Abstract: OBJECTIVE: The thesis compare the effects of alternate rapid maxillary expansion and constriction before maxillary traction and direct anterior traction in the early permanent dentition skeletal class Ⅲ. Simultaneously compare the stability of upper anterior teeth.Accordingly explore a more suitable treatment method. METHODS: Twenty patients with Class III malocclusion were selected from the Department of Orthodontics, Stomatology Hospital of Shanxi Medical University. They were randomly divided into an expandsion and contraction group and unexpanded group. The sample in expansion and contraction group was repeatedly expanded for 8 weeks. 8 weeks later,the anterior traction was started at the same time as the unexpanded group, the cephalometric measurement indicators before and after treatment were analyzed and compared after 3 months. RESULTS: The values of SNA, ANB, U1-SN, MP-SN and UL-EP increased after treatment in the expansion group (P<0.05). SNA, ANB, U1 after treatment in the non-expanded group The values of -SN, MP-SN and UL-EP were all increased, and the differences were statistically significant (P<0.05). The changes of SNA, ANB, U1-SN, MP-SN and UL-EP before and after treatment in the two groups. The difference was statistically significant (P<0.05). The degree of change in the expansion and contraction group was higher than that in the non-expanded group. The correlation between the anterior teeth and the lingual direction of the expansion and contraction group was only related to the degree of ANB change before and after treatment. Statistically significant, the two are positively correlated. Conclusion: Repeated expansion and contraction of the skeletal class III malocclusion before volition in the dentition period has a better clinical effect than direct anterior traction, but it will cause a certain degree of loosening of the upper anterior teeth.

Key words: anterior traction, exparison and contraction before maxillary traction, the stability of upper anterior teeth