[Transfer of 45Ca during amelogenesis studied by autoradiography and electron microscopy]

45Ca transfer through the stratum intermedium and the secreting ameloblasts towards enamel has been studied by quantitative electron microscopical autoradiography in tooth-germs of newborn cats following intravenous injection of the isotope. Two transfer pathways were demonstrated. The relatively more important direct path passed through the stratum intermedium and ameloblast intercellular spaces and reached the enamel directly. The second pathway consisted in an intracellular transfer through the ameloblasts. 45Ca penetrated the cell through its basal pole. The mitochondria were the most highly labeled organelles at the different experimental time intervals studied. A maximum of radioactivity was respectively noticed at 30 min and 1 h in the endoplasmic reticulum and the Golgi apparatus. A total absence of silver grains was noted over the secretory ameloblastic bodies. At 6 h, the highest labeling was observed over enamel and especailly over the inner enamel along the enameldentin junction.