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That's a Nice Crop Of Teeth You Got There

Growing a new tooth in the jawbone of a mouse provides the first fully functional organ grown in any animal by transplanting so-called 'germ cells.'

Tooth knocked out? New research suggests someday you could replace it by simply growing a new one.

According to study recently published online in the journal Proceedings of the National Academy of Sciences, a group of Japanese scientists have successfully grown a fully functional tooth in an adult mouse using specially engineered stem cells taken from a mouse embryo.

In order to grow the new tooth, the research team, led by Etsuko Ikeda and Ritsuko Morita of the Tokyo University of Science, sought to recreate the processes that occur while an animal is undergoing normal embryonic development. The new tooth, therefore, grew after a biologically engineered "tooth germ" — a group of seed-like stem cells loaded with all the necessary information to eventually form a mature tooth — was implanted into a bony hole in the upper jawbone of an adult rat following the removal of a regular molar.

After about five weeks, the new tooth emerged from the gums of the adult rat and eventually grew to the "plane of occlusion" with the opposing molars, creating a perfect interlocking bite with the teeth below. And because the researchers had injected a green fluorescence protein in the original tooth germ to track the development of the tooth, it also happened to glow green under the right lighting conditions.

Besides the green glow, the scientists found that the replacement teeth were equal in hardness to and had the same structure of regular teeth — including enamel, dental pulp and blood vessels. Additionally, neural fibers from the "host" animal eventually re-entered the pulp and periodontal ligaments of the new tooth. Because these fibers can sense noxious stimulations and pain, the observation suggests that the body can re-establish neurological connections vital to the functioning of the replacement organ as it regenerates within the body.

The finding could help remedy one of the main problems with manmade tooth implants. "It is known that the perception of mechanical forces during [chewing] is limited in implant patients," the authors wrote. "Thus, the restoration of nerve functions is also critical for tooth regenerative therapy and future organ replacement therapy."

The results mark the first reported success of a fully functional organ grown in any animal body by transplanting bioengineered organ germ cells. And because organ germ cells are the starting blocks for most of the organs in the body, the scientists believe their research could eventually lead to the regeneration of more complex organs to replace those lost or damaged by disease, age or injury.

"The ultimate goal of regenerative therapy is to develop fully functioning bioengineered organs which work in cooperation with surrounding tissues," the authors said. "This study represents a substantial advance and emphasizes the potential for bioengineered organ replacement in future regenerative therapies."

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