Caries Tied to Insufficient Fluoride in Korea

Fluoridated water may be common in the United States, but not in Korea. In 1981, Korea launched a water fluoridation program, but its reach declined from 12.7% to 6.1% of the population between 2000 and 2012. Researchers, then, have noted a significant inverse association between dietary fluoride intake and the prevalence of dental caries.
The study analyzed results from the 4th Korea National Health and Nutrition Examination Survey (2007-2009), focusing on 167 male and 147 female 5-year-olds. These subjects had physical and nutritional examinations including oral examinations, and their parents had completed a health questionnaire.
Based on that data, the researchers estimated the fluoride intake of these children to be 0.35 mg/day, or 0.016 mg per kilogram of body weight per day, with higher decayed or filled surfaces indices for children who had lower dietary fluoride intake. The widely accepted optimal fluoride intake is between 0.05 and 0.07 mg per kilogram of body weight.
Previous studies have indicated that Koreans get 63.9% of their daily fluoride from food, while 97% use fluoride toothpastes. Overall, though, the researchers concluded that the fluoride intake via food was less than optimal and that community caries prevention programs including water fluoridation and supplementation would be beneficial.
The study, “Association Between Estimated Fluoride Intake and Dental Caries Prevalence Among 5-Year-Old Children in Korea,” was published by BMC Oral Health.

Just on 314 people? Anyway it isn't lack of fluoride it's a bad diet that causes caries.