The first thing that comes to mind when you think of your mouth is probably eating - or kissing! But your mouth's a lot more than an input slot for food or a tool for smooching your sweetie. Your mouth and teeth form your smile, which is often the first thing people notice when they look at you. The mouth is also essential for speech: The tongue (which also allows us to taste) enables us to form words with the help of our lips and teeth. The tongue hits the teeth to make certain sounds. The th sound, for example, is produced when the tongue brushes against the upper row of teeth. If a person has a lisp, that means the tongue touches the teeth instead of directly behind them when saying words with the s sound.

Without our teeth, we'd have to live on a liquid diet or a diet of soft, mashed food. The hardest substances in the body, the teeth are necessary for mastication - a fancy way of saying chewing - 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, or break down, food. This makes the mouth one of the first steps in the digestive process. Read on to find out how each aspect of the mouth and teeth plays a role in our daily lives.

Basic Anatomy of the Mouth and Teeth

The mouth is lined with mucous membranes (pronounced: myoo-kus mem-branes). Just as skin lines and protects the outside of the body, mucous membranes line and protect the inside. Mucous membranes make mucus, which keeps them moist. (graphic omitted)

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 from the nose above. The soft palate forms a curtain between the mouth and the throat (or pharynx - pronounced: fa-rinks) to the rear. The soft palate contains the uvula (pronounced: yoo-vyoo-luh), the dangling fleshy object 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 projections called papillae. Our taste buds are located here. The four types of taste buds - sweet, salty, sour, and bitter - are grouped in different parts of the tongue.

Three pairs of salivary glands in the walls and floor of the mouth 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 (pronounced: or-bik-yoo-lar-iss or-iss), allows for the lips' mobility. The reddish tint of the lips comes from underlying blood vessels, which is why the lips can bleed so easily with injury. The inside part of the lips connects to the gums.

There are several types of teeth:

Incisors are the squarish, sharp-edged teeth at the front and middle of the mouth. There are four on the bottom and four on the top. To the sides of the incisors are the long, sharp canines, two on the bottom and two on the top. The upper canines are sometimes called eyeteeth. Behind the canines are the premolars, or bicuspids. There are two sets, or a total of four premolars, in each jaw - one behind each of the canines on the bottom and one behind each canine on the top.

The molars, situated behind the premolars, have points and grooves. There are 12 molars in the adult mouth - two sets each of first, second, and third molars in both the upper and lower jaw. The third molars are called wisdom teeth. Wisdom teeth get their name because, as the last teeth to erupt, they break through when a person is becoming an adult and is supposedly wiser. Wisdom teeth are not essential today, but some people believe they evolved thousands of years ago when human diets consisted of mostly raw foods that required extra chewing power. Because wisdom teeth can crowd out the other teeth, a dentist may need to remove them. This often happens during a person's teenage years.

Each tooth is made of four types of tissue: pulp, dentin, enamel, and cementum. The pulp is the innermost portion of the tooth. Unlike the outer parts of the tooth, the pulp is soft. It is made of connective tissue, nerves, and blood vessels, which nourish the tooth. The pulp has two parts: the pulp chamber, which lies in the crown (or top part of the tooth) and the root canal, which is in the bottom part of the tooth that lies beneath the gums. Blood vessels and nerves enter the root through a small hole at the very bottom of the tooth and extend through the canal into the pulp chamber. Dentin surrounds the pulp. A hard yellow substance that is mostly made up of mineral salts and water, dentin makes up most of the tooth. It is the dentin that gives the tooth its slightly yellowish tint.

Both the dentin and pulp cover the whole tooth from the crown into the root. But the outermost layer covering the tooth is different, depending on whether it sits above the gum or below it. Enamel, the hardest tissue in the body, covers the crown. Under the gum line, a bony layer of cementum covers the outside of the root and holds the tooth in place within the jawbone. Cementum is as hard as bone but not as hard as enamel, which enables the tooth to withstand the pressure of chewing and protects it from harmful bacteria and changes in temperature from hot and cold foods.