Periodontal Ligament

Histology of the Periodontal Ligament

• The periodontal ligament (PDL) is connective tissue surrounding the tooth root, connecting it to the bone.
• It's continuous with the gingiva and communicates with bone marrow through vascular channels.
• At the root apex, the PDL merges with the dental pulp.

Intended Learning Outcomes

• Define the periodontal ligament and its functions.
• Explain periodontal ligament development and its role in tooth development.
• Discuss the cellular and extracellular components of the PDL.
• Explain the nerve and blood supply to the PDL.
• Discuss the location, origin, insertion, and significance of principal fibres in the PDL.

What is the Periodontal Ligament?

• The PDL is the connective tissue surrounding the tooth root, connecting it to the bone
• It's continuous with the connective tissue of the gingiva and communicates with the marrow spaces through vascular channels in the bone.
• At the root apex, the PDL merges with the dental pulp.

Functions of Periodontal Ligament

• Sensory: The PDL detects pressure, pain, and touch.
• Nutritive: The PDL provides nutrients to the tooth.
• Physical: The PDL helps resist forces of mastication, preventing tooth movement and damage.
• Formative & Remodelling/ Resorptive (i.e., adaptation): The PDL helps in shaping and adapting to changing demands.

Width of PDL in Different Loading Conditions

• The width of the PDL varies depending on the loading conditions.
• Heavy loaded: 0.35mm (near crest), 0.28mm (middle), 0.30mm (near fundus).
• Normally loaded: 0.14mm (near crest), 0.10mm (middle), 0.12mm (near fundus).
• Functionless: 0.10mm (near crest), 0.06mm (middle), 0.06mm (near fundus).

PDL on a Radiograph

• The radiograph shows the PDL as a periodontal space (radiolucent).
• This space is between the lamina dura and the cementum.
• The width of the space is narrower in permanent teeth than in deciduous (baby) teeth.

Development of PDL

• The PDL forms from the dental follicle shortly after root development begins.
• Fibroblasts in the follicle become active and produce fibres that gradually become oblique and attach to the tooth, cementum, and bone.
• As the tooth erupts, more fibres develop and attach to new cementum and bone.

Structural Elements of PDL

• Cells: Resorptive, Synthetic, Progenitor, Defence
• Extracellular Substance: Ground substance, Fibres

Blood Supply to Periodontal Ligament

• The principal blood supply comes from superior and inferior alveolar arteries.
• Vessels from the alveolar bone, apical vessels, and anastomosing vessels from the gingiva also contribute.
• Vessels freely anastomose within the ligament and occupy the interstitial spaces.

Nerve Supply to Periodontal Ligament

• The PDL contains sensory and autonomic nerves.
• Sensory nerves detect pressure, pain, and touch.
• Autonomic nerves are thought to regulate blood flow.
• Branches of the trigeminal nerve (cranial nerve V) supply sensation and movement to the area.

Fibres of Periodontal Ligament

• PDL fibres are made from collagen.
• They are organized into groups based on orientation and function (resembling spliced ropes).
• Principal fibres are embedded in cementum and bone, called Sharpey's fibres.

Principal Fibre Groups

• Alveolar crest: Located just beneath the junctional epithelium, preventing tooth extrusion.
• Horizontal: Runs parallel to alveolar crest fibres, resisting horizontal forces.
• Oblique: Located at an angle to tooth axis (from apex toward the cervical region) resisting masticatory forces.
• Apical: Runs from the tooth apex and is inserted into the socket, resisting vertical, luxative, and twisting forces, while protecting delicate nerves and vessels.
• Interradicular (transseptal): Runs through the gingival mucosa to connect neighbouring teeth, resisting rotational forces.

Gingival Fibre Group

• Separate set of fibres found within the lamina propria of marginal gingiva.
• This group is associated with the gingiva proper (gingival tissue).

Ground Substance

• Ground substance consists of collagen fibres and water (approximately 70%).
• It functions in exchanging metabolites, binding ions and water, orientating fibres, and aiding in tooth support and binding mechanisms.
• Tissue fluid pressure is important, and it's around 10 mm Hg above atmospheric pressure.

Age Changes

• Age-related changes in the PDL include a decrease in cells, increased fibrous tissue, reduced vascularity, and narrowing of the periodontal space (with occasional scalloping of tissues).

Clinical Considerations

• Clinicians should consider the age-related changes, effects of different loading conditions, blood and nerve supply, and the function of all the fibres during patient evaluations.

Further Learning

• Review diagrams and illustrations for clarity.
• Further research into specific terms (e.g., fibroblasts, vascularity) could reinforce learning.
• Refer to any relevant textbook materials for additional details and clarity.