Autoradiographic evidence of cyclical entry of calcium into maturing enamel of the rat incisor tooth.

Adult rats were injected intraperitoneally with radioactive calcium and allowed to survive for periods up to 60 min. Animals were then killed and the upper incisors were removed. Soft tissue was removed from the teeth by dissection and with Clorox. Teeth were then coated with photographic emulsion and, after 17 days, the emulsion on the specimens was developed. Black bands of reduced silver indicated areas of radioactivity where calcium had entered the enamel. These bands were separated by narrower bands of non-radioactive enamel. It was judged that calcium did not gain entry into the enamel in these areas of enamel at this particular time. The patterns made by the bands of calcium entry and restriction were similar to patterns which show where striated border and non-striated border maturation ameloblasts cover the maturing enamel. Maturation ameloblasts with a striated border cover a larger area of the maturing enamel than do maturation ameloblasts without a striated border. It is considered that the maturation ameloblasts with a striated border are engaged in calcium entry into the maturing enamel.