Alligators Can Grow New Teeth, So Why Not Humans?

Scientists are trying to understand organ regeneration in hopes of stimulating new growth in humans.

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The key to keeping a sparkling set of pearly whites might lie with patients that dentists won't have any interest in seeing—alligators.

An alligator can regenerate a lost tooth up to 50 times. In what must come as good news for hockey players, researchers at the University of Southern California are studying alligators' teeth to see if doctors could one day stimulate adult humans to automatically replace a tooth if they lose one.

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The research was published Monday in Proceedings of the National Academy of Sciences.

According to lead author Cheng Ming Chuong, alligator's teeth are very similar to humans, and his team may have discovered why they have regenerative properties.

Chuong says that alligators' teeth grow in sets of three: They have an adult tooth in their mouth, a replacement or "baby" tooth in waiting in case of a lost tooth, and then a stem cell that can become a replacement tooth if necessary.

"When the mature tooth falls out, the second one becomes a mature one, and the stem cell becomes a baby one. Interestingly, they are able to do this process repeatedly," he says. "In humans, we have a similar structure when we're born, but we don't have any stem cell there under normal conditions."

Though the understanding necessary to make regenerative medicine a possibility in humans is still far off, Chuong says that one day scientists will be able to inject hormones or molecules that will cause humans to grow new teeth.

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"We have to understand the molecular pathway involved," he says. "We will need the ability to position and control the process in a strategic way."

The ability to regenerate cells isn't completely without precedent in humans, Chuong says.

"In a way, our hair can keep regenerating multiple times in our life. But human teeth only have one chance—when we change from [baby] teeth to permanent teeth," he says. "The motivation for studying this is so that we'll one day be able to do this."

Chuong says that the DNA of humans contains the genetic material necessary to grown teeth and even regenerate other parts of the body, but that code isn't "turned on."

Regeneration is relatively common in the animal kingdom—certain types of salamanders can regenerate limbs, lobsters and stone crabs can grow new claws, starfish can grown new appendages and many types of predators, including sharks and alligators, can regenerate teeth.

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"Primitive animals have more robust regenerative power. Humans have more specialized cells, and the price we pay for that specialization is that we have fewer stem cells around," he says. "The percentage of stem cells in lower animals is much higher than it is in humans."

For now, the process is in its infancy as scientists are just beginning to understand the processes of regeneration in more primitive animals.

"I like to think we are learning the grammar of a new language. Once we learn more rules, we will be able to write an essay or a poem or a book," he says.

 

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