The inability to open and close the mouth may be caused by developmental deformity of the jaws, joint dislocation, jaw fracture and other reasons. 1. Jaw developmental deformity: there is a kind of maxillofacial deformity called open bite, which is characterized by strong occlusal ability of the back teeth but tilting of the front teeth, i.e., there is a gap between the incisal edges of the upper and lower front teeth. 2. Joint dislocation: It may be an acute anterior dislocation of a joint or a joint injury leading to dislocation in other directions. With the evolution of human beings, the movement of temporomandibular joints has become more flexible, so patients can have anterior dislocation of the joints without any causative factors, presenting with an open mouth that cannot be closed. 3. Jaw fracture: mainly maxillary or mandibular fracture. If the maxilla is fractured, anterior occlusion will occur. If the mandible is partially fractured, occlusal disorders may occur, presenting with an open mouth that cannot be closed. When the patient can’t open and close his mouth, he should go to the hospital in time for examination and relevant treatment under the doctor’s guidance.