1. Clinical Research Center of Shaanxi Province for Dental and Maxillofacial Diseases, College of Stomatology, Xi'an Jiaotong University, Xi'an, China.
2. Department of Orthodontics, Stomatological Hospital, Xi'an Jiaotong University, Xi'an, China.
3. Department of Orthodontics, Xi'an No.1 Hospital, Xi'an, China.