Histology of the 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's connective tissue, connecting with the 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 how the PDL develops as part of tooth development.
• Discuss cellular and extracellular components of the PDL.
• Explain the nerve and blood supply to the PDL.
• Discuss the location, origin, insertion, and significance of the PDL's main fibers.

Assessment

• Formative: Class participation, quizzes.
• Summative: E-assessment, unseen case study.

GDC Learning Outcomes

• Describe relevant dental, oral, craniofacial, and general anatomy.
• Explain anatomical application in patient management.

What is the Periodontal Ligament?

• The PDL is connective tissue surrounding the root, connecting it to the jaw bone.

Functions of Periodontal Ligament

• Sensory: Detects pressure, pain, and touch.
• Physical: Supports and stabilizes teeth during chewing.
• Nutritive: Supplies nutrients for bone and tooth health.
• Formative/Remodeling: Shapes and remodels the tissues.

Average Width of PDL

• 0.2mm (range 0.15mm to 0.38mm)
• Width varies based on loading conditions, like heavy, normal, or functionless chewing.

PDL on a Radiograph

• Appears as periodontal space.
• Radiolucent area between alveolar bone proper and cementum.
• Narrower in permanent teeth than in deciduous teeth.

Development of PDL

• Forms from the dental follicle after root development begins.
• Initial fibers lack organization but become oblique to the tooth.
• Early fibers are apical to the cemento-enamel junction.
• More fibers develop and attach to the cementum and bone.
• Cemental Sharpey's fibers appear first, and then Sharpey's fibers in bone.
• Alveolar fibers extend and grow wider into the middle zone.
• Fibers gain thickness and strength during occlusal function.

Structural Elements of PDL

• Cells: Synthetic, resorptive, progenitor, defense, rests of Malassez.
• Extracellular substance: Ground substance, fibers

Blood Supply to Periodontal Ligament

• Superior and inferior alveolar arteries supply the PDL.
• Apical vessels, penetrating vessels (from bone), and anastomosing vessels (from gingiva)
• Vessels interconnect within the PDL.

Nerve Supply to Periodontal Ligament

• Two types of nerves: sensory and autonomic.
• Branches from the second and third divisions of the fifth cranial nerve (trigeminal).

Fibres of Periodontal Ligament

• Composed of collagen from the apex and cervical margin of the tooth.
• Principal fibers organized by orientation and functions.
• Distribute mastication forces and speech pressure.
• Embedded into cementum and bone—Sharpey's fibers.

Principal Fibre Groups

• Alveolar crest: Runs downwards & outwards, to prevent tooth extrusion.
• Horizontal: Runs at right angles along tooth's long axis, resists horizontal & tilting forces
• Oblique: Runs obliquely, largest group resisting vertical masticatory forces.
• Apical: Fans out and inserts into the apex, resists twisting forces..
• Interradicular: Resists vertical and lateral movement of the teeth.
• Transseptal (Interdental): Runs through gingival mucosa connecting neighbouring teeth.

Alveolar Crest Group Fibres

• Location, Origin, Insertion — runs downward and outward into alveolar socket
• Significance—prevent tooth extrusion and resists lateral tilting.

Horizontal Group Fibres

• Location, Origin, Insertion —runs at right angles to tooth's axis into alveolar bone
• Significance—resists horizontal and tilting forces.

Oblique Group Fibres

• Location, Origin, Insertion —runs obliquely in coronal direction, into alveolar bone
• Significance—greatest group, resists vertical masticatory forces.

Apical Fibres

• Location, Origin, Insertion—fans out irregularly and inserts into the tooth's apex
• Significance —resists vertical and twisting forces.

Inter-radicular Group Fibres

• Location, Origin, Insertion—within the septum between tooth roots.
• Significance—resists vertical and lateral movement.

Interdental Ligament/Transseptal Fibres

• Runs through gingival mucosa, connecting neighbouring teeth.
• Inserts into cementum, over alveolar crest
• Resists rotational forces.

Gingival Fibre Group

• Adjacent fiber groups within the marginal gingiva's lamina propria.

Ground Substance

• Collagen fibres, water (70%), and tissue fluid pressure above atmospheric.
• Functions—metabolic exchange, binding materials and supporting/anchoring the teeth

Age Changes

• Decrease in cells and vascularity, increasing fibrous tissue.
• Narrowing of PDL, visible scalloping in calcified tissues.

Clinical Considerations

• Discussion topic: Clinical implications of age-related changes and PDL characteristics.