Here is a demonstration of splitting tissue engineered teeth early in their development process so as to multiply the number of teeth produced. Researchers have for years now been able to grow functional teeth from cells in rodents, either by implanting suitable cells into the jaw, or more recently growing entire teeth outside the body. Work on refining the techniques involved continues apace, and one might well ask what is taking so long in moving these advances to human medicine. Dentistry is usually one of the more rapid areas of progress in clinical medicine, and it is getting on for near a decade now since the first demonstrations of teeth grown from cells in mice:
Researchers have found a way to - literally - multiply teeth. In mice, they were able to extract teeth germs, groups of cells formed early in life that later develop into teeth, split them into two, and then implant the teeth into the mice's jaws, where they developed into two fully functional teeth. Teeth are a major target of regenerative medicine. Approximately 10 percent of people are born with some missing teeth, and in addition, virtually all people lose some teeth to either accidents or disease as they age. Remedies such as implants and bridges are available, but they do not restore the full functionality of the teeth. Growing new teeth would be beneficial, but unfortunately humans only develop a limited number of teeth germs, the rudimentary cell groups from which teeth grow.
"We wondered about whether we might be able to make more teeth from a single germ." To demonstrate that it might be feasible, the group focused on the fact that teeth development takes place through a wavelike pattern of gene expression involving Lef1, an activator, and Ectodin, an inhibitor. To manipulate the process, they removed teeth germs from mice and grew them in culture. At an appropriate point in the development process, which turned out from their experiments to be 14.5 days, they nearly sliced the germs into two with nylon thread, leaving just a small portion attached, and continued to culture them. The hope was that signaling centers - which control the wave of molecules that regulate the development of the tooth - would arise in each part, and indeed this turned out to be true. The ligated germs developed naturally into two teeth, which the team transplanted into holes drilled into the jaws of the mice.
The teeth ended up being fully functional, allowing the mice to chew and feel stimulus, though they were only half the size of normal teeth, with half the number of crowns - a result that could be expected given that the researchers were using already developed germs. Significantly, they were able to manipulate the teeth using orthodontic methods, equivalent to braces, and the bone properly remodeled to accommodate the movement of the teeth.