1. Department of Stomatology, Beijing Friendship Hospital, Capital Medical University, Beijing, China
2. Department of Stomatology, Beijing Electric Power Hospital, Beijing, China
3. Xiangya Stomatology Hospital and School of Stomatology, Central South University, Changsha, Hunan, China
4. Capital Medical University School of Stomatology, No. 4 Tian Tan Xi Li, Beijing, China