In vitro penetration of 125I-amelogenin into the enamel and enamel organ of rat incisors.

This work attempted to introduce pre-labelled intact amelogenins into developing rat enamel in vitro. The intention was ultimately to trace the fate of such proteins in the developing enamel matrix and to examine the effect of these and other molecules on ameloblast behavior. The penetration of 125I-amelogenin (25 KDa) directly into the young enamel of rat incisors, in vitro, keeping the enamel organ intact is described. The enamel (an extension approximately 8 mm from the apical end of the tooth) together with the enamel organ, was separated from the underlying dentine and placed over a strip of filter paper covering a well of micro-culture slide filled with Eagle's medium containing 125I labelled amelogenin and incubated at 37 degrees C. The enamel faced the strip of filter paper and so was adjacent to the medium. After 1 h pieces were either washed in cold medium, fixed and embedded in Epoxy-resin, or incubated in cold medium for another 1 to 10 h at 37 degrees C before embedding. One-micron thick sections were processed for autoradiography and the results showed a decreasing gradient of silver grain concentration from the dentino-enamel junction towards the enamel organ. It is expected that by determining the nature of the labelled material incorporated into the enamel and enamel organ the fate of amelogenins could be better understood.