Objective To evaluate the optimal time for fixed appliance treatment and the relation between orthodontic treatment and growth of Angle class Ⅱ division 1 malocclusion during growth periods. Methods 60 patients with Angle class Ⅱ division 1 malocclusion were selected according to the cervical vertebral maturation （CVM） method for the assessment of mandibular growth made by Baccetti, including non-extraction group and control group in the growth peak, and non-extraction group and control group after growth peak. The number of
male and female in each group was the same. All the lateral cephalometric photos before and after treatment were analyzed. Results Soft and hard tissues had been changed after treatment. The bone effect of non -extraction
group in the growth peak after treatment was better than the non-extraction group after the growth peak（P＜0.05）, but no statistically significant difference was found in most parts of teeth and soft tissues between the two groups （P＞0.05）. Conclusion The development of maxilla is restrained and the growth of mandible and chin is stimulated after non-extraction treatment of Angle class Ⅱ division 1 malocclusion during growth period. In order to get a better bone effect, treatment should be given as early as possible in the growth peak.
