The longstanding public health practice of adding fluoride to public drinking water systems in the United States is facing new challenges and bans in some places, and experts have warned that the change would come with significant costs – both to the health of children and the health care system.

A new study projects what the effects of removing fluoride from water nationwide would be—and the findings are a dentist’s nightmare.

Researchers estimated 7.5% more U.S. children would get cavities, affecting 25.4 million additional teeth, if fluoridation were banned nationwide