The prevalence of dental fluorosis has increased significantly in recent decades, due primarily to the caries-preventive use of fluoride. The accepted tenet has been that dental fluorosis is a problem that results solely from excessive fluoride intake during the time of tooth development. However, it is becoming increasingly apparent that there is also considerable individual variation in predisposition to fluorosis. In our work with the Iowa Fluoride Study (R01-DE09551), we have observed great variation in fluorosis severity within a given category of fluoride intake. The central hypothesis of this application is that dental fluorosis involves a complex interplay between individual genes (which set the threshold for development of fluorosis) and specific environmental exposures, including dietary patterns of fluoride intake and other nutrients. As part of the Iowa Fluoride Study, a large cohort has already been recruited and maintained for more than 13 years, with detailed longitudinal fluoride intake, dietary intake, and medication usage data, as well as surface-specific fluorosis phenotype data in the primary and mixed dentitions. As part of the Iowa Bone Development Study (R01-DE12101), which utilizes the Iowa Fluoride Study cohort, genetic material has been collected from over 600 cohort children and 970 parents, and genotypes are available for a substantial number of candidate genes potentially related to bone development. The subset of these genes is also reasonable candidates for roles in tooth morphogenesis and mineralization. The proposed secondary data analyses will examine these genes in light of dental fluorosis phenotypes, in order to identify specific genes/pathways that influence fluorosis, and to understand how these genes interact with fluoride and other factors (e.g., calcium intake, medications) to modify an individual's risk for dental fluorosis in both the primary and permanent dentitions. Genetic strategies include population- and family-based (child-parent trio) association studies with single nucleotide polymorphisms (SNPs), as well as specific haplotype analyses. The proposed work will be the first human study to specifically assess genetic factors and gene-environment interaction in dental fluorosis development. The novel information obtained will also assist in planning future studies. Knowledge gained may lead to useful strategies to identify those at increased risk for fluorosis so that more individualized fluoride regimens can be developed and applied. ? ? ?