1.The purpose of this study is to detect the differences of carotid atherosclerosis severity between patients with or without OSAHS(Obstructive Sleep Apnea and Hypopnea Syndrome) in a cross-sectional study in a large sample. 2.Then a longitudinal control study is conducted to observe the progress of the carotid atherosclerosis by vascular ultrasonography and the occurrence of cerebrovascular events after the intervention of the oral appliance for treating OSAHS，and finally explore the feasibility of using oral appliance to treat OSAHS in primary prevention of ischemic stroke.