amelogenesis

Amelogenesis is the biological process by which dental enamel, the hard outer layer of teeth, is formed. It occurs during tooth development as ameloblasts in the enamel organ secrete and mineralize an extracellular enamel matrix, producing the protective outer coating that covers each tooth crown.

The process proceeds in stages. In the presecretory stage, cells of the inner enamel epithelium differentiate into ameloblasts. In the secretory stage, ameloblasts secrete enamel matrix proteins (predominantly amelogenin, with ameloblastin and enamelin) and non-collagenous proteins, forming a partially mineralized matrix and organizing enamel prisms via their Tomes’ processes. In the maturation stage, the organic matrix is degraded and removed by enamel matrix proteases such as MMP-20 (enamelysin) and KLK-4 (kallikrein-related peptidase 4). Concurrently, mineral crystals grow and fuse, producing mature, highly mineralized enamel that is about 96 percent mineral by weight and essentially devoid of collagen.

Enamel is formed only by ameloblasts, cells derived from the inner enamel epithelium. Once formed, mature enamel is acellular, avascular, and noninnervated. The enamel organ typically produces crown enamel before tooth eruption, and formation completes before eruption for each tooth.

Disorders of amelogenesis include amelogenesis imperfecta, a group of inherited defects that alter enamel quantity or quality. Phenotypes are categorized as hypoplastic (thin enamel), hypomaturation (soft or mottled enamel), and hypocalcified (poor mineralization). Mutations in genes such as AMELX, ENAM, MMP20, and KLK4 underlie these conditions.

Because enamel does not regenerate, any enamel loss due to caries, abrasion, or erosion is permanent and often requires restorative or protective treatment.