VISUALIZATION OF C¹⁴ IN THE TOOTH MATRIX AFTER ADMINISTRATION OF LABELED HEXOSES

¹ Department of Anatomy, McGill University, Montreal, Canada

The fate of glucose uniformly labeled with C¹⁴ was investigated in 3 groups of rats injected 3 days after birth and sacrificed between 3 hours and 6 months later. Teeth and associated tissues were examined using the coating method of radioautography. In addition, a group of rats given mannose-1-C¹⁴ was examined in the same manner. The distribution of labeled glucose and mannose was qualitatively indistinguishable.

In the enamel organ, the radioactive carbon of glucose is taken up into the pre-enamel matrix where it is arranged as a layer in close contact with the apex of the ameloblasts. During the next few days, as new pre-enamel is formed, the radioactive layer is seen within the zones of calcification (young and maturing enamel) and appears broader and less intense. With time, the radioactivity is no longer detectable. The available evidence indicates that labeled glucose has been taken up into large-sized molecules (presumably carbohydrates) of the pre-enamel matrix, which may be turned over rapidly.

In the dentinal organ, the radioactive carbon of glucose is taken up into the predentinal matrix, where it is arranged as a layer in close contact with the apex of the odontoblasts. As new predentin is continually deposited, the radioactive layer appears in the calcified zone, that is, in dentin proper. The labeled layer remains at a constant distance from the dentinoenamel junction and retains the same intensity throughout the 6-month experimental period.

The rapid decrease in the widespread radioautographic reactions observed in enamel and most soft tissues is in contrast to the stability of the dentinal reactions which persist indefinitely unless eroded by attrition. Similarly, stable material has been found in bone matrix, cartilage, and collagenous fibers. It is suggested that collagen is the common stable element present in these tissues.