Chemically distinct stages in developing human fetal enamel

Chemical analyses and the appearance of developing enamel from maxillary first incisors of human fetuses aged 5–9 months distinguished two stages during this period of development. The first corresponded to the production of forming enamel, which was soft, translucent and partially mineralized, and the second to the maturation or secondary mineralization of enamel. The final stage in enamel development, i.e. the mature, hard enamel is, however, generally absent in the tooth of the 9 month old fetus. The concentrations of P and Ca of the forming enamel in the tooth axis did not change significantly, varying between 9–12 and 21–26 per cent by weight, respectively. However, the P and Ca concentrations rose steeply across the boundary between the forming and the maturing enamel to reach a maximum value of 17 and 35 per cent, respectively, in the second stage.