Electron probe analysis of maturation ameloblasts of the rat incisor and calf molar

Rapidly frozen upper incisor teeth of rats and molar teeth of calves were freeze fractured, freeze dried and dry dissected in preparation for energy dispersive x-ray emission microanalysis in the scanning electron microscope. Successive zones of ameloblasts adjacent to maturing rat incisor enamel were examined, beginning with cells adjacent to the least mature enamel and progressing to cells over increasingly more mature enamel. Pronounced Kalpha1,2 x-ray peaks were obtained for P, S, Cl, K and Fe but not for Ca. Ca levels were also very low compared with P, S, Cl and K in calf molar maturation ameloblasts, whereas they were high in the distal poles of the secretory odontoblasts in the same specimens. The findings indicate that both intra- and extracellular Ca levels are extremely low in maturation ameloblasts. It is concluded that Ca is neither stored nor concentrated in large amounts by the maturation ameloblasts prior to its entry into the enamel. The suggestion is made that the maturation ameloblasts might regulate entry of calcium into enamel by serving as a selective barrier.