PDL Flashcards
What are the four primary functions of the periodontal ligament (PDL)?
• Supportive – suspends the tooth in the alveolus
• Sensory – detects tactile pressure and pain (proprioception)
• Nutritive – supplies nutrients via blood vessels to cementum, bone, and gingiva
• Formative/Remodeling – contains cells that synthesize/resorb collagen, bone, and cementum
What is the average width of the periodontal ligament and how does it change with age or function?
• Average width = 0.2 mm
• Increases with functional load (e.g., clenching, grinding)
• Decreases with age or lack of function (e.g., unerupted teeth)
Which cell type is most abundant in the PDL and what is its function?
• Fibroblasts – synthesize and degrade collagen fibers and ground substance; key for maintenance
What are Sharpey’s fibers and where are they found?
• Terminal ends of principal collagen fibers
• Embedded in cementum and alveolar bone
• Function: Anchor the tooth by attaching PDL fibers to hard tissue
List the five principal (alveolodental) fiber groups of the PDL.
- Alveolar crest fibers
- Horizontal fibers
- Oblique fibers
- Apical fibers
- Interradicular fibers (only in multirooted teeth)
Which PDL fiber group is most numerous and resists vertical intrusive forces?
• Oblique fibers – insert coronally into alveolar bone, resist masticatory compressive forces
What is the role of the transseptal fibers?
• Span between cementum of adjacent teeth
• Maintain interproximal contact and tooth alignment
• Not a principal fiber group; part of supracrestal tissue attachment
What types of collagen are most abundant in the PDL?
• Type I – primary structural component
• Type III – involved in repair and early development
• Also contains small amounts of Types V, VI, XII
What are the epithelial rests of Malassez and why are they clinically significant?
• Remnants of Hertwig’s epithelial root sheath
• Located in the PDL
• May proliferate into radicular cysts under inflammation or trauma
How does the PDL respond to orthodontic movement?
• Tension side – osteoblasts deposit new bone
• Compression side – osteoclasts resorb bone
• PDL fibers remodel in response to force, allowing tooth movement
What is the effect of aging on the periodontal ligament?
• Becomes narrower
• Decreased cellularity and vascularity
• Increased cementum deposition
• Reduced regenerative capacity
Which gingival fiber group encircles the tooth and maintains gingival contour?
• Circular fibers – located in the free gingiva; help maintain shape and position of gingiva
What is the function of oxytalan fibers in the PDL?
• Elastic-like fibers aligned with blood vessels
• Help maintain vascular patency and resist mechanical strain
Why is the PDL space important in vitality testing?
• Pain to percussion may reflect PDL inflammation, not necessarily pulp necrosis
• Helps differentiate endodontic from periodontal pathology
Name three regenerative cell types found in the PDL.
• Cementoblasts – produce cementum
• Osteoblasts – produce alveolar bone
• Undifferentiated mesenchymal stem cells – can differentiate into multiple periodontal cell types
What arteries supply blood to the periodontal ligament?
• Branches of the superior and inferior alveolar arteries
• Also receives contributions from the facial, lingual, and greater palatine arteries
What is the nerve supply to the PDL and what types of fibers are present?
• Innervated by branches of the trigeminal nerve (CN V)
• Contains myelinated A-beta fibers (touch, pressure) and unmyelinated C fibers (pain)
• Responsible for proprioception, allowing detection of occlusal force and position
What makes up the ground substance of the PDL and what is its function?
• Rich in proteoglycans (e.g., decorin), glycoproteins (e.g., fibronectin), and water
• Function: Acts as a hydraulic cushion, distributes forces, and maintains tissue hydration
What is the role of the apical fiber group in the PDL?
• Stabilizes the tooth by preventing extrusion
• Protects the neurovascular bundle at the tooth apex
• Found around the apex of the root
In which teeth are interradicular fibers found, and what do they do?
• Found only in multi-rooted teeth
• Extend from cementum of one root to the interradicular septum
• Resist torquing, tipping, and dislodging forces
What causes PDL widening, and what does it indicate clinically?
• Caused by trauma from occlusion, inflammation, or orthodontic forces
• Seen radiographically as widened PDL space
• May indicate tooth mobility or pathology
What is ankylosis and how does it relate to the PDL?
• Pathologic fusion of cementum and alveolar bone
• Results in loss of PDL space
• Leads to infraocclusion, especially in growing patients
How does the PDL contribute to tooth proprioception?
• Contains mechanoreceptors and sensory fibers
• Detects forces and provides feedback to the masticatory system
• Helps coordinate chewing and protect teeth from overload
What role do undifferentiated mesenchymal cells play in the PDL?
Serve as a cell reservoir for regeneration
Can differentiate into fibroblasts, osteoblasts, or cementoblasts
Crucial for healing after trauma or periodontal surgery
