Difficulty opening the mouth is a clinical manifestation of temporomandibular joint disorder syndrome also known as TMJ syndrome, which is one of the common disorders of the oral and maxillofacial region. Among temporomandibular joint disorders, this disease is the most common. It is prevalent in young adults, with the highest prevalence between the ages of 20 and 30. The main features of this disease are soreness and pain in the joint area, popping during movement, and mouth opening movement disorder. Most of the joint dysfunction, the prognosis is good; but a very small number of cases can also occur organic changes. Etiology: 1, trauma factors Many patients have a history of local trauma. For example, they have borne external impact, sudden biting hard objects, opening the mouth too wide (such as yawning) and other acute trauma; there are often chewing hard food, grinding teeth at night as well as unilateral chewing habits, etc. These factors may cause joint contusion or injury. These factors may cause joint contusion or strain, masticatory muscle group dysfunction also has a certain impact on the occurrence of this disease. 2, occlusal factors Many patients have obvious occlusal relationship disorders. For example, the cusp is too high, excessive wear of teeth, too many missing molars, bad dentures, intermaxillary distance is too low, and so on. The disorders of occlusal relationship can destroy the balance of function between the internal structure of joints and promote the occurrence of this disease. 3.Systemic and other factors Neuropsychiatric factors may have some relationship with this disease. For example, some patients have emotional impatience, nervousness, easily agitated and so on. In addition, some patients have a history of rheumatism, and some cases are related to cold.