1. Department of Orthodontics, Peking University School and Hospital of Stomatology, National Center of Stomatology, National Clinical Research Center for Oral Diseases, National Engineering Laboratory for Digital and Material Technology of Stomatology, 22 Zhongguancun South Avenue, Haidian District, Beijing 100081, P. R. China
2. Department of Dental Medical Center, China-Japan Friendship Hospital, Beijing 100029, P. R. China
3. Central Laboratory, Peking University School and Hospital of Stomatology, Beijing 100081, P. R. China