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INTRODUCTIONPeriodontal ligament is an integral part of periodontium.

The periodontium is an attachment apparatus of the teeth. It is a connective tissue organ, which is covered by epithelium on top surface.

Teeth are attached to the bone of the jaws by periodontium.

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The periodontal ligament is a soft, fibrous specialized connective tissue which is present in the periodontal space, which is situated between the cementum of root of the tooth and the bone forming the socket wall.

The periodontal ligament extends coronally up to the most apical part of connective tissue of gingiva.

Because the collagen fibers are attached to the cementum and alveolar bone, the ligament provides soft tissue continuity between the mineralized connective tissues of periodontium.

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CELLULAR COMPOSITIONThe cells of periodontal ligament are categorized as: 1. Synthetic Cells a) Osteoblasts b) Fibroblasts c) Cementoblasts 2. Resorptive Cells a) Osteoclasts b) Cementoclasts c) Fibroblasts 3. Progenitor Cells4. Epithelial Cell rests of malassez5. Connective Tissue cells a) Mast cells b) Macrophages 4

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EXTRACELLULAR SUBSTANCEExtra cellular substance comprises the Extra cellular substance comprises the

following:following:

1.1. Fibers Fibers a) Collagen a) Collagen b) Oxytalan b) Oxytalan

2.2. Ground SubstanceGround Substancea) Proteoglycans a) Proteoglycans b) Glycoproteinsb) Glycoproteins

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PERIODONTAL FIBERSThe most important element of periodontal ligament has The most important element of periodontal ligament has

principal fibers, the principal fibers are principal fibers, the principal fibers are collagenouscollagenous in in nature and a arranged in bundles and follow a nature and a arranged in bundles and follow a wavy wavy coursecourse. .

Collagen is a high molecular weight protein.Collagen is a high molecular weight protein.

Collagen macromolecules are Collagen macromolecules are rod like rod like and are arranged and are arranged in form of fibrils. Fibrils are packed side by side to form in form of fibrils. Fibrils are packed side by side to form fibers. fibers.

Vitamin CVitamin C help in formation and repair of collagen. help in formation and repair of collagen.

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Half life of collagen fibers is between 3 to 23 Half life of collagen fibers is between 3 to 23 days and collagen imparts a unique days and collagen imparts a unique combination of flexibility and strength to tissue.combination of flexibility and strength to tissue.

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TYPES OF PERIODONTAL LIGAMENT FIBERS

1. TRANSEPTAL GROUPThese fibers extend interproximally over alveolar bone These fibers extend interproximally over alveolar bone

crest and are embedded in the cementum of adjacent crest and are embedded in the cementum of adjacent teeth.teeth.

They are They are reconstructedreconstructed even after the destruction of even after the destruction of alveolar bone resulting from periodontal disease.alveolar bone resulting from periodontal disease.

These fibers may be considered as belonging to the These fibers may be considered as belonging to the gingiva because they gingiva because they do not have osseous attachment. do not have osseous attachment.

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DIAGRAM OF PRINCIPAL FIBER GROUPS

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ALVEOLAR CREST GROUPThese fibers extend obliquely from the cementum These fibers extend obliquely from the cementum

just beneath the junctional epithelium to alveolar just beneath the junctional epithelium to alveolar crest. crest.

Fibers also run from the cementum over the Fibers also run from the cementum over the alveolar crest and to fibrous layer of periosteum alveolar crest and to fibrous layer of periosteum covering alveolar bone. covering alveolar bone.

The alveolar crest fibers prevent extrusion of tooth The alveolar crest fibers prevent extrusion of tooth and resist lateral tooth movements. and resist lateral tooth movements.

The incision of these fibers during periodontal The incision of these fibers during periodontal surgery does not increase tooth mobility unless surgery does not increase tooth mobility unless significant attachment loss has occurred. significant attachment loss has occurred.

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3. 3. HORIZONTAL GROUP HORIZONTAL GROUP

Horizontal fibers extend at Horizontal fibers extend at right angles to long axis of tooth right angles to long axis of tooth from the from the cementum to alveolar bone.cementum to alveolar bone.

4.4. OBLIQUE GROUP OBLIQUE GROUP

Oblique fibers, Oblique fibers, the largest group the largest group in periodontal ligament, extend from in periodontal ligament, extend from cementum in a coronal direction obliquely to bone. They cementum in a coronal direction obliquely to bone. They bear the bear the brunt of vertical masticatory stresses brunt of vertical masticatory stresses and transfer them into tension on and transfer them into tension on

the alveolar bone.the alveolar bone.

5.5. APICAL GROUP APICAL GROUP

The apical fibers radiate in a rather irregular manner from the The apical fibers radiate in a rather irregular manner from the cementum to bone at apical region of the socket. They cementum to bone at apical region of the socket. They do not occur on do not occur on

incompletely formed roots. incompletely formed roots. 13

INTER-RADICULAR FIBERSThe interradicular fibers fan The interradicular fibers fan out from the out from the

cementum to the tooth in furcation areas of cementum to the tooth in furcation areas of multirooted teeth.multirooted teeth.

The remodeling of fibers take place in intermediate The remodeling of fibers take place in intermediate plexus. This allows adjustments in the ligament, plexus. This allows adjustments in the ligament, which which accommodate small movements of tooth.accommodate small movements of tooth.

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OXYTALAN FIBERSThese are These are immature elastic fibers immature elastic fibers restricted to restricted to

walls of blood vessels and are oriented in an axial walls of blood vessels and are oriented in an axial direction. direction.

The function is to The function is to support the bloods vessels in support the bloods vessels in the periodontal ligament.the periodontal ligament.

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NERVE SUPPLYNerves found in ligament pass through foramina in Nerves found in ligament pass through foramina in

alveolar bone. alveolar bone.

The nerves are the branches of The nerves are the branches of second and third division second and third division of fifth cranial nerve (trigeminal nerve) of fifth cranial nerve (trigeminal nerve) and follow same and follow same path as blood vessels. path as blood vessels.

These nerve fibers provide sense of These nerve fibers provide sense of touch, pressure, pain touch, pressure, pain and proprioception and proprioception during mastication.during mastication.

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CEMENTICLESCementicles are small calcified bodies present in the Cementicles are small calcified bodies present in the

periodontal ligament.periodontal ligament.

They may form into large calcified bodies and fuse They may form into large calcified bodies and fuse within cementum or remain free.within cementum or remain free.

These are found in old age.These are found in old age.

The degenerated epithelial cells form a nidus for The degenerated epithelial cells form a nidus for calcification. calcification.

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FUNCTIONS1. PHYSICAL FUNCTIONA)A) Provision of Provision of soft tissue ‘casing” soft tissue ‘casing” in order to in order to

protect the vessels and nerves from injury due to protect the vessels and nerves from injury due to mechanical forces.mechanical forces.

B)B) Transmission of occlusal forces to bone.Transmission of occlusal forces to bone. Depending on type of force applied, axial force Depending on type of force applied, axial force

when applied causes stretching of oblique fibers when applied causes stretching of oblique fibers of periodontal ligament. of periodontal ligament.

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Transmission of this Transmission of this tensional force tensional force to alveolar bone to alveolar bone encourages bone formation rather then bone resorption.encourages bone formation rather then bone resorption.

But when But when horizontal or tipping force horizontal or tipping force is applied, the tooth is applied, the tooth rotates around the axis.rotates around the axis.

When a greater force is applied, displacement of facial When a greater force is applied, displacement of facial and lingual plates may occur.and lingual plates may occur.

The The axis of rotation axis of rotation in a single rooted tooth is located in in a single rooted tooth is located in area between the apical and middle third of root. area between the apical and middle third of root.

In multirooted tooth, axis of rotations is located In multirooted tooth, axis of rotations is located at at furcation area.furcation area.

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C) C) Attaches the teeth to the bone.Attaches the teeth to the bone.

D) Maintains the gingival tissues in their proper D) Maintains the gingival tissues in their proper relationship to the teeth.relationship to the teeth.

E) E) “Shock absorption” “Shock absorption” resists the impact of resists the impact of occlusal surfaces. Due to its property of shock occlusal surfaces. Due to its property of shock absorption the teeth are slightly more mobile in absorption the teeth are slightly more mobile in early morning than in evening. early morning than in evening.

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2. FORMATIVE & REMODELLING FUNCTIONCells of the periodontal ligament have the Cells of the periodontal ligament have the

capacity capacity to control the synthesis and resorption to control the synthesis and resorption of cementum, ligament and alveolar bone.of cementum, ligament and alveolar bone.

Periodontal ligament undergoes constant Periodontal ligament undergoes constant remodeling, old cells and fibers are broken down remodeling, old cells and fibers are broken down and replaced by new ones.and replaced by new ones.

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3 .NUTRITIONAL FUNCTIONBlood vessels of periodontal ligament provide Blood vessels of periodontal ligament provide

nutrition to the cells of periodontium, because they nutrition to the cells of periodontium, because they contain contain various anabolites and other substances, various anabolites and other substances, which are required by cells of ligament.which are required by cells of ligament.

Compression of blood vessels (due to heavy forces Compression of blood vessels (due to heavy forces applied on tooth) leads to necrosis of cells. applied on tooth) leads to necrosis of cells.

Blood vessels also Blood vessels also remove catabolites.remove catabolites.

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4 .SENSORY FUNCTIONThe nerve bundles found in periodontal ligament, divide into

single myelinated nerve, which later on lose their myelin sheath and end in one of the four types of nerve termination:1. Free endings, carry pain sensations. 2. Ruffini like mechanoreceptors located in the apical area. 3. Meissener’s corpuscles are also mechanoreceptors located primarily in mid-root region. 4. Spindle like pressure endings, located mainly in apex.

Pain sensation is transmitted by small diameter nerves, temperature by intermediate type; pressure by large myelinated fibers.

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