The oral cavity is the initial part of the digestive tract. The anterior fissure communicates with the outside world and then continues to communicate with the pharynx through the pharyngeal isthmus. There are teeth, tongue and other organs in the mouth. The front wall of the oral cavity is the lip, the side wall is the cheek, the top is the palate, and the bottom of the oral cavity is the mucosa and muscles. The oral cavity is divided into an oral vestibule with an anterolateral part and an oral pillar with a posterior medial part by upper and lower dental arches. When the upper and lower teeth bite, the oral vestibule can communicate with the inherent oral cavity through the space behind the third molar. Clinically, when the patient's teeth are clenched, an opener or cannula can be placed through this passage to inject drugs or nutrients, and at the same time, tongue biting can be prevented.