Variations in growth of the enamel crown in human teeth and a possible relationship between growth and enamel structure.

A method for estimating, from measurements made in ground sections of mature teeth, the rate at which enamel formation extends over the crown during tooth development is described and used to examine enamel formation in the human dentition. The enamel extension rate varied with distance from the cusp along the enamel-dentine junction in permanent teeth, falling from a high level near the cusp to a constant minimum value. The early rate was higher, and the distance over which the rate fell to the minimum greater, on tall cusps. In deciduous teeth, limited data suggested that the rate may be fairly constant over the crown surface. The mean extension rate was about five times greater in deciduous than in permanent teeth. A function describing a stretching effect on newly-differentiated ameloblasts, arising from the geometry of the advancing margin of forming enamel, and dependent in part on the extension rate, was derived. This effect might influence ameloblast secretory area and hence prism size. The stretching effect was significantly smaller in deciduous than in permanent teeth. In conformity with this, prism domain area, a quantity measured in mature enamel and based on the geometrical relationship between ameloblasts and prisms, was significantly smaller in deciduous than in permanent enamel.