An immunohistochemical study on hard tissue formation in a subcutaneously transplanted rat molar.

While dental pulp undergoes calcification following tooth replantation or transplantation, we actually know little about these mechanisms. We therefore conducted histological and immunohistochemical evaluations of mineralized tissue that formed in the pulp of rat maxillary molar transplanted into abdominal subcutaneous tissue. One, 2, 3, and 4 weeks post-transplantation, the teeth were investigated immunohistochemically using antibodies to osteocalcin (OCN), osteopontin (OPN), bone sialoprotein (BSP), dentin sialoprotein (DSP), and tissue non-specific alkaline phosphatase (TNAP). In the 1st week after transplantation, cell-rich hard tissue was formed at the root apex. At 2 weeks, formations of hard tissue, with few cells in the root canals and bone-like tissue in the coronal pulp chamber, were noted. After 3 and 4 weeks, the amounts of these hard tissues were increased. The immunolocalization of OCN, OPN, and BSP was seen strongly in coronal and apical hard tissues, but weakly in the root hard tissue. Conversely, DSP localized in the root hard tissue, but not in other newly formed hard tissues. At 1 week, TNAP localized along the periphery of the apical hard tissue and the lower surfaces of root predentin. These results demonstrate that the newly formed hard tissues in the pulp cavity of subcutaneously transplanted molars could be classified into three types, suggesting that these might be formed by type-specific cells.