Incorporation of iron in rat incisor enamel

ABSTRACT – The electron microprobe technique was used to study the accumulation of iron in rat incisor ameloblasts as well as the subsequent release of iron from the cells and deposition into the outer layer of the enamel. Starting about 3 mm from the developing end, a gradual accumulation of iron occurred in the ameloblasts. At a stage where the iron content of the cells had reached a maximal level, and the calcium content of the adjacent hard tissue had reached the level of mature enamel, the initial incorporation of iron in the enamel was seen. In the iron incorporation zone the iron content of the enamel increased from less than 0.1 % to about 9 % and the iron content of the ameloblasts was gradually reduced. Concomitant with the increase of iron in the enamel, a decrease of the calcium content was observed in the same region, indicating a withdrawal of calcium from the enamel. Since the incorporation of iron occurs at a stage where the enamel is highly mineralized, the processes involved can hardly be explained as an interaction with the organic matrix. The key to the understanding of these processes should therefore be sought in the adjacent cell layer.