Objective To investigate the changes in expression of gelatinase（MMP- 2, MMP- 9） in young rat condylar cartilage during functional mandibular advancement. Methods Sixty male 5- week old SD rats were divided into experimental and control groups. The mimic functional appliances were used in experimental group rats. The animals were sacrificed after 1, 2, 4 weeks. The immunoreactivity of gelatinase was detected by immunohistochemistry. Results In normal mandibular condylar cartilage, the immunoreactivity of MMP- 2 was rather strong, the immunoreactivity of MMP- 9 was very weak. Following functional mandibular advancement, the expression of MMP- 9 was significantly increased（P
