For Christmas, a few miniature pigs in a University of Southern California lab got new roots for their front teeth, courtesy of stem cells from human teeth. This regeneration of mammalian tooth root, reported in last week's inaugural issue of PloS ONE, could have clinical applications that would have a big impact on oral surgery procedures such as root canals.

An international team headed by dentistry researcher Songtao Shi focused its efforts on stem cells found in the root apical papilla, tissue connected to the tip of the root that is responsible for the root's development. Previous efforts by Shi and his colleagues involved the harvesting of stem cells from the dental pulp, the tissue at the center of a tooth, commonly referred to as the nerve.

Shi and his team compared the performance of apical papilla cells to pulp cells both in vitro and in mouse models. Shi found that the apical papilla cells, which he says can be considered "as younger stem cells" than pulp cells, provided better tissue regeneration--leading to the formation of all root tissues as well as dentin and cementum, the support substances located in the crown and root, respectively.

After identifying the appropriate stem cells for creating a new root, Shi's team replaced an incisor extracted from a miniature pig, which has a similar dental structure to humans, with stem cells from the extracted wisdom teeth of 18- to 20-year-old humans.

Three months after loading the apical papilla stem cells into the incisor socket of the pig, the researchers fitted a porcelain crown over the mineralized roots and ligaments developing there. The crown was then subjected to four weeks of normal tooth function. Six months after the implantation of the stem cells, the researchers reported that the tooth had a strength that, according to Shi, was "not quite as strong as the original tooth, but we believe it is sufficient to withstand normal wear and tear."

George T. Huang, a professor of dentistry at the University of Maryland, Baltimore, says Shi's bioroot is preferable to the dental implant used currently, partly because the original tooth root has a ligament layer between the jawbone and the root itself. This ligament, which is missing in implants, serves both to adhere the tooth to the jaw and to provide a cushion during biting. Huang adds that implants are susceptible to loosening and increased risk of gum disease, due to an "unnatural relationship with the bone.

"These stem cells may become the cell source to regenerate the dental pulp tissue as well as new dentin to repair decayed dentin via tissue engineering technologies, making root canal treatments less invasive," he says of Shi's finding.