1. Department of Stomatology, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, Chengdu, Sichuan 610072, P.R. China
2. School of Medicine, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054, P.R. China
3. West China School and Hospital of Stomatology, Sichuan University, Chengdu, Sichuan�610063, P.R. China
4. Department of Head and Neck Surgery, Sichuan Cancer Hospital, Chengdu, Sichuan 610041, P.R. China