Periodontal Ligament: Definition, Function & Development

• The session aims to enable students to define the periodontal ligament, explain its functions, development in tooth development, and discuss its cellular components.
• Students will explain the nerve and blood supply and the location, origin, insertion, and significance of the periodontal ligament's principal fibers.

Assessment

• Two types of assessment are used; formative and summative
• Formative includes Class contribution and Quiz
• Summative includes E-assessment and Unseen case
• GDC Learning Outcomes: Describe relevant and appropriate dental, oral, craniofacial and general anatomy and explain their application to patient management.

Periodontal Ligament Definition

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

Functions of Periodontal Ligament

• The periodontal ligament has several functions:
• Sensory
• Nutritive
• Physical
• Formative
• Resorptive

Width of PDL

• Average PDL width is 0.2mm, with a range of 0.15mm to 0.38mm.

PDL Width in Different Loading Conditions

• Near crest of alveolus: Heavy loaded is 0.35mm, Normally loaded is 0.14mm, and Functionless is 0.10mm.
• Middle of alveolus: Heavy loaded is 0.28mm, Normally loaded is 0.10mm, and Functionless is 0.06mm.
• Near fundus of alveolus: Heavy loaded is 0.30mm, Normally loaded is 0.12mm, and Functionless is 0.06mm.

PDL on Radiograph

• On radiographs, the ligament appears as the periodontal space.
• It shows as a radiolucent area between the lamina dura of alveolar bone proper and radiopaque cementum.
• The PDL is narrower in permanent teeth than in deciduous teeth.

Development of PDL

• PDL forms from the dental follicle shortly after root development begins.
• As the crown comes to the oral mucosa, fibroblasts in the follicle become active and produce fibers.
• Initially, fibers lack organization but then become oblique to the tooth.
• First fibers are apical to the CEJ and give rise to gingivodental fibers.
• As eruption progresses, more fibers develop and become attached to new cementum and bone.
• Sharpey's fibers appear first in cementum, then in bone.
• SFs in bone are fewer and more spaced out.
• Alveolar fibers extend into the middle zone to join the lengthening cemental fibers, gaining thickness and strength during occlusal function.

Structural Elements of PDL

• Cells
• PDL
• Synthetic
• Resorptive
• Progenitor
• Defence
• Epithelial Rests of Malassez
• Fibres
• Ground substance
• Extra cellular substance

Blood Supply to the Periodontal Ligament

• Principal blood supply comes from superior and inferior alveolar arteries.
• These include apical vessels, penetrating vessels from the alveolar bone, and anastomosing vessels from the gingiva
• Vessels anastomose freely within the ligament, occupying the interstitial spaces.

Nerve Supply to the Periodontal Ligament

• Two types of nerves: Sensory and Autonomic
• Branches of the second and third division of the 5th cranial nerve (trigeminal nerve).

Fibers of Periodontal Ligament

• All fibers are made from collagen.
• PDL is wider near the apex and cervical margin of the tooth.
• Most are principal fibers, organized into groups according to orientation and function, resembling spliced ropes.
• Functions includes Distributing mastication and speech forces.
• Principal PDL fibers are embedded into cementum and bone = Sharpey's fibers.

Principal Fiber Groups

• These consist of 5 groups with main principal fibers.
• Alveolar crest group
• Horizontal group
• Oblique group
• Apical group
• Interradicular group
• Overall function is to resist rotational forces.

Alveolar Crest Fiber Group

• Location: Just beneath the junctional epithelium
• Origin: Cementum, below CEJ
• Insertion: Runs downwards and outwards & inserts into alveolar crest
• Significance: Prevents tooth extrusion from the socket and resists lateral, tilting, and intrusive tooth displacement

Horizontal Group Fibers

• Location: Limited to the coronal one-fourth of PDL
• Origin: Cementum, apical to the alveolar crest group
• Insertion: Runs at right angles to the long axis of the tooth & inserts into the bone apical to the alveolar crest
• Significance: Resists horizontal and tipping forces

Oblique Group Fibers

• Location: Two-thirds of the length of the PDL
• Origin: Cementum
• Insertion: Runs obliquely in the coronal direction & inserts into the alveolar bone
• Significance: Largest group, resists vertical masticatory forces, thereby preventing tooth intrusion.

Apical Group Fibers

• Location: Root tip
• Origin: Cementum, around the apex of the tooth
• Insertion: Fans out irregularly and inserts into the apex of the socket
• Significance: Found in incompletely formed roots, resists vertical, luxative, and twisting forces, protects delicate nerves and vessels at the apex

Inter-radicular Group Fibers

• Location: Found in multi-rooted teeth
• Origin: Cementum
• Insertion: Inter-radicular septum
• Significance: Resists vertical and lateral movement; tipping, torquing, and luxation are also resisted; periodontal disease leads to total loss of fibers

Interdental Ligament or Transseptal Fibers

• Fibers that run through gingival mucosa to connect neighboring teeth.
• They insert interdentally into the cervical cementum of neighboring teeth over the alveolar crest.
• Fibers travel from cementum to cementum with no bony attachment.
• These resist rotational forces and keep teeth in alignment.

Gingival Fiber Group

• Name given to separate but adjacent fibre groups found within lamina propria of marginal gingiva
• These consists of Circular group, Dentogingival group, Dentoperiosteal group, Alveologingival group

Ground Substance

• Content:
  • Collagen fibers
  • Water 70%
  • Tissue fluid pressure high, 10mm Hg above atmospheric pressure
• Functions:
  • Exchange of metabolites
  • Ion & water binding
  • Fiber orientation
  • Tooth support and binding mechanisms

Age Changes

• Decrease in cells
• Increase in fibrous tissue
• Decrease in vascularity and mitotic activity
• Narrowing of PDL width
• Scalloping seen on calcified tissues (bone, cementum)- PDL attached to the peaks of these scallops

Explore the periodontal ligament: its definition as connective tissue linking the tooth root to bone. Understand its functions, development during tooth formation, and cellular components. Also learn about its nerve and blood supply, fiber origins, insertions, and clinical importance.