The disturbed pattern of mineralization of developing enamel of the rat incisor after the oral administration of SrCl2 and NaF was investigated in an attempt to disclose possible mechanisms which might not be readily detectable under normal conditions, but which may control the progressive mineralization of developing enamel, especially during the maturation stage. Undemineralized ground sections of upper incisors were examined by contact microradiography, tetracycline labeling, and electron microprobe analysis. It was clear that Sr and F disturb the pattern of mineralization during the maturation stage in a characteristic fashion. Sr inhibits the early stage of maturation in which mineralization progresses from the surface toward the middle layer, whereas F accelerates the same stage prominently. At the late stage of maturation, the pattern of hypomineralization is different in the enamel of Sr- and F-treated rats. Mineralization in the inner and innermost layers of the Sr-treated rats and that in the outer layer of the F-treated rats ceases earlier than that in the controls, although the enamel is still hypomineralized.
At the latest stage of maturation, Fe penetrates more deeply into the hypomineralized enamel of the Sr- and F-treated rats, because of the higher porosity of the matrix.
These results suggest that the maturation stage is not a simple, continuous process, but rather is composed of substages (phases) which have different control mechanisms and in which mineralization progresses in different modes and rates.
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