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Biomedical subjects

D F Poole

Publications and source records attributed to D F Poole.

At least 19 recordsLinked to original sources
PubMed1993

Relationships between birefringence and mineral content in artificial caries lesions of enamel.

The microradiographic mineral content and birefringence in water and Thoulet's solution were measured at selected points in sections of caries-like lesions. Birefringence was not related to mineral content in sound superficial enamel immersed in Thoulet's solution or in the lesion body immersed in water. For the surface layer of the lesion, birefringence in water could be used to obtain qualitative information about mineral content. For the lesion body, birefringence in Thoulet's solution was linearly related to mineral content and can be used to estimate the latter with a standard error of about 7 vol%. The intrinsic birefringence for the lesion body was estimated as -34.5 (+/- 2.3) x 10(-4); This value may also be valid for other parts of the lesion. From consideration of ionic sizes, it is argued that Thoulet's solution cannot necessarily penetrate all enamel pores accessible to water. It appeared that there is a progressive fall in the content of pores inaccessible to Thoulet's solution in the surface layer of the lesion as demineralisation increases.

Birefringence↗
PubMed1990

Rapid monitoring of fluoride (F-) levels in blood plasma.

Evidence exists that plasma F- concentrations of 1.0 part/10(6) are nephrotoxic and that much lower levels disturb enamel mineralization. Ingested F(-)-containing gels, tablets and toothpastes all raise plasma F- levels significantly, as does prolonged exposure to fluorine-containing anaesthetic gases. There is, therefore, a continuing need to determine the total F- burden accruing in any given individual from multiple sources, as well as the average plasma F- burden which could be carried without risk to kidneys or teeth. To meet this need by facilitating fast and accurate monitoring of plasma F- levels, a new method has been devised and tested. A specific ion F- electrode in conjunction with a combination pH electrode forms a differential cell very sensitive to low concentrations of F-. When compared with the performance of a single F- electrode plus Ag/AgCl reference electrode, the differential cell is not only as consistent and accurate but also has a much shorter response time (2 vs. 20 min) and requires a much smaller sample volume (0.05 vs. 1.0 ml). In healthy subjects the mean plasma F- level was 0.044 (+/- 0.001) parts/10(6); in three patients undergoing prolonged (24 h) sedation with the fluorine-containing gas isoflurane, mean plasma F- rose to 0.275 (+/- 0.025) parts/10(6). No binding of F- to plasma components occurred at the operating pH (1.2) of the differential cell and plasma could be stored for at least 40 days at low temperature (4 degrees C) without alteration to measured F- values.

Blood Chemical Analysis↗
PubMed1989

The rapid measurement of fluoride concentrations in stored human saliva by means of a differential electrode cell.

For the purpose of rapid measurement, the performance of a differential cell, consisting of a combination pH electrode and a F- electrode and used at low pH (1.2), was compared with the use of a single F- electrode at pH 5.0. The differential cell proved to be as accurate and consistent as the single electrode: its response time was 2 min for a saliva volume of 50 microliters; the response time of the single electrode was 20 min with a saliva volume of 1000 microliters. Analysis of salivary supernatant fluid provided an unreliable guide to the original salivary F- concentrations but if fresh whole saliva was acidified to pH 1.2 immediately upon collection, the original baseline values were repeatedly obtained when measurements were made at intervals over a storage period of 14 days at 4 degrees C. Immediate acidification thus provides a satisfactory method for collecting samples from separate populations and then transporting them at leisure to a laboratory for direct measurement at pH 1.2 with the differential cell.

Calcium↗
PubMed1986

Superficial fluoride levels and response to in-vitro caries-like lesion induction of enamel from Bristol (U.K.) and Birmingham (U.K.) human deciduous teeth.

Surface enamel fluoride levels were measured in deciduous canine teeth from Bristol, with non-fluoridated water supplies, and Birmingham, with fluoridated water supplies. Three populations studied were from Bristol (teeth shed before 1960), Bristol (after 1975) and Birmingham (after 1975). Up to 75 micron from the enamel surface, fluoride concentrations of post-1975 Bristol and Birmingham teeth were, respectively, X 1.3 and 3.4 greater than those of pre-1960 Bristol teeth. The increase in the Bristol teeth is presumably due mainly to the increased use of fluoride-containing toothpastes, that in Birmingham to fluoridated water plus the use of fluoride toothpastes. No difference in the rates of penetration into enamel of acid-gel induced, caries-like lesions were found between the two Bristol populations; Birmingham teeth showed a reduction of 10 per cent in penetration rate. It is suggested that raised fluoride levels in surface enamel do not reduce solubility sufficiently to account, by themselves, for the recent nationwide marked reduction in caries in children. Possibly, the raising of plaque fluoride levels is a more important factor, affecting demineralization, remineralization and bacterial activity.

Acid Etching, Dental↗
PubMed1985

Modified procedure for the quantitative estimation of pore volumes in carious dental enamel by polarizing microscopy.

The polarizing microscope was used to make two estimates of pore-volume fraction in carious enamel. Estimates from form birefringence were always much lower than estimates from the intrinsic birefringence of the enamel solid and were too low for carious enamel. The discrepancy cannot be explained except in part as being due to re-precipitation of mineral during lesion formation. The discrepancy may arise largely from the unjustified assumption that the whole tissue acts as a Wiener composite body. Form birefringence is probably produced only by a fraction of the tissue. A model which reconciles the two pore-volume estimates and enables calculation of the composite body fraction and of the volume fractions of solid within this fraction and in the tissue as a whole is described. It appears that polarizing microscopy will require the conjoint application of other techniques for quantitative estimation of pore-volume fractions.

Birefringence↗
PubMed1984

Uptake of fluoride by human surface enamel from ammonium bifluoride and consequent reduction in the penetration in vitro by caries-like lesions.

In-vitro fluoride uptake by mid-coronal, premolar enamel surfaces from topically-applied solutions of NH4HF2 was determined using a multi-electrode system for fluoride and calcium analyses. In tooth surfaces dehydrated with 100 per cent ethanol before the topical application of 1 per cent aqueous NH4HF2, there was a 2-3-fold increase in fluoride concentration up to a depth of 50 microns and fluoride enhancement to a total depth of 100 microns into the enamel. Caries-like lesions were induced in vitro in both treated and untreated enamel by the use of acidified, 6 per cent hydroxymethyl-cellulose gel containing 0.04 per cent hydroxyapatite at pH 4.5. After 120 days exposure, the mean depth of lesion penetration in the controls was 149 (+/- 34) microns. No lesions occurred in half the treated specimens; in specimens with lesions, the mean depth of penetration was 19 (+/- 3) microns. Thus, NH4HF2 was a potent inhibitor of caries-like lesion formation in vitro.

Acid Etching, Dental↗
PubMed1982

Surface area and pore size analysis for human enamel and dentine by water vapour sorption.

The water sorption apparatus described allowed water sorption isotherms to be plotted on several samples simultaneously, with the added possibility of recording their nuclear magnetic resonance spectra for any points on the isotherm. Water sorption showed that human dentine had a saturated water content (removable in vacuo at room temperature) of approx. 10 per cent w/w (21 per cent v/v), probably in micropores or associated with the organic phase, and a specific surface of approx. 150 m2/g. A similarly measured water content for outer enamel was approx. 0.9 per cent w/w (2.7 per cent v/v), with a specific surface of 5.5 m2/g. For whole enamel, the slightly larger values of 1.15 per cent w/w (3.4 per cent v/v) and 8.7 m2/g were obtained. Results are shown to depend upon the conditions of measurement. Pore-size distribution analysis of enamel and dentine by water sorption, in this study and in investigations by others, is shown to be subject to many uncertainties and of doubtful value. Some uncertainty is also believed to apply to surface area measurements.

Adsorption↗
PubMed1981

Structure and porosity of human cervical enamel studied by polarizing microscopy and transmission electron microscopy.

Dehydration by alcohols and concentrated solutions of highly soluble salts caused refractive changes in enamel which were enhanced in the cervical regions. Electron microscopy showed crystals in cervical enamel to vary from normal orientation, size and habit to marked disorientation and reduced size. Consequent increases in surface area and inter-crystalline volume could account for the exaggerated optical behaviour. The changes in optical properties of enamel occurred only when the osmotic pressures of the imbibing solutions exceeded 500 atm. It is proposed that the internal pore system may take up water freely but exclude large hydrated molecules and ions which thereby create a negative pressure on the water contained in these pores. Once this negative pressure exceeds the tensile strength of the water-pore system, molecules may be torn from their attachment sites, and possibly from each other, so that a sudden evacuation of the pores is accompanied by a simultaneous reduction in refractive index. It is likely that such sudden evacuation would alter the potential of the pore surfaces to react with small molecules and ions subsequently invading the tissue.

Absorption↗
PubMed1976

Attrition: possible mechanisms of compensation.

Attrition, or wear of the occlusal surfaces of the teeth, may not only be physiologically normal, but necessary for function. Since occlusal wear must lead to reduction in tooth length, significant dimensional changes in facial morphology are inevitable unless mechanisms exist to compensate for attrition. Secondary dentine formation, alveolar growth, and adaptive changes in the masticatory muscles can provide this compensation, and may be part of a complex system by which an effective level of masticatory function is maintained even when attrition is extreme.

Adult↗