At the Tokyo University of Science a group of scientists was able to grow functional teeth from stems cells that were planted in the mouth of mice.
This is a really important step in the stem cell studies because this is the first time that a full organ has been developed; the next step could be replacing organs that have been damaged or lost. Up until now, this technology has been limited to replacing little parts of tissues into animals.
The experiment that is described, in the paper published in the journal Proceedings of the National Academy of Sciences, consisted of first removing the upper first molars from five-week old mice. After that the scientists wait three weeks to transplant the germs (stem cells) into the jawbones of the mice after confirming that there were no remaining components of the tooth root. These stem cells had all the instructions necessary to grow a tooth. Also the cells were marked with a green fluorescent protein which was used to track the genes in the buds which grew into fully formed teeth with the usual structures. Additionally these teeth were as hard as normal teeth and had nerves that responded to pain stimulation.
From this the study said that we can assume the technique could provide a prelude to "the ability to grow new, fully functional bioengineered organs inside the body from stem cells or other germ cells”
http://www.guardian.co.uk/science/2009/aug/03/bioengineered-teeth-grown-in-mice