Ultrastructural cell response to tension stress during mandibular distraction osteogenesis

The response of cells in the distraction gap during mandibular distraction osteogenesis was recorded by transmission electronic microscopy. We distracted the mandible on both sides in eight adult goats. Two animals were killed at 8, 16, 32, and 48 days, respectively, after activation of the device. The specimens were harvested and processed for histological and ultrastructural examination. The results showed that the cells and newly-formed extracellular matrix (ECM) were aligned with the tension vector. In the early stage of distraction osteogenesis, cells in the distraction gap were of the active proliferative phenotype. They then differentiated into fibroblast-like cells and osteoblasts, showing ultrastructural characteristics of the active synthetic and secretory phenotypes. Newly-formed collagen, bone canaliculi, and mineralisation of the ECM were clearly evident during distraction osteogenesis. Our results show that at the ultrastructural level cell proliferation is activated by tension and stress during the early stages, and synthetic and secretory function stimulated during the later stages of mandibular distraction osteogenesis.