Caries in primary dentition and social class in high and low fluoride areas.

Of the two random samples studied, the first represented 6--8 year-old residents of a natural high fluoride area (n = 115) and resident of all other areas of Finland (n = 1219). The second sample was representative for 7--9-year-old children participating in public dental care in one Finnish country. Structured questionnaires were used to collect data on social class; caries diagnoses were made by local dentists in municipal dental clinics. Children in the highest social class had the lowest caries experience in both high and low fluoride areas. Differences between middle and lower social class children were small. Fluoride affected caries in the primary dentition similarly in all social classes; in both samples this was shown statistically by nonsignificant interaction between social class and fluoride. In Finland, differences between social classes in caries in the primary dentition cannot be removed solely by implementing water fluoridation.