Mouth and Teeth

A smile is the facial expression that most engages others. With the help of the teeth — which provide structural support for the face muscles — the mouth also forms a frown and other expressions that show on your face.

The mouth also plays a key role in the digestive system, but it does much more than get digestion started. The mouth — especially the teeth, lips, and tongue — is essential for speech. The tongue, which allows us to taste, also helps form words when we speak. The lips that line the outside of the mouth both help hold food in while we chew and pronounce words when we talk.

With the lips and tongue, teeth help form words by controlling air flow out of the mouth. The tongue strikes the teeth as certain sounds are made.

The hardest substances in the body, the teeth are also necessary for chewing (or mastication) — the process by which we tear, cut, and grind food in preparation for swallowing. Chewing allows enzymes and lubricants released in the mouth to further digest food.

Here's how each aspect of the mouth and teeth plays an important role in our daily lives.

Basic Anatomy of the Mouth and Teeth

The entrance to the digestive tract, the mouth is lined with mucous membranes. The membrane-covered roof of the mouth is called the palate. The front part consists of a bony portion called the hard palate, with a fleshy rear part called the soft palate. The hard palate divides the mouth and the nasal passages above. The soft palate forms a curtain between the mouth and the throat, or pharynx, to the rear. The soft palate contains the uvula, the dangling flesh at the back of the mouth. The tonsils are located on either side of the uvula and look like twin pillars holding up the opening to the pharynx.

A bundle of muscles extends from the floor of the mouth to form the tongue. The upper surface of the tongue is covered with tiny bumps called papillae. These contain tiny pores that are our taste buds. Four main kinds of taste buds are found on the tongue — those that sense sweet, salty, sour, and bitter tastes. Three pairs of salivary glands secrete saliva, which contains a digestive enzyme called amylase that starts the breakdown of carbohydrates even before food enters the stomach.

The lips are covered with skin on the outside and with slippery mucous membranes on the inside of the mouth. The major lip muscle, called the orbicularis oris, allows for the lips' mobility. The reddish tint of the lips comes from underlying blood vessels. The inside portion of both lips is connected to the gums.

There are several types of teeth. Incisors are the squarish, sharp-edged teeth in the front of the mouth. There are four on the bottom and four on the top. On either side of the incisors are the sharp canines. The upper canines are sometimes called eyeteeth. Behind the canines are the premolars, or bicuspids. There are two sets, or four premolars, in each jaw.

The molars, situated behind the premolars, have points and grooves. There are 12 molars — three sets in each jaw called the first, second, and third molars. The third molars are the wisdom teeth, thought by some to have evolved thousands of years ago when human diets consisted of mostly raw foods that required extra chewing power. But because they can crowd out the other teeth or cause problems like pain or infection, a dentist might need to remove them.