The odontoblast process extends to the dentinoenamel junction: an immunocytochemical study of rat dentine

The length and extent of the odontoblast cell process in dentine has been the subject of controversy for many years. Here an immunofluorescence technique has been applied at the light microscope level to rat coronal dentine to localize the intracellular components actin and tubulin. Adult rats were perfused with periodate-lysine-paraformaldehyde fixative, teeth were extracted, the molar crowns were demineralized, dehydrated, wax embedded, and 6 micron sections were prepared. The sections were postfixed in -20 degrees C acetone and then incubated with affinity-purified rabbit anti-actin or anti-tubulin antibodies, followed by fluorescein-conjugated goat anti-rabbit immunoglobulin. Intratubular immunofluorescence labeling for tubulin extended to the dentinoenamel junction, whereas labeling for actin, although extending to the dentinoenamel junction, was more prominent in the pulpal third of the rat dentine. Areas in which odontoblast processes are known not to occur, i.e., the atubular dentine, were not labeled by either antibody. The presence of actin- and tubulin-containing structures extending to the dentinoenamel junction is consistent with the hypothesis that the odontoblast process traverses the dentine for up to 3-4 mm, all the way to the dentinoenamel junction. Furthermore, the different staining patterns for actin-containing microfilaments as compared to tubulin-containing microtubules suggest that these two filamentous systems may have different roles in the function of the odontoblast process.