1. Department of Second Dental Center, Peking University School and Hospital of Stomatology, Beijing 100101, P.R. China
2. Department of Third Dental Center, Peking University School and Hospital of Stomatology, Beijing 100083, P.R. China
3. Stomatology Department, Changle People's Hospital, Weifang, Shandong 262400, P.R. China
4. Department of Orthodontics, School and Hospital of Stomatology, Cheeloo College of Medicine, Shandong University and Shandong Key Laboratory of Oral Tissue Regeneration and Shandong Engineering Laboratory for Dental Materials and Oral Tissue Regeneration, Jinan, Shandong 250012, P.R. China