The study on the role of heat shock protein (Hsp) 25 during dental and periodontal regeneration after tooth replantation

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The regeneration process of the odontoblast cell layer incident to tooth injury has not been fully understood. The purpose of the present study was to clarify the fate and regeneration process of odontoblasts during the pulpal healing following tooth replantation in rat molars by immunocytochemistry using antibodies to heat shock protein (Hsp) 25, immunocompetent cells and protein gene product (PGP) 9.5, as well as by histochemical periodic acid-Schiff (PAS) reaction. In untreated control teeth, intense Hsp 25-immunoreactivity was found in the cell bodies of odontoblasts. Tooth replantation caused loss of Hsp 25-immunoreactions in the coronal dental pulp during postoperative days 1-3. At postoperative 3 days, many immunocompetent cells accumulated along the pulp-dentin border, and subsequently Hsp 25-immunoreactive cells replaced them, concomitant with re-innervation. These findings indicate that the time course of changes in the expression of Hsp 25-immunoreactivity reflects the degeneration/regeneration process of odontoblasts. Furthermore, the temporal appearance of the immunocompetent cells might participate in odontoblast differentiation as well as in the initial defense reaction. After 14 days, the replanted pulp showed two regeneration patterns; reparative dentin and bone-like tissue formation. The occurrence of PAS-reactive cells in the pulp space and the absence of Hsp 25-immunopositive cells at the pulp-dentin border suggested that the migration of the dental follicle-derived cells into the pulp space and the subsequent total death of the original pulpal cells are decisive factors to elicit bone-like tissue formation in the replanted pulp. Further studies are needed to clarify the mechanisms of bone-like tissue formation in the dental pulp following tooth replantation.