Abstract: PURPOSE: To investigate the effect of early treatment of Class II division 1 malocclusion with T4K appliance on soft and hard tissue changes and prognosis of patients with mixed teeth. METHODS: Twenty patients with Class II malocclusion, 11 males and 9 females, aged from 9 to 14 years, with an average age of 11.05 years, were selected. All patients were treated with T4K appliance for 12 months. The changes of soft and hard tissues before, 12 months after and 36 months after orthodontic treatment were measured and compared, to explore the stability of T4K appliance in the treatment of Class Ⅱ division 1 malocclusion. The data were analyzed with SPSS 25.0 software package. RESULTS: The hard tissue indexes U1-NA, U1-NA, L1-NB, L1-NB were significantly decreased (P<0.05) and U1-L1 was significantly increased (P<0.05). Soft tissue index UL-U1, LL-L1 increased significantly (P<0.05);overjet, overbite, E-upper-lip, E-lower-lip decreased significantly (P<0.05); nasolabial angle, sulcus dip, soft tissue thickness significantly increased (P<0.05). There was no significant difference between 12 months and 36 months after treatment (P>0.0.5). CONCLUSIONS: T4K appliance used for early treatment of Class Ⅱ malocclusion can correct patients' poor oral habits, improve the relationship between oral and maxillofacial soft and hard tissues, with good long-term efficacy and stable curative effect.

Key words: T4K appliance, Angle II Malocclusion, Soft and hard tissue changes