What is Difficulty Opening the Mouth? The normal degree of mouth opening is equivalent to the width of the index, middle and ring fingers when they are brought together. Clinically, there are many diseases that can cause mouth opening restriction, it is generally believed that if the patient opens his mouth to accommodate only two fingers, it is known as mild mouth opening restriction; if the degree of mouth opening can only accommodate one finger, it is known as moderate mouth opening restriction; if even one finger can not be accommodated after opening the mouth, it is known as dental clenching. Then how to conduct a comprehensive examination of the difficulty in opening the mouth? Auxiliary diagnosis commonly used methods are: 1, X-ray flat film (joint Xue’s position and condylar trans-pharyngeal lateral position), can be found to have joint space changes and bone changes, such as sclerosis, bone destruction and hyperplasia, cystic degeneration, etc.. 2, arthrography (upper cavity imaging is often used because of easy operation, and lower cavity imaging is less used in China), which can find the displacement of the articular disk, perforation, changes in the attachments of the articular disk and changes in the cartilage surface. In recent years, many scholars have applied arthroscopy to detect early changes of the disease, such as congestion, oozing blood, adhesion of the articular disc and synovial membrane, and the formation of “joint rats” by undifferentiated and mature cartilage-like tissues. Since there are many types of the disease, treatment varies. Therefore, a type-specific diagnosis should be made. For example, extrapterygoid muscle spasm, reversible articular disk displacement or articular disk penetration. Clinical manifestations and diagnosis of difficulty in opening the mouth: 1, if the patient opens the mouth to accommodate only two fingers, known as mild restriction of opening the mouth; 2, if the degree of opening the mouth to accommodate only one finger, known as moderate restriction of opening the mouth; 3, if the mouth is opened and even a finger can not be accommodated is known as clenching of the teeth.