1. Department of Stomatology, Affiliated Longhua People’s Hospital, Southern Medical University, Shenzhen, Guangdong 518109, P. R. China
2. Department of Stomatology, Nanfang Hospital, Southern Medical University Guangzhou, Guangdong 510515, P. R. China
3. The Affiliated Stomatology Hospital, Foshan University, Foshan, Guangdong 528000, P. R. China