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Biomedical subjects

N H Wilson

Publications and source records attributed to N H Wilson.

At least 163 records · Page 9Linked to original sources
PubMed1990

Radiovisiography for imaging root canals: an in vitro comparison with conventional radiography.

Radiovisiography is a rapid, low-dose, digital imaging system that utilizes a small, intraoral sensor in place of radiographic film. Because of these characteristics, it may be particularly suitable for use in endodontics. Consequently radiovisiography and conventional film radiography for the imaging of root canals were compared in vitro. There was no statistically significant difference between the percentage of length of root canal visible on conventional film and that visible on radiovisiographic images. Thus, radiovisiography may be considered to be of equal value to conventional film radiography for the imaging of root canal systems in vitro.

Dental Pulp Cavity↗
PubMed1990

Effects of approximal finishing strips.

The effects of a representative sample of approximal finishing strips on the surfaces of restorations, the approximal margins of restorations and on the surfaces of enamel adjacent to restorations have been evaluated using scanning electron microscopy. The results indicate that the sample of finishing strips investigated tend to damage the surface of enamel and fail to leave restorations with either ideal surface finish or marginal adaptation. Guidelines are suggested for the choice of approximal finishing strips in selected clinical situations.

Dental Bonding↗
PubMed1989

The use of gloves in cross-infection control. A historical note.

Routine glove wearing has been an integral part of surgery for almost a century, but it has only recently been considered appropriate for dentists and their staff while treating patients. This paper traces the history of glove use in surgery and compares this with experience of glove use in dentistry at the present time.

Communicable Disease Control↗
PubMed1989

Image analysis of radiolucencies in approximal enamel: a comparison of xeroradiographic and conventional film images.

Xeroradiographic and conventional film bitewing images of radiolucencies in approximal enamel were compared using a computer-aided image analysis system. Densitometric analysis of the conventional film types used in the study showed that the "lead foil free" film exhibited lower overall density when compared with conventional D-speed film. Computer-aided image analysis of radiolucencies in approximal enamel found that xeroradiographs depicted a higher degree of demineralization and a larger area than conventional radiography with the "lead foil free" film.

Adolescent↗
PubMed1989

Some physical factors influencing tactile perception with disposable non-sterile gloves.

Some of the physical factors considered to influence tactile perception with disposable, non-sterile gloves have been investigated. While it is apparent that tactile perception is influenced by a number of factors, the results of the present work indicate an inverse relationship between dentists' assessments of tactile awareness and stiffness measurements of the glove material.

Dentists↗
PubMed1989

The teaching of posterior composites: a worldwide survey.

The findings of a worldwide survey of the teaching of posterior composites have been reported. In most schools in at least Africa, Australasia, Europe, North America and Japan (mean response, 70 per cent) the undergraduate course in operative dentistry includes some consideration of posterior composites. However, the teaching in relation to these materials is typically limited and rarely includes practical exercises let alone requirements to gain clinical experience of the use of these materials. The data collected in respect of the materials and techniques considered appropriate for posterior composites was essentially consistent and in keeping with most of the recent authoritative literature in this field. It is concluded that many schools should review their approach to the teaching of posterior composites.

Bicuspid↗
PubMed1989

The nature and effects of composite finishing pastes.

Specimens of composite resins, contoured and finished with a series of microfine diamonds, were finished with a selection of commercially available composite finishing pastes. The resulting surfaces were examined using scanning electron microscopy (SEM) and surface profilometry. Samples of the pastes were investigated using SEM and energy dispersive X-ray spectroscopy. All the paste systems employed an abrasive of similar composition and particle size. The selection of finishing pastes produced marked improvements of the surfaces of the composite resins. The small differences measured between the performances of the four finishing pastes included in this study could not be corroborated by SEM evaluation. Therefore, within the limitations of this study, there was little evidence to suggest that any one paste system was superior to the others. The results of this study indicate that commercially available composite resin finishing pastes of the type investigated may be used to improve the surface of all types of contemporary composite resins and may be of particular value in finishing the concave surfaces of restorations of composite resins following contouring and finishing with microfine diamond burs.

Composite Resins↗
PubMed1989

Effects of a solution of a succinic aldehyde on elastomeric impressions.

This study investigates the effect of a 10 per cent solution of a succinic aldehyde on impressions of three representative elastomeric materials. For each material ten specimens were required for each of six immersion periods ranging from 10 min to 72 h at 23 degrees C and including immediate and delayed immersions. Control groups, each of five specimens, were investigated in air and water. The specimens were formed against a standard ruled block (ADA No. 18). Before and after immersion/storage the impression surface of each specimen was assessed, scored and measured to determine dimensional stability and any attenuation and loss of detail. The results indicate that following all immersion/storage periods there was no loss of detail. Whereas dimensional changes of c. -0.5 per cent and +1.0 per cent were observed for the addition and condensation cured silicones, respectively, after 72 h immersion in the solution, zero dimensional changes were observed following the recommended immersion period for sterilization (4 h). However, with the polyether impressions, a 4 per cent expansion occurred after 4 h in the test solution and 9 h in the aqueous control. No significant differences were found between data relating to immediate and delayed immersions. It is concluded that the immersions in the test solution had no effect on surface detail; only the silicone impressions exhibited acceptable dimensional stability during prolonged immersions (4-72 h) in the test solutions and aqueous control, and that the polyether specimens withstood immersion in the test solution for the 10-min period recommended for disinfection.

Aldehydes↗
PubMed1989

EP 171: a high affinity thromboxane A2-mimetic, the actions of which are slowly reversed by receptor blockade.

1. Replacement of the four-carbon omega-terminus in 9,11-endoxy-10a-homo prostaglandin H2 with a p-fluorophenoxy group produces a compound (EP 171) with very high agonist potency at TP-receptors. 2. On six isolated smooth muscle preparations EP 171 was 33-167 times more potent as a TP-receptor agonist than U-46619 (11,9-epoxymethano PGH2); EC50 values ranged from 45 to 138 pM. The actions of EP 171 were difficult to study because of their slow onset and offset. For example, on the guinea-pig trachea the time required for 50% reversal of EP 171-induced contractions during washout was about 3 h. 3. On the pig pulmonary artery, a more rapidly responding preparation, it was possible to show that the TP-receptor antagonist EP 092 blocked the contractile actions of EP 171 and U-46619 to similar extents: pA2 = 8.09 and 8.15 respectively. 4. EP 171 was also a very potent activator of human blood platelets, being about 90 times more potent than U-46619. Both shape change (0.1 nM) and aggregation (1 nM) were slow in onset, a profile not previously observed for a thromboxane A2-mimetic. 5. When potencies at TP-, EP1-(guinea-pig fundus) and FP-(dog iris sphincter) receptors were compared, EP 171 showed a higher specificity as a TP-receptor agonist than either STA2 or U-46619. These studies also showed that contrary to earlier reports, the guinea-pig fundus does contain TP-receptors mediating muscle contraction. However, the maximal response due to activation of TP-receptors was only about 35% of the PGE2 maximum. 6. Established responses to EP 171 were slowly reversed following addition of a high concentration of a TP-receptor antagonist (EP 092, GR 32191 or BM 13177). Faster reversals of three less potent 16-p-halophenoxy prostanoids and U-46619 were obtained. Half-times for offset (and onset) of agonist action appeared to correlate with potency rather than with lipophilicity. 7. Competition between the agonists and a radio iodinated PTA2 derivative ([125I]-PTA-OH) for binding to TP-receptors on intact human platelets was studied. IC50 values correlated well with aggregating potency, EP 171 having the lowest IC50 of 2.9 nM. The true Ki for EP 171 may be about 1 nM if both its racemic nature and reduction of initial free ligand concentration due to TP-receptor binding are taken into account. 8. It is concluded from a comparison of agonist potency rankings that subclassification of the TP-receptor is not warranted at this time. The factors that may be responsible for the slow kinetics of EP 171 action are discussed.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1989

Functional and ligand binding studies suggest heterogeneity of platelet prostacyclin receptors.

1. This study describes attempts to compare prostacyclin (IP-) receptors in human, pig, horse, rabbit and rat platelets and in circular muscle of human, rabbit and dog mesenteric and pig gastroepiploic arteries. Three stable prostacyclin analogues, iloprost, cicaprost and 6a-carba-prostacyclin (6a-carba-PGI2) and a prostaglandin endoperoxide analogue EP 157 (previously shown to mimic prostacyclin on human platelets) were used. 2. Our main conclusion is that prostacyclin receptors on human, pig and horse platelets are similar in nature, but distinct from those on rabbit and rat platelets. Functional studies (inhibition of aggregation) showed that iloprost and cicaprost always had similar potencies whereas 6a-carba PGI2 was much more potent than EP 157 on rabbit and rat platelets (300 and 1000 fold on a molar basis) compared with human, pig and horse platelets (2, 7 and 7 fold respectively). Measurement of initial rates of cyclic AMP production confirmed these orders of potency. 3. Although pig platelets were quite sensitive to inhibition by EP 157 (threshold = 10 nM in some experiments), maximal inhibition of aggregation was not always achieved (20 microM). EP 157 also produced only small elevations of cyclic AMP and inhibited rises in cyclic AMP induced by iloprost. It is possible that EP 157 has a lower efficacy than iloprost at the IP-receptor and on pig platelets it can sometimes act as a partial agonist. 4. Human, pig and horse platelet membranes bound [3H]-iloprost at 30 degrees C and this binding was inhibited by the four prostanoids. On human and pig membranes the order of potency was cicaprost = iloprost greater than 6a-carba PGI2 greater than EP 157. The order of potency may be similar on horse platelet membranes, but the analysis is complicated by the presence of a second component of [3H]-iloprost binding that is inhibited by iloprost and 6a-carba PGI2 but not by cicaprost. This binding may be due to the presence of an EP1-receptor, since iloprost and 6a-carba PGI2 but not cicaprost are known to have potent EP1-receptor agonist actions on smooth muscle preparations. IC50 values for cicaprost inhibition on human, pig and horse membranes were 110, 90 and 165 nM respectively. The need for IP-receptor radioligands of greater specificity is apparent from these studies. 5. Minimal binding of [3H]-iloprost to rabbit and rat platelet membranes was obtained at 30 degrees C. Lowering the incubation temperature to 4 degrees C and ensuring that the temperature did not rise during the filtration process increased binding and allowed inhibition curves to be obtained. The results suggest a lower binding affinity for [3H]-iloprost, associated with a higher dissociation rate for the radioligand-receptor complex. IC50 values for cicaprost were 900nm for rabbit and 640nm for rat platelets. In a similar manner to horse platelet membranes, the presence of a second binding site for [3H]-iloprost was detected on rabbit platelet membranes. 6. Sensitivity to the relaxant action of iloprost on the arterial smooth muscle preparations decreased in the order: human mesenteric, dog mesenteric, rabbit mesenteric, pig gastro-epiploic. Cicaprost was always slightly more potent than iloprost (1.2-2.8 fold). On the pig vessel preparation 6a-carba PGI2 did not produce complete relaxation. The possibility that this is due to an opposing contractile action mediated via EP1 or EP3 receptors is discussed. 7. EP 157 relaxed the human, pig and rabbit arterial preparations at concentrations 100-200 times those of iloprost. This correlates well with its IP-receptor agonist potency on human, pig and horse platelets. The results obtained with EP 157 further demonstrate the potential difficulties in separating platelet inhibitory and vasodilator properties of prostacyclin mimetics in man.

Animals↗
PubMed1989

Non-sterile glove use: a review.

The increasing incidence of infections which may be transmitted from patient to dentist, and vice-versa, have brought about increased awareness of the cross-infection control procedures necessary to prevent transmission of disease during dental treatment. The wearing of gloves is of primary importance in this respect. The problems associated with glove use are discussed in the light of recent research, and recommendations are made regarding their use.

Communicable Disease Control↗
PubMed1988

Dietary linoleic acid, gastric acid, and prostaglandin secretion.

Basal and pentagastrin-stimulated gastric acid secretion, fasting serum gastrin concentrations, and the gastric output of prostaglandin E and its major metabolite 13,14-dihydro 15-keto prostaglandin E2 were measured in 9 normal subjects before and after 14-20 days of dietary supplementation with linoleic acid. Mean maximal gastric acid output fell from 36.0 +/- 3.3 (SEM) to 30.1 +/- 2.9 mmol/h (p less than 0.05), although mean basal acid output was not significantly affected (8.3 +/- 2.1 and 7.2 +/- 1.7 mmol/h, respectively). Mean fasting serum gastrin concentrations increased from 19.2 +/- 3.1 to 30.9 +/- 3.8 ng/L (p less than 0.01) after linoleic acid, probably because of acid suppression. The mean output of prostaglandin E increased from 498 +/- 110 to 1254 +/- 465 ng/h (p less than 0.05); that of its metabolite increased from 165 +/- 18 to 1168 +/- 645 ng/h (p less than 0.01). These findings show that in normal subjects essential fatty acid weakly inhibits gastric acid secretion, but considerably increases gastric prostaglandin output.

Adult↗