One annoying fact of life is losing teeth. Since humans only get two sets of teeth, losing an adult dinner grinder means either going without or replacing it with a substitute made of something like ceramic or metal. A more natural solution is the subject of a project by a team of scientists in Japan that is working on growing multiple, fully-functional teeth and implanting them in mice.

Tooth development in humans is a complex process that depends on what's called the "tooth germ." This is a mass of cells formed early in life from the ectoderm and ectomesenchyme in the jaw. In the early stages, these germs are relatively simple in structure and the team from the RIKEN Center for Developmental Biology and Tokyo Medical and Dental University led by Takashi Tsuji hit on the idea of taking one germ, dividing it, and then growing new, multiple teeth in the laboratory.

The key to this was an observation by the team that tooth development depends on the wave-like interaction of the activator protein coding gene Lef1 and Ectodin, an inhibitor of bone morphogenetic proteins. They reasoned that if they waited for a particular point in the 14.5-day growth process, they could use a bit of nylon thread to cut the germ in two. If this was done right, the signaling center that controls the tooth's growth would develop in both germs, so both could grow into fully-formed teeth.

Having successfully divided the germs and grown the teeth, the team then transplanted them into holes drilled into the jaws of a mouse. These grew and could be manipulated with dental appliances similar to braces. The result was teeth that could chew and feel sensation, though they were only half as large as normal teeth and had half as many crowns.

"Our method could be used for pediatric patients who have not properly developed teeth as a result of conditions such as cleft lip or Down syndrome, since the germs of permanent teeth or wisdom teeth could be split and implanted," says Tsuji . "In the future, we could also consider using stem cells to grow more germs, but today there are barriers to culturing such cells, which will need to be overcome."

The team's research was published in Scientific Reports.

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