1. Department of Epidemiology; Public Health College; Nantong University; Nantong Jiangsu Province China
2. Department of Endodontics; Institute of Hard Tissue Development and Regeneration; the Second Affiliated Hospital of Harbin Medical University; Harbin China
3. Department of Hygienic Microbiology; Public Health College; Harbin Medical University; Harbin China
4. Department of Statistics; Public Health College Nantong University; Nantong Jiangsu Province China