Considering the temporomandibular joint disorder and oral mucous membrane fibrosis, the inability to open the mouth after eating betel nut. 1. Temporomandibular joint disorder: betel nut has more crude fiber, long-term chewing betel nut can appear biting muscle fatigue, excessive wear and tear of teeth, temporomandibular joint disorder, resulting in the displacement of the joint discs and the symptoms of opening the mouth. It can be accompanied by joint pain and other symptoms. 2. Oral mucosal fibrosis: long-term betel nut chewing can make the oral mucosal epithelium atrophy, mucosal sclerosis in the form of cords, oral mucosal fibrosis, limited mouth opening or mucosal ulceration and pain and other symptoms, severe cases of teeth closed, open mouth symptoms. Chewing betel nut can also induce oral cancer, betel nut is recognized as one of the carcinogens in the world, it is recommended to change the habit of chewing betel nut.