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Mouth and Teeth

Your smile, formed by your mouth at your brain's command, is often the first thing people notice when they look at you. It's the facial expression that most engages others. With the help of the teeth - which provide structural support for the face muscles - your mouth also forms your frown and lots of other expressions that show on your face.

The mouth also plays a key role in the speech. The tongue, which allows us to taste, also enables us to 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 th sound, for example, is produced by the tongue being placed against the upper row of teeth. If your tongue touches your teeth when you say words with the s sound, you may have a lisp.

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, or break down, food. Without our teeth we'd have to eat nothing but soft, mashed food. Eating would not be quite as enjoyable!

Read on to find out 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 kinds of taste buds are grouped together on certain areas of 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, sometimes a dentist will need to remove them.

Human teeth are made up of four different types of tissue: pulp, dentin, enamel, and cementum. The pulp is the innermost portion of the tooth and consists of connective tissue, nerves, and blood vessels, which nourish the tooth. The pulp has two parts - the pulp chamber, which lies in the crown, and the root canal, which is in the root of the tooth. Blood vessels and nerves enter the root through a small hole in its tip and extend through the canal into the pulp chamber.

Dentin surrounds the pulp. A hard yellow substance consisting mostly of mineral salts and water, it makes up most of the tooth and is as hard as bone. It's the dentin that gives teeth their yellowish tint. Enamel, the hardest tissue in the body, covers the dentin and forms the outermost layer of the crown. It enables the tooth to withstand the pressure of chewing and protects it from harmful bacteria and changes in temperature from hot and cold foods. Both the dentin and pulp extend into the root. A bony layer of cementum covers the outside of the root, under the gum line, and holds the tooth in place within the jawbone. Cementum is also as hard as bone.

Normal Development of the Mouth and Teeth

Humans are diphyodont, meaning that they develop two sets of teeth. The first set of 20 deciduous teeth are also called the milk, primary, temporary, falling-off, or baby teeth. They begin to develop before birth and begin to fall out when a child is around 6 years old. They're replaced by a set of 32 permanent teeth, which are also called secondary or adult teeth.

Around the 8th week after conception, oval-shaped tooth buds consisting of cells form in the embryo. These buds begin to harden about the 16th week. Although teeth aren't visible at birth, both the primary and permanent teeth are forming below the gums. The crown, or the hard enamel-covered part that's visible in the mouth, develops first. When the crown is fully grown, the root begins to develop.

Between the ages of 6 months and 1 year, the deciduous teeth begin to push through the gums. This process is called eruption or maintaining healthy teeth and avoiding tooth decay and gum disease. Some common mouth and dental diseases and conditions - some of which can be prevented, some of which cannot - are listed below.

Disorders of the Mouth:

• Aphthous stomatitis (canker sores). A common form of mouth ulcer, canker sores occur in women more often than in men. Although their cause isn't completely understood, mouth injuries, stress, dietary deficiencies, hormonal changes (such as the menstrual cycle), or food allergies can trigger them. They usually appear on the inner surface of the cheeks, lips, tongue, soft palate, or the base of the gums, and begin with a tingling or burning sensation followed by a painful sore called an ulcer. Pain subsides in 7 to 10 days, with complete healing in 1 to 3 weeks.
• coxsackie virus, which causes hand, foot, and mouth disease. Enteroviral stomatitis is marked by small, painful ulcers in the mouth that may decrease a child's desire to eat and drink and put him or her at risk for dehydration.
• Herpetic stomatitis (oral herpes). Children can get a mouth infection with the
• Impacted wisdom teeth. In many people, the wisdom teeth are unable to erupt normally so they either remain below the jawline or don't grow in properly. Dentists call these teeth impacted. Wisdom teeth usually become impacted because the jaw isn't large enough to accommodate all the teeth that are growing in and the mouth becomes overcrowded. Impacted teeth can damage other teeth or become painful and infected. Dentists can check if a person has impacted wisdom teeth by taking X-rays of the teeth. If, after looking at the X-rays, a dentist thinks there's a chance that impacted teeth may cause problems, he or she will usually recommend that the tooth or teeth be removed (extracted).
• Malocclusion is the failure of the teeth in the upper and lower jaws to meet properly. Types of malocclusion include overbite, underbite, and crowding. Most conditions can be corrected with braces, which are metal or clear ceramic brackets bonded to the front of each tooth. The wires connecting braces are tightened periodically to force the teeth to move into the correct position.