Based on recent literature, the dynamics of mesenchymal cells in transplantation of various tissues and matrices, as well as the origin of new odontoblasts which participate in the formation of the dentin bridge, are described. Experiments involving implantation of pulp, periosteum, perichondrium, treated dentin, and bone matrices were performed to emphasize the capability of these cells to produce hard tissue. Light and electron microscopic and autoradiographic studies were carried out to clarify the origin of replacement odontoblasts. It appears that the pulp cells, endothelial cells, and pericytes become undifferentiated mesenchymal cells following pulp exposure. These mesenchymal cells differentiate into odontoblasts, which subsequently produce a dentin matrix. Pulp tissues auto-grafted to non-pulpal sites, elaborated bone (or osteodentin) matrix, but they did not graft to tubular dentin. An experiment on dentin bridge formation, using germ-free rats, demonstrated that the pulp tissue has intrinsic healing potential. Therefore, it was concluded that the ability of pulp tissue to elaborate hard tissues depends on its environment.
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