Cementum covers the root of the tooth

The root is the part of the tooth that fits into its socket or alveolus in the maxilla or mandible. Cementum is a thin layer of bone-like material that is secreted by cemento-cytes, cells that closely resemble osteocytes. Like bone, cementum is 65% mineral. The lacunae and canaliculi in the cementum contain the cementocytes and their processes, respectively. They resemble those structures in bone that contain osteocytes and osteocyte processes.

Unlike bone, cementum is avascular. Also, the canaliculi in cementum do not form an interconnecting network. A layer of cementoblasts (cells that resemble the osteoblasts of the surface of growing bone) is seen on the outer surface of the cementum, adjacent to the periodontal ligament.

Collagen fibers that project out of the matrix of the cementum and embed in the bony matrix of the socket wall form the bulk of the periodontal ligament. These fibers are another example of Sbarpey's fibers (Fig. 15.15). In addition, elastic fibers are also a component of the periodontal ligament. This mode of attachment of the tooth in its socket allows slight movement of the tooth to occur naturally. It also forms the basis of orthodontic procedures used to straighten teeth and reduce malocclusion of the biting and grinding surfaces of the maxillary and mandibular teeth. During corrective tooth movements, the alveolar bone of the socket is resorbed and resynthesized, but the cementum is not.

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