Scientists have come a step closer to replacing missing teeth with implants grown from stem cells.
Researchers succeeded in engineering hybrid human-mouse teeth coated in enamel with developing roots.
In future, it is hoped the work will lead to dentures being replaced by real substitute molars grown from "seeds" planted into a patient's jaw.
The technique involved growing cells from human gum tissue and combining them with tooth stem cells from mouse embryos. The combination cell clusters were transplanted into adult mouse kidneys where they grew into recognisable tooth structures.
Examination showed that they contained dentin - the main structural material of teeth - as well as hard protective enamel. There was also evidence of viable root formation.
Two kinds of cell were used to make the bioengineered teeth. Epithelial "surface lining" cells were taken from the gum tissue and mesenchymal cells from the mouse embryos.
Mesenchymal stem cells can develop into a range of different tissues, including bone, cartilage and fat.
Professor Paul Sharpe, who led the research at King's College London's Dental Institute, said: "Epithelial cells derived from adult human gum tissue are capable of responding to tooth-inducing signals from embryonic tooth mesenchyme in an appropriate way to contribute to tooth crown and root formation and give rise to relevant differentiated cell types, following in-vitro (in a living body) culture.
"These easily accessible epithelial cells are thus a realistic source for consideration in human biotooth formation. The next major challenge is to identify a way to culture adult human mesenchymal cells to be tooth-inducing, as at the moment we can only make embryonic mesenchymal cells do this."
The findings are published in the latest issue of the Journal Of Dental Research. Previous research has shown that embryonic teeth are capable of developing normally in the adult mouth. It would not be ethical or practical to use human embryos in dentistry.