Ultrastructural characterization of extracellular matrix vesicles in the mineralizing fronts of apical cementum in cats.

Fine structure and the organic-inorganic relationship in mineralized fronts of cementum was studied with post-embedding demineralization and staining method. Typical matrix vesicles were observed between apical cementum and cementoblasts. Some vesicles were enclosed by a unit membrane; others contained needle-like crystals. Cementum crystals were found on unstained sections as filament- and needle-like structures which disappeared completely on EDTA treatment; similarly-shaped structures re-appeared following uranyl and lead staining. These findings suggest that matrix vesicles might act as initiators of additional cementogenesis and that crystal ghosts seen in cementum consist of organic materials.