Periodontal ligament

The periodontal ligament (PDL) is a group of specialized, and dynamic connective tissue fibers that attach a tooth to the alveolar bone. The PDL is inserted into the root cementum on one side and on the other side, the alveolar bone.


The PDL is comprised of the following: principal fibers, blast and clast cells, loose connective tissue, oxytalan fibers and Cell Rest of Malassez.

Alveolodental Ligament

The alveolodental ligament is the primary principal fiber group. The alveolodental ligament consists of five different fiber subgroups which include: alveolar crest, horizontal, oblique, apical and interradicular on multirooted teeth. Other principal fibers which do not include the alveolodental ligament are the transseptal fibers.

These fibers aid the tooth’s ability to withstand natural compression forces which occur during routine use such as chewing and they remain embedded in the bone. The ends of the principal fibers which are found within the cementum or alveolar bone proper are the Sharpey fibers.

Transseptal Fibers

Transseptal fibers are the fibers which extend over the alveolar bone crest interproximally. These fibers are embedded into the cementum of the adjacent teeth. In this location, they form an interdental ligament. These fibers work together to maintain properly aligned teeth. Because these fibers do not contain an osseous attachment, they are considered to belong to the gingival tissue.

Loose Connective Tissue

Loose connective tissue is made up of fibers, cells, extracellular matrix, nerves and blood vessels. The extracellular compartment contains Type 1, 3, and 5 collagen fiber bundles which are embedded in intercellular substance. The PDL collagen fibers are categorized based on their orientation and their location on the tooth. These cells include fibroblast, defence cells and undifferentiated mesenchymal cells.

Cell Rest of Malassez

These groups of epithelial cells are located in the mature PDL after the disintegration of Hertwig epithelial root sheath during the formation of the root. They form a network of nerves which surround the tooth. In the later stages of life, Cell Rests of Malassez might proliferate with inflammation which may lead to lead to the formations of radicular cysts.

Oxytalan Fibers

Oxytalan fibers are unique to the PDL and are naturally elastic. The fivers insert into the cementum and run in two different directions. The fibers run both parallel to the root surface and oblique to the root surface. The thought is that the function maintains the patency of blood vessels during times of occlusal loading. However, additional research is needed to fully determine the function and ability of the oxytalan fibers.


It is estimated that the PDL is comprised of nearly 70% water. It is also thought to have a significant impact on the strength of the tooth and its ability to withstand high levels of stress. The completeness and vitality of the PDL are critical components of a functional tooth.
In most cases, the PDL ranges from about 0.15 to 0.38mm wide. The thinnest part of the PDL is located in the middle third of the root. The PDL’s width reduced over time as the patient ages.


PDL cells are one of the numerous cells which are derived from the dental follicle. This occurs following the formation of the crown and once the roots begin developing. These cells remodel the dental follicle in order to form the PDL. The formation of PDL begins at the cementoenamel junction and proceeds in an apical direction.