The role of the mouth (clinically known as the oral cavity) mainly includes mastication, articulation, swallowing and sensory functions. 1. Chewing is one of the important functions of the mouth, which utilizes the teeth to grind the food adequately and the digestive enzymes in saliva to carry out the initial decomposition of the food in order to utilize the gastrointestinal tract for absorption. Chewing can also promote the replacement of milk teeth and stimulate the normal development of the jawbone. 2. Pronunciation: The oral cavity can use the tongue and teeth to control the pronunciation of language communication, is a unique human communication. 3. Swallowing: The oral cavity utilizes the tongue and other chewing muscles to transport food to the esophagus to complete the swallowing of food. 4. Sensation: The oral cavity is rich in sensory functions, with taste, touch and pain, in order to feel external stimuli and make corresponding stress response.