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Biomedical subjects

J Middleton

Publications and source records attributed to J Middleton.

At least 19 recordsLinked to original sources
PubMed1992

Stresses induced by edgewise appliances in the periodontal ligament--a finite element study.

The quantification of stress in the periodontal ligament is an important concept, as stress in this tissue is transmitted to the alveolus, with subsequent bone remodelling and tooth movement. A number of clinical studies have suggested figures for such an optimal stress range. This study makes use of a finite element technique to determine the stress induced in the periodontal ligament in three dimensions when a maxillary canine tooth is subjected to an orthodontic force similar to that produced by an edgewise appliance. The maximum stress induced at the cervical margin of the periodontal ligament was 0.072 N/mm2, while the maximum stress induced at the level of the apical foramen was 0.0038 N/mm2. These results are discussed in the light of known clinical experience and compared with the stresses produced in the periodontal ligament by other orthodontic forces. The findings would suggest that even with 'perfect' edgewise mechanics it would be difficult to obtain canine movement by pure translation or 'bodily movement.'

Alveolar Process↗
PubMed1991

The pattern and timing of cutaneous hair follicle innervation in the rat pup and human fetus.

The postnatal development of hair follicle innervation was studied in the rat hindlimb using a silver stain which detects large and medium calibre cutaneous nerve fibres. The pattern and timing of innervation in relation to postnatal changes in follicle growth were studied providing new data on nerve-target interactions in the developing peripheral nervous system. Sensory axons begin to leave the dermal plexus and grow towards follicles at P (postnatal day) 3 but do not start to innervate them until P7 or achieve an adult appearance until P19. The first terminals are circumferential, followed some days later by the appearance of palisade endings. The number of axons innervating a hair follicle increases steadily with age until P19 and there is no evidence of exuberant innervation of follicles during development. Hair follicle density in the rat is maintained during development due to waves of small, vellus follicle growth later in postnatal life as the skin grows. The percentage of follicles innervated however, decreases from the second postnatal week onwards presumably because late developing vellus hairs do not become innervated. Comparative analysis in human fetal abdominal skin using the same silver stain reveals a similar sequence and pattern of innervation to the rat over the period of 22 to 35 weeks EGA (estimated gestational age). Human skin does not, however, undergo the late waves of follicle growth seen in the rat. Follicular density decreases and the percentage of innervated follicles increases in the third trimester of fetal life.

Animals↗
PubMed1991

An outbreak of Legionnaires' disease in Gloucester.

Fourteen people living in or near the city of Gloucester fell ill with Legionnaires' disease caused by Legionella pneumophila serogroup (SG) 1 between 27 August and 27 October 1986. Another patient had fallen ill on 30 May. Nine of the 15 were diagnosed retrospectively during a case finding exercise. There were three deaths. Three cases of Pontiac fever were also diagnosed. The source was probably one or more wet cooling towers. Nineteen premises in the city with such towers were identified, and three just outside Gluocester. Samples from 11 of the 22 premises grew Legionella spp.; from nine of these L. pneumophila SG 1 (Pontiac) was isolated. The efficacy of regular addition of biocide in addition to hypochlorite added at the time of disinfection in inhibiting the growth of Legionella spp. was demonstrated. A survey of patients' movements during their likely incubation period showed that there was no single building that all patients had visited, but there were two areas of the city which nearly all had visited or passed through by car. A case-control study demonstrated an association with one of these areas. Cooling towers near both areas may have been sources but the evidence is insufficient to incriminate any single one. The unexpected finding of L. pneumophila SG 1 (Pontiac) in nine towers supports the hypothesis that there may have been multiple sources. Cooling towers may have been contaminated by mains water or by drift from other towers.

Adult↗
PubMed1991

A stress analysis of the periodontal ligament under various orthodontic loadings.

The accurate modelling of teeth under orthodontic load in the laboratory has many shortcomings in that it has not been possible to integrate methods, such as three-dimensional models, photo-elastic stress analysis, laser holographic interferometry, and animal studies, to give comprehensive and repeatable results. In this study, using a three-dimensional finite element model of a human maxillary canine tooth, the maximum principal stresses in the periodontal ligament produced by various orthodontic forces were determined. 1 Newton tipping forces produced stresses at the cervical margin of the periodontal ligament as high as 0.196 N/mm2 and apical stresses up to -0.034 N/mm2, while rotatory forces of two equal, but opposing forces of 0.5 Newton at the cervical margin of the crown produced cervical margin stresses ranging between -0.035 and 0.051 N/mm2, and apical stresses of between 0.0018 and 0.0027 N/mm2. These stresses are examined and discussed in relation to previous clinical, laboratory, and histological studies.

Computer Simulation↗
PubMed1991

A finite element study of canine retraction with a palatal spring.

The use of a removable appliance to retract a maxillary canine tooth into a first premolar extraction space is one of the most commonly performed orthodontic procedures. However, unwanted movements may occur, including excessive tipping, rotation, and flaring of the tooth. The present investigation by the use of a finite element model quantifies some of the initial stresses produced within the periodontal ligament when two obliquely directed forces are applied to a maxillary canine tooth. In simulating the action of a removable appliance it attempts to relate the stress patterns to the nature of the subsequent tooth movement.

Cuspid↗
PubMed1979

A quantitative cytochemical study of acid phosphatases in rat liver parenchymal cells of different ploidy values.

The Vickers M86 integrating microdensitometer has been used to quantify the cytochemical reaction for acid naphthol AS-BI phosphatase activity in isolated, rat liver parenchymal cells. Data are presented which validate the method. The use of this method together with that of the Feulgen reaction to estimate nuclear ploidy value in the same cell, has shown that there is an increase in acid phosphatase activity of up to 100% when the euploidy value of the liver cell doubles. It has been further shown that 70--80% of this enzyme activity is ouabain-sensitive, regardless of the euploidy value. The data may be interpreted to indicate that the extra gene copies of the polyploid cells are operative.

Acid Phosphatase↗
PubMed1978

Gram-negative endocarditis caused by Campylobacter fetus.

Campylobacter fetus is a rare cause of endocarditis that is difficult to diagnose because of the fastidiousness of the organism. The source of infection is unknown and it may involve a normal or previously damaged aortic valve. The onset is insidious, and if there is a prior history of recent onset of fever, thrombophlebitis, and diarrhea, infection caused by this organism should be considered. Echocardiography may be useful. The organism is sensitive to a variety of antibiotics, including the combination of penicillin and streptomycin. The prognosis and survival are good.

Adult↗
PubMed1978

Perinatal mortality: assisting parental affirmation.

The health professional's role does not cease with perinatal death, but shifts towards the prevention of postmortem psychiatric sequelae in the parents. A multidisciplinary bereavement service has found that an increased awareness of the final processes of "viewing" and "burial" diminishes the production of fearful speculations both by parents and staff, and allows them to cooperate more fully in dealing with the tragedy.

Adaptation, Psychological↗
PubMed1975

An electrophysiological analysis of the effects of reserpine on adrenergic neuromuscular transmission.

1 An electrophysiological study has been made of the effects of depleting synaptic vesicles (i.e. small vesicles less than 60 nm diameter) of their transmitter with reserpine on the quantity of transmitter released by nerve impulses, using the amplitude of the synaptic potential as a measure of transmitter release. 2 Pretreatment of adrenergic nerve terminals with reserpine sufficient to deplete the terminals of 70% of their noradrenaline (NA) did not change the total number of synaptic vesicles in the terminals, but did reduce the number with a large granular core as well as the quantity of NA released by a single nerve impulse by 80%. 3 Pretreatment of adrenergic nerve terminals with reserpine and iproniazid, to decrease vesicular NA but enhance cytoplasmic NA, had the same effect on synaptic vesicles and on the NA released by a single nerve impulse as did reserpine alone. 4 During a short train of impulses at high frequencies in reserpine pretreated terminals, the quantity of NA released by successive impulses increased until a steady-state release was reached comparable to that in untreated preparations. This facilitated release could be quantitatively predicted in terms of the addition of the individual potentiations introduced by each impulse in the train. 5 These results are consistent with the idea that each quantum of transmitter is stored in a synaptic vesicle, and that these may be released by nerve impulses directly from the terminal by a process of exocytosis.

Animals↗
PubMed1975

An electrophysiological analysis of the effects of amine-uptake blockers and alpha-adrenoceptor blockers on adrenergic neuromuscular transmission.

1 An electrophysiological study has been made of the effects of either blocking noradrenaline (NA) uptake or alpha-adrenoceptors on conduction in adrenergic preterminal axons and on NA release. 2 The excitatory junction potential (e.j.p.) evoked by a single stimulus increased slightly in duration (maximum 20%) in the presence of high concentrations of desipramine or cocaine (larger than or equal to 1 mug/ml) but there was no change in the spontaneous miniature excitatory junction potential (m.e.j.p.s); the single compound preterminal action potential was decreased in amplitude by a maximum of 10%. The e.j.p., m.e.j.p. and the terminal action potential were not altered by lower concentrations of these drugs (less than mug/ml). 3 The increased decline of the e.j.p. amplitude observed during the first few hundred impulses at high frequencies (10 Hz) in the presence of desipramine or cocaine was accompanied by a similar decline in the amplitude of the preterminal compound action potential, suggesting that the latter gave rise to the former. 4 These observations suggest that the action on post-synaptic alpha-adrenoceptors of NA released by single impulses is terminated by diffusion, and that any NA which is subsequently taken up into nerves is metabolized. 5 All the alpha-adrenoceptor blocking drugs tested reversed the normal depression in e.j.p. amplitude observed during the first few hundred impulses at high frequencies to facilitation; this was unaccompanied by any changes in the preterminal compound action potential. 6 Alpha-Adrenoceptor blocking drugs did not alter the potentiating effect which a conditioning impulse had on the amplitude of the e.j.p. evoked by a subsequent test impulse. The facilitated release of NA during trains of impulses was quantitatively predicted in terms of the addition of the individual potentiations introduced by each impulse in the train. 7 It is suggested that if there is an auto-inhibition of NA release, then it is unlikely that the pre- and post-synaptic alpha-adrenoceptors are identical.

Action Potentials↗