STRUCTURAL ASPECTS OF THE REVERSAL PHASE OF ALVEOLAR BONE REMODELING

The ultrastructure of the reversal line during alveolar bone remodelli ng was investigated in the rat. Surface bone remodelling along the per iosteum of the mandible was induced by the extraction of opposing maxi llary molars. With transmission EM the reversal line was seen to be co mposed of a superficial electron-dense amorphous layer and a deep fila mentous layer at 7 d after extraction. The reversal line exhibited str ong alkaline phosphatase activity and contained acid mucopolysaccharid e. Scanning EM of the surface of the line, exposed by sonication in di stilled water, showed papillary structures, the surface of which appea red granular and exhibited a crystalline appearance. The tips of colla gen fibrils of new bone were attached to the top of the papillae in th e front area of bone formation. It is suggested that the reversal line is involved in the coupling of bone resorption and formation.