WASHINGTON (Reuters) - Japanese researchers said on Sunday they had grown normal-looking teeth from single cells in lab dishes, and transplanted them into mice.

They used primitive cells, not quite as early as stem cells, and injected them into a framework of collagen, the material that holds the body together.

After growing them, they found their structures had matured into the components that make teeth, including dentin, enamel, dental pulp, blood vessels, and periodontal ligaments.

They were "arranged appropriately when compared with a natural tooth," the researchers reported in the journal Nature Methods.

The teeth grew and developed normally when transplanted into a mouse, said Takashi Tsuji of the Tokyo University of Science in Chiba, Japan and colleagues.

They said their method was the first to show an entire organ could be replaced using just a few cells.

"To restore the partial loss of organ function, stem cell transplantation therapies have been developed," they wrote.

"The ultimate goal of regenerative therapy, however, is to develop fully functioning bioengineered organs that can replace lost or damaged organs after disease, injury or aging."

Reuters Photo: A mouse is seen in a file photo. Japanese researchers said on Sunday they had...

"Our reconstituted tooth germ generates a complete and entirely bioengineered tooth," they wrote.

"This study thus provides the first evidence of a successful reconstitution of an entire organ via the transplantation of bioengineered material," they added.

"Our present findings should also encourage the future development of organ replacement by regenerative therapy."