The tooth is made up of four tissues: enamel, dentin, cementum, and pulp. enamel,dentin, and cementum are relatively hard since the contain considerable mineral content, especially calcium.
Enamel is the white, protective external surface layer of the anatomic crown. It is highly calcified or mineralized, and is the hardest substance in the body. Its mineral content is 95% calcium hydroxyapatite, The remaining substances include 5% water and enamel matrix. It develops from the enamel organ (ectoderm) and is a product of ameloblasts.
Cementum is the dull yellow external layer of the tooth root. The cementum is very thin, especially next to the cervical line. It is composed of 65% calcium hydroxyapatite (mineralized and calcified), 35% organic matter (collagen fibers), and 12% water. Cementum is about as hard as bone but considerably softer than enamel. It develops from the dental sac (mesoderm), and is produced by cells called cementoblasts.
The cementoenamel junction (also called the CEJ) separates the enamel of the crown from the cementum of the anatomic root. This junction is also known as the cervical line, it surrounds the neck or cervix of the tooth.
Dentin is the hard yellowish tissue underlying the enamel and cementum. Mature dentin is composed of about 70% calcium hydroxyapatite, 18% organic matter (collagen fibers), and 12% water, making it harder than cementum but softer and less brittle than enamel. Dentin develops from the embryonic dental papilla (mesoderm). The cells that form dentin, called odontoblasts are located at the junction between pulp and dentin.
The dentinoenamel junction is the inner surface of the enamel cap where enamel joins dentin. The cementodentinal or dentinocemental junction is the inner surface of cementum where cementum joins dentin.
The pulp cavity has a coronal portion (pulp chamber) and a root portion (pulp canal or root canal). The pulp cavity is surrounded by dentin. Nerves and blood vessels enter the pulp through apical foramina. It develops from the dental papilla (mesoderm).