Fragmentation of the distal portion of Tomes' processes of secretory ameloblasts in the forming enamel of rat incisors.

In order to investigate enamel and dentin phospholipid metabolic pathways, two separate experiments were carried out. Firstly, rats were given chloroquine, a drug which induces a lipidosis-like disease. Extensive accumulation inside lysosomes was seen in all the groups of cells in the forming part of the rat incisor, except secretory ameloblasts which were unaffected by the drug. Secondly, the uptake and fate of 3H-choline were studied by radioautography on rats fed either normally or on an essential fatty acid deficient diet (EFAD). Four hours after the injection of the precursor, incorporation reached a maximum then decreased gradually. At 4 days the forming enamel displayed higher silver grain density than any other compartment. In EFAD rats 3H-choline incorporation was decreased drastically in each compartment except in the forming enamel which was not affected by the deficiency. The longer retention of the labeling in the forming enamel and the lack of lysosomal accumulation in chloroquine-treated secretory ameloblasts support the hypothesis that fragments of the distal Tomes' process are released during enamel formation. Disconnected from the cells, membrane remnants are neither reinternalized nor subjected to further degradation inside lysosomes.