Effect of long-term administration of fluoride on physico-chemical properties of the rat incisor enamel.

Rats were maintained on drinking water containing different amounts of fluoride (0, 9, 23 45, 68, and 113 ppm) for 70 days. Physico-chemical properties of the incisor enamel were examined after fluoride administration, using contact microradiography, histochemistry, and microhardness tests. The tooth enamel formed during high fluoride exposure showed marked hypocalcification. Much of organic substance in the enamel seemed to have been retained. In addition, the microhardness of enamel showed a marked decrease. These changes were most prominent in the outer region of enamel and were proportional to the concentration of fluoride administered. Such changes following fluoride administration indicated inhibition of enamel maturation, i.e., an inhibition of the progressive depposition of minerals and/or in inhibition of organic matrix withdrawal by ameloblasts. Enamel seemed more affected by fluoride than dentine.