Periodontal ligament
From Wikipedia, the free encyclopedia
The periodontal ligament is a specialized connective tissue that attaches a tooth to the jaw bone. This ligament helps the tooth withstand large compressive forces which occur during chewing, without destruction of the adjacent alveolar bone.
Another function of the periodontal ligament is to serve as a source of sensation. There are pressure sensitive receptors within the periodontal ligaments which help the brain discern the amount of force being placed on a tooth, during chewing for example. This is important since the outer covering of the tooth, enamel has no sensory receptors itself.
Contents |
[edit] Development of the Periodontal Ligament
Shortly after the beginning of root formation and the formation of outer dentinal layer of root, the periodontal ligament is formed. The external and internal dental epithelia proliferate from the cervical loop of dental organ to form a Hertwig’s epithelial root sheath. This sheath is double layered. Because of growth changes, the root sheath is stretched and then it fragments to form the discrete clusters of the epithelial cells called as “epithelial rests of Malassez”. Now the periodontal ligament formation occurs. The Enamel organ and Hertwig’s epithelial root sheath are surrounded by a dental sac that is formed by condensed cells. A thin layer of these cells lies adjacent to the dental (enamel) organ. This is known as dental follicle. The cells of the dental follicle divide and differentiate into the cementoblasts, fibroblasts and osteoblasts. The Fibroblasts synthesize the fibers and ground substance of the periodontal ligament. These fibers of the periodontal ligament then get embedded at one end into the newly formed cementum laid down by cementocytes and at the other end into the bone laid down by osteoblasts. When tooth erupts in the oral cavity, these fibers get oriented in a characteristic manner. The fiber bundles of the periodontal ligament gradually thicken after the teeth have been in function for sometime
[edit] Structure of the Periodontal Ligament
The periodontal ligament is considered to be part of the periodontium - the supporting tissue of a tooth. It is about 0.2 millimeters in width, which decreases with age. The periodontal ligament has fibers composed of Type I and Type III collagen. Compared to most other ligaments of the body, these are highly vascularized.
[edit] Types of fibers
Individual fibers of the ligament have a diameter of 55 nanometers. These fibers are categorized according to their orientation to the tooth.
[edit] Transeptal fibers
Transeptal fibers run between two adjacent teeth in the same jaw. They run from the cementum just apical to where the gums attach to a tooth and insert at the cementum of an adjacent tooth at about the same level. Transeptal fibers are believed to be responsible for returning teeth to their original state after orthodontic therapy. Although technically part of the gingival ligament, these fibers are frequently included in studies involving the periodontal ligament.
[edit] Alveolar crest fibers
Alveolar crest fibers attach to the cementum just apical to the cementoenamel junction, run downward, and insert into the alveolar bone.
[edit] Horizontal fibers
Horizontal fibers attach to the cementum apical to the alveolar crest fibers and run perpendicularly from the root of the tooth to the alveolar bone.
[edit] 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 primarily responsible in absorbing the chewing forces on the tooth. They are hence the main support of the tooth.
[edit] Apical fibers
Apical fibers are at the apex of a root. They attach from the cementum and insert to the surrounding bone at the base of the socket.
[edit] Interradicular fibers
Interradicular fibers are only found between the roots of a multi-rooted tooth, such as a [[Molar (tooth)|molar]s]. They also attach from the cementum and insert to the nearby alveolar bone.
[edit] See also
[edit] References
- Ten Cate, A.R. Oral Histology: development, structure, and function. 5th ed. 1998. ISBN 0-8151-2952-1.
alveolar bone - cementum - gingiva - periodontal ligament
