Periodontal LigamentPeriodontal Ligament

Introduction

Soft fibrous specialised connective tissue present in periodontal space b/w cementum of root & bone forming the socket wall

Other names Gomphosis Desmodent Pericementum Dental Periosteum Alveo-dental ligament Periodontal membrane

Is the dense, fibrous connective tissue ...

Average width is 0.2mmNonfunctional,unerupted Heavy occlusal stressHour-glass shapedWidest cervically

Evolution

Reptiles teeth are ankylosed to bone & growth is by sutures

Mammals teeth are suspended by ligaments in sockets & growth is by cartilage

Hertwigs Epith Root Sheath

Epithelial Rests of Malassez

Cells of dental follicle migrate to root dentin

Migrated follicular cells – cementoblast lay cementum

Other cells of dental follicle differentiate into fibroblast, synthesize fibers & extra cellular

substance of PL

Dental follicle cells

CONSTITUENTS OF THE PDL…..

1.Fibres 2.Ground

substance3.Cells 4.Blood

vessels 5.Nerves6.lymphatics

PRINCIPAL FIBERS -

Primarily composed of type I collagen fibrils.

Also contains oxytalan fibers -related to the microfibrillar component of elastic fibers.

Principal fibers of the PDL

Alveolar crest groupHorizontal groupOblique groupApical groupInterradicular group

ALVEOLAR CREST FIBRES-

HORIZONTAL FIBERS -

OBLIQUE FIBRES -

APICAL FIBERS -

INTER RADICULAR FIBRES -

TRANSEPTAL FIBRES -

•Do not have osseous attachment•Run from cementum to cementum•Reconstructed even after destruction

Arrangement of principle fibres –

Previously –

Fibres embedded in bone intercalated with fibres from cementum

Recent evidence – fibres cross entire width but en route branch & join adjacent fibre

Intermediate plexus –

Randomly arranged

SHARPEYS FIBRES -

ELASTIC FIBRE SYSTEM

FIBRES OF THE PDL -

FIBRES & CELLS OF THE PDL….

collagen

These are principal fibres of the periodontal ligament.

Type1 & type 3 collagen are present.They are high molecular weight protein

attached to small number of sugars & glycoproteins.

They are rod like & arranged in the form of bundles or fibres.

Oxytalan fibres

These are elastic fibres found in the PL They are restricted to the walls of the blood

vessels.They originate from cementun or bone & are

embedded into walls of the blood vessels.They support blood vessels in the PL.

CELLS OF THE PDL -

1.Fibroblasts2.Cementoblasts3.Cementoclasts4.Osteoblasts5.Osteoclasts6.Epithelial cell rests7.Defense cells –

macrophage leucocytes

lymphocytes mast cells plasma

cells

FIBROBLASTS-

Most numerous

65% of total cells

Densely packed population

Parallel to the collagen

fibres

Oriented along principal

fibresInterconnected by desmosomes. Nexus type junctions.

Prominent nucleus- flat, disc

shaped

Occupys 30% of cell space

Single distinct nucleolus

Clearly defined nuclear pores

Spindles / flat disks

Long ovoid nuclei, numerous

Cytoplasmic processes

Mitochondria – numerous, well

distributed

Lysosomes – large , membrane

bound vesicles

CEMENTOBLASTS & CLASTS -

Only observed during phases of active cementum deposition Oval to cuboidal shape Basophilic due to high % membrane bound and free ribosomes Easy to recognize, even under the light microscope Cementoblasts lining the cementum- plump cells, rich in cytoplasm Squat, cuboidal cells with large nuclei Structure – depends on activity

CEMENTOBLASTS & CLASTS -

Only observed during phases of active cementum deposition Oval to cuboidal shape Basophilic due to high % membrane bound and free ribosomes Easy to recognize, even under the light microscope Cementoblasts lining the cementum- plump cells, rich in cytoplasm Squat, cuboidal cells with large nuclei Structure – depends on activity

OSTEOBLASTS -

Near bone surfaceForm a layer of

cuboidal cellsBasophilic cytoplasmProminent nucleusNumerous orgenellesGet incorporated as

osteocytes

OSTEOCLASTS - Seen adjacent to the bone surface Irregular distribution Appear only in active resorption / deposition Form a continuous layer lining the osteoid Located in Howships lacunae.Large & multinucleatedRuffled border, clear/annular zone

Progenitor cells

Other cells

Epithelial cell rests of mallasezMast cells macrophages

GROUND SUBSTANCE

They are present between cells & fibers of the PL.

They contain GAG ;hyaluronic acid & proteoglycan & glycoproteins like fibronectin & laminin.

They control fibrillogenesis & fiber orientation.

They transport food to cells & waste products from cells to blood vessels.

Glycoproteins

Fibronectin; this is in filamentous form & promotes attachment of cells to collagen fibrils.it is involved in cell migration & orientation.

Tenascin; this glycoprotein is present adjacent to alveolar bone & cementum.

Interstitial tissue

Blood vessels,lymphatics & nerves of PL are surrounded by loose connective tissue which are called interstitial tissue

Structures present in the connective tissue

Blood vessels LymphaticsNervesCementicles

Blood vessels

The PL has rich vascular supply from superior & inferior alveolar arteries.

Blood vessels derived from; branches from apical vessels branches from intraalveolar vessels branches from gingival vessels

BLOOD SUPPLY -

Multiple supplyAverage diameter– 20υmGlomeruli-like arterio

venous shunts Veins- prominent beneath

JECirculus –Wong & Sims

1971

Lymphatics

The lymphatic drainage is from PL to the alveolar bone.they follow the path of blood vessels.

Nerve supply

Nerves pass through apical foramen to enter the PL.

Finer branches enter middle & cervical portions of the PL through openings in the alveolar bone

Types of nerves

Non myelinated nerves; they are autonomic nerves having a diameter of 0.5µm & supply blood vessels.

Myelinated nerves; they are sensory nerves having a diameter of 5µm.the sensation of pain,pressure & touch are felt by finer myelinated nerves & proprioception through larger myelinated nerves.

Free nerve endings –

sensory

More near cementum

For pain perception

Ruffini type endings –

mechanoceptors

Extraordinarily defined

pressure sensation

Coiled meissners- midroot region, mechanoceptors

Spindle-like endings – apex, surrounded by fibrous capsule

Cementicles

These are small calcified bodies present in the periodontal ligament.

They may remain free in the connective tissue or may fuse into large calcified mass.

They may be joined with cementum to form excementoses.

Degenerated epithelial cells form the nidus for their calcification.

CEMENTICLES

Functions of the PL

PhysicalFormativeNutritiveSensoryHomeostasis

Aging of the PL

As the aging occurs in the PL the number of cells & their activity decreases.

Scalloping occurs in the cementum & the alveolar bone.

There is increase in elastic fibers & decrease in vascularity,mitotic activity.

There is decrease in width & masticatory musculature strength.

Clinical considerations

Width of PL varies from 0.15-0.38mm,it decreases with age.

Gingivitis,Periodontitis.Trauma to ligament.Orthodontic tooth movement.Dental granuloma. Regeneration of PL.

GINGIVITIS,PERIODONTITIS

PERIODONTAL DISEASE

ORTHODONTIC TOOTH MOVEMENT

DENTAL GRANULOMA

PERIODONTAL REGENERATION

GTR

Guided tissue regeneration

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