Chinese researchers have used cells generated from urine to make structures that resemble human teeth. Eventually, they hope that human stem cells could provide the basis for a tooth bud that could be transplanted into the jaw of the patient.

For the current experiment, published in the journal Cell Regeneration, the researchers transplanted stem cells into mice and were able to grow “teeth” that have many of the qualities of human teeth: elasticity, pulp, dentin, and enamel-forming cells, according to Medical News Today.

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There are some limitations: the new structures are only about a third as hard as human teeth, and the success rate is just 30 percent. The researchers hope that using human cells instead of mouse cells will resolve those issues, the next step ”toward the final dream of total regeneration of human teeth for clinical therapy,” they wrote. And if the patient’s own cells were used, the risk of rejection by the body is negated.

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Not everyone thinks that pee is the best source for stem cells, however.

“It is probably one of the worst sources; there are very few cells in the first place and the efficiency of turning them into stem cells is very low,” Chris Mason, a researcher at University College, London, told the BBC. “You just wouldn’t do it in this way.”

Bacteria in urine make the risk of contamination higher than other sources, Mason said.

“The big challenge here is the teeth have got a pulp with nerve and blood vessels which have to make sure they integrate to get permanent teeth,” he said.

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