The tooth consists of two major parts: the crown and the root. In most cases only the crown of the tooth is visible in the mouth. The root is below the gingiva (gumline) and is anchored to the bone. In some cases, when the person has had gum problems or has brushed very hard, a portion of the root may be visible in the mouth. The root contains a center portion known as the root canal. This area can become involved when someone has a tooth abscess or infection. In this case, the treatment of a root canal abscess is completed (usually by an endodontist) by removing the live canal material and replacing it with a filling material. This saves the tooth from extraction (pulling the tooth).
The teeth are made up of four different types of material: the enamel, dentin, pulp, and cementum. The enamel covers the crown of the tooth and is the hardest substance in the body. The cementum is the substance that covers the root of the tooth. The dentin is underneath the enamel and dentin and is much softer. When a cavity forms in the enamel and continues into the dentin, it progresses very rapidly to the pulp, since the dentin is very soft. The pulp, is in the center of the tooth (root canal), and contains the nerves and blood vessels that supply the tooth with sensations of tooth sensitivity or pain.