The tooth is made up of four different tissues. The enamel is the strong white covering that protects the tooth from wear and tear of chewing food. Dentin supports the enamel. It is a hard, yellow material that carries the nerves in your teeth. The pulp is the center of the tooth. It contains nerves, blood and lymph vessels. This part is where the tooth receives nourishment and transmits signals to the brain. The fourth part is called the cementum. This covers the root of the tooth. It attaches the teeth to the bones in your jaw.The key reason teeth turn the yellowish tint is that when people eat, drink, or smoke, a layer of film develops on the tooth