[Bifocal odontogenic calcified epithelial tumor (Pindborg's tumor). A morphologic and ultrastructural study].

Histoenzymologic and ultrastructural examinations were conducted on a doubly located calcified odontogenic epithelial tumor. The cells of the tumor, developing in both the maxilla and mandible, differed from those of the common ameloblastoma, being all of the malpighian type without any secretory polarity. Furthermore, optical and electronic microscopy showed evidence of marked alkaline phosphatases and ATPases activity in their numerous peripheral microvilli. These identical activities to those of the stratum intermedium could suggest the origin of the tumor from these latter cells. But, like the preameloblasts of the dental germ, these tumoral cells produce in their intracytoplasmic vesicles and then excrete into the stroma, a granulofilamentous substance, pseudo-amyloid, which could thus represent an abnormal protein of the enamel matrix. The calcifications, mainly present in this amyloid-like substance, are the expression of an attempt to mineralize this abnormal matrix. Stromal calcifications may result from a sketchy odontogenetic induction, as shown by the intense activity of ATPases and alkaline phosphatases on the fibroblastic cytoplasm membranes.