Abstract: Objective To analyze the effect of correcting mouth breathing and the variation of facial hard and soft tissue of class II malocclusion with mouth breathing by Twin-block in the growth peak.Methods 30 cases in growth peak with class II malocclusion and mouth breathing were selected.They were treated with Twin-block appliance, the treatment lasted for 12 months.The correction rate of mouth breathing was counted at 3, 6, 9 and 12 months after treatment respectively,the re-examination was conducted 6 months after treatment.Lateral cranial radiographs or models were measured before treatment, after treatment and 6 months after treatment.The results were analyzed with SPSS 26.0.Results The effective correction rate of mouth breathing increased with time, SNB, NP-FH, L1-MP increased, ANB, Y axis, U1-SN decreased, B'Li-FH, LiB'Pg', NsPg'-FH, GSnPg' increased, NsLs-FH, NsLi-FH decreased, these differences were statistically significant(P<0.05).After treatment for 6 months, the anterior overbite overjet remained stable.Conclusion The mouth breathing were corrected effectively, the growth of the mandible was stimulated, and the soft tissue profile was improved in growth peak by Twin-block appliance.

Key words: Twin-block, mouth breathing, class Ⅱ malocclusion, growth peak