Duanqing Pei from the Chinese Academy of Sciences in Guangzhou and colleagues took stem cells from human urine and used them to grow teeth inside mouse kidneys. The stem cells, implanted under the outer layer of the mouse's kidney, transformed into dental epithelial tissue, which develops into the enamel, while the rest of each tooth was formed from mouse cells.
Pei claims that a method for using mice to grow teeth containing only human cells "could be easily designed".
The work is promising but figuring out what governs the size and shape of different teeth is going to be a big problem in making it useful, says Mark Bartold from the University of Adelaide in Australia, who works on regenerative dental medicine. "It doesn't take a genius to figure out there's a big difference between an incisor and a molar tooth," he says.