An international team of scientists led by Prof Cheng-Ming Chuong from the University of Southern California has discovered unique cellular and molecular mechanisms behind tooth renewal in American alligators (Alligator mississippiensis).

Their findings, published in the Proceedings of the National Academy of Sciences, pave the way for tooth regeneration in people.

“Humans naturally only have two sets of teeth – baby teeth and adult teeth. Ultimately, we want to identify stem cells that can be used as a resource to stimulate tooth renewal in adult humans who have lost teeth. But, to do that, we must first understand how they renew in other animals and why they stop in people,” Prof Chuong said.

Whereas most vertebrates can replace teeth throughout their lives, human teeth are naturally replaced only once, despite the lingering presence of a band of epithelial tissue called the dental lamina, which is crucial to tooth development.

Because alligators have well-organized teeth with similar form and structure as mammalian teeth and are capable of lifelong tooth renewal, the team reasoned that they might serve as models for mammalian tooth replacement.

“Alligator teeth are implanted in sockets of the dental bone, like human teeth. They have 80 teeth, each of which can be replaced up to 50 times over their lifetime, making them the ideal model for comparison to human teeth,” explained study lead author Prof Ping Wu, also from the University of Southern California.

The team found that each alligator tooth is a complex unit of three components – a functional tooth, a replacement tooth, and the dental lamina – in different developmental stages. The tooth units are structured to enable a smooth transition from dislodgement of the functional, mature tooth to replacement with the new tooth. Identifying three developmental phases for each tooth unit, the researchers conclude that the alligator dental laminae contain what appear to be stem cells from which new replacement teeth develop.

“Stem cells divide more slowly than other cells,” said co-author Prof Randall Widelitz of the University of Southern California.

“The cells in the alligator’s dental lamina behaved like we would expect stem cells to behave. In the future, we hope to isolate those cells from the dental lamina to see whether we can use them to regenerate teeth in the lab.”

The team also intends to learn what molecular networks are involved in repetitive renewal and hope to apply the principles to regenerative medicine in the future.

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Bibliographic information: Wu P. et al. Specialized stem cell niche enables repetitive renewal of alligator teeth. PNAS, published online May 13, 2013; doi: 10.1073/pnas.1213202110