Difficulty in opening the mouth is a common symptom seen in oral surgery outpatients, and in severe cases it is also known as dental closure. The coordinated contraction and relaxation of the oral and maxillofacial lifting muscles ensure the normal movement of the jaw bone, which enables the smooth completion of mouth opening, mouth closing, chewing, swallowing and speech, etc. The normal degree of mouth opening is the width that one can put one’s three fingers together into the mouth, and if one can only put one’s two fingers together, one can say that the mouth opening is restricted. So, which diseases can cause difficulty in opening the mouth? 1, inflammatory infection: the most common mandibular wisdom teeth pericoronitis, acute periapical infection of the mandibular molars caused by the spread of deep gap infection of the jaws and face, stimulating the chewing muscle groups, causing spasm and difficulty in opening the mouth. This situation is possible through anti-infection treatment, incision and drainage of pus, removal of lesions, mouth opening restriction is possible links. 2, jaw fracture: common in traumatic jaw fracture, such as zygomatic arch zygomatic fracture, mandibular condyle fracture can cause mouth opening difficulties, fracture after the jaw movement is limited, muscle contusion, swelling pain, mouth opening will also be affected. After the fracture is repositioned and treated, the restricted mouth opening can be cured. 3.Tumor: Oral and maxillofacial tumor invasion destroys the normal structure of the mandibular joint and hinders the normal movement of the joint or causes spasm of the chewing muscles, which will also cause difficulty in opening the mouth. For example, tumor of inferior temporal recess, tumor of pterygopalatine recess, malignant tumor of maxillary sinus invading the posterior wall, nasopharyngeal carcinoma, etc. can cause difficulty in opening the mouth due to tumor invading the pterygoid and temporal muscle groups. 4.Temporomandibular joint dysfunction syndrome: It mainly refers to a group of diseases caused by the imbalance and dysfunction of the masticatory muscle groups, resulting in difficulty in opening the mouth. Temporomandibular joint disorder, before the onset of the disease, there are mostly mental factors such as tension, insomnia, unilateral chewing habits, joint overload, abnormal occlusal relationship, injury and other precipitating factors, showing restricted mouth opening, abnormal opening type, pain in the joint and surrounding muscles during opening and chewing, joint popping and murmurs can occur, and some patients can be accompanied by migraine. 5, temporomandibular joint ankylosis: generally due to septicemia in the joint area or hematoma in the joint cavity after trauma, mechanization gradually forms joint fusion, a few can be caused by rheumatoid arthritis, patients can barely open their mouths, acquired joint injury, infection leads to joint concavity, joint disc and condylar breakthrough bad, and the formation of fibrous or bony adhesions, so that the function of the mandibular joint is completely lost. Intra-articular ankylosis occurs mostly in children under 15 years of age, septic otitis media secondary to infection is most common, and can also be caused by hematogenous infection or trauma; extra-articular ankylosis is mostly caused by noma, local scar contracture after trauma or radiotherapy. 6, hysterical dentition: young female patients are common, with a previous history of hysteria, unique personality characteristics, psychiatric factors before the onset, often sudden difficulty in opening or dentition, suggesting that treatment can mostly be alleviated. 7, tetanus: tetanus dental closure more than a history of trauma, unique bitter smile face, corneal arch symptoms, in accordance with the principles of tetanus treatment. 8, the newborn mouth opening difficulties: in addition to tetanus should be considered by the use of high birth forceps damage to the jaw joint caused by obstructed labor. 9, temporomandibular joint disk prolapse: acute temporomandibular joint dislocation or late temporomandibular joint disease makes the joint disk prolapse resulting in difficulty in opening the mouth. 10, scars: radioactive scars, post-burn scars, trauma, inflammation and other causes of maxillofacial scar contracture can cause difficulty in opening the mouth. 11, scleroderma: scleroderma causes difficulty in opening the mouth, the facial skin is hard and leathery thinning, accompanied by general fever and joint pain. 12, congenital cervical ectopia: congenital cervical ectopia can also lead to difficulty in opening the mouth, the patient has abnormal sensation, retroauricular area and neck involvement pain, X-ray can be taken to make a clear diagnosis. 13, eosinophilic fasciitis: eosinophilic fasciitis is a connective tissue disease, which also leads to difficulty in opening the mouth, generalized muscle weakness, muscle pain, contracture, sclerosis, increased peripheral blood count, accelerated blood sedimentation, and increased immunoglobulin. 14, masticatory muscle ossification myositis: trauma or unknown causes of masticatory muscle hardening and thickening, line film shows masticatory muscle calcification and joint area periosteal hyperplasia.