Mild restriction of mouth opening is clinically known as mild restriction of mouth opening, which means that only two fingers can be placed between the incisal edges of the upper and lower incisors, about 2.0-2.5 cm. Mild restriction of mouth opening is usually caused by pathological factors, such as temporomandibular joint diseases, oral and maxillofacial interstitial infections, oral and maxillofacial injuries, malignant tumors and other diseases. If the symptom appears, you should go to the hospital to clarify the cause and treat it in time. I. Temporomandibular joint disease: Mild mouth opening restriction is mostly seen in temporomandibular joint disorder and temporomandibular joint ankylosis, which is more serious and will affect the patient’s life. 1. Temporomandibular joint disorder: before the onset of the disease, there may be biting of hard objects, joint popping, etc. At the onset of the disease, there may be mild mouth opening restriction, pressure points at the temporomandibular joint and masticatory muscles, and the midline deviates to the affected side when opening and closing the mouth; 2. Temporomandibular joint 2. Temporomandibular joint ankylosis: it can be caused by infection and injury, with mild restriction of mouth opening, as the disease progresses, the degree of restriction of mouth opening can gradually increase, or even completely unable to open the mouth, patients with juvenile onset can also lead to maxillofacial developmental deformities, such as inconsistent facial development of the affected side, or chin recession leading to bird’s mouth deformity. Oral and maxillofacial interstitial infections: such as peri-coronitis of wisdom teeth, peri-maxillary cellulitis, mandibular osteomyelitis, etc. The infection leads to mild mouth opening restriction, accompanied by local redness, swelling, heat and pain, and the degree of mouth opening restriction can be increased when the infection is aggravated, which is a more serious situation. Third, oral and maxillofacial injuries: mostly caused by external impact or trauma and other factors. The fracture of mandible causes spasm of masticatory muscle, or the fracture of zygomatic arch and zygomatic bone is displaced and presses the rostral prominence, which leads to mild restriction of mouth opening, mostly accompanied by pain and swelling at the fracture site; external trauma inside and outside the mouth forms scar contracture after healing, which can also lead to mild restriction of mouth opening and touching the adherent scar strips inside and outside the mouth. It is a more serious phenomenon. Fourth, malignant tumors: such as malignant tumors in the buccal mucosa, posterior molar area, lateral side of the soft palate and posterior maxillary sinus, etc., can affect the masticatory muscles in the late stage, leading to mild mouth opening restriction, which further aggravates with the progress of the disease and is accompanied by pain, bad odor and cachexia. It is also a serious condition.