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| Teeth Regrown For The First Time |
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| posted on Tuesday, November 28, 2006 |
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TEETH REGROWN FOR THE FIRST TIME
By Hamish Clarke
Cosmos Online
Monday, November 27, 2006
Original Link
SYDNEY - For the first time researchers have been able to induce the growth of replacement teeth in mammals. Unlike other vertebrates, mammals normally lose the ability after they replace their milk teeth in infancy.
"Our results may have implications for organ regeneration and bioengineering of teeth and the understanding of the genetic basis of the evolution of teeth," the authors said in a paper published in the U.S. journal Proceedings of the National Academy of Sciences.
The research was conducted at the University of Helsinki, Finland, as well as in Berlin and Kyoto, using mouse tissue.
Most vertebrates -- famously including sharks -- have continuous tooth generation, meaning that lost teeth are replaced with new teeth as needed. Somewhere in their evolution mammals, including humans, lost this capacity, with the sole dental replacement being permanent teeth for milk teeth.
"Intriguingly, a trend in mammalian evolution has been a reduction of number and renewal of teeth, concomitant with the evolution of progressively more complex...teeth," the researchers said.
Irma Sesloff, from the University of Helsinki, and fellow researchers stimulated a molecular trigger, called the Wnt pathway, in tooth buds extracted from mouse embryos.
Tooth buds from mice with the activated Wnt pathway gave rise to dozens of teeth with normal tooth enamel, developing roots and the usual dentin interior. The new teeth were observed to bud off from previously developed teeth, which is how tooth renewal proceeds in other vertebrates.
However the teeth weren't quite like normal mouse molars in every respect. Typically mouse molars have several points, or cusps, but the teeth from the experimental mice were simple and cone-shaped.
The authors concluded complex teeth may have been a trade-off with the ability to grow new ones at will. "These results may implicate Wnt signaling in tooth renewal, a capacity that was all but lost when mammals evolved progressively more complicated tooth shapes," they said.
The findings may also provide a greater understanding of cancer of the teeth. There were parallels between the teeth grown in mice with hyperactive Wnt signalling and odontomas, which are tumor-like malformations consisting of multiple small teeth -- sometimes over 100.
The demonstration that tooth renewal can be restored in modern day mice given the right conditions is reminiscent of the 2003 finding that chicken still possess genes from their dinosaur days -- now silenced -- involved in tooth generation.
More importantly, it means that the potential for continuous tooth generation may also have been retained in humans. The ability to harness this latent power will depend on the progress of future research in the area. If tooth regeneration becomes viable, it will be good news for boxers, the elderly and other people whose teeth have gone walkabout.
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