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Biomedical subjects

C Robinson

Publications and source records attributed to C Robinson.

At least 19 recordsLinked to original sources
PubMed1992

Thermal analysis of commercial Gutta-percha using differential scanning calorimeter and dynamic mechanical thermal analysis.

Gutta-percha is the most widespread root canal filling material and knowledge of its chemical and thermomechanical properties is of a great interest to its use in clinical dentistry. In the present investigation, the results from differential scanning calorimeter were compared with those obtained by dynamic mechanical thermal analysis. A significant correlation was established between these results and the chemical composition of six different commercial samples of gutta-percha.

Calorimetry, Differential Scanning↗
PubMed1992

Effect of moisture and aging on gutta-percha.

The purpose of this article was to study the plasticizing effect of controlled levels of different humidities on native and commercial gutta-percha samples. It was expected that the results might provide the practicing endodontist with invaluable insight into the mechanical properties of commercial gutta-percha cones (i.e. retrievability, malleability, flexibility, torsional, and bending ability). The "conditioning" of the gutta-percha samples depended greatly on the percentage of compatible and incompatible substances. Mixtures of native gutta-percha with compatible substances (e.g. wax) showed greater elongation, tensile strength, and number of rotations but lower deformation angle than mixtures of native gutta-percha with incompatible substances (e.g. salts, metal oxides). The observed lower values for tensile strength and torsional strain and higher value for elongation and number of rotations for wet samples compared with the dry ones were attributed to the plasticizing effect on gutta-percha of the insertions of water molecules in the polymer chains.

Drug Storage↗
PubMed1992

Perceptions of pediatricians' helpfulness: a national study of mothers of young disabled children.

A national sample of 503 mothers of young children (up to six years of age) with developmental disabilities was surveyed to determine the extent to which their family pediatricians are helpful in providing information and support. The respondents ranged from lower-middle to upper class, with the mean SES reflective of middle socio-economic status. Their children had a variety of disabilities that qualified them to receive early intervention services. The majority of the mothers found their pediatricians helpful about issues related directly to their child's medical condition. However, few found them helpful with issues relating to the effect of the disability on their child's development, or to their own personal or family needs.

Child↗
PubMed1992

Enamel ultrastructure in pigmented hypomaturation amelogenesis imperfecta.

Hypomaturation amelogenesis imperfecta (AI) is a hereditary condition of enamel that is presumed to result from defects during the maturation stage of enamel development. This study characterized the enamel ultrastructure and enamel crystallite morphology, as well as the distribution of organic material in enamel affected with pigmented hypomaturation AI. Enamel exhibiting autosomal recessive pigmented hypomaturation AI was sectioned or fractured and examined using light microscopy, scanning electron microscopy and transmission electron microscopy. Enamel samples were treated with 30% NaOCl or 8 M urea to remove organic components and determine the effect of deproteinization on crystallite morphology. These were compared with untreated normal enamel samples. The enamel crystallites in hypomaturation AI exhibited considerable variability in size and morphology. Examination of deproteinized tissue indicated that the AI crystallites had a thick coating, presumably of organic or partially mineralized material, which was not visible in normal enamel. The results of this investigation provide further evidence that hypomaturation AI is associated with the retention of organic material that is most probably enamel protein. Enamel protein retention is likely to be involved in the inhibition of normal crystallite growth resulting in the morphological crystallite abnormalities associated with this disorder.

Amelogenesis Imperfecta↗
PubMed1992

Influence of occlusion on the fluoride distribution in rat molar cementum.

This study was undertaken to examine the influence of occlusion on the fluoride distribution in cementum following an experiment in which the occlusion in rats was locally altered by extracting the upper left molar. These and control rats with normal occlusion were given water containing 0 or 100 ppm fluoride for 12 weeks. The fluoride distributions in cementum from both first lower molars of the same animal were compared. The fluoride concentrations had increased throughout the tissue as a result of increased fluoride administration, irrespective of any changes in occlusion. They were, as usual, generally highest at or near the cementum surface and decrease towards the interior of the tissue. Where there had been a change in occlusion, the thickness of cementum was less than that of the contralateral tooth, but, despite this, the fluoride profiles in contralateral teeth were similar in both experimental and control rats. In the experimental rats, on the other hand, the total fluoride tended to be lower, and the mean fluoride tended to be higher in left molars without antagonists. These findings were never seen in the control rats. It was concluded that the alteration in occlusion influenced the fluoride distribution in the cementum through its effect on the rate of cementum formation.

Animals↗
PubMed1992

The role of albumin in developing rodent dental enamel: a possible explanation for white spot hypoplasia.

The uptake of serum albumin by maturation-stage rodent enamel and the resulting effects on the growth of enamel crystallites were investigated in vitro. Albumin uptake was demonstrated by means of gel electrophoresis and confirmed by Western blotting with use of monoclonal antibodies. Measurement of crystal size was carried out by direct TEM measurement of enamel crystallite outlines after incubations in metastable solutions of calcium phosphate. The ability of endogenous enamel enzymes to degrade albumin was investigated by substrate-specific zymography. The results showed that albumin could be taken up by maturation-stage enamel and produce inhibition of crystallite growth. There was no detectable proteolytic activity in the enamel against albumin substrate, which suggests that albumin entering enamel by extravasation in vivo may produce incomplete tissue maturation, resulting in a white, opaque appearance on eruption.

Animals↗
PubMed1992

Immune responsiveness and risk of illness in U.S. Air Force Academy cadets during basic cadet training.

It has been proposed, but not confirmed, that environmental stressors alter immune function and increase the risk of viral infection among healthy individuals. We evaluated this hypothesis, examining the relationship among stress, immune function, and illness in 96 first-year U.S. Air Force Academy cadets during orientation and 4 weeks later during the stressful environment of Basic Cadet Training (BCT). Perceived stress and well-being levels of cadets were assessed via questionnaire. Immune responsiveness was analyzed by PHA-stimulated thymidine uptake in mononuclear leucocytes and by serologic evidence of reactivation of the Epstein-Barr virus (EBV). We documented significant declines in in vitro PHA-induced lymphocyte transformation (-35%; p less than 0.05) and subjective well-being (-19%; p less than 0.05) from orientation to BCT with corresponding, significant increases in perceived stress (+32%; p less than 0.05). Despite significantly altered in vitro immune responsiveness, there was no serologic evidence of EBV reactivation nor was there an association between these measures and risk of illness as determined by medical chart review and self-reported symptoms. These results suggest that reduced in vitro immune responsiveness during a moderate stressor may not necessarily lead to an increased risk of infection and/or reactivation of EBV in normal individuals.

Aerospace Medicine↗
PubMed1979

Matrix and mineral changes in developing enamel.

An investigation of the changes taking place in the enamel and the enamel organ during enamel development has been carried out by analyzing small samples of tissue dissected from developing incisors of rat and bovine incisors. Observations showed that the synthesis of the enamel matrix and its subsequent loss were associated chiefly with a change in the major matrix components. This consisted of a selective loss of amelogenin components prior to secondary mineralization. Before this loss, some increase in the proportion of smaller molecular weight components suggested the possibility of limited breakdown. Even at the earliest stages examined, significant concentration of mineral ions was present. This increased steeply after most of the organic matrix had been removed. The Ca/P ratio of this mineral was constant throughout development. The concentration of minor inorganic ions (F, Mg and CO3) decreased as the tissue developed and a tendency was observed for certain ions (F, 32PO4) to penetrate and concentrate in the enamel, apparently as a consequence of the lost matrix being replaced by water, just prior to the steep increase in mineral content of the tissue.

Amelogenesis↗
PubMed1978

Clinical electrophysiological effects of atenolol--a new cardioselective beta-blocking agent.

Atenolol, a cardioselective beta-blocking agent, at dose levels of 0.03, 0.06, and 0.12 mg/kg intravenously, produced prolongation of atrioventricular nodal conduction in 22 patients with suspected coronary artery disease. In a dose of 0.12 mg/kg body weight atenolol produced significant prolongation of sinus cycle length, sinus node recovery time, atrioventricular node conduction, and the effective and functional refractory periods of the atrium and the atrioventricular node. No significant effects were observed on the His Purkinje system or the effective refractory periods of the ventricle. In these actions atenolol closely resembles propranolol. However, because in contrast to propranolol it increases atrial refractoriness, it may have advantages in the treatment of atrial arrhythmias.

Atenolol↗
PubMed1978

Haemodynamic effects of atenolol in patients with coronary artery disease.

The haemodynamic effects of atenolol, a new cardioselective beta-blocking agent, have been studied at rest in 8 patients with coronary artery disease. The drug was administered intravenously in cumulative doses of 0.03, 0.06, and 0.12 mg/kg body weight. A significant decrease in heart rate was associated with a fall in cardiac output. However, this cardiac output fall was not entiely rate dependent, since stroke volume fell significantly both during spontaneous sinus rhythm and when heart rate was maintained constant by atrial pacing. A dose related and significant reduction occurred in left ventricular dP/dt max without significant change in left ventricular filling pressure or mean aortic pressure. Total peripheral resistance at rest rose after atenolol. The haemodynamic findings more closely resemble those which follow intravenous propranolol than those after intravenous practolol in a similar group of patients. These actions of atenolol suggest that it may be a useful agent in the treatment of patients with angina pectoris.

Adult↗
PubMed1978

Comparison of atenolol with propranolol in the treatment of angina pectoris with special reference to once daily administration of atenolol.

Fourteen patients with angina pectoris completed a double blind trial of atenolol 25 mg, 50 mg, and 100 mg twice daily and propranolol 80 mg thrice daily. In comparison with placebo, all active treatments significantly reduced anginal attacks, consumption of glyceryl trinitrate, resting and exercise heart rate, resting and exercise systolic blood pressure, and significantly prolonged exercise time. There was no significant difference between the effects of propranolol and atenolol. Nine patients completed a further trial comparing atenolol given once or twice daily. Both regimens were effective and there was no significant difference between the reductions in anginal attacks, glyceryl trinitrate consumption, systolic blood pressure, or heart rate. Twenty-four-hour ambulatory electrocardiograms showed that atenolol consistently reduced heart rate throughout the 24-hour period whether given once or twice daily. Atenolol is a potent antianginal agent which, in most patients, is likely to be effective once daily.

Adult↗