ELECTRON-MICROSCOPIC AND HISTOCHEMICAL-STUDIES OF THE MONONUCLEAR ODONTOCLAST OF THE HUMAN

Background: Osteoclasts and odontoclasts are multinucleated giant cell s which resorb hard tissue by the ruffled borders. Recently, the autho rs reported the presence of a mononuclear osteoclast with a ruffled bo rder in vitro. However, its presence in vivo has not been shown. To de monstrate the presence of a mononuclear odontoclast in humans, the pre sent study used human deciduous teeth. Methods: After fixation and dec alcification, tartrate-resistant acid phosphatase (TRACPase) activity was detected with the azo dye method, and then TRACPase-positive cells were observed on resorbing areas of teeth. TRACPase-positive cells co uld be distinguished from other cells by light microscopy, and the cel ls for investigation were serially sectioned by alternating semithin a nd ultrathin sections to observe their ultrastructure and three-dimens ional organization. Results: TRACPase activity was detected in both mu ltinucleated odontoclasts and a mononuclear cell from serial sections. By electron microscopy, most of the multinucleated odontoclasts had r uffled borders and clear zones. A mononuclear TRACPase-positive cell w ith a ruffled border and clear zone was reconstructed three-dimensiona lly by NIKON COSMOZONE 2SA. The reconstruction showed that this cell h ad one irregularly shaped nucleus and a wide ring-shaped clear zone an d a small ruffled border. Under the ruffled border, this cell formed a small lacuna on the dentin surface. The results suggested that this c ell was a mononuclear odontoclast. Conclusions: The present study conc ludes that cells with ruffled borders and clear zones observed by tran smission electron microscopy can be identified as odontoclasts or oste oclasts irrespective of the number of nuclei.(C) 1994 Wiley-Liss, Inc.