Left undisturbed by brushing and flossing, the bacteria in your mouth will form a sticky film called plaque. Left further undisturbed, plaque will turn hard and yellow, calcifying on teeth as dental calculus, also known as tartar.
At this point, the tartar is very durable. Just ask these Neanderthals, whose 40,000-year-old tartar scientists recently analyzed to figure out the real paleo diet. Tartar grows in layers—almost like tree rings—entombing DNA from tiny bits of food as well as bacteria in the mouth. Forty thousand years later, scientists can analyze that DNA to reconstruct what was going on in the mouths of long-dead Neanderthals.
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