EFFECTS OF EXPANSIVE FORCE ON THE DIFFERENTIATION OF MIDPALATAL SUTURE CARTILAGE IN RATS

In an attempt to clarify the effects of biomechanical tensional force on chondrogenic and osteogenic differentiation of secondary cartilage, the midpalatal sutures of 4-week-old Wistar male rats were expanded b y orthodontic wires which applied 20 g force for 4, 7, 10, and 14 days , The differentiation pathways in the midpalatal suture cartilage were examined by immunohistochemistry for osteocalcin, type I and type II collagen, and von Kossa histochemistry, Although the midpalatal suture s of the control animals consisted mainly of two separate secondary ca rtilages with mesenchyme-like cells at their midlines, type I collagen -rich fibrous tissue began to appear at day 4 and increased at the mid line of the cartilage with days of experiment, At the end of the exper iment, type I collagen-rich and calcified bone matrix appeared at the boundary between the precartilaginous and the cartilaginous cell layer s, Most of the cartilaginous tissues were separated from each other an d the midpalatal suture was replaced by osteocalcin-positive intramemb ranous bone and fibrous sutural tissue, These results strongly suggest that tensional force changed the phenotypic expression of collagenous components in secondary cartilage, which may reflect the differentiat ion pathway of osteochondro progenitor cells.