If you read our earlier blog on 3D models and dental health then you’ll know that the skeletons excavated from Palace green have quite a lot of dental calculus. If dental plaque is not adequately removed from teeth, it can mineralise, forming dental tarter, also known as dental calculus. As plaque mineralises, it entombs and preserves anything trapped within it, including disease-causing pathogens and proteins linked to the human immune system. Dental calculus also occasionally traps proteins and DNA from food sources, including foods that can be difficult to identify based on traditional archaeological evidence, things like leafy greens and milk products.
These pathogens and proteins can be linked to diseases specific to oral health but also to conditions affecting the rest of the body – identifying these systemic disease causing organisms (pathogens) is something that I am particularly interested in. Last year, working as a part of an international team, we recovered the first ancient DNA evidence for the pathogens associated with bacterial pneumonia, influenza, meningitis, and gonorrhoea from the mouths of medieval skeletons! The recovery of pathogenic DNA doesn’t mean the individuals necessarily suffered from that particular disease or infection, but it does confirm that the individual had been exposed to these pathogens.
The researchers in Durham have already been able to identify some of the diseases the Scottish soldiers suffered from because they caused recognisable changes to the soldier’s bones. But many conditions do not cause changes in the bones to occur, or the disease is so fast acting that bony changes do not have time to occur before an individual dies. I am hoping that by analysing the calculus samples we may find evidence of conditions that the soldiers suffered from that have not left traces in their bones. These may even be the diseases that killed them, although we couldn’t prove this as the presence of the pathogenic DNA doesn’t mean the individual was even infected with the disease, just that they had been exposed to it.
Taking the samples
A few weeks ago I visited Durham to take calculus samples from the teeth of the Scottish Soldiers. Thirteen of the Palace Green skeletons had teeth with calculus deposits and these were carefully removed using a dental descaler, exactly like the hygienist does when they clean your teeth at the dentists. I also collected a tiny bone fragment from each skeleton in order to identify and reconstruct microbial contamination from the burial environment.
What happens next
The calculus samples are now with me in York, where we have already started the process of extracting the proteins from the dental calculus. We identify the proteins using mass spectrometry, and categorise them into human proteins, microbial proteins and dietary proteins. Later we will also extract the DNA in our ancient DNA clean-room facility. The dental calculus will be chemically decontaminated and we follow very strict protocols in our lab to avoid contamination from modern sources. We use something called a ‘shotgun approach’, which maximises DNA recovery by amplifying all of the DNA trapped in the calculus (this will include DNA from viruses, bacterial, micro-organisms, fungi). Once the DNA has been recovered we identify what it has come from by using various DNA databases. This means we can quantify the opportunistic, systemic and oral pathogens in each skeleton.
Author: Camilla Speller
Department of Archaeology, University of York
Camilla is a Lecturer in Archaeology at the University of York. Her research investigates past human-environmental interactions through ancient DNA and protein analysis. She is interested in what can be learnt about health and diet in the past using information obtained from dental calculus. Working as part of a multi disciplinary team in York Camilla has been investigating the history of periodontal disease in ancient skeletons through the biomolecular analysis of dental calculus