Normal mouth opening: when opening the mouth, the above three fingers can be placed vertically between the incisal edge of the upper and lower incisors (equivalent to about 4-4.5cm): When opening the mouth, only the index finger can be placed vertically (equivalent to about 1.7cm); 3, mouth opening difficulties Ⅲ degree: when opening the mouth, the distance between the upper and lower incisors is less than the horizontal diameter of the index finger; 4, the teeth are closed: completely unable to open the mouth. So why people have problems with the degree of mouth opening, clinical superficial analysis is as follows: 1, dental inflammation: wisdom teeth pericoronal inflammation and swelling, which can spread to the edge of the occlusal and pterygoid muscles, which leads to tension spasm of this muscle appears mouth opening difficulties; 2, gap infection: periapical infection of molar teeth further leads to gap infection, such as occlusal gap, pterygoid gap, temporomandibular gap, etc., which can lead to the adjacent muscles are inflammatory invasion occurs 3. Malignant tumors: Malignant tumors located in the medial and lateral occlusal muscles and deep facial areas will cause difficulty in opening the mouth as long as they invade the occlusal muscles, and malignant tumors located in the infratemporal and temporal gaps will invade the temporal muscles, the internal pterygoid muscles and the external pterygoid muscles, all of which can cause difficulty in opening the mouth; 4. (2) Intermaxillary contracture: The inelastic scar tissue formed after the ulceration of the intermaxillary soft tissues mainly restricts the movement of the TMJ; (3) Displacement of the joint disc: The displacement of the joint disc will prevent the sliding of the condyle and thus intermittent difficulty in opening the mouth. 5. Trauma: (1) fracture of zygomatic arch of zygomatic bone, especially the fractured piece or displaced end may compress and irritate the temporal muscle, resulting in difficulty in opening the mouth; (2) fracture of the condyle of the temporomandibular joint, resulting in the inability of the articular process to move, resulting in difficulty in opening the mouth; (3) rupture of the articular disc and tear of the articular ligament may result in difficulty in opening the mouth. 6, tetanus: after being stabbed by contaminated rusty nails, especially into the deep tissue is very easy to lead to tetanus bacillus infection, the disease has an incubation period of about 20 days, the earliest symptoms may be difficult to open the mouth, should be noted; 7, oral mucosa fibrous lesions: long-term chewing betel nut or excessive consumption of spicy food will stimulate the oral mucosa fibrous changes, oral mucosa loss of stretch and elasticity resulting in mouth opening Difficulty in opening the mouth.