Early bone healing events in the human extraction socket.

The tooth extraction socket is unique in terms of a bone-healing defect in that it contains the remnants of periodontal ligament fibroblasts attached to the socket wall. Although these cells have an osteogenic potential in vitro, the origin of cells populating the human extraction socket is unknown and may include bone marrow, periosteum and pericytic cells. Recently, monoclonal antibodies (AML-3, SB-10 and SB-20) have become available which can identify cells undergoing osteogenic differentiation. The aim of this work was to investigate the pattern of osteoblast differentiation in the human extraction socket using these markers. Immunolocalization was used to identify the osteoprogenitor cell population in the extraction sockets of three patients. Runx2 was most strongly expressed by the osteoblasts at the socket margin and in the surrounding marrow spaces. Osteoprogenitor, pre-osteoblast and osteoblast cells surrounded the newly formed trabeculae, and expressed on their cell surface antigens which reacted with the SB-10 and SB-20 antibodies. In a specimen with the tooth and periodontium present, both osteo-blasts and periodontal ligament fibroblasts were immunoreactive with SB-10, and SB-20 and also expressed Runx2. There was heterogeneity of expression of these osteogenic markers e.g. not all osteoblasts expressed Runx2. We have shown that osteoprogenitor cells in the residual periodontal ligament and bone marrow may contribute to bone regeneration following tooth extraction.