Nobody looks forward to having a cavity drilled and filled by a dentist. Now there's an alternative: an antimicrobial liquid that can be brushed on cavities to stop tooth decay — painlessly.

The liquid is called silver diamine fluoride, or S.D.F. It's been used for decades in Japan, but it's been available in the United States, under the brand name Advantage Arrest, for just about a year.

The Food and Drug Administration cleared silver diamine fluoride for use as a tooth desensitizer for adults 21 and older. But studies show it can halt the progression of cavities and prevent them, and dentists are increasingly using it off-label for those purposes.

Ari Armstrong has the right reaction:

So the Japanese have been using this drill-free treatment for "decades," yet we in the United States have had to wait until last year to get it. And the only reason we can get it now to treat cavities is that it happens to be allowed as on "off-label" use for what the FDA officially approved it for.