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Periodontal ligament

The periodontal ligaments are considered part of the periodontium, as they are supporting tissue of a tooth. These ligaments are a specialized connective tissue that attach teeth from the cementum to the surrounding alveolar bone. They are about .2 millimeters in width, which decreases with age.

Since teeth are not embedded in bone directly, large compressive forces can occur on teeth without destruction of the bone. Instead, the tooth, pulling downward on the periodontal ligaments, create tension which is actually the stimulus for bone growth.

Another function of the periodontal ligaments is to serve as a method for sensation. There are recepetors within the periodontal ligaments which sense differing amounts of tension. This helps the body discern the amount of force being placed on a tooth, during chewing for example, because enamel has no sensory receptors itself.

The periodontal ligament has fibers composed of Type I and Type II collagen. Compared to most other ligaments of the body, these are highly vascularized.

Types of Fibers

Individually having a diameter of 55 nanometers, fibers of the periodontal ligament are catagorized by their orientation to the teeth. They are organized together along the tooth and serve different fuctions.

Transeptal Fibers

Transeptal fibers run between two adjacent teeth in the same arch. They attach from the cementum just apical to where the gums attach to one tooth and insert at the cementum of an adjacent tooth. Transeptal fibers are believed responsible for returning teeth to their original state after orthodontic therapy. Although techinically part of the gingival ligament, it is frequently included in studies involving the periodontal ligament.

Alveolar Crest Fibers

Alveolar crest fibers attach to the cementum just apical to the cementoenamel junction, run downward, and insert into the alveolar bone.

Horizontal Fibers

Horizonal fibers attach to the cementum apical to the alveolar crest fibers and run perpendicularly from the root of the tooth to the alveolar bone.

Oblique Fibers

Oblique fibers are the most numerous fibers in the periodontal ligament. They attach apical to the horizontal fibers and run diagonally toward the crown of the tooth inserting to the alveolar bone there. Because they are the most numerous, these fibers are believed to be the most responsible in compensating for the chewing forces directed on the teeth.

Apical Fibers

Apical fibers are at the apex of a root. The attach from the cementum and insert to the surrounding bone at the base of the socket.

Interradicular fibers

Interradicular fibers are only found between the roots of a multi-rooted tooth, such as a molar. They also attach from the cementum and insert to the nearby alveolar bone.