Lasers are used frequently in medicine to destroy tissue, by making tiny surgical cuts, erasing spider veins, and banishing body hair. This week, researchers showed that low-power lasers can be used for the opposite purpose: to regrow missing tissue.
In a new study, the researchers used a laser to stimulate the stem cells within the teeth of rats. That could someday provide a simple way to avoid painful root canals. More significantly, researchers say, it may also work in other ways, perhaps encouraging wound healing and bone regeneration.
At lower power, laser light can be used to stimulate biological processes, says Parveen Arany, first author of the study who is a dentist and researcher at the National Institutes of Health. But Arany, who led the work while in David Mooney’s lab at Harvard’s Wyss Institute, says that studies using low-power lasers therapeutically have not always had impressive results.
Arany and his colleagues drilled holes in the molars of rats, exposing the soft pulp inside that contains dental stem cells. The researchers treated the teeth with low-power laser light and then attached temporary caps on the teeth. After 12 weeks, the treated teeth showed enhanced production of dentin, a bone-like tissue that is one of the main components of teeth.
Normally, when the dentin in teeth decays away to expose the pulp, it requires a root canal to fix it—digging out the pulp and replacing it and the outer tooth with inert materials. The study raises the possibility that root canals could be avoided by stimulating the body’s own cells to regenerate some parts of a tooth. (Unfortunately, unlike the cells that make dentin, those that can regenerate the tooth’s outer enamel are lost in childhood, but Arany says his team is looking at regenerating other tissues of the tooth.)
The researchers studied why lasers have this effect. They found that the light produces chemicals called reactive oxygen species that switch on a growth-stimulating molecule called TGF-beta. The study shows “how a physical form of energy is able to induce a biological response,” Arany says. But because reactive oxygen species can also harm tissue, he had to find the right dose to get a beneficial effect, which may explain why previous results had been mixed.
Scientists have investigated various ways of coaxing stem cells to differentiate into cells of specific tissues in order to replace or regenerate tissue, a process that often involves harvesting and manipulating the cells and exposing them to molecules that promote differentiation. Using light to spur the cells to produce those molecules themselves and differentiate into tissues would be much easier. It would also pose fewer regulatory hurdles. Arany says that because TGF-beta is known to promote growth and differentiation in many tissues, lasers may work in other applications as well.
“It’s a noninvasive technique, which makes it appealing,” says Anne George, a dental regeneration researcher at University of Illinois at Chicago College of Dentistry. “It’s something that can be easily tested out in clinical trials.” Arany says his team is planning to test the therapy in humans.