All About Teeth

The types of teeth are:

• 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 — two behind each of the canines on the bottom and two behind each canine on the top.
• The molars, situated behind the premolars, have points and grooves. There are 12 molars in the adult mouth — three sets in each jaw called first, second, and third molars. 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 or cause problems like pain and infection, 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, 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.

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