1. Department of Epidemiology, School of Public Health, The Fourth Military Medical University, No. 169, Changle West Road, Xi’an, Shaanxi 710032, China
2. School of Mechanical Engineering, Xi’an University of Science and Technology, No. 58, Yanta Road, Xi’an, Shaanxi 710054, China
3. Clinics of Stomatology, Naval Logistics Branch of Hangzhou Sanatorium, Nanjing Military Area Command, Yuhuangshang Road, No. 76, Hangzhou, China
4. College of Engineering, Design and Physical Sciences, Brunel University, Uxbridge, UK