A histological study of the short-term effects of fluoride on enamel and dentine formation in hamster tooth-germs in organ culture in vitro.

First maxillary molars in early stages of secretory amelogenesis were exposed in vitro to fluoride (F-) concentrations ranging between 2.63 microM and 2.63 mM for up to 3 days. In contrast to the dentine papilla, which seemed unaffected by F- in concentrations up to 1.31 mM, the enamel organ was dose-dependently extremely sensitive for F-. Young ameloblasts which became secretory in vitro were in particular sensitive and did not secrete enamel adjacent to new, in vitro-formed dentine. Hypermineralization of the dentine at the enamel-dentine junction suggested that these ameloblasts still transport and deposit minerals. 52 microM was the lowest concentration of F- that inhibited deposition of enamel in the cervical-loop region. Ameloblasts, secretory at the time of exposure to F-, in concentrations of 52 microM up to 1.31 mM secreted an abnormal, amorphous, von-Kossa-negative enamel matrix. 1.31 mM of F- was the lowest concentration which induced the formation of a hypermineralized band in the pre-exposure enamel. 2.63 mM of F- was highly toxic for the enamel organ but had only moderate effects on the dentine papilla.