Dept. of Conservative Dentistry and Endodontics, Guanghua School of Stomatology, Hospital of Stomatology, Sun Yat-sen University; Guangdong Provincial Key Laboratory of Stomatology, Guangzhou 510055, China. Faculty of Dentistry, the University of Hong Kong, Hong Kong. Dept. of Conservative Dentistry and Endodontics, Guanghua School of Stomatology, Hospital of Stomatology, Sun Yat-sen University; Guangdong Provincial Key Laboratory of Stomatology, Guangzhou 510055, China. Electronic address: maisui@mail.sysu.edu.cn.