Plasma fluoride levels and enamel fluorosis in the rat

This study examined the relationship between transient peak plasma fluoride levels (subcutaneous injections) as well as lower but relatively constant levels (subcutaneous constant infusion) and the occurrence of disturbances in the enamel mineralization of the rat incisor as determined microradiographically. The fluoride doses were administered for 1 week, and the animals were killed 2 weeks later. Once daily peak plasma fluoride levels of 10 μM were uniformly associated with disturbances in the mineralization of the enamel, but once daily peak levels of 5 μM were not. Neither were twice daily 5-μM peaks. Relatively constant plasma fluoride levels, which averaged 3.3 μM, were associated with an increased incidence of changes in enamel formation and levels of 4.7 μM consistently associated with disturbances in enamel mineralization. These findings suggest that (1) the rat is a better model for the study of human enamel fluorosis than previously believed, and (2) slightly elevated but relatively constant plasma fluoride levels are more likely to be associated with the occurrence of fluorotic disturbances in the mineralization of enamel than are the more rare high and transient peak levels.