Dentin formation in so-called "fibro-osteo-cemental" lesions of the jaw: histologic, electron microscopic, and immunohistochemical investigations.

Two cases of the so-called fibro-osteo-cemental lesions of the jaws, containing unusual deposits of hard tissue, are described. There were peculiar spheroid calcifications or larger masses forming small cavities with a radial arrangement and discontinuous blasts extending with axonlike cell processes toward an acellular core. For further definition, electron microscopic and immunohistologic studies were done. The most conspicuous features were abundant intracytoplasmic vimentin filaments in the blasts, tight junctions, matrix vesicle formation, a globular accretion pattern, and so-called matrix maturation. These findings militate against an osseous or cementous nature of this hard tissue. Rather, both the light and electron microscopic findings are highly compatible with the assumption that the blasts are odontoblasts and that an immature type of dentin is formed. In addition to fibroblasts, osteoblasts, and cementoblasts, apparently also a further descendant of the ectomesenchyme--the odontoblasts with dentin formation--may participate in the so-called fibro-osteo-cemental lesions.