Figure 1. Schematic illustration of the events relevant to early enamel mineralization. The ameloblasts regulate mass transport (e.g., ions and organic matter) from blood circulation to the extracellular space and vice versa. The mineralizing environment is comprised of the secreted matrix proteins and proteases, and varieties of ions and soluble moieties. Post-secretory processing of the matrix proteins yields soluble moieties prior to removal from the forming enamel. Tissue organization is guided by the molecular architecture of the matrix proteins, while the driving force for precipitation is determined by activities of common ions in the enamel fluid. The resulting crystal formation is characterized by the initial precipitation of acidic precursors, thin ribbons in morphology, and the consecutive epitaxial overgrowth of carbonato-apatite.