Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - MilkTeeth (MilkTeeth: a biogeochemical investigation of ancient weaning and dairy Milk consumption using human Teeth)

Teaser

Enamel is the hardest biomaterial in the mammal body. It has a high survivorship in the burial environment and resists alteration, making it ideal for archaeological research. Enamel is not remodelled over the lifetime of an animal and biogenic isotopes are preserved. Dental...

Summary

Enamel is the hardest biomaterial in the mammal body. It has a high survivorship in the burial environment and resists alteration, making it ideal for archaeological research. Enamel is not remodelled over the lifetime of an animal and biogenic isotopes are preserved. Dental development of teeth is known for many mammals, making it possible to synchronise isotope data to periods of time in an animal’s life, with intratooth sampling increasing resolution and providing life history information within a more discrete timeframe (Figure 1). What is less well known is the process and rate by which enamel formation occurs. Enamel is known to develop starting at the apex of the crown and progressing toward the enamel-root junction, but the rate of this progress is not uniform. Not only the timing but the rate of mineral formation can potentially impact isotopic fractionation, this has generated uncertainty in assigning a time frame to dietary/life events indicated through isotope analysis of intratooth samples. MilkTeeth, therefore, used both (i) isotopes to investigate ancient human milk consumption, and (ii) “Tender” Energy X-ray Spectroscopy (TES) to investigate chemical element inclusion during enamel mineralisation. The former is an effort to build new techniques, and to push the limit of existing techniques, for investigating ancient diet through the analysis of mineralised tissue, with the focus being on mobility (strontium [Sr]) and dietary (calcium [Ca], nitrogen [N] and carbon[C]) isotopes. The latter has been carried out in order to better understand the process and timing of enamel mineralisation.
MilkTeeth, at the heart it is a project about people and their diets, especially in regard to ancient milk and dairy food consumption. The human desire for dairy foods has resulted in millions of dairy animals around the world being used to supply this demand, which in turn contributes billions of euros to the global economy. This is a tremendous change from dairy’s humble start during the Neolithic period (~7000-5700 cal. BC). Milk is also a food that provides vital dietary nutrients, and deficiencies in these nutrients are known to have a negative health impact, thus milk and other dairy foods have the potential to improve people’s health and nutritional status. With that said, dairy foods are a significant element in the modern debate about dietary health and nutrition. Research has spoken both to the health risks and benefits of including dairy in the human diet, especially as it relates to bone health, diabetes and heart disease. Additionally, a lack of milk during critical periods of infant development can have huge implications for infant/childhood health and survivorship. Understanding enamel mineralization is the critical first step needed to enable our use of isotope and trace-element chemistry results to unlock a wealth of dietary information about the lives of humans in the past.

Work performed

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

Final results

MilkTeeth generated a wide range of information and largely succeeding in its goals to investigate mineralisation timing/processes while also building new isotope tools for archaeological scientists to use in the investigation of ancient human milk consumption.