Every year, untreated tooth decay sends thousands of young US children to emergency departments for dental problems doctors can't treat.

Many eventually undergo surgery under general anesthesia, while others endure pain and infection.

Now, a simple, inexpensive liquid called silver diamine fluoride (SDF) could spare many of those children. Applied to a cavity with a tiny sponge-tipped applicator in about a few second's time per tooth, SDF arrests decay without drilling, shots, or sedation.

Dentists have used SDF successfully for decades in many countries, and off label in the United States since 2014, when it was approved as a medical device to treat tooth sensitivity. However, it has lacked the large US population clinical trials for efficacy and safety that are needed for FDA approval as a drug to treat cavities.

Now, a University of Michigan-led clinical trial has produced that evidence.

Published in JAMA Pediatrics, the Phase III trial enrolled 830 children under age 6 who were recruited through dental offices, pediatric medical practices, and Head Start and Early Head Start programs in Michigan, New York, and Iowa.

Researchers found that SDF arrested tooth decay in more than half of children's affected baby teeth when treated at 6-month intervals. Unlike conventional treatment, which removes part of the tooth before placing a filling, SDF is simply painted onto the cavity.

"This is a very effective and safe treatment—even in children as young as 1," said Margherita Fontana, professor of dentistry at the University of Michigan School of Dentistry and the study's lead investigator.

Tooth decay is the most common chronic disease of childhood, affecting more than 40% of US children. Left untreated, cavities can cause severe pain, infection, difficulty eating and sleeping, missed school, and repeated medical visits.

SDF may be especially valuable for very young children, older adults, people with developmental or physical disabilities, patients with severe dental anxiety, and others who cannot easily tolerate or access conventional dental treatment, Fontana said.

Its primary drawback is cosmetic, she said. The silver permanently darkens the decayed portion of the tooth.

"If we want more children and families to benefit from this treatment, we need rigorous evidence showing both that it works and that it's safe. From a public health perspective, if we want broader implementation across the United States, including in medical settings, we need carefully collected data in US populations, and we now have that," Fontana said.