1. Department of Pathogenic Biology, School of Basic Medicine, Qingdao University, Qingdao, Shandong, P. R. China
2. Department of Special Medicine, School of Basic Medicine, Qingdao University, Qingdao, Shandong, P. R. China
3. School of Public Health, Qingdao University, Qingdao, Shandong, P. R. China
4. Oral Research Center, Qingdao Municipal Hospital, Qingdao, Shandong, P. R. China