Mouth

Mouth entrance to the digestive and respiratory tracts. The mouth, or oral cavity, is ordinarily a simple opening in lower animals; in vertebrates it is a more complex structure. In humans, the mouth is defined in front and at the sides by the lips, jawbone, teeth, and gums; in the rear it merges with the throat. The roof of the mouth is composed of the hard and soft palates and the floor of the mouth is formed by the tongue, a muscular structure that contains the organs of taste (taste buds).

Stomatitis

Stomatitis is an inflammation of the mucous lining of any of the structures in the mouth, which may involve the cheeks, gums, tongue, lips, throat, and roof or floor of the mouth.
The inflammation can be caused by conditions in the mouth itself, such as poor oral hygiene, dietary protein deficiency, poorly fitted dentures, or from mouth burns from hot food or drinks, toxic plants, or by conditions that affect the entire body, such as medications, allergic reactions, radiation therapy, or infections.