What Is Cementum?
Cementum is a hard layer of tissue that helps the periodontal ligament attach firmly to a tooth. Made of cementoblasts, cementum slowly forms over a lifetime.
Cementum is a hard, calcified layer of tissue that covers the root of the tooth. On its outer side, cementum is attached to the periodontal ligament; on its inner side, the dentin. Along with the periodontal ligament, alveolar bone and gingiva, cementum helps a tooth stay in its place. In fact, if it weren't for cementum, the periodontal ligament wouldn't be able to attach firmly to a tooth.
Slowly formed throughout life, cementum is created when the root of the tooth excretes cementoblasts. Though cementoblasts are somewhat of a mystery, it is known that cementum is yellow in color and softer than dentin. Its chemical makeup is similar to that of bone -- but unlike bone, cementum is avascular (not supported by blood vessels).
Types of Cementum
There are three types of cementum: acellular cementum, cellular cementum and afibrillar cementum. Acellular cementum covers about 1/3-1/2 of the root and has little to no cellular components. Cellular cementum covers about 1/3-1/2 of the apex and is permeable. Afibrillar cementum sometimes extends onto the enamel of the tooth.