The expression of TGFβ1 mRNA in the early stage of the midpalatal suture cartilage expansion

INTRODUCTION: The application of an orthodontic expansion force induces bone formation at the midpalatal suture because of cell proliferation and differentiation. Expansion forces may stimulate the production of osteoinductive cytokines, such as transforming growth factor β1 (TGFβ1), in the progenitor cells. OBJECTIVES: This study determined the role of TGFβ1 in the early stage of midpalatal suture cartilage expansion. METHODS: A rectangular orthodontic appliance was placed between the right and left upper molars of 4-week-old rats. The initial expansion force was 50 g. Animals in the control and experimental groups were sacrified on days 0, 2, and 5 and 6 µmm thick sections were prepared for an in situ hybridization technique. RESULTS: Two days after the application of force, prechondroblastic and undifferentiated mesenchymal cells distributed along the inner side of the cartilaginous tissue had high levels of TGFβ1 transcription. On day 5, the TGFβ1 transcription was found in osteocytes and osteoblastic cells on the surface of newly formed bone. Immunohistochemistry using Osteocalcin-Pro (OC-Pro) confirmed osteoblastic activity. Conclusions: Results suggest that the expansion of midpalatal suture cartilage induces differentiation of osteochondroprogenitor cells into osteoblasts after stimulation by cytokine productio