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Biomedical subjects

F McDonald

Publications and source records attributed to F McDonald.

At least 73 records · Page 4Linked to original sources
PubMed1991

Effect of bracket and wire composition on frictional forces.

Previous work on friction has considered movement of single teeth along an archwire. The aim of this investigation was to consider friction in buccal segment attachments during overjet reduction involving sliding mechanics. A buccal segment model was constructed to compare friction in steel and ceramic brackets, using steel and nickel titanium wires of two sizes along with a new experimental polymeric wire. The results indicate that friction during overjet reduction is minimized by using larger dimension rectangular wires and by using steel rather than nickel titanium. Comparing steel with ceramic brackets in series, the latter show greater frictional resistance, but only when used with the smaller rectangular wires. The combined effect of environment, ligation, bracket, and archwire significantly reduced the difference. Clinically, there may, therefore, be little to choose between steel and ceramic brackets in the buccal segments, with wire choice as determined by tooth displacement being more important. Comparison of the results with those obtained using single brackets illustrates the problems of interpreting results from friction experiments. The polymeric archwire in its present form was found to be unsuitable for use in orthodontics.

Acetals↗
PubMed1990

An in vivo assessment of muscular activity and the importance of electrical phenomena in bone remodelling.

Modified orthopaedic pins were placed close to the medial and distal epiphyses of the tibia in 4 anaesthetised rabbits, in order to allow the application of controlled external loading cycles. Rosette strain gauges were placed at midshaft level, where the greatest compressive and tensile strains were expected during loading. Two weeks later, following stabilisation of the pins by bone healing, the animals were anaesthetised again and silver-silver chloride electrodes were attached close to the strain gauges in order to measure the changes in electrical potential difference. A sinusoidal load cycle was exerted between the pins with peak levels of 100 N or 250 N depending on the age of the animal. A fluctuation in potential difference, in synchrony with the strain recorded by the strain gauges, was recorded. The maximum potential difference was 2.2 mV, and it was not possible to exceed this with increased bone strain. After demonstration of the piezoelectric effect, repeated stimuli were applied to the sciatic nerve, producing a twitch in the muscles adjacent to the tibia. The electric potential difference from the muscles completely overwhelmed the local potential difference at the bone surface. A further two animals were prepared as previously described, and one electrode was placed on the endosteal surface. The electrical events mirror the changes found across the limb. The stimulus to bone remodeling, as distinct from growth, is usually loading in association with muscular activity. The fact that the changes in electrical fields at the bone surface are predominantly those originating in the muscles indicates that local electrical phenomena generated by bone strain cannot be the factors initiating the cellular response that is responsible for bone remodeling.

Animals↗
PubMed1989

The condylar disk as a controlling factor in the form of the condylar head.

The articular disk has been implicated as a controlling factor of the form of the condylar head. In a study investigating the role of articular function on the condylar cartilage, 35 adult Wistar rats (mean weight 327 g) were operated on to establish the effects of loss of the disk and capsule on the form of the condylar head. These animals had their zygomatic arch and disk removed on one side, while a neutral procedure was performed on the opposite side to act as a control. The results showed extremely unusual shapes to the form of the condylar head and implicated the disk as the controlling factor. Studies with tritiated thymidine also showed an increase in proliferative activity.

Animals↗
PubMed1989

An unusual presentation of polyostotic fibrous dysplasia.

A case of polyostotic fibrous dysplasia with increased bone density on radiographic presentation but a normal histologic appearance of dense trabecular bone is presented. Peculiar to this case of fibrous dysplasia was that treatment took place relatively late in the patient's life.

Female↗
PubMed1988

Taste acuity and zinc metabolism in captopril-treated hypertensive male patients.

Hypogeusia is a reported side effect of captopril. Linkage of hypogeusia to zinc deficiency has been suggested. We objectively assessed taste acuity using Henkin's three-drop stimulus technique and measured plasma zinc (PZn) level and urinary zinc excretion in 31 hypertensive patients. Of these, 11 were long-term, high-dose captopril recipients (more than 6 months, 266 +/- 34 mg/day), six were short-term captopril recipients (less than 6 months, 104 +/- 40 mg/daily dose), and the remaining 14 served as noncaptopril controls. Compared to controls, the long-term captopril group had significantly higher taste detection and recognition thresholds, lower PZn (91 +/- 3 vs. 100 +/- 3 micrograms/dl, P less than 0.05) and higher urinary zinc excretion (1017 +/- 89 vs. 609 +/- 76 micrograms/day, P less than 0.005). The short-term captopril group did not differ significantly from the noncaptopril group except for higher taste-recognition thresholds for NaCl and sucrose (P less than 0.05). Discontinuing captopril improved taste acuity and almost normalized zinc parameters in two patients on long-term captopril. These results suggest that abnormalities of taste are commonly associated with captopril therapy and may be related to changes in zinc metabolism. This is especially true in patients on long-term, high-dose captopril therapy.

Captopril↗
PubMed1987

A case report of superimposition on cranial base.

A case is reported where superimposition on Cranial Base produced the appearance that therapeutic modification of mandibular growth had occurred. However, the patient's growth status did not support this concept, being 17 years and 1 month of age at the commencement of treatment.

Adolescent↗
PubMed1986

Renal effects of SK&F 82526 in anesthetized rats.

Dopamine affects renal hemodynamics, renal tubular functions, and the secretion of renin. We have studied the renal effects of SK&F 82526 (an agonist which is selective for the DA1 subclass of dopamine receptors) in anesthetized rats. Infused intravenously at 0.005 mumol/min/kg, this drug increased renal plasma flow and the clearances of PAH and insulin, effects which are consistent with decreased renovascular resistance. Concomitantly, urine flow and K excretion increased, and Na excretion tended to increase. All these effects of SK&F 82526 were antagonized by intravenous metoclopramide (1 mumol/min/kg). Despite its diuretic effect and despite its lack of effect on arterial blood pressure, SK&F 82526 increased arterial plasma renin concentration, suggesting a stimulatory effect on renin secretory rate. Taken together, our results demonstrate that the renal effects of SK&F 82526 mimic those of dopamine.

Animals↗
PubMed1986

The surgical exposure and application of direct traction of unerupted teeth.

This article presents a retrospective study of patients treated for impacted maxillary canines by a combined surgical and orthodontic approach. All patients were assessed radiographically by means of a lateral skull radiograph and an orthopantograph. No posteroanterior radiographs were taken. Facial or lingual position within the arch was not determined, the height and inclination of the canine being deemed more important. At surgery, a facial flap was raised first in all cases. Only if access and isolation were poor was a palatal flap raised. Bone was removed as necessary. One contention of this article is that the amount of bone removed is not important. It is the manner in which the soft tissues and, in particular, the periosteum are handled that ultimately affects the results of the surgical treatment. An attachment was bonded onto the tooth and the wound closed. The tooth was then actively extruded, a removable appliance being preferable because more vertical control of anchorage is possible.

Alveolectomy↗
PubMed1982

Antiarrhythmic effects of Org 6001 in rats: correlation with plasma and tissue drug concentrations.

The antiarrhythmic effects of Org 6001 following oral administration in the rat have been assessed and correlated with plasma, myocardial and skeletal muscle drug concentrations. Arrythmias were induced by coronary artery ligation in anaesthetized rats. Org 6001 (10, 20, 50 and 100 mg/kg given 1 h before ligation) significantly reduced mortality and the incidence of ventricular fibrillation in the 0-30 min post ligation period. Only the highest dose of drug also significantly reduced the number of ventricular ectopic beats following ligation. A linear relationship was observed between the oral dose and the Org 6001 concentrations in plasma and skeletal muscle determined 90 min after drug administration. The Org 6001 concentration in the myocardium was not linearly related to the administered dose and Org 6001 appeared to be concentrated to a higher extent in cardiac than in skeletal muscle at that time. No statistically significant difference in drug levels in the ischaemic left ventricle and normal right ventricle plus septum was observed. The antiarrythmic effect of Org 6001, as measured by changes in the incidence of ventricular fibrillation, correlated with myocardial concentrations of the drug.

Androstanols↗