INDUCTION OF ODONTOBLAST-LIKE CELL-DIFFERENTIATION IN DOG DENTAL PULPS AFTER IN-VIVO IMPLANTATION OF DENTIN MATRIX COMPONENTS

The effects of dentine extracellular matrix components on dental mesenchymal cells were studied by light and transmission electron microscopy after their implantation at central sites of mechanically exposed pulps in dog molar teeth. The implants were Millipore filters that had been soaked with solutions containing 30 or 300 mu g/ml of an EDTA-soluble fraction of rabbit incisor dentine. Control filters were soaked with dog albumin or phosphate buffered saline. Columnar, polarized cells were consistently seen after 8 days in close proximity to the filters coated with both concentrations of dentine matrix components. Characteristic features of these polarized cells included widened cisternae of the rough endoplasmic reticulum, a rich microfilamentous network in the long cytoplasmic extensions invading the filter pores and numerous cytoplasmic bodies. These cells also showed evidence of functional as well as cytological differentiation. Polarized processing of secretory granules could be observed after 8 days' implantation, and also the presence of matrix vesicles and deposition of a fine, collagenous matrix into the filters apically to the distal end of the cytoplasmic processes. After 24 days' implantation, secretion of a tubular matrix could be consistently seen in association with the odontoblast-like cells. No changes in cell organization or matrix synthesis were seen after implantation of control filters. These studies demonstrate that bioactive components present in the EDTA-soluble dentine matrix fraction are able to directly induce cell polarization and apical secretion of tubular matrix when implanted in contact with dental pulp cells at sites remote from the odontoblast layer.