Xue Feng1, Zhenhua Yang2, Juan Dai2, Rong Li2. 1. Department of Orthodontics, School of Stomatology, Fourth Military Medical University, Xi'an, Shaanxi 710032, China. 1054030184@qq.com. 2. Department of Orthodontics, School of Stomatology, Fourth Military Medical University, Xi'an, Shaanxi 710032, China.