The fluorosis risk index: a method for investigating risk factors.

The fluorosis risk index (FRI), a new index developed for use in analytical epidemiologic studies, is designed to permit a more accurate identification of associations between age-specific exposures to fluoride sources and the development of enamel fluorosis. The FRI divides the enamel surfaces of the permanent dentition into two developmentally related groups of surface zones, designated either as having begun formation during the first year of life (classification I) or during the third through sixth years of life (classification II). Data from the first use of this index in a population-based case-control study are given to illustrate the high reliability of the index, its validity, and its unique utility for the identification of risk factors of enamel fluorosis.