The crown is the part of the tooth that is visible above the gumline. It is covered by a hard shell of enamel known as the anatomical crown. The enamel is hard enough to endure the strain of a lifetime of biting, chewing and grinding. It also protects the tooth from bacteria and changes in temperature when eating hot or cold foods. Nonetheless, it is brittle and may crack or chip. The enamel is translucent, and most of the color of the tooth actually is produced by the dentin below the enamel.

As people age, their gums often start to recede, which makes the crown appear larger as more of the root becomes exposed. Conversely, the crown may appear smaller as the enamel gradually wears away over time. The area of the tooth where the crown meets the root is called the neck (cemento-enamel junction).

The root is the part of the tooth that pushes into the upper (maxilla) or lower (mandible) jawbone, and the structure of the root differs from tooth to tooth. For example, canines and incisors have a single root, while molars may have up to four roots depending on the location in the mouth. Each root has a tiny opening at the bottom called the apical foramen. Blood vessels and nerves enter the root through this space.

A substance called cementum covers the tooth root and attaches to fibers that fasten the root to the jawbone. Similar to enamel, it is a hard protective layer of the tooth.

Just beneath the enamel (covering the crown) and the cementum (covering the root) is the dentin. This substance resembles bone and makes up most of a tooth’s structure and is responsible for the tooth’s color. It typically has a whitish to yellowish hue. As people grow older, the dentin usually darkens or discolors. Exposure to too much fluoride or to certain antibiotics (e.g., tetracycline) during pregnancy also can cause discoloration of teeth in children.