Just as you enter adulthood, your wisdom teeth make their presence known in the far reaches of your mouth. Wisdom teeth — officially the third molars — are the last set of teeth to come in, usually between 17 and 25 years of age, in the so-called “age of wisdom.”

For some, these teeth come in fine. For many others, wisdom teeth don’t come in properly (if at all), are vulnerable to disease, and need to be removed to protect a healthy mouth.

It’s estimated that 95 percent of American 18-year-olds “have wisdom teeth, and most of them have little if any chance to function in a normal manner,” says Louis Rafetto, DMD, an oral and maxillofacial surgeon in Wilmington, Del.

So if wisdom teeth are virtually useless in millions of mouths, why do we have them? One theory lies in the mouths of our ancestors. Early humans needed an extra row of teeth to chew their food: a diet of uncooked, hard items like roots, nuts, and meat. “I’m not an expert on anthropology, but clearly the need for and utility of wisdom teeth in the past exceeds that of the need of today,” says Dr. Rafetto.

Although it’s uncommon, some people born today never develop wisdom teeth. Why? It’s likely because of the size reduction in our jaw and face over the past 20,000 years, says John Hawks, PhD, an assistant professor of anthropology at the University of Wisconsin in Madison and an expert in human evolution. He adds that lack of wisdom teeth is more common in agricultural populations than in hunter-gatherers (like Aboriginal Australians) today.

The Trouble With Wisdom Teeth

Anatomy is at the root of most problems with wisdom teeth, says Thomas Dodson, DMD, MPH, a professor of oral and maxillofacial surgery at Harvard School of Dental Medicine and director of the Center for Applied Clinical Investigation at Massachusetts General Hospital in Boston. “Either jaws are too small or teeth themselves are too big for the jaw,” he says. This adds up to a crowded mouth. Dr. Dodson says Mother Nature probably programmed third molars to come in during the late teens or twenties, when the jaw would be big enough for another set of molars.

But today, wisdom teeth often don’t cooperate with Mother Nature’s plan. Because of the lack of space, molars can grow sideways, only partially emerge from the gums (called “partially impacted wisdom teeth”), or get trapped in the gums and jawbone (“impacted wisdom teeth”). Dodson says partially impacted wisdom teeth are chronically contaminated with bacteria associated with infection, inflammation, tooth decay, and gum disease. Because they’re so far back in the mouth, it’s hard to keep them clean and get rid of the bacteria. Fully impacted wisdom teeth also can get infected and disturb the position of the other molars. These consequences can spread outside of the mouth, causing other health problems.

Even when wisdom teeth come in fully (“erupted” out of the gums), they can still pose a problem for a healthy mouth. Here, it’s all about location, location, location. The third molars are so far back in the mouth that it’s easy for food to get trapped, leading to more bad news: plaque, cavities, and gum disease, says Dodson. Many people just can’t reach them to brush and floss well enough.

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