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Biomedical subjects

A Richards

Publications and source records attributed to A Richards.

At least 127 records · Page 7Linked to original sources
PubMed1989

Enamel fluoride in relation to severity of human dental fluorosis.

The aim of this study was to test whether the concentrations of fluoride in fluorotic human enamel are related to the degree of severity of dental fluorosis classified according to the index described by Thylstrup and Fejerskov. Teeth representing the entire spectrum of human dental fluorosis were analyzed. Fluoride concentrations were determined by serial acid-etching from surface to interior of blocks of enamel cut from each tooth. Fluoride was measured by ion electrode and calcium by atomic absorption spectrophotometry. The results showed that the pattern of distribution of fluorotic enamel is similar to that described for normal enamel. Increasing severity of fluorotic lesions was associated with increasing concentrations of fluoride throughout the enamel. It is concluded that although further studies are required to establish the relative contribution of fluoride which may be taken up posteruptively by fluorotic enamel, the findings support the hypothesis that the TF index reflects increasing exposure to fluoride during tooth development.

Chi-Square Distribution↗
PubMed1989

The course of tardive dyskinesia in patients on long-term neuroleptics.

Results are presented of five consecutive annual examinations using the Abnormal Involuntary Movement Scale for 101 community-based chronic psychiatric patients. These 101 patients had a history of longer and more consistent neuroleptic treatment than the 231 patients who initially entered the study, so no conclusions about prevalence of TD can be drawn. At each examination two-thirds of this group showed signs of TD; however, only 45% were TD positive at most examinations and 24% were best described as having fluctuating TD status. Of those patients who were consistently TD positive, 82% showed no overall significant change in summed AIMS scores, 11% improved and 7% became worse.

Adult↗
PubMed1988

Mixed-list presentation and visual field asymmetry: attempts to differentially activate the hemispheres.

Mixed lists of abstract nouns and random forms were presented in an attempt to induce differential activation of the two hemispheres. For Expt. 1, nine probability levels, from P = 0.1 to P = 0.9 for both nouns and forms were examined. Prior to the presentation of each trial a cue was presented which gave the probability of that trial being either a noun or a form. For Expts. 2 and 3, eleven mixed blocks were presented, each containing a different proportion of nouns and forms. The activational model predicts right visual field (RVF) advantages for both stimulus types when nouns are more probable or more frequent than forms, and left visual field (LVF) advantages for both stimulus types when forms are more probable than nouns. The structural model predicts RVF and LVF advantages for nouns and forms respectively, regardless of their probability of occurrence. It was found that the more probable or frequent the stimulus type the faster the response. However, all 3 experiments offered some support for the structural model and no support for the activational model.

Adolescent↗
PubMed1988

Unrecognized invasive carcinoma in vulvar intraepithelial neoplasia (VIN).

Sixty-nine patients having had pretreatment biopsy diagnosis of vulvar intraepithelial neoplasia were treated with surgical excision of all visible lesions. Complete surgical specimens were submitted for pathological study in an attempt to identify occult invasive vulvar carcinoma. Unsuspected invasion was noted in 13 patients (18.8%). Superficial invasion (less than 1 mm) was seen in 8 patients, 4 had greater than 1 mm of invasion, and one verrucous carcinoma was identified. Patients of advancing age with disease that had a raised and irregular surface pattern were more likely to have lesions with occult invasion. Treatment that utilizes ablative techniques cannot be recommended based on the use of preoperative representative biopsies.

Adult↗
PubMed1988

Clinicopathological study of neurological complications due to hypertensive disorders of pregnancy.

Forty-three women with neurological complications secondary to eclampsia or severe pre-eclampsia were studied by CT scanning and in six intracranial pressure (ICP) monitoring was carried out. In seven women who died, neuropathological findings were correlated with clinical features. Cerebral oedema was present in 27 of the patients studied and the severity of oedema correlated to the duration of intermittent seizures. In five of the six women who had ICP measured, this was found to be transiently high. Intracranial haemorrhage was demonstrated in four of the 43 women, all of whom died. Hypoxic-ischaemic cerebral damage and fibrinoid necrosis were the most important neuropathological lesions identified. The management of neurological complications of eclampsia may be placed upon a more rational basis by an understanding of the mechanisms responsible for these lesions.

Adolescent↗
PubMed1988

Mineral and protein concentrations in enamel of the developing permanent porcine dentition.

Calcium, phosphorus and protein analyses have been performed on developing permanent enamel from the mandibular dentition of the domestic pig. The pattern of mineralization and protein loss was similar from tooth to tooth and similar to teeth from other species. Comparison of different teeth at the same developmental stages (secretion--stage 1, transition--stage 2 and maturation - stage 3) revealed remarkably similar concentrations of calcium, phosphorus, and protein regardless of tooth type. These data were similar to those from other deciduous dentitions, except that maturing/mature tissue in the pig seemed less well mineralized.

Age Factors↗
PubMed1988

Maturation in developing permanent porcine enamel.

Mineral content per tissue volume was investigated in developing permanent porcine enamel and contrasted with weight-related data. Levels of mineralization were correlated directly with the histological appearance of the overlying enamel organ. Magnesium concentrations were measured at different stages of enamel development. Mineral levels rose from approximately 30% per volume of tissue during the secretory stage to approximately 60% in mature tissue. This is much lower than final mineral levels in enamel of other species. Enamel containing low mineral levels was adjacent to tall secretory ameloblasts which had reduced in height by approximately 50% at a point corresponding to the beginning of the maturation stage. Magnesium concentrations remained relatively constant throughout the secretory stage, at 0.2% Mg by weight. These rose by 3-4 times in the enamel of the maturation stage. The low levels of mineralization in the mature porcine enamel did not appear to be due to enamel pathology, and the possibility of porcine teeth erupting in an immature, partially porous condition is discussed.

Ameloblasts↗
PubMed1987

Compressive strength, ash weight, and volume of vertebral trabecular bone in experimental fluorosis in pigs.

The aim of the investigation was to measure the effect of fluoride on vertebral trabecular bone compressive strength and to correlate this with fluoride-induced changes in bone density. This correlation would express changes in the quality of bone during fluoride treatment. Pigs were used in the experiment because their trabecular bone structure and remodeling sequences are very similar to the human. Eight animals receiving a supplement of 2 mg F-/kg b.w. per day from age 8-14 months were compared with 8 control animals. Morphologic measurements in the animals receiving fluoride supplement showed a significant increase of 17% in bone density and a smaller, insignificant increase of 3% in ash weight analyses. Meanwhile, the mechanical parameters for the fluorotic animals were unchanged (maximum compressive strength, maximum stiffness, and energy-absorption capacity) or decreased (normalized compressive strength = maximum compressive load corrected for ash density). It is concluded that the increased bone mass during the initial stages of fluoride treatment does not necessarily indicate an improved bone quality. The discrepancy between bone mass and strength could be either a permanent or a temporary phenomenon and requires further investigation.

Animals↗
PubMed1987

The effects of independently validated strategies on visual hemifield asymmetry.

The study described here employed a sentence-picture verification task in order to examine the effects of different information-processing strategies on hemisphere performance of this task. The original task was slightly modified to allow brief presentation of the picture stimulus to either the left or right visual field. A simple strategies model of hemisphere function would predict an RVF advantage when using a linguistic strategy and an LVF advantage when using a pictorial strategy. Experiment 1 included no explicit instructions on which strategy to employ, thus allowing subjects to use their naturally preferred strategy whilst Expt 2 used explicit instructions to induce the appropriate strategies in two separate experimental blocks. Examination of the data for both experiments strongly supports the claim that the strategies were successfully induced, but in neither case was any clear-cut support for the strategies model of hemisphere function obtained.

Adolescent↗
PubMed1987

Developmental stages in permanent porcine enamel.

Developing permanent teeth of different ages were obtained from Danish Landrace pigs. Visibly distinct zones on their enamel surfaces were shown to correspond to changes in chemical composition previously reported for other species. The time of appearance, rate of progress and duration of each stage was determined for each tooth type.

Animals↗
PubMed1986

Aetiology of postmenopausal bleeding in black women in Durban.

The aetiological distribution of postmenopausal bleeding in 100 consecutive black patients is reported. Malignant lesions of the genital tract were found in 54%. The results of these studies do not show the dramatic decrease in the incidence of malignancy as a cause of postmenopausal bleeding seen in the USA and Europe. Reasons for this are discussed.

Black or African American↗