The absorptive activity of ameloblasts during the maturation of enamel

The activity of ameloblasts during the maturation of enamel was investigated by means of autoradiography. Young rats were given daily injections of radioactive sulfur. Injections were started when the rats were five days old and continued until some of the rats were 12 days old. Developing teeth were removed at different times and prepared for autoradiography. In every specimen that was examined, silver grains were found over enamel that was adjacent to tall, secretory ameloblasts. These cells have been identified as being engaged in matrix formation. At the end of matrix formation, the tall ameloblasts become structurally reorganized, and the reorganized cells now act on the enamel as it matures. Despite the fact that the animals receive daily injection of labeled sulfur, the silver grains over the maturing enamel decrease and silver grains are observed over the cytoplasm of the shortened ameloblasts. It is concluded therefore that one of the activities of the reorganized (transporting) ameloblasts is to remove sulfur or a sulfated compound from the enamel during its maturation.