sciencehabit writes "When an adult loses a tooth, there's no hope of growing a new one—unless you've got a mouse kidney handy. In a new study, researchers injected human gum tissue extracted during oral surgery into the molars of fetal mice. After giving the cells a week to get used to each other, the scientists implanted the chimeric concoction into the protective tissue surrounding the kidneys of living mice. There, 20% of the cells developed into objects recognizable as teeth, complete with the root structures missing from artificial tooth implants. The next step is to transplant these so-called 'bio-teeth' back into human mouths and see if they grow into something that we can chew on—or rather, with."