Morphology of the teeth of the American alligator (Alligator mississippiensis): Fine structure and chemistry of the enamel.

Functional teeth from young American alligators (120 cm to 260 cm total length) were prepared for scanning electron microscopy (SEM) and electron microprobe analysis (EPMA) of the elements of the enamel layer. On the tip of the tooth, the enamel layer is thick, but over the crown it gradually reduces in thickness until it disappears near the cement-enamel junction. The enamel layer is distinguished by inner and outer layers. The inner layer is formed of separated, irregularly shaped blocks composed of small crystals. In the outer layer, the enamel crystals are closely packed and oriented perpendicularly to the surface. Radially oriented, lamella-like structures of the enamel are elongated, crystallized bands which extend from the inner to the outer layer of the enamel as reported by Kvam (Acta Odontol. Scand. 17:745-751, 1959). The highest density of crystals occurs in the enamel layer before complete calcification. Concentrations of iron, copper, and fluoride are located approximately 20 μm below the surface of the enamel in the outer layer where crystals are closely packed. The concentration of trace elements (e.g., Fe, F, Cu) is related to the formation of hydroxyapatite.