Department of Endodontics, Beijing Stomatological Hospital, School of Stomatology, Capital Medical University, Beijing, 100050, China. Affiliated Stomatology Hospital of Guangzhou Medical University, School of Stomatology, Guangzhou Medical University, Guangdong, 510140, China. Department of Endodontics, Beijing Stomatological Hospital, School of Stomatology, Capital Medical University, Beijing, 100050, China. endolihong@qq.com.