Dental benefits of limited exposure to fluoridated water in childhood.

The effect of limited exposure to fluoridated water in childhood is of potential importance in highly-mobile modern society, but the subject has not been well-studied. This longitudinal study assessed caries experience and S. mutans proportions from fissure plaque in school-children who lived for at least the three years of the study in a non-fluoridated community (0.2 mg/L). Residence histories permitted division of the cohort into those who had lived all their lives in non-fluoridated communities, and those who had lived for some time previously in a fluoridated community. The children were aged 6-7 years at the beginning of the three-year study. Children with previous residence in the fluoridated communities developed 26.8% less caries in their permanent teeth during the study than did the children who had lived in non-fluoridated communities all their lives (p = 0.04), and had 29.8% less caries after three years (p = 0.02). Differences between the groups in S. mutans proportions from fissure plaque, sampled at six-monthly intervals throughout the study, could not be demonstrated. The dental benefits observed could not be attributed to socio-economic differences between the groups. Despite evidence that the benefits of limited ingestion of fluoridated water are topical in nature, the fact that many of the affected teeth in this study were unerupted at the time of the fluoride exposure means that pre-eruptive benefits cannot be ruled out.