The periodontal ligament is a cluster of fibers that attach individual teeth to alveolar bone. This periodontal ligament inserts into the cementum of the tooth on one side, and is attached on the alveolar bone on the other side. The periodontal ligament is made of fibers, connective tissue, and different types and formations of cells. The main cluster of fibers is the alveolodental ligament; this is made up of alveolar crest fibers, horizontal fibers, oblique fibers, apical fibers, and interradicular fibers. Transseptal fibers are also present. Each of these fibers is named based on their location in the mouth and the direction in which they run or radiate, and each type of fiber plays a specific role in the mechanics of the teeth. Collectively, these fibers help the teeth bear the considerable pressures and compressive forces that are present during chewing. The ends of the fibers that enter the cementum or the alveolar bone are called Sharpey fibers.
The connective tissue of the periodontal ligament contains additional types of fibers as well as collagen, cells, nerves, and blood vessels. The periodontal ligament also contains Cell Rests of Malassez, which are epithelial cells that are residual from root formation. If they proliferate when the periodontium is inflamed, they may lead to the formation of radicular cysts in late adulthood. Oxytalan fibers, which are unique to the periodontal ligament, are elastic and are believed to help maintain the accessibility of the blood vessels during the forces of chewing.
Otherwise, the periodontal ligament is estimated to be made up of 70% water, which helps the teeth withstand the significant stress loads of chewing. The ligament ranges in width from .15 to .38 mm; the width of the periodontal ligament gradually narrows with age. The cells of the periodontal ligament are present in the dental follicle when the roots of the teeth are developing; the cells remodel the dental follicle and become the periodontal ligament, which begins at the junction between cementum and enamel and which develops in an apical direction, toward the root, or apex, of each tooth.
The periodontal ligament serves a few specific functions. It supports the teeth, absorbing and transferring the load of biting and chewing from the teeth to the alveolar bone. Rich with nerve cells, the periodontal ligament also transmits information about the teeth and the direction and level of forces the teeth withstand. The periodontal ligament also contains different types of blood vessels that help maintain the vitality of the overall ligament and aid in support of the teeth. Finally, the periodontal ligament contains progenitor cells that can help maintain and repair the alveolar bone. The periodontal ligament may undergo trauma if exposed to excessive occlusal forces, also known as the forces of biting and chewing, which may result in a loosened tooth or pain while eating. Additionally, the periodontal ligament may undergo significant detrimental changes when chronic periodontal disease is present; these changes may result in the eventual detachment of the periodontal ligament from the tooth and therefore the loss of the tooth.