(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.
It sounds curious now, but in the early 20th century dentists were divided on the cause of dental decay. Was it due to an underlying disease? Was it due to overall diet? Or was it due just to sweets?
Clues pointed to the role of sweets: Orphans in childrens' homes too poor to provide sweets had fewer cavities than the general population; dental decay among conscripts declined during sugar rationing in WWI.
Facing a national epidemic of tooth repair too expensive to undertake, the Swedish government decided to focus on prevention, and commissioned a study on the role of diet and sweets. It was funded by the sugar industry.
A mental institution
The perfect place to perform such a study, they decided, was the Vipeholm Mental Institution, a large facility just outside Lund, Sweden. In 1935 it had been turned into a home for people with severe intellectual and developmental disabilities.
"These 'idiots,' which was a medical classification at the time, were gathered from smaller wards all over the country," Kanger explained. "In the beginning they had 650 people and it grew up to over a thousand."
In medical terms at the time, an "idiot" was a person with an IQ below 25, who functioned at the level of a normal toddler. An "imbecile" had a IQ of between 26 and 50, whose intelligence was about that of a child of seven. "Morons" functioned at about the intellectual level of a child of 12.
These "children" typically ranged in age from 15 to 70, Kanger said. Average life expectancy was low.
"There were big, big halls where they actually were just running around, with no activities at all at the start," Kanger said. "They were bathed in cold water if they were too troublesome. Some of them lay in beds all the time.
"In the beginning, it was actually a terrible place for most people. It became better over the years, with more therapies," he said.