Objective To investigate the prevalence and characteristics of tooth agenesis among orthodontic patients treated in Xining First People's Hospital of Qinghai Province. Methods A total of 2 911 patients treated during 2007 to2012 were selected,and divided into 3 groups: 1 missing-tooth group,2 missing-teeth group and up to 2 missing-teeth group. Relevant data were collected and analyzed. Results The prevalence of congenital tooth agenesis was 7. 7%,and tooth agenesis was more prevalent in females than in mal...