correlated with daily geomagnetic activity (aa values) for the northern hemisphere. Only thyroxine levels were correlated (r = 0.66) significantly with the daily geomagnetic activity; the strongest association (rho = 0.76) occurred between thyroxine levels and the geomagnetic activity (Kp values) during the previous night (2:00 A.M. to 5:00 A.M. local time). These results support the hypothesis that suppression of (nocturnal) melatonin levels by increased geomagnetic activity attenuates the tonic inhibition by this pineal compound upon thyroidal metabolism.

Adult↗

PubMed1995

Leakage of amalgam and Super-EBA root-end fillings using two preparation techniques and surgical microscopy.

An in vitro dye leakage study was conducted to test the root-end sealing ability of amalgam with varnish or Super-EBA using two root-end preparation techniques and surgical microscopy. Sixty-four single-rooted teeth were instrumented and obturated with gutta-percha. Teeth were randomly placed into four groups. Two groups received perpendicular root-end resections, 3-mm-deep ultrasonic root-end preparations, and either amalgam with varnish or Super-EBA root-end fillings. The other two groups received beveled root-end resections, 3-mm-deep micro-handpiece preparations, and either amalgam with varnish or Super-EBA. All root-end procedures were performed at x5 to x8 magnification. Micro-leakage was assessed at 4 months using methylene blue dye and a passive hydrostatic pressure technique. Statistical analysis showed that, regardless of technique, Super-EBA leaked significantly less than amalgam with varnish. There was no significant difference between the two root-end resection and preparation techniques.

Chi-Square Distribution↗

PubMed1994

Cast prosthesis removal using ultrasonics and a thermoplastic resin adhesive.

Nonsurgical endodontic procedures are routinely performed on teeth with existing cast restorations. The internal anatomy of the tooth and location of the root canals may be obscured by a crown or fixed partial denture. Tooth morphology and canal location may, therefore, be better visualized without the cast restoration in place. This article describes a conservative technique to remove an existing cast restoration to facilitate nonsurgical root canal treatment.

Crowns↗

PubMed1994

The lateral radiograph: an aid to labiolingual position during treatment of calcified anterior teeth.

A technique is described to obtain a lateral view of an anterior tooth using a regular periapical film. This procedure helps determine the relative labiolingual position of instruments during the nonsurgical treatment of calcified canals. No additional armamentarium is required other than what is used in the daily practice of endodontics. This technique has other applications as well.

Dental Pulp Calcification↗

PubMed1993

Effect of powder/liquid ratio on physical and chemical properties of C&B Metabond.

The purpose of this study was to examine the effect of varying the powder/liquid ratio on the physical properties and the degree and rate of curing of C&B Metabond cement. The powder/liquid ratios evaluated had no effect on the tensile bond strength of Rexillium III to etched enamel or on the retention of cemented full cast crowns. The higher P/L ratio resulted in an increased vertical displacement of the cemented crowns. The rate of monomer conversion and the total conversion were not affected significantly by the different P/L ratios.

Analysis of Variance↗

PubMed1992

Retention strengths of three cements using full crown preparations restored with amalgam.

The tensile bond strength of noble and non-noble castings luted with adhesive resin cements and zinc phosphate cement to prepared extracted teeth having received MOD amalgam restorations were compared. The crown preparations were standardized on the extracted teeth to produce axial wall length and taper consistent with that seen clinically. Results indicated the resin luting agents were significantly more retentive than the zinc phosphate cement and for each cement there was no difference in the casting alloy used.

Analysis of Variance↗

PubMed1991

Spatial realignment using the hybrid resin-bonded bridge.

As an alternative to a conventional fixed partial denture, a modification of the hybrid resin-bonded bridge was used to compensate for a spatial discrepancy accentuated by a missing tooth. The proximal margins of the restoration were extended onto the facial surfaces of the abutment teeth to create a partially veneered surface. The abutment teeth were widened by shifting the embrasure into the edentulous space, thus creating more esthetic proportions.

Cementation↗

PubMed1990

Effect of internal microblasting on retention of cemented cast crowns.

Microblasting of cast mental crowns is considered a standard procedure in most laboratories and an effective alternative to acid pickling. During the process of devesting and finishing, the surfaces of cast restorations are microblasted with an abrasive agent. This investigation measured the retention of type III cast gold crowns after cleansing with pickling solution (group I) or microblasting with 50-micron aluminum oxide (group II) or 50-micron glass beads (group III). Microblasting the internal surface of cast crowns with 50-micron aluminum oxide significantly improved the retention of castings luted with zinc phosphate cement.

Adhesiveness↗

PubMed1988

Interactions of cyclosporine with renal proximal tubule cells and cellular membranes.

Cyclosporine-induced nephrotoxicity is a limiting factor in the clinical use of cyclosporine. Since the manner in which cyclosporine interacts with proximal tubule cells and their membranes may provide insight into the cellular pathophysiology of cyclosporine toxicity, experiments were undertaken to characterize the interactions of cyclosporine with proximal tubule cells, renal brush border membranes, and renal cortical mitochondria. Cyclosporine bound to isolated rat renal brush border membranes in a saturable manner with a Kd of 0.38 microM and an nmax of 0.33 nmoles/mg protein. Scatchard analysis suggested that the interaction of cyclosporine at low concentrations with brush border membranes was consistent with a partitioning process rather than binding to a specific membrane component. Cyclosporine inhibited rat renal cortical mitochondrial respiration in a dose-dependent manner, with 8 microM as a threshold dose. This inhibitory effect was greater for respiration supported by succinate than pyruvate-malate. TMPD-ascorbate-supported respiration was unaffected. Suspensions of rabbit renal proximal tubule segments were incubated in vitro with 0.5-500 microM 3H-cyclosporine to measure the kinetics of cyclosporine uptake. Uptake was rapid (80% after 10 min) and saturable at 100 microM, with 9 nmoles cyclosporine/mg protein accumulated. Incubation of suspensions of enriched in rabbit renal proximal tubule segments with 10 microM cyclosporine in vitro for 2 hr with or without 22.5 min of hypoxia, or for 16 hr without hypoxia, had no effect on a variety of quantitative metabolic parameters of cell injury, including basal and uncoupled tubule respiratory rates and tubule K+, Ca++ and adenine nucleotide levels. These results demonstrate that cyclosporine interacts with critical renal membrane components at low concentrations but this interaction does not result in proximal renal tubular cell injury acutely in vitro.

Adenosine Triphosphate↗

PubMed1988

Glutathione protects against exogenous oxidant injury to rabbit renal proximal tubules.

Glutathione, comprising a major portion of cellular nonprotein thiols, plays a central role in a diverse group of cell metabolic functions. Glutathione and related enzyme systems have been shown to protect against both toxin and oxidant-induced injury in several organ systems. The role of glutathione in protecting renal epithelia against oxidant stress has not been investigated previously. We report here the response of enriched, isolated rabbit renal proximal tubule segments to oxidant stress induced by tert-butyl hydroperoxide. In addition, the effects of glutathione depletion by various biochemical means and of exogenous glutathione supplementation on the response of tubule segments to tert-butyl hydroperoxide exposure are described. Depletion of cell glutathione by several distinct methods potentiates oxidant-induced injury. Augmentation of cellular glutathione affords significant protection against exogenous oxidant stress. The protective effect of glutathione may reside in its ability, in conjunction with glutathione peroxidase, to arrest the propagation of lipid peroxidation and, therefore, to minimize alterations in plasma membrane permeability. The results of this study do not exclude the possibility that glutathione prevents tert-butyl hydroperoxide induced oxidation of critical sulfhydryl groups of catalytic or structural proteins associated with control of cell cation homeostasis. These results confirm the important role of glutathione in protecting renal tubular epithelia against oxidant stress.

Adenosine Triphosphate↗