An ultrastructural study of calcifying odontogenic cyst, especially calcified material

The ultrastructural features of calcification in a case of calcifying odontogenic cyst (COC) were studied. Scanning electron microscopic examination of the inner parts of the cyst wall revealed many short microvilli, and X-ray microanalysis of the high-density masses in the intercellular parts showed prominent calcium peaks, which meant that these masses were calcified materials. On transmission electron microscopic observations, many calcifications exhibited a distinctive ring formation around the periphery of a central core that consisted of an amorphous structure. These calcifications were observed with necrotic remnants of nuclear material and many identifiable mitochondria, thin fibers, and epithelial cells. The cytoplasm of ghost cells consisted of numerous short electron-dense tonofilament bundles. Needle-like structures were shown in the tonofilament bundles. X-ray diffraction analysis showed that the needle-like crystals were hydroxyapatite. It is suggested that calcification in a COC may be related to degenerative mitochondria and tonofilament bundles of ghost cells.