When most of us think of dental plaque, we picture a dentist scolding us for skipping floss. But for archaeologists, hardened plaque—known as dental calculus—is proving to be one of the most valuable records of ancient life. These tiny crusty deposits on prehistoric teeth preserve genetic material so well that they can reveal what people ate, what diseases they battled, and even what kinds of work they might have done.
Christina Warinner, a biomolecular archaeologist at Harvard and the Max Planck Institute for Evolutionary Anthropology, helped pioneer this field. Years ago, she realized that the hardened plaque on ancient teeth contained remarkably well-preserved DNA. To her surprise, the samples yielded more genetic information than almost any other type of ancient tissue. In effect, dental tartar had been storing microscopic clues about human history all along.
Studying ancient DNA is usually difficult. It breaks down quickly, and most archaeological remains are contaminated with modern material. Yet plaque offers a unique advantage: once it hardens, it seals in fragments of DNA from the mouth’s microbial community. By sequencing these fragments, Warinner’s team reconstructed the oral ecosystem of people who lived hundreds or even thousands of years ago. They found familiar bacteria that still live in our mouths today, but also pathogens and antibiotic resistance genes, showing that the arms race between humans and microbes stretches back deep into prehistory.
Dental calculus also preserves evidence of diet. In some individuals, researchers found traces of milk proteins, a sign that those people consumed dairy long before lactose tolerance became common. These discoveries shed light on how cultural practices like herding and dairying spread through ancient populations.
Perhaps the most striking find came from an 11th- or 12th-century woman whose plaque contained tiny flecks of ultramarine pigment. The rare mineral, ground from lapis lazuli, was used to create the brilliant blue inks in illuminated manuscripts. Her teeth suggest she was actively working with the pigment—an extraordinary clue that women may have played a bigger role in producing medieval books than previously assumed.
Each hardened speck of tartar is, in a sense, a time capsule. Locked within are the microbes, meals, and materials that passed through a person’s daily life. By prying open these capsules, scientists are piecing together intimate portraits of people long gone—reminding us that even something as ordinary as plaque can hold extraordinary stories about who we are and where we came from.