The communities of bacteria that live in our mouths have changed drastically since the Middle Ages, according to a new study of remains buried in a medieval Danish cemetery. And it turns out that some people may have been more predisposed to tooth and gum disease than others, thanks in part to the bacterial communities that lived in their mouths.

Ancient dental plaque

Biochemist Rosa Jersie-Christensen of the Novo Nordisk Foundation Center for Protein Research sampled hardened dental plaque, called calculus, from the skeletal remains of 21 Danish men who lived in the village of Tjærby between 1100 and 1450 CE. She and her colleagues chose men for the study because male immune systems tend to have stronger inflammatory responses, which would make it easier to find proteins associated with inflammation.

Overall, the men’s dental health wasn’t great—about what you might expect from a group of medieval villagers. All 21 showed some signs of gum disease, or periodontitis, along with at least minor cavities. Several had lost teeth sometime before their death.