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Biomedical subjects

A S Hallsworth

Publications and source records attributed to A S Hallsworth.

At least 19 recordsLinked to original sources
PubMed2002

Organic material and the optical properties of the dark zone in caries lesions of enamel.

Sections of uncavitated natural caries lesions of human enamel were extracted with various solvents and examined by polarizing microscopy. After lipid extraction, the dark zone enlarged by 19-162% and its birefringence increased, while after protein extraction it shrank by 37-92% and became less birefringent. It is concluded that occlusion of submicroscopic pores by organic material largely accounts for the optical properties of the dark zone. The results are not consistent with occlusion of pores by reprecipitation of mineral. On the basis of previous work, organic material in this location could influence demineralization and remineralization.

Calcium↗
PubMed1990

Effect of surface zone deproteinisation on the access of mineral ions into subsurface carious lesions of human enamel.

It has been proposed that the so-called intact surface zone of carious lesions of enamel could restrict the ingress of mineral ions and hinder remineralisation. The present study was intended to determine the role of organic (proteinaceous) material in restricting the movement of mineral ions into carious lesions in vitro. Natural carious lesion surfaces were divided into two halves. The experimental half was de-proteinised using hypochlorite, the control half remained untreated. The whole tooth was exposed to 45Ca in solution, and 45Ca uptake into experimental and control tissue was measured by image analysis of autoradiographs prepared from lesion sections. The results indicated that uptake was improved by removal of organic material.

Acid Etching, Dental↗
PubMed1989

Porosity determination of cast investment by a wax-infiltration technique.

A reproducible method of determining the porosity (pore volume) of cast investment materials is described. This procedure, requiring no highly specialized equipment, involved the infiltration of a test sample with paraffin wax and the weighing of the wax-infiltrated sample in both air and water. Pore-volume wax is then extracted with chloroform and the sample reweighed. The difference in weight is used to calculate the porosity of the investment material. Pore-volume data thus obtained are comparable to those resulting from standard techniques and far more sophisticated (and expensive) instrumentation. The porosities of hand-mixed samples of gypsum-bonded, phosphate-bonded and silica-bonded investments were 53.9 per cent, 36.9 per cent and 31.4 per cent and those of the vacuum-mixed samples were 52.5 per cent, 31.3 per cent and 26.9 per cent, respectively. The results show that gypsum-bonded investments were more porous than phosphate-bonded investments while silica-bonded investments were the least porous. Hand-mixed samples appeared to have greater porosity than vacuum-mixed samples.

Calcium Sulfate↗
PubMed1989

A microbiological study of early caries of approximal surfaces in schoolchildren.

A cross-sectional epidemiological study has been undertaken to relate the bacterial composition of approximal dental plaque with the earliest stages of caries development in schoolchildren. Small samples of plaque were removed from multiple sites around the contact areas of 42 premolars extracted for orthodontic reasons from 29 schoolchildren (mean age = 13.5 yr). Caries diagnosis was based on polarized light microscopy and contact microradiography of thin sections cut through the sample sites. Fifty-seven percent of sites (37/60) showed histological evidence of demineralization. Both the isolation frequency and the mean percentage viable count of mutans streptococci and Actinomyces viscosus were higher at sites with early caries, although mutans streptococci could not be detected at 37% of sites with early caries. At these latter sites, the proportions of Veillonella were markedly reduced. Lactobacilli were rarely isolated and were never recovered from caries-free surfaces. Analysis of the data shows that the relationship between plaque bacteria and enamel is neither merely passive nor indifferent, and that particular stages of lesion formation may be associated with different combinations of bacteria.

Adolescent↗
PubMed1988

Volume distribution and concentration of protein, mineral and water in developing bovine enamel.

The percentage volume of enamel occupied by mineral, matrix protein and water was determined at each of four stages. Protein decreased throughout development from 20 to 30 per cent to a minimum of 2-3 per cent in mature tissue. Mineral content remained fairly consistent during secretion (15-20%) rising to 70-80 per cent in mature enamel. Water content rose from varying levels to 60-70 per cent at the secretion/maturation boundary decreasing to about 20 per cent in mature enamel. The loss of protein and subsequent delay in the onset of mineral increment resulted in tissue porosity. The duration of this hydrated, porous stage may determine susceptibility of the tissue to, for example, fluoride ion.

Animals↗
PubMed1987

The use of scanning electron microscopy in studying enamel caries.

SEM studies related to carious change in dental enamel are reviewed, and their contribution to understanding the mechanism of formation of the early enamel lesion and of its repair evaluated. SEM has contributed significantly to understanding the mechanism of enamel dissolution at the level of the single crystal. Etching studies have yielded useful information on the effect of enamel structure on the pattern of acid dissolution at the microscopic level and have highlighted the importance of re-precipitation phenomena in modifying the pattern of mineral loss. High-resolution studies have provided interesting quantitative data on changes in crystal size, and also information on changes in crystal shape and orientation, during lesion formation and remineralization. However, further work is required in this area to clarify uncertainties about sampling bias and to relate the observed changes more precisely to the larger-scale structure of the tissue. Numerous observations on the surface morphology and internal structure of carious lesions have been made but preparation techniques used to date introduce artifact to a greater or lesser extent and interpretation of some of these results is therefore handicapped. We propose the use of a methacrylate replication technique as the method of choice for studying pore distribution in carious enamel and present preliminary results using this technique.

Dental Caries↗
PubMed1984

Distribution and uptake of magnesium by developing deciduous bovine incisor enamel.

Magnesium concentrations determined in deciduous bovine enamel at different stages of development were similar to those previously published for human and rat enamel ranging from 0.1 to 0.4 per cent. Highest concentrations, i.e. greatest uptake, occurred after secretion, in the transitional and maturing enamel. Uptake had occurred throughout the tissue thickness and was not confined to the surface. Magnesium probably enters enamel in the tissue fluid which replaces the organic matrix. Some magnesium is lost as fluid is replaced by calcium and phosphate but part is retained probably on or near crystal surfaces.

Animals↗
PubMed1978

A method for the study of internal spaces in hard tissue matrices by SEM, with special reference to dentine.

Infiltration of a porous hard tissue with methyl methacrylate, followed by dissolution of the tissue provides a three-dimensional methacrylate cast of spaces within the tissue. Examination of such a cast by scanning electron microscopy provides information on the nature and extent of the pore system to a degree that cannot readily be visualized by the direct examination of fractured surfaces. The findings described concern human dentine but the technique may have a wider application in studies on the internal structure of other hard tissues.

Dental Enamel Permeability↗