1. Faculty of Public Health; Medicine College of Xi'an Jiaotong University; Key Laboratory of Environment and Genes Related to Diseases; Ministry of Education; Key Laboratory of Trace Elements and Endemic Diseases; Ministry of Health; Xi'an; Shaanxi 710061; China
2. Department of Orthopedics Surgery; The Second Affiliated Hospital; Medicine College of Xi'an Jiaotong University; Xi'an; Shaanxi 710004; China
3. Department of Orthodontics; Stomatological Affiliated Hospital; Medicine College of Xi'an Jiaotong University; Xi'an; Shaanxi 710004; China