Cellular elements 4Types- connective tissue cells (Fb, Cb, Ob) - epithelial rest cells -immune system cells - cells associated with neurovascular elements

Connective tissue cells Fibroblast- - most common cells in the PDl - ovoid or elongated cells and exhibit pseudopodia like process - synthesize collagen and have the capacity to phagocytose old collagen fib and degrade them by enzyme hydrolysis.

Cementoblast - They are the cells responsible for secreting the organic matrix of cementum in the PDL. Osteoblast - They are found on the surface of the alveolar bone.

Epithelial rest cells - Epithelial rest of Malassez are considered as remnants Hertwigs root sheath which disintegrates during root development. - Most numerous in apical and cervical areas. - when stimulated, may participate in the formation of periapical cyst and lateral root cyst.

Immune system cells Include – neutrophils, lymphocytes, macrophages, mast cells and eosinophils. These cells as well as those associated with neurovascular elements, are similar to the cells in other connective tissues.

Ground substance GAG (glycosaminoglycans) - Hyaluronic acid - Proteoglycans GP (glycoproteins) - fibronectin - Laminin Water (70%)

Functions of ground substance Helps in transportation of water, electrolyte, nutrients, and metabolites, to and from CT cells, thus is essential for the maintenance of the normal function of CT.

PDL may also contain calcified masses called cementicles which are adherent to detached from root surface. Cementicles may develop from calcified epithelial rest, around small spicules of cementum or alveolar bone traumatically displaced in to PDL, from calcified sharpey’s fib, and from calcified thrombossed vessels in PDL.

Functions of PDL 1.Physical 2.Formative 3.Remodelling 4.Nutritional 5.Sensory

Physical function 1.Provision of soft tissue “casing” to protect the vessel and nerves from injury to mechanical forces. 2. Transmission of occlusal forces to the bone. 3. Maintenance of gingival tissues in their proper relationship to the teeth. 4. Resistance to the impact of occlusal forces (shock absorption).

SHOCK ABSORPTION 2 theories- -Tensional theory -Viscoelastic system theory

Formative and remodeling function PDL have the regenerative capacity in providing the cell lineage namely ob, cb and fb. Thus it help in the formation and resorption of cementum and bone during physiological tooth movement and repair of injuries.

Nutritional and sensory function PDL supplies nutrients to the cementum, bone and gingiva by way of blood vs and also provide lymphatic drainage. The PDL is abundantly supplied with sensory nerve fib capable of transmitting tactile, pressure and pain sensations by the trigeminal pathway.

There are 4 types of neural terminations are present in PDL 1.Free ending- which have tree like configuration and carry pain sensation 2.Ruffinian corpuscles- Mechanoreceptors (in apical areas) 3.Meisners corpuscles- Mechanoreceptors (in midroot areas) 4.Spindle like receptors- Pressure and vibration receptors/

Homeostasis With the presence of both formative and resorptive activity the PDL provides a homeostasis in the tissue environment.

Blood supply 3 sources- 1. Apical vs 2. penetrating vs from alveolar bone 3. Anastomosing vs from gingiva Maxilla- sup alv artery mandibli- inf alv artery Venous drainage of PDL accompanies the arterial supply.

Nerve supply 1. Anatomic 2. Sensory

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