X-Ray Micro-Analysis of the Mineralization Patterns in Developing Enamel in Hamster Tooth Germs Exposed To Fluoride in Vitro During the Secretory Phase of Amelogenesis

Abstract

The developing enamel from three-day-old hamster first maxillary (M1) molar tooth germs exposed to fluoride (F-) in vitro was analyzed for its mineral content by means of the energy-dispersive x-ray micro-analysis technique. The aim of this study was to obtain semi-quantitative data on the F--induced hypermineralization patterns in the enamel and to confirm that the increase in electron density observed in micrographs of F-treated enamel (Lyaruu et al., 1986, 1987b) is indeed due to an increase in mineral content in the fluorotic enamel. The tooth germs were explanted during the early stages of secretory amelogenesis and initially cultured for 24 hr in the presence of 10 ppm F- in the culture medium. The germs were then cultured for another 24 hr without F-. In order to compare the ultrastructural results directly with the microprobe data, we used the same specimens for both investigations. The net calcium counts (measurement minus background counts) in the analyses were used as a measure of the mineral content in the enamel. The aprismatic pre-exposure enamel, deposited in vivo before the onset of culture, was the most hypermineralized region in the fluorotic enamel, i.e., it contained the highest amount of calcium measured. The degree of the F--induced hypermineralization gradually decreased (but was not abolished) in the more mature regions of the enamel. The unmineralized enamel matrix secreted during the initial F- treatment in vitro mineralized during the subsequent culture without F-. The calcium content in this enamel layer was in the same order of magnitude as that recorded for the newly deposited enamel in control tooth germs cultured without F-. From these results, and in combination with the ultrastructural data obtained in previous studies, it is concluded that in vitro: (1) F- treatment during the secretory phase of amelogenesis induces hypermineralization of the pre-exposure enamel; (2) F- decontrols or abolishes enamel crystal growth in length and promotes crystal growth in thickness, thus producing enamel hypermineralization; and (3) enamel matrix secreted during F- exposure retains its capacity to support crystal growth when F- is removed from the culture environment.