Archaeological dental calculus is a calcified form of dental plaque that contains a treasure trove of information about our past. By studying ancient calcified biofilm, as well as other particles in the mineral matrix, we can investigate a wide variety of aspects of human history. This includes the evolution of our oral microbiome and specific microbes, the human host, diet and cultural practices. The study ”Understanding the microbial biogeography of ancient human dentitions to guide study design and interpretation” published in FEMS Microbes explores the microbial distribution in ancient oral cavities. Zandra Fagernäs, Irina Velsko and Christina Warinner explain for the #FEMSmicroBlog what we can learn about our own past from archaeological dental samples. #FascinatingMicrobes
Which tooth to study from archaeological dental samples?
The environmental conditions within the mouth vary across teeth, as there are gradients in oxygen availability and nutrient supply. Also, adult humans have 32 teeth, each with 4-5 surfaces on which dental calculus – or tooth tatar – can form.
At the same time, individuals living in the past frequently experienced antemortem tooth loss. Consequently, it can be difficult, if not impossible, to consistently sample calculus from the same tooth across individuals.
However, comparing calculus sampled from different oral niches may introduce biases, as the microbial communities can vary simply due to differing environmental conditions. This is known for living bacteria in dental plaque. Yet, it is not clear if the same patterns apply to dental calculus or if these patterns persist in archaeological samples.
In contrast to dental plaque from living people, studying archaeological dental calculus is more complex due to potential changes in the oral microbiome with time. After a person dies, environmental microbes colonize the calculus, potentially creating new patterns or eroding existing ones. This creates difficulties in designing studies and interpreting results to avoid biases or inaccurate conclusions caused by sampling location.
After a person dies, environmental microbes colonize the calculus, potentially creating new patterns or eroding existing ones.
One way around this issue is to sample multiple teeth across the mouth and average the results. Yet, dental calculus is a limited archaeological material. Since biomolecular analyses irreversibly destroy the samples, sampling should be limited to preserve the material.
Additionally, there is not always much calculus available to sample. From very ancient individuals, such as Neanderthals, for example, only a single milligram may be available to study.
Analysing 4000-year-old teeth
The study ”Understanding the microbial biogeography of ancient human dentitions to guide study design and interpretation” published in FEMS Microbes addresses this question by analyzing dental calculus from four Iberian Chalcolitic individuals (ca. 4500-5000 years old). These ancient individuals had nearly all of their teeth, with dental calculus present on most teeth, which is uncommon in the archaeological record. One of the individuals also had a pathology on one side of the jaw, causing excessive accumulation of dental calculus and allowing to compare deposits spanning a wide range of sizes.
The metagenomic study of the preserved microbiome showed that the main source of variation was the individual from which the sample was taken. This means that a single sample can represent an individual, thereby decreasing the amount of material that is destructively analyzed.
However, depending on the oral niche, the study detected minor patterns between species’ aerotolerance. As a result, the study recommends that the sampling location be recorded and noted in analyses.
Ancient teeth tell stories
The study looked further at the patterns of non-microbial factors. This included the amount of human DNA that is incorporated into dental calculus and the environmental microbes that colonized the remains after the individual died.
These factors were of interest, as they can guide which teeth to target or to avoid. For example, to study the human genome, samples with a higher proportion of human DNA may be targeted. On the other hand, including the least environmental contamination is desired in most studies. However, it needs to be taken into account that both human DNA and environmental microbes are distributed randomly across the mouth.
In archaeological samples, both human DNA and environmental microbes are distributed randomly across the mouth.
To conclude, this study has provided valuable information about microbial variation within dental calculus. These results can assist other researchers in designing effective sampling strategies for their studies. Hopefully, these strategies will help preserve as much as possible of this finite archaeological resource while providing accurate knowledge about our own past.
- For a more detailed discussion on individual microbial groups, read the paper “Understanding the microbial biogeography of ancient human dentitions to guide study design and interpretation” by et al. (2022).
About the authors of this blog
Christina Warinner is an Associate Professor of Anthropology at Harvard University and Group Leader of Microbiome Sciences in the Department of Archaeogenetics at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. She specializes in the analysis of ancient DNA and proteins, and her research focuses on the study of ancient biomolecules to better understand past human diet, health, and the evolution of the human microbiome. In addition to her research, she is passionate about public education and outreach and created the Adventures in Archaeological Science coloring book. She is also engaged in the open science movement and her research group has been actively involved in improving scholarly communication, data sharing and research transparency.
Zandra Fagernäs is a PhD candidate in Microbiology at Friedrich Schiller University Jena, where she was also a member of the Warinner Group at the Max Planck Institute for Evolutionary Anthropology. Recently, she accepted a new postdoctoral research position in palaeoproteomics in the Welker Group at the University of Copenhagen, where her research focuses on method development for the study of ancient biomolecules. Aside from her research, she is also passionate about science communication and sharing archaeological science research with the general public.
About this blog section
The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.
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