Development of enamel in human fetal teeth.

The present study concerns enamel development in human fetal teeth. Chemical analysis and the appearance of developing enamel from maxillary and mandibular central and lateral incisors of human fetuses aged from five to nine mo distinguished two main stages during this period of development. The first stage 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 enamel at this stage appeared opaque when dried. The transition of forming enamel to maturing enamel was accompanied by a decrease in protein concentration, a distinct change in amino-acid composition, and a rise in the concentration of calcium and phosphate. Ultraviolet and chloronaphthalene inhibition studies revealed that the third and final stage in enamel development, the mature hard enamel, was generally absent, but was found in a very small percentage of maxillary and mandibular central incisors from nine- and ten-month-old fetuses, at the incisal tip. In both maxillary and mandibular canine teeth, only the forming stage in enamel development was observed during the fetal period. Further studies relating the length of each zone in enamel to fetal age provided information relative to the timing and rate of enamel development in each tooth.