Structure of Developing Enamel

The structure of developing enamel can be considered on many levels of order, from the development of the final morphology of individual hydroxyapatite crystals to their incorporation and final arrangement into superassemblies of prismatic, interprismatic, and aprismatic enamel. In general terms, as Boyde and Jones have noted, the division of the mineral into a large number of relatively small, discrete crystals provides a material that is hard and durable, yet has some degree of flexibility. The basic visible unit of enamel is the hydroxy apatite crystal. The increasing mineralization ot enamel may involve either continuous fusion of nuclei or continuous growth of preexisting crystals. In many species a significant portion of the matrix may constitute the interrod enamel that forms as packing material between and around the rods. The morphology of the matrix can be visualized by normal histological techniques, at the ultrastructural level using transmission or scanning electron microscopy, or using specific antibodies in immunohistochemical and immunocytochemical techniques.