The initiation of osteodentin formation in the rat incisor after adriamycin administration

In order to study the initiation of osteodentin formation in rat incisors, animals were injected intravenously with adriamycin (5 mg/kg body weight), and killed from 2 to 7 days after injection by perfusion with a 2.5% buffered glutaraldehyde solution. Control animals, injected with only physiological saline, were treated in the same manner. Three days after adriamycin injection aggregations of mesenchymal cells were observed along the mesial and lateral walls of the pulp chamber. Between 3 days and 7 days osteodentin production was observed at the sites where the mesenchymal aggregations were previously observed. Electron microscopic observations revealed that the cells involved in the aggregates were larger and contained more profiles of rough endoplasmic reticulum and secretion granules than the unaffected pulp cells. The osteodentin matrix first appeared as a scant deposition of collagen fibers between the cells. As more collagen fibers were deposited the matrix became much denser. Some cells that initially formed the mesenchymal aggregates were completely enclosed by the increased deposition of the matrix. It therefore appears that osteodentin formation, as observed in the rat incisor pulp after adriamycin administration, is the result of an abnormal differentiation of pulp mesenchymal cells.