Abstract: Objective To observe the effect of modified Twin-Block appliance on the profile and PAR index of children with class Ⅱ division 1 malocclusion. Methods Data of 42 children with skeletal class Ⅱ division 1 malocclusion in the Department of Stomatology of our hospital from December 2016 to May 2019 were retrospectively analyzed. The patients were divided into observation group and control group, with 21 cases in each group. The patients in the observation group were treated with modified Twin-Block appliances during the stage Ⅰ, and the control group was treated with the traditional Twin-Block appliances for six months. During the stage Ⅱ, both groups were treated with the standard edgewise archwire appliances. The X-ray cephalometric measurements were used to analyze the profile of the children. The changes of PAR index before and after treatment were compared between the two groups. Results After 6-month treatment, compared with the control group, the base angle of the lower lip and the angle of buccal and labial groove increased in the observation group, and the distance between the convex point of the lower lip and the H-line decreased (P＜0.05); at the same time, the anterior teeth arrangement, posterior teeth arrangement, buccal occlusion, coverage, overbite (occlusion), midline and par total score significantly decreased in the observation group compared with those of control group (P＜0.01). Conclusion The modified Twin-Block appliance is helpful to improve the profiles and postoperative PAR indices of children with class Ⅱ division 1 malocclusion, and it is worthy of clinical application.

Key words:  modified Twin-Block appliance, skeletal Class Ⅱ division 1 malocclusion, PAR index, treatment outcome evaluation, orthodontics