The Ontogeny Of Mammalian Enamel

The ontogeny of mammalian enamel is reviewed briefly in this chapter. Ameloblast differentiation and function, as they are currently understood, are presented. The significance of Tomes' process during the secretory phase of amelogenesis is emphasized. Tomes' process morphology controls the orientation of the matrix proteins, the alignment of the hydroxyapatite crystallites and ultimately the prismatic or non-prismatic patterns of mature enamel. During the maturation phase of amelogenesis mineralization is completed and as much as 90% of the enamel proteins degraded and removed from the enamel by maturation ameloblasts. The mature enamel structure reflects several aspects of the process of amelogenesis. Cyclic patterns of enamel deposition in primate teeth are represented by cross-striations, striae of Retzius and perikymata. The motions of the secretory ameloblasts, or more precisely, of their Tomes' processes, produce the curvilinear course of the enamel prisms. The latter are, in part, responsible for such phenomena as Hunter-Schreger bands. Any explanation of the genesis of these bands must take into account the developmental constraints presented by cellular movements of an intact sheet of secretory ameloblasts.