| |  | | | | People have two sets of teeth, the baby (also called primary teeth) and permanent teeth. Baby teeth can begin erupting at six months of age, and will continue until about 33 months. Baby teeth can begin shedding from six years of age. Children have 20 primary teeth, and will develop 32 permanent teeth by age 13.
Teeth consist of enamel, dentin, cementum, and pulp tissue. Enamel is calcified tissue that is the hardest substance in the body. It covers the outer layer of the tooth in a protective shell. It contains no nerve endings and is not sensitive to a dentist's drill. (Tooth anatomy image)
Dentin, the next layer of the tooth, makes up about 75 percent of a normal adult tooth. It has about the same density as bone, but contains special cells, called odontoblasts, that are sensitive to temperature and touch. These threadlike cells extend throughout the dentin in the tooth. Their job is to regenerate new dentin from the nutrients delivered by the blood cells. When the dentin is damaged (when it loses a portion of the protective enamel, for example) the odontoblasts relay responses to the nerves, which usually register feelings from mild discomfort to severe pain.
The center of the tooth and its soft tissues are known as the pulp, which extends to the bottom of the root. Pulp is comprised of blood vessels that carry oxygen and nutrients back and forth from the heart. These help keep the tooth in top working condition and protect it from infection. Extremely sensitive nerves also line the inside of the tooth. These nerves respond to multiple stimuli such as heat, cold and pressure.
Cementum covers the entire surface of the root, and is very thin, about the thickness of a fingernail. The main purpose of the cementum is to connect the tooth's root to the bone of the jaw. By forming a bond, it acts like a shock absorber for the tooth.
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