Bone from infants/young children and adult first molar dental enamel were analysed from Medieval and post-Medieval people from Aberdeen, Scotland. This research was to ascertain if Ca isotope values could act as a proxy for milk consumption. Milk contains different constituent parts that are associated with different elements: Ca (milk minerals) and N (milk protein). The Aberdeen samples demonstrated that the combination of 44Ca and 15N values have the potential to not only identify nursing/weaning evidence, but possibly dietary stress or atypical feeding practices (positive or negative correlation of 44Ca and 15N values). Ca isotope analysis of human dental enamel shows evidence of milk related dietary change. Ca isotope values near the apex of the crown are depleted in 44Ca (milk in the diet) with gradual enrichment of 44Ca (increasingly less milk in the diet) moving toward the enamel-root junction. There is some complexity, but the indications are of a milk related dietary change in early childhood, likely related to nursing/weaning (Figure 2 and Figure 3). These results support the idea that Ca isotope values in human mineralised tissue may stand as a proxy for milk in the diet of past humans. The Aberdeen enamel samples were also analysed for Sr isotope values, but indications of mobility outside of the Aberdeen region were not observed.
The work at Brookhaven National Laboratory was focused on X-ray Fluorescence (XRF) imaging and Microprobe XANES analysis of dental calculus and enamel. The enamel analysed for XRF and XANES was from modern lamb first (M1) and second (M2) molars. The M2 teeth were in active growth at the time of death, with mature enamel at the apex, and the very earliest stages of enamel formation near the base (dental roots had not started to form). Figure 4 is XRF images from the surface of an M2. Pixel brightness/darkness are indicative of differences in element concentration. Both element inclusion in the enamel and elements associated with surface food residues near the apex are observed. Figure 5 shows an M1and M2 from the same lamb that were sampled for calcium isotope analysis. These teeth were later cut down the middle, bisecting the sample areas for TES element imaging and XANES analysis. Figure 6 is an element map of the bisected M1 and M2, with the large maps being P (grey) and the smaller Red-Blue-Green maps between the Ca isotope sample sites being S (red), Mg (blue) and Sr (green). The images identify element inclusion during different stages of mineralisation, making plain the differences between mature enamel (the M1 and the top half of M2) and immature, amorphous enamel in the earliest stages of mineralisation (base of M2). Of the three elements, S appears to have the most significant role in the earliest stages of mineralisation, but is replaced by Sr and Mg in later stages, likely in close association with Ca. In all of the element images it is clear to see there is a significant offset in mineralisation timing between dentin and enamel. The S rich early stage amorphous enamel at the base on M2 is resting on what appears to fully mineralised, mature dentin, indicating a formation offset between the two dental tissues of several months. This has big implications for trying to align dental samples from these two tissues for isotope analysis and to synchronise them both to the same period in an animal’s life.
TES XRF element images for K, P, Sr and S were also made of human dental calculus (Figure 7). Unlike enamel, there are no indication of variation of element inclusion during the mineralisation process and the structure is uniform. While XRF element images of enamel and calculus are very different from each other, XANES showed that they match closely, and both identify as apatite (Figure 8). Publications of these results are currently in production. Many of these results have been presented at professional conferences in 2018: Goldschmidt, US, 8th International Conference on Synchrotron Radiation and Neutrons in Art and Archaeology, UK, 24th Annual Meeting of the European Association of Archaeologists, ES, 8th International Symposium on Biomolecular Archaeology, DE and in 2019: UK Archaeological Sciences Conference, UK.
