Paravascular cells in endosteal spaces of alveolar bone contribute to periodontal ligament cell populations

Endosteal spaces of alveolar bone communicate with the periodontal ligament and may contribute to its cell populations. We examined cell proliferation and migration in endosteal spaces and in the periodontal ligament contiguous with these spaces. Radioautographs of mouse mandibular molar were prepared from animals pulse-injected with 3H-Tdr and sacrificed in groups of 22 mice each at 1 h, 1, 3, and 7 d after labeling. Cell counts, labeling indices, grain counts, and progenitor cell ratios were determined. The data indicate that endosteal spaces are enriched with 3H-Tdr-labeled progenitor cells whose progeny rapidly migrate out of the compartment. The periodontal ligament contiguous with the endosteal spaces exhibited 5 times as many labeled cells as other sites in this tissue. Thickened areas of cementum were coincident with the openings of endosteal spaces in over 64% of observations. The data are consistent with the hypothesis that cells migrate from endosteal spaces into the periodontal ligament and there express the phenotype for osteoblasts or cementoblasts.