Ultrastructural observations of dental epithelial cells and enameloid during enameloid mineralization and maturation stages in stingrays, Urolophus aurantiacus, an elasmobranch

The fine structure of enameloid and dental epithelial cells in tooth germs of sepia stingrays, Urolophus aurantiacus, an elasmobranch, during enameloi d mineralization and enameloid maturation was investigated using light and transmission electron microscopy. The findings suggest that dental epitheli al cells are involved in the degeneration and removal of the enameloid matr ix during later stages of enameloid formation, and its peak is during the m ineralization stage. During the mineralization stage, a large number of def ined crystals were observed in the enameloid layer. In demineralized sectio ns, small fragments of cell membrane and electron-dense fibrils remained. T he inner dental epithelial (IDE) cells contained well-developed smooth endo plasmic reticulum, and many vesicles, vacuoles and granules containing elec tron-dense substance. Thick lamina densa was found beneath the distal end o f the IDE cells. The outer dental epithelial (ODE) cells possessed many mit ochondria, small electron-dense bodies, vesicles and intermediate filaments , and the capillaries usually approached the ODE cells. During the maturati on stage, the IDE cells were reduced in height, and had many lysosomal bodi es, vesicles, and mitochondria in the distal cytoplasm. The ODE cells becam e smaller. The lamina densa was almost absent and the distal end of the IDE cells often seemed to be in direct contact with the enameloid surface.