Open wide, this won't hurt a bit. That might actually be true if the dentist's drill is replaced by a promising low-powered laser that can prompt stem cells to make damaged hard tissue in teeth grow back. Such minimally invasive treatment could one day offer an easy way to repair or regrow our pearly whites.

When a tooth is chipped or damaged, dentists replace it with ceramic or some other inert material, but these deteriorate over time.

To find something better, researchers have begun to look to regenerative medicine and in particular to stem cells to promote tissue repair. Most potential stem cell therapies require the addition of growth factors or chemicals to coax dormant stem cells to differentiate into the required cell type. These chemicals would be applied either directly to the recipient's body, or to stem cells that have been removed from the body and cultured in a dish for implantation.

But such treatments have yet to make it into the doctor's clinic because the approach needs to be precisely controlled so that the stem cells don't differentiate uncontrollably.

Praveen Arany at the National Institute of Dental and Craniofacial Research in Bethesda, Maryland, and his colleagues wondered whether they could use stem cells to heal teeth, but bypass the addition of chemicals by harnessing the body's existing mechanisms.

"Everything we need is in the existing tooth structure the adult stem cells, the growth factors, and exactly the right conditions," says Arany.

So they tried laser light, because it can promote regeneration in heart, skin, lung, and nerve tissues.

To mimic an injury, Arany's team used a drill to remove a piece of dentin the hard, calcified tissue beneath a tooth's enamel that doesn't normally regrow from the tooth of a rat. They then shone a non-ionising, low-power laser on the exposed tooth structure and the soft tissue underneath it. This allowed the light to reach the dental stem cells deep inside the pulp of the tooth.

Twelve weeks after a single 5-minute treatment, new dentin had formed in the cavity. Similar dentin production was seen in mice and in cultured human dental stem cells.

It not quite the end of the dentist's intervention though, they would still need to cap the tooth to protect it, because the stem cells that produce enamel are not present in adults.

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Forget the dentist's drill, use lasers to heal teeth