Divisions and Components of the Teeth
In addition to having very specific functions each tooth has a specific location and contains specific shapes that aid in its function. All teeth, though different in shape, have the same anatomical parts. Each tooth has a clinical crown (crown that is exposed to the oral cavity), anatomic crown (from the CEJ to the cusps), and root(s). The tooth is attached to the underlying alveolar bone with fibers known as the periodontal ligaments.
Each tooth is made up of the same four components: enamel, dentin, cementum and pulp.
Enamel is the substance that covers the anatomic crown of the tooth, is the hardest substance in the body and is somewhat translucent. It is created by cells known as ameloblasts. The enamel is the first line of protection for the tooth. It can withstand biting pressure but does not have the ability to regrow once fully formed. If there has been minor demineralization (become more porous) occurring, it can remineralize (harden) and thus stop the tooth decay process with proper nutrition and oral care.
The dentin is the substance that lies beneath the enamel and the cementum in the tooth. Dentin is created by cells known as odontoblasts. It is not as hard as enamel and it makes up the major portion of the tooth. The dentin is comprised of microscopic tubes known as dentinal tubules. There are three types of dentin. Primary dentin is what is present when the tooth erupts. Secondary dentin continues to form during the life of the tooth. Reparative dentin can form in response to inflammation/irritation or trauma. The color of the dentin reflecting through the enamel is what is responsible for the color (hue and tint) of the tooth. Because dentin is softer than enamel, if decay passes through the enamel (demineralization) and invades the dentin, it can spread very rapidly here. The enamel and the dentin meet at an area known as the DEJ or dentoenamel junction.
The cementum is the substance that covers the root of the tooth. It is also very thin and not as hard as the enamel but has a similar hardness to bone. Cells known as cementoblasts form cementum. There are fibers that project from the cementum and attach it to the alveolar bone. The cementum can be abraded by such things as the bristles of a stiff toothbrush. Also, if the cementum becomes exposed to the oral cavity through gingival recession, this surface can become very sensitive to temperature changes in the mouth (hot and cold). The enamel and cementum meet at an area known as the CEJ or cementoenamel junction.
The pulp is the final component, and it is where all the nerves and blood vessels that supply the tooth are housed. The pulp is divided into two areas: the pulp chamber, located in the crown of the tooth; and the pulp canals, which are located in the root(s) of the tooth. If the pulp area becomes exposed to decay, a bacterial infection can occur and may require root canal therapy in order to save the tooth. When the teeth first erupt, the pulp chamber and canals are very large, but as secondary dentin forms, the pulp area decreases.
Figure 5. Basic Tooth Anatomy.