Abstract
This study was performed to investigate the formation of reparative dentin experimentally produced in rat molars. Special attention was paid to the morphology and functions of the dentin-forming cells involved.
The cells in the pulp affected by cavity preparation were investigated both ultrastructurally and enzyme-cytochemically. The capacity of these cells to synthesize and secrete dentin matrix was also examined by 3H-proline autoradiography. A lead-labeling technique (Okada and Mimura, 1938) was used to record the formation rate of the reparative dentin by injecting rats with EDTA-Pb.
The odontoblasts, the processes of which had been damaged by the experimental cavity preparation, degenerated soon afterwards. The formation of the reparative dentin began within 5 days after cavity preparation, and was most active from the 5th to the 15th day. On the 3rd day, multilayers of spindle-shaped cells appeared in the pulp along the affected area of dentin. The cells became double or single-layered by day 7. Although the spindle-shaped cells on days 3 and 7 were different in shape from intact odontoblasts, they possessed well-developed Golgi apparatus, rough endoplasmic reticula and intense alkaline phosphatase activity along the cell membrane indicative of the presence of high matrix-orming activity in these cells. The patterns of 3H-proline labeling indicated that these cells were responsible for the formation of reparative dentin. By the 18th day, the cells lining the newly formed reparative dentin had become typical, well differentiated odontoblasts. The metabolic turnover of proline in the differentiated odontoblasts was less on day 18 than on day 7. The patterns of lead-labeling and 3H-proline autoradiograph and the ultrastructural features of the odontoblasts all indicated that additional dentin formation in the same area of control teeth was negligible throughout the experimental period.
It was concluded that the formation of reparative dentin was initiated by spindle-shaped odontoblast-like cells which possess high matrix-formation potential, induced by the stimulus of cavity preparation. While continuously secreting reparative dentin matrix, the odontoblast-like cells gradually developed into typical odontoblasts.
