1. College and Hospital of Stomatology, Hebei Medical University, Shijiazhuang, Hebei, China (mainland)
2. Department of Epidemiology and Statistics, School of Public Health, Hebei Medical University; Hebei Province Center for Disease Prevention and Control, Shijiazhuang, Hebei, China (mainland)
3. Department of Stomatology, No. 2 Hospital of Baoding, Baoding, Hebei, China (mainland)