The visible portion of the tooth is the crown. The outer surface of the crown is made of enamel. Just beneath the enamel is dentin, a substance harder than bone. The gum surrounds the base (root) of the tooth.
The root of the tooth extends down into the jaw bone and provides circulation and sensation to the tooth. The root contains blood vessels and nerves, which supply circulation and sensation to the entire tooth. This area is known as the "pulp" of the tooth.
The jaw bone is attached to all of the teeth and provides stability and mobility for the mouth and teeth for chewing. The lower jaw bone is called the mandible and the upper jaw bone is called the maxilla.
Lingen MW. Head and neck. In: Kumar V, Abbas AK, Fausto N, eds. . 8th ed. Philadelphia, Pa: Saunders Elsevier; 2009:chap 16.