Abstract
This study was attempted to elucidate the ultrastructural and cytochemi cal characteristics of lingual dentin formation of rat incisors where no subsequent enamel formation took place. Special attention was paid to the initial calcification mechanism of mantle dentin by matri x vesicles.
The ultrastructural characteristics of the developing lingual dentin from the regions near the cervical loop to the established calcified dentin resembled those of the labial dentin formatio n of rat incisors except for the cytodifferentiation of inner enamel epithelial cells (IEE).
Enzyme cytochemistry of Ca2+-Mg2+-ATPase was performed using a modified Sundstrom and Mornstad's method after decalcification with EDTA. Near the cervical loop area, intense reaction products were demonstrated in the plasma membrane of the outer enamel epithelial cells as well as IEE. In the area where matrix vesicle calcification appeared, reaction products gradually disappeared from IEE and conversely were demonstrated in the plasma membrane of odontoblasts as well as the matrix vesicles. All the reactions disappeared once the dentin calcification was established.
Alkaline phosphatase (ALPase) was seen in the distal plasma membrane of IEE in the vicin - ity of the cervical loop, and its intensity gradually decreased towards the site of the initial calcification. The reaction products were also seen in the matrix vesicles as well as in the plasma membrane of odontoblasts at the more advanced stage. The closer to the initial site of calcification, the more strongly the odontoblasts and matrix vesicles reacted. When a layer of calcified dentin was established, the enzyme activity gradually decreased from the odontoblasts.
The results of this study suggest that both Ca2+-Mg2+-ATPase and ALPase activities play an important role in the initial calcification of dentin and that the matrix vesicles in the lingual dentin of rat incisors may be derived from odontoblasts.
