The role of biomechanical stress on the cell proliferarion and differentiation in condylar cartilage

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In order to study the role of biomechanical force on craniofacial bone growth, we have developed a new experimental model in which we transplanted the vascularized hemi-mandible of a young rat to the neck of another, age-matched, inbred rat using microvascular anastomosis (heterotopic hemi-mandible transplantation model).1) We measured the vascular flow of the graft by using radioactive microshere method and laser Doppler flowmetry. The result showed that there was no significant difference in vascular flow between grafts and controls (hemi-mandible of recipient rats).2) We performed transplantation using 6-week-old rats, and investigated the proliferation and differentiation of the condylar cartilage cells in the graft. The condyle of the grafted hem-mandible were taken 2, 4, 7 and 14days after transplantation. They were fixed, decalcified and embedded in paraffin. Sections 5μ m thick were then cut and the distribution of type I and type II collagen was studied by using goat anti-type I /type II collagen. Type I collagen was present adjacent to the proliferative cell layer, where type II collagen is present in normal condition.3) To confirm above mentioned results, we performed a supplementary study using a rat heterotopic head transplantation model. We transplanted the whole head of 3-week-old rats to the body of 8-week-old rats using microvascular anastomosis. The condyle of the grafts was taken 2, 4 and 7 days after transplantation. They were processed in the same manner as hemi-mandible transplantation model and the distribution of type I and type II collagen was studied. The results were same as those in hemi-mandible transplantation model.These results domonstrated that mechanical force play an important role in the proliferation and differentiation of condylar cartilage cell.