Methods: GFP-labeled molars were extracted and immediately transplanted into a pre-formed subcutaneous pouch in the abdominal region of wild-type recipient rats. At 5-30 days after the transplantation, the transplanted teeth were fixed and embedded in paraffin. The origin of the osteoblast-like cells was examined immunohistochemically by using GFP-specific antibody. Observations on osteoblast-like cell differentiation were also made by using alpha-SMA-, Smad4-, and Runx2- specific antibodies.
Results: Five days after the transplantation, initial hard tissue was found on the surface of dentin at the root apex. At 10 days, woven bone-like tissue had also formed apart from the dentin at the upper region of the pulp. After 20 days, these hard tissues expanded within the pulp cavity and became histologically similar to bone. GFP-positive cells were localized in the osteoblast-like cells within the root apex as well as in the upper pulp. Immunohistochemical observation of alpha-SMA, a marker for undifferentiated cells, showed a positive reaction in cells surrounding this bone-like tissue within the upper pulp, but not in those within the root apex. Immunoreactivities of Smad4 and Runx2 were detected in the hard tissue-forming cells within both areas.
Conclusions: Bone-like tissues induced by tooth transplantation are thought to have originated from 2 different types of pulpal cells, such as progenitor cells having hard tissue-forming ability and undifferentiated cells possessing osteogenic potential.