Initiation of ectopic epithelial calcification in a calcifying odontogeniccyst

Ultrastructural observation was performed on a calcifying odontogenic cyst (COC) associated with an odontoma and arising in the right mandibular regio n of an 8-year-old Japanese boy. Four types of cells were identified in the epithelial layer of the COG. The basal cells were low columnar in shape an d contained some intracellular organelles. They were attached to the neighb oring cells with a few desmosomes and resembled inner enamel epithelium of the normal enamel organ. The stellate reticulum-like cells, polygonal in sh ape, possessed desmosomes and many cytoplasmic projections. Some intracellu lar organelles and a few bundles of tonofilaments were observed in the cyto plasm. The light oval cells that were pale staining with toluidine blue con tained dilated membranous organelles and many relatively evenly distributed tonofilaments. These cells were usually scattered in the vicinity of the f ocal accumulations of ghost cells, and the cell membrane was discontinuous in parts. The ghost cells contained many bundles of tonofilaments that were 60-240 nm in diameter and arranged in various directions. No intact intrac ellular organelles were noted in the cytoplasm. They were attached to the n eighboring ghost cells with some desmosomes and their cell membrane Mras di scontinuous in parts. A variety of vesicles, 90-450 nm in diameter, were sc attered among the tonofilament bundles. Some of these contained needle-like crystals that were considered to be initial calcification sites in ghost c ells. These vesicles presented morphological similarities to matrix vesicle s, and it is therefore suggested that matrix vesicle-like structures are de eply involved with initiation of calcification of ghost cells in COC.