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Cementum is the part of a human tooth that is the layer of rigid connective tissue below the gumline covering the root. It is thickest at the bottom point of the tooth. The primary functions of cementum are to protect the root and assist in holding the tooth securely in the gum socket.
Yellowish in color, this tissue has a dull surface. It is softer than the dentine and enamel that cover the exposed portion of the tooth. The fibers of the periodontal membrane — the fleshy tissue between the tooth and the gum socket — are embedded within the cementum. As the tooth crown wears down with age, specialized cementoblast cells are stimulated to produce new tissue around the root of the tooth.
The cementoblasts are created within the dental pulp — the mass of blood vessels and nerves located in the interior center of the tooth. Cells continually create new cementum because it is not as durable as enamel. By contrast, the enamel is produced only during fetal development.
Cementum is similar to bone in that it contains calcium; but, as opposed to bone, it is avascular. This means it is not supplied by blood vessels. The tissue can easily be worn away or destroyed, and its replacement ensures that the periodontal ligaments are continually strengthened to hold the tooth securely in place over time.
There are three different types of cementum. The acellular cementum covers about one-third of the tooth adjacent to the interface with the enamel. Afibrillar cementum is a small layer that can extend from the acellular cementum onto the enamel. The cellular cementum is the thickest layer, covering roughly the lower two-thirds of the root.
The primary risk to the health of this tissue is gum recession. This generally occurs over age 40 and is due to either excessively hard brushing or the initial stages of gum disease. With gum recession, the gum tissue pulls away from the tooth and begins to expose the cementum and the root.
This tissue is thinnest at the interface with the enamel, which generally is the area that becomes exposed. This makes it highly vulnerable to erosion during brushing. Erosion can cause tooth sensitivity, lead to decay, and cause root damage. Excessive damage can cause tooth loss through the release of the periodontal ligaments that hold the tooth in place.