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