Humans can’t grow new teeth. But we’re not alone. Most mammals can’t. But many reptiles and fish can grow hundreds, or even thousands of new teeth in a lifetime. The reason has to do with how reptiles and mammals evolved differently over 300 million years ago.

Following is a transcript of the video:

Humans need dentists. It’s a fact. In 2017 alone, Americans spent $124 billion on dental visits. And an estimated 90% of adults in the US have fillings.

But many animals don’t have this problem. Because they can regrow their teeth replacing old, damaged ones with brand new pearly whites.

Wouldn’t it be great if you could do that? Well, there’s actually an important trade off for this nuisance.

Only a handful of mammals can regrow teeth multiple times, compared to the 50,000 species of reptiles and fish. Take geckos, for example, who will replace all 100 teeth, or so, every 3 to 4 months. And since geckos can live for 6 to 10 years, they’ll grow anywhere from 1,800 to 4,000 teeth in a lifetime! It’s all thanks to a special type of cell in their gums, called stem cells.

Stem cells are handy because they can morph into different cells when needed. Like tooth stem cells to build new teeth. Humans have these stem cells when we’re younger. But after our adult teeth grow in, the stem cells die and disappear.

To understand why, let’s take a journey back in time. To about 320 million years ago, when mammals and reptiles split off. In addition to the many obvious differences another change that eventually emerged was tooth shape. Reptiles, for example, are what’s called generalists. Meaning they eat the animals they can get their teeth on. And for that, they needed teeth with the same size and shape, to keep prey from escaping their mouths. Mammals, on the other hand, developed more specific diets. Like grazers who only eat grass and hunters who rip flesh from their kills. As a result, mammals evolved different shaped teeth for different purposes. And it’s this difference, that could also explain why most mammals can’t regrow more teeth.

Now, let’s say you could regrow your molars multiple times, for example. It’s important that the top and bottoms sets match up. Otherwise, they can’t grind up food as efficiently. It sounds good in principle, but with each new set, there’s a risk that the regrown teeth won’t line up. So the leading theory is that adult humans can’t regrow our teeth because it was better for survival to only grow one, well-aligned adult set.

However, if you still wish you could regrow a tooth, there may be a way in the future. Using lasers and drugs, scientists have helped rats and mice regrow damaged tissue in cavity-ridden teeth. With the idea that if you can regrow tooth tissue, you can eventually regrow entire teeth.

Though no human testing has been done, yet. So continue to see your dentist! At least for the time being.

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Why Humans Can't Regrow Teeth