The Parts of a Tooth
Teeth may look like they are a solid mass of very hard bone-like material but actually they are live organs of the human body with different parts, each of them performing a specific action. Under their protective exterior we can find the live part of the tooth with nerves that help the teeth feel sensations like hot, cold, or pain and blood vessels that nourish them and help them to stay alive and healthy.
When you look at the teeth in your mouth you do not see the full tooth but only the part of the tooth that is visible above the gums, the crown. The rest of the tooth lies under the gums inside the jaw bone and it is known as ‘root’ of the tooth.
The crown is the visible part of the tooth that you can see above the gum line (clinical crown).
It is covered externally by a very hard calcified outer layer, known as enamel. Under the enamel there is a layer of dentin with the pulp at the center of the tooth. The anatomical limit of the crown is the end of the tooth area that is covered by enamel. However the anatomical crown may not always be exactly in line with the initial definition about the visible part of the tooth given for the clinical crown. In younger people with healthy gums the gingival tissue will usually cover some of the anatomical crown, making the visible crown to look smaller. The opposite can also happen, when there is gum recession and root exposure. Then some part of the root becomes visible making the crown to look larger and the tooth longer than it really is.
The size of the crown may decrease with age due to the natural wear from chewing, or due to habits as grinding teeth (bruxism). Malocclusion (bad bite) may also speed up the wear down of the chewing side of the crown.
The crown shape and size differs significantly between the different types of teeth.
- Incisors have a flat and board shape with narrow sharp edge.
- Canines have a more conical shape with a pointed edge.
- Premolars and molars have a bigger crown with much broader chewing surface and a varying number of raised pointed parts (cusps).
The root is the part of the tooth that is under the gum line embedded in the jaw bone, either the maxilla (upper jaw) or mandible (lower jaw). In anatomical terms it is the part of the tooth that is covered by cementum, a hard classified material but softer from the enamel that covers the crown. The root is the part of tooth that provides support and keeps it in place at the jaw with the help of the periodontal ligaments. Generally, it is the 2/3 of the overall length of the tooth.
Different types of teeth have different number of roots and root shape and size (also depending on their location in the mouth).
- Incisors have a single conical root.
- Canines also have a single root but much longer for providing stability.
- Premolars have one root, except the upper jaw first premolars which have two roots.
- Molars may have two, three, or up to four roots depending on their type and location in the mouth (usually 2 for the molars of the lower jaw and 3 roots of the upper jaw).
At the end of each root there is a small opening called the apex or apical foramen. Blood vessels and nerves pass through this opening to enter the tooth. The apex is connected with the pulp chamber at the center of the tooth via the root canals that run through the center of each root.
The Neck (Cervical line)
The neck of the tooth (also called as cervical line) is the line formed at the point where the crown meets the root. In anatomical terms, it is the point where the enamel meets the cementum, also called the cemento-enamel junction (CEJ).