In the new study, tissue engineer Takashi Tsuji of Tokyo University and colleagues started with separate populations of the two cell types that make teeth: epithelial cells and mesenchymal cells. Isolating the two types from the tooth germ--the nascent tooth tissue that hasn't erupted from the gum--of a mouse embryo, the researchers expanded each cell population to 105 cells each. They then injected both populations into a drop of collagen.Jeremy Mao of the Columbia University College of Dental Medicine in New York City says the Japanese scientists' work is an "important milestone" in tooth generation because the generated teeth keep growing and integrate surrounding structures after they're implanted. Science Magazine says the ability to grow human teeth is still "years away" because the scientists' technique currently involves harvesting cells from an embryo at a certain age of development. However, Takashi Tsuji and his team are now looking for adult human stem cells that can grow into teeth.
After 16 days, the cells had developed into another tooth germ. The scientists extracted the incisor of a separate mouse and popped the budding tooth into its cavity. The tooth developed normally, the team reports in the current online edition of Nature Methods, with pulp, blood vessels, and the beginnings of roots. The researchers say their method can also be used to make whiskers, which arise from the same cell types.