Teeth consist of enamel, dentin, cementum, and pulp tissue. Enamel 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. Dentin forms the next layer of the tooth. Dentin makes up about 75% 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 together known as the pulp, which extends to the bottom of the root. The pulp is made of blood vessels, which 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. It is very thin, about the thickness of a fingernail. The main purpose of 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.