Periodontal Ligament-summer

The Periodontal Ligament Dr. Khansa Ababneh

The Periodontal Ligament The PDL is the connective tissue that surrounds the root and attaches it to the alveolar bone

Physically small, functionally Continuous with the connective tissues of the important gingiva and communicates with marrow spaces in bone

PDL Subjected to continuous mechanical loading High turnover rate Embryonic-like tissue

PDL Composed of – – – – –

Fibres Cells ECM Nerves Blood & lymphatic vessels

General Functions of PDL Tooth support Proprioception Regulation of alveolar bone volume

Fibres Most important are the principal fibres. Other fibres are oxytalan and eluanin fibres (immature elastic fibres).

Principal fibres Type I and III collagen Type I arranged in bundles Follow a wavy course Terminal portions inserted into cementum and bone are termed Sharpey’s fibres Types V & VI collagen

Groups of fibres Transseptal group Connect adjacent teeth

Alveolar crest group Resist extrusion, lateral movements

Horizontal group Resist lateral movements

Oblique group Receive the bulk of vertical forces

Apical group Resist intrusion & extrusion

Interradicular group Furcation areas of multirooted teeth

Formation of Principal Fibres Sharpey’s fibres start to form before cementum and alveolar bone are mineralised.

Collagen Fibre Bundles

Sharpey’s fibres At insertion, PDL fibres are fully or partially mineralised High levels of non-collagenous proteins , such as osteopontin

Cells Fibroblasts Osteoblasts Cementoblasts Defence cells: macrophages, mast cells, eosinophils

Osteoclasts Sensory cells Epithelial rests of Malassez

Epithelial rests of Malassez

Interconnected Network

Fibroblasts Formation & remodeling of PDL fibres necessitates special signaling system Different populations (origin, protein sysnthesis; ALP)

ECM Collagen PG Glycoproteins: 

fibronectin, tenascin, undulin

Growth factors Cytokines

Functions of PDL ☻ ☻ ☻ ☻

Mechanical (physical) Formative Nutritive Sensory

Physical Functions Protection of vessels and nerves Transmission of occlusal forces to bone (tension & compression)

Attachment of teeth to bone Maintenance of gingival position Shock absorption

Theories regarding mechanical function of the PDL

Tensional theory Viscoelastic theory Thixotropic theory

Force Transmission Vertical forces Horizontal or tipping forces Axis of rotation Hourglass shape of PDL

Shape & structure of PDL are adapted to its function 

During normal function



During orthodontic treatment

Normal

Jiggling Forces

Widened PDL Adaptation

After Occlusal Adjustment