1. Department of Orthodontics II, The Affiliated Hospital of Qingdao University, Qingdao, Shandong 266000, P.R. China
2. Department of Nursing and Hospital Infection Management, The Affiliated Hospital of Qingdao University, Qingdao, Shandong 266000, P.R. China
3. Department of Orthodontics, Xiaoshan Branch of Hangzhou Stomatology Hospital, Hangzhou, Zhejiang 310000, P.R. China
4. School of Stomatology of Qingdao University, Qingdao, Shandong 266000, P.R. China