Silver diamine fluoride?

Via the Washington Post, this interesting item: 

DENVER — Dental hygienist Jennifer Geiselhofer often cleans the teeth of senior patients who can't easily get to a dentist's office. But until recently, if she found a cavity, there was little she could do..

...But now Geiselhofer has a weapon to obliterate a cavity with a few brushstrokes.

Silver diamine fluoride is a liquid that can be painted on teeth to stop decay. Fast, low-cost and pain-free, the treatment is rapidly gaining momentum nationwide as the cavity treatment of choice for patients who cannot easily get a filling, such as the very young or the very old.

“It has been life-changing for my patients,” said Geiselhofer, who has been using the treatment for about 18 months...

...Silver diamine fluoride has been used in other countries for decades, and studies have proved it safe. Its biggest downside is that it permanently turns the decayed area black — a turnoff, in particular, for people with decay on a front tooth. Dental providers say the black spots can be covered by tooth-colored material for an extra cost. For older adults, Geiselhofer said, a dark spot is a small price to pay for a treatment that stops cavities quickly, with no drilling, needle prick or trip to the dentist required...

I didn't know about this compound. I imagine the black coloring has to do with the silver. Who knew?