1. Department of Stomatology; General Hospital, Tianjin Medical University; Tianjin 300052 People's Republic of China
2. School of Dentistry; Hospital of Stomatology, Tianjin Medical University; Tianjin 300070 People's Republic of China
3. Center of Stomatology, China-Japan Friendship Hospital; Beijing 100029 People's Republic of China
4. Academic Committe, Bybo Dental Group; Beijing 100062 People's Republic of China