Origin of enamel prisms and Hunter-Schreger bands in reptilian enamel

Enamel prisms in mammalian enamel structure including human are considered to have originated in the reptilian enamel. The author has reported the original pattern of enamel prisms and of Hunter-Schreger bands in fossil reptiles of Mosasaurus sp. and Phytosaurus sp. The origin of the patterns of crystallite groups appear to arise in the fossil reptiles. Mosasaurus sp. had an island pattern and Phytosaurus sp. had a slender pattern. These two types are of various sizes, and are formed by variable numbers of ameloblasts. The number of ameloblasts involved in the formation of the crystallite group may change during amelogenesis. The present study observed the initial crystallite groups as enamel islands, in the surface of the early secretory stage of amelogenesis of living Alligator mississippiensis. These crystallite groups become bigger and more uniform in size during amelogenesis, being formed by several ameloblasts in the maturation stage. The border of crystallite groups observed appear as the lamella in human enamel. These crystallite groups may develop into the enamel prisms and Hunter-Schreger bands.