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A figure from the paper shows one of the tooth-like structures removed from a mouse kidney three weeks after the human tissue was implanted with tissue from the jaw of a mouse. (Cai et al./Cell Regeneration)

Stem cells generated from human urine have been used by Chinese scientists to grow structures in mice resembling human teeth.

The ability to "regenerate teeth with patients' own cells" is an "ideal solution" to the loss of teeth through accidents or disease, the researchers say in a paper describing their results in the peer-reviewed, open access journal Cell Regeneration this week.

While most cells in our tissues, such as muscle cells and red blood cells, are highly specialized, stem cells have the potential to grow into many different types of cells. Because of that, many researchers have been trying to use them to regenerate entire new organs.

The Chinese researchers, led by Duanqing Pei and Jinglei Cai at the Chinese Academy of Sciences Key Laboratory of Regenerative Biology and Guangdong Provincial Key Laboratory of Stem Cell Biology and Regenerative Medicine, generated stem cells from kidney lining cells in human urine and grew them under special conditions into sheets of epithelial tissue — a type that includes skin and teeth.

They implanted the human tissue with tissue from the jaw of a mouse embryo – to encourage it to grow into a tooth  – in the kidney of a mouse. Three weeks later, they collected tooth-like structures with the hardness "found in the regular human tooth." Closer examination showed that the human tissue had turned into cells called ameloblasts that secrete enamel, the hard, bone-like substance on the outside of the tooth.

Pei and his team first reported their technique to generate stem cells from urine in 2011.

That has advantages over traditional techniques such as removing a chunk of a person's skin, acknowledged William Stanford, a University of Ottawa researcher who holds a Canada Research Chair in integrative stem cell biology.

"Who really wants a centimetre squared taken out of them?" he mused.

Growing various kinds of human tissues inside a mouse kidney is a common technique used by stem cell biologists, Stanford said.

"It's a developmental biology trick," he told CBC News in a phone interview.

In the course of doing so, researchers will occasionally grow what looks like teeth by accident.

The Chinese researchers have modified the technique to grow teeth intentionally, Stanford said. However, he questioned whether teeth were the most useful thing to try to grow, since there are already implants and other artificial replacements for teeth that work quite well.

James Ellis, a developmental and stem cell biologist at Sick Kids Hospital in Toronto, said in an email that scientists would have to be able to regenerate human teeth without the use of mice and their tissues in order for it to be actually practical for use in dentistry.

"This will be very challenging," he added.