1. The enamel: makes up the protective outer surface of the crown of the tooth.
2. Dentin: Makes up the majority of the inner surface of the tooth. It cannot normally be seen except on X-rays.
3. Pulp: This is the area inside the tooth that holds the nerves and blood vessels of the tooth. It is the center of the tooth and is in both the crown and root of the tooth.
4. Cementum: Makes up the outer surface of the root of the tooth. It is much softer than enamel.
Dr. James L. Johnson