Objective To study parathyroid hormone-related protein（PTHrP） expression during forward mandibular positioning and compare it with the expression during natural growth in different seasons. Methods Sixty-four SD rats were randomly divided into experimental and control groups. Each group were randomly divided into four groups according to seasons. Immunohistochemical（IHC） methods were used to test the protein expression of PTHrP. Macro- scopic and microscopic approach were applied to analyze the results. Results PTHrP expressed in mandibular condylar cartilage（MCC）, the expression was accelerated and enhanced when the mandible was positioned forward. Furthermore, there was a seasonal rhythm in the protein expression of PTHrP in both experimental and control groups. The protein expression in spring group rose more than other groups. Conclusion The functional appliance therapy can enhance the protein expression of PTHrP. The enhancement has a seasonal rhythm, which indicates that for the functional treatment better results can be achieved in spring.
