There the cells multiplied and developed, arranging themselves into tooth germs—clumps of cells that give rise to teeth.
When surgically implanted into the belly of a mouse, the germs grew into primitive teeth within a couple weeks, the researchers showed.
These teeth could then be implanted into a mouse's mouth, where nearly every time they took root and nerves grew into them.
The researchers were even able to implant a tooth germ directly into the mouth of an adult mouse—in an empty socket where a tooth had been pulled—and grow a new tooth in the jaw.
Some scientists say the new work doesn't show much progress over existing techniques.
The teeth grown using Tsuji's method never develop beyond a very primitive stage, and there is no way to select what kind of tooth they develop into, the scientists point out—both huge obstacles to developing true replacement teeth.
(Read a National Geographic magazine story on the controversy over stem cells.)
But according to Jeremy Mao of New York's Columbia University, "this study represents an important contribution to the field of tooth regeneration.
"It is likely one of the many challenging milestones before a whole tooth can be bioengineered for patients," he said.
"The key advance of this study rests on the implantation of reconstituted embryonic tooth germ cells."
But, he added, there's still a lot of work to be done before this is ready for people, such as scaling up the method so it can be done efficiently for growing many teeth.
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