(CNN)Today it sounds like a Halloween horror story, concocted to scare children out of eating too much candy.
But in the late 1940s in Sweden, children and adults with mental disabilities were deliberately fed sticky candies to see what would happen to their teeth.
"I've seen dental records of this. Every tooth was black," said Swedish journalist Thomas Kanger, who has written about the children. "I'm talking about every tooth damaged and it went on for years."
An epidemic of cavities
In Sweden in the 1930s, studies found even 3-year-old children had cavities in 83% of their teeth. Such extensive decay wasn't unusual; dental care was very poor in most countries.
Treatment was basically non-existent and rotting teeth were typically pulled. Toothlessness was so prevalent in the United States that the military restricted recruits for World War I and World War II to men who had six intact opposing teeth.