Periodontology Anatomy - Periodontal ligament

Marin Contemporary Perio & Implant Concepts

The periodontal ligament, which is often abbreviated as the PDL, is a group of specialized connective tissue fibers that attach the tooth to the alveolar bone. The PDL inserts into root cementum on one side and onto alveolar bone on the other.

The tissues of the periodontium combine to form a dynamic and active group of tissues. The alveolar bone (C) is mostly surrounded by the subepithelial connective tissue of the gingiva. It is covered by the various characteristic gingival epithelia. The cementum that overlays the tooth root is attached to the adjacent cortical surface of the alveolar bone by the alveolar crest (I), horizontal (J) and oblique (K) fibers of the periodontal ligament.

Structure

The PDL consists of principal fibers, loose connective tissue, blast and clast cells, oxytalan fibers and Cell Rest of Malassez.

Alveolodental ligament

The primary principal fiber group is the alveolodental ligament, which consists of five different fiber subgroups. These fiber subgroups include the following: alveolar crest, horizontal, oblique, apical and interradicular on multirooted teeth.

These fibers help the tooth to withstand the natural compression forces that occur while chewing and remain embedded in the bone. The ends of the principal fibers that are within the cementum or alveolar bone proper are called Sharpey fibers.

Transseptal fibers

Transseptal fibers (H) extend over the alveolar bone crest and are embedded in the cementum of adjacent teeth where they form an interdental ligament. These fibers work to keep the teeth aligned. These fibers may be considered as belonging to the gingival tissue as they do not have an osseous attachment.

Loose connective tissue

Loose connective tissue contains fibers, extracellular matrix, cells, nerves and blood vessels. The extracellular compartment consists of Type 1, 3, and 5 collagen fibers bundles that are embedded in intercellular substance. The PDL collagen fibers are categorized according to how they are oriented and located along the tooth. The cells include the following: 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 when the root is formed. They form a plexus that surrounds the entire tooth. Cell Rests of Malassez can be the cause of cyst formations later in life.

Oxytalan fibers

Oxytalan fibers are unique to PDL and are naturally elastic. It inserts into the cementum and runs in two different directions; parallel to the root surface and oblique to the root surface.

Composition

The PDL substance is estimated to contain up to 70% water. It is thought to have a significant effect on the tooth's strength and ability to withstand stress. The completeness and vitality of the PDL are critical for a tooth to function.

The PDL width usually ranges from 0.15 to 0.38mm in its thinnest part which is located in the middle third of the root. The width progressively lowers with age. The PDL is a portion of the periodontium which acts as the attachment of the teeth to the surrounding alveolar bone through the cementum.

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