The mouth, where food is broken down for swallowing, farms the first part of the digestive tract (see Mastication); it converts vibrations produced by the larynx (voice box) into speech; and it is used in breathing.
The roof of the mouth consists of a hard bony pa late at the front and a soft fleshy palate behind. Most of the floor of the mouth is formed by the tongue, which contains specialized cells, sensitive to taste, known as taste buds. Surrounding the palate and tongue are the teeth, wh1ch are set in the shock-absorbent tissue of the gums. Enclosing them all are the cheeks and lips, which contain a ring of muscle that helps keep food in the mouth. The inside of the mouth is lined with mucous membrane, which is lubricated with saliva produced by three pairs of salivary glands.
The most common deformities of the mouth, other than alignment of the teeth (see Malocclusion), are cleft lip and pa late (a split in the upper lip and a gap in the roof of the mouth). They may occur alone or together. Infections of the mouth are common. They include an abscess around the root of a tooth (see Abscess, dental) and oral candidiasis (thrush), a fungal infection that produces sore, creamcolored patches on the lining of the mouth. Noninfective conditions that also cause discoloration include leukoplakia (marked by thickened white or gray patches) and the more rare lichen planus (in which a white network of raised tissue develops). Extremely common are mouth ulcers, painful white or yellow open sores that may develop anywhere on the mucous membrane. Cysts, fluid- or semisolid-filled swellings, may also occur on the lining of the cheek or the floor of the mouth. Any lump, sore, or ulcer in the mouth that persists for more than three or four weeks should be seen by a physician. In rare cases, the abnormality is an early sign of a malignant growth (see Mouth cancer).