The tiny ultrasound machine fits into a patient’s mouth on a braces bracket or a removable plastic crown, where it gently massages gums and stimulates dental growth from the root.

It is wireless and is controlled by a pocket-sized remote carried by the user.

The team at the University of Alberta in Canada hope the low-intensity pulsed ultrasound (LIPUS) system, which is smaller than a pea, will be available to the public within two years.

It is currently being designed to help repair fractured or diseased teeth, but in the future could help sports players or children who have a tooth knocked out. And eventually the same technology could even be used to grow bones, raising the possibility that people could make themselves taller.

Dr Tarak El-Bialy, one of the lead researchers, said the tool meant broken roots could now be fixed.

"And because we can regrow the tooth root, a patient could have his own tooth rather than foreign objects in his mouth," he said.

The system needs to be activated for 20 minutes a day for four weeks for noticeable results.