Odontoblast processes in human dentin revealed by fluorescence labeling and transmission electron microscopy

In the present undertaking, the distribution of odontoblast processes in human dentin was determined through the DiI carbocyanine dye fluorescent staining of the cell membrane, while F-actin was identified by rhodamine-phalloidin. Confocal laser scanning microscopy revealed intense labeling for both agents in inner dentin, while transmission electron microscopy (TEM) identified dentinal tubules including odontoblast processes in this area, each process being surrounded by a cell membrane and containing an abundance of filamentous structures. Electron-dense "lamina limitans" lined the dentinal tubules. Individual cell processes became narrower toward the middle area, and their overall numbers decreased as well under TEM. Labeling for F-actin was absent in both middle and outer dentin, while faint labeling for DiI was visible along the dentinal tubules as far as the dentino-enamel junction (DEJ), where it was also recognized within the tubules themselves. Under TEM, the dentinal tubules lined with electron-dense structures were, in fact, empty in the middle and outer dentin. Immediately below the DEJ, however, the tubules manifested dense concentrations of fine granular material. Our study, therefore, appears to suggest that odontoblast processes do not extend beyond the inner dentin of fully erupted human premolars.