Geneticists could induce for the first time the regrowth of teeth in mammals. Unlike other vertebrates, mammals - including humans - can replace only their milk teeth and after that, teeth lack this capacity. "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 researchers commented in the Proceedings of the National Academy of Sciences.

The other vertebrates - and when we think about teeth we refer to sharks, snakes and crocodiles - have continuous tooth replacement, old teeth being continuously removed by the new teeth (photo). During mammalian evolution, this capacity was lost. The mammalian trend was a reduction in number and a renewal of teeth, but at the same time, that mammal's teeth got more and more complex.

The researchers activated a molecular trigger, called the Wnt pathway, in embryonic mouse tooth buds. The activated Wnt pathway provoked the growth of dozens of teeth with normal tooth enamel, roots and internal dentin. The new teeth budded off from previously developed teeth, in the same way they grow in less developed vertebrates. But the new teeth were not like normal mouse molars, or, like normal mammal molars, in their shape. Mouse molars have several cusps while the new teeth were simple and cone-shaped.

It is like an evolutionary trait: complex mammalian teeth changed for 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," explained the research team.

The findings may also provide a greater understanding of teeth cancer. The teeth regrowth in mutated mice was very similar with hyperactive Wnt signaling and odontomas (teeth cancer), human tumor-like malformations consisting of multiple small teeth, sometimes over 100.

The regrown teeth in mammals (thus in humans also) is just a silenced trait, but the mammalian genome still possesses the genes involved, as a previous study proved that birds still possess the genes for teeth growth, only that they are inhibited.

Exploiting this latent potential would be good news for those categories confronted with teeth loss.