PubMed · 14785346
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A CHARNOT. 1950. [Darmous].. https://pubmed.ncbi.nlm.nih.gov/14785346/
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The adventus Saxonum is a crucial event in English protohistory. Scholars from a range of disciplines dispute the scale and demographic profile of the purported colonizing population. The 5th-7th century burial ground at West Heslerton, North Yorkshire, is one of the few Anglian cemeteries where an associated settlement site has been identified and subjected to extensive multidisciplinary postexcavation study. Skeletal and grave good evidence has been used to indicate the presence of Scandinavian settlers. A small, preliminary study using lead and strontium isotope analysis of tooth enamel, mineralized in early childhood, from Neolithic/Early Bronze Age (n = 8), Iron Age (n = 2), and Early Anglo-Saxon (n = 32) skeletons, was carried out to directly investigate this hypothesis. Results suggest that lead provides dissimilar types of information in different time periods. In post-Roman England, it appears to reflect the level of exposure to circulated anthropogenic rather than natural geological lead, thus being a cultural rather than geographical marker. Consequently, only strontium provides mobility evidence among the Anglian population, whereas both isotope systems do so in pre-Roman periods. Strontium data imply the presence of two groups: one of "local" and one of "nonlocal" origin, but more work is required to define the limits of local variation and identify immigrants with confidence. Correlations with traditional archaeological evidence are inconclusive. While the majority of juveniles and prehistoric individuals fall within the "local" group, both groups contain juveniles, and adults of both sexes. There is thus no clear support for the exclusively male, military-elite invasion model at this site.
The early stages of enamel surface dissolution (erosion) are of high scientific relevance; however, little is known about if and to what extent these early stages, which result in the softening of the enamel surface, are reversible. The present study investigated the possible rehardening of surface softened enamel in two separate experiments in vitro, employing physiologically relevant demineralization and remineralization times and remineralizing solutions possessing chemical properties close to those of human saliva. Atomic force microscopy (AFM) based nanoindentation has been used to study the nanomechanical properties and the ultrastructure of polished enamel samples as affected by demineralization/remineralization cycles. In contradiction to previous studies employing microhardness techniques, no enamel rehardening has been observed after remineralization; however, the demineralization schemes used in the present study (short treatments with a citric acid buffer) are not comparable to the ones used in previous studies, making a comparison difficult. A mineral deposition after remineralization on softened enamel samples has been observed by AFM; however, a protective effect of this deposited layer could not be revealed. The exposure of softened enamel samples to either a remineralizing solution or a mineral water led to an improved acid resistance of these samples as shown in a demineralization/remineralization cycle. The present study has demonstrated that AFM based nanoindentation is a useful tool to investigate the demineralization and remineralization of surface softened enamel with high accuracy.
Samples of human dental enamel and hydroxyapatite were equilibrated at 5 mg/40 ml for 9 days at 37 degrees C with acetate buffers adjusted to a range of saturations with respect to hydroxyapatite. Sigmoidal apparent solubility distributions, in which the fraction dissolved was plotted against--log(ion activity product for hydroxyapatite) (pIHA), were constructed. About 10% of the hydroxyapatite and 14% of the enamel was very soluble, dissolving even at pIHA 55. The apparent solubility distributions for both solids were invariant with pH (4.5, 5.0, 5.5), within experimental error, showing that solubility was controlled by a phase with the stoichiometry of hydroxyapatite, probably in the form of a surface layer or complex on the crystals, in agreement with other studies on carbonate-apatites and bone mineral. The pIHA at 50% dissolution was employed as an average value. The pIHA (50%) values for pooled data (58.76 for enamel and 60.17 for hydroxyapatite) were lower than the respective pIHA previously measured by conventional equilibration techniques. However, the average pIHA measured for enamel was higher than that obtained by the same technique in another study, possibly because of differences in specimen preparation and equilibration time. The possible implications of the findings for understanding the process of dental caries are discussed.