PerioDontal Ligament

Periodontal Ligament

Dr. Syed Sadatullah

Assistant ProfessorCollege of Dentistry

King Khalid University Abha

ObjectivesAt the end of this chapter the student should be able to understand the development process and histology of periodontal ligament.

Sub topicsTopic 1. IntroductionTopic 2. Development of Periodontal LigamentTopic 2. Histology of Periodontal Ligament

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1. Introduction

Periodontal ligament (PDL) is connective tissue that connects the cementum of the root to the alveolar bone proper, hence the name ligament

The thickness of the PDL varies from tooth to tooth and its position in relation to the root.

The thinnest portion of the PDL is near the middle of the root.

The width of PDL shows a progressive decrease with age.

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The PDL has a heterogeneous population of mesenchymal cells that when induced differentiate into fibroblasts, cementoblasts and osteoblasts

The fibroblasts also have the capacity to form PDL, Cementum and Alveolar bone any time in health.

The factors secreted by PDL fibroblasts inhibit mineralization and prevent ankylosis of the tooth.

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The PDL is always in a state of remodelling.

Functions of PDL

1.Formative

2.Supportive

3.Protective

4.Sensory

5.Nutritive

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2. Development of PDLDuring the initial stages of root formation the follicular cells show increased proliferation

The innermost cells of the follicle near the forming root differentiate into cementoblasts and the outer most cells differentiate into osteoblasts

The centrally located cells differentiate into fibroblasts

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Fibroblasts produce the periodontal ligament fibers.

They get embedded in the developing cementum and alveolar bone.

At first, all the developing fibers of the periodontal ligament run obliquely in a coronal direction from tooth to bone. This changes as the tooth erupts.

The part of PDL fibers present in the cementum and alveolar bone are called Sharpey’s fibers.

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Dr.S

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Dr.S

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Dr.S

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2 Histology of PDL

PDL like any other connective tissue is composed of cells and extracellular components

Cells

1.Fibroblasts

2.Cementoblasts

3.Osteoblasts

4.Osteoclasts

5.Undifferentiated mesenchymal cells

6.Epithelial cell rests of Malassez

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Extracellular components

1.Collageneous fibers

2.Elastic fibres

3.Ground substance

4.Nerves

5.Blood vessels

The main fibres are the principal fibres and additional fibres are oxytalan fibres

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Principal fibresThe fibre bundles that exit the cementum and alveolar bone and form the periodontal ligament are called principal fibres.

According to the location of these fibres they can be dentoalveolar fibres or gingival fibres

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Dentoalveolar fibre group

1. Alveolar crest group – near the cervical region

2. Horizontal fibre group – near the midroot

3. Oblique fibre group – immediately above apical group

4. Apical fibre group – near the apical area of the root

5. Interradicular group – between two roots

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Gingival fibre group

A. Dentogingival group – these fibres are the most numerous, extending from the cervical cementum to the lamina propria of the gingiva.

B. Alveologingival group – these fibres extend from the alveolar crest to the lamina propria of the gingiva.

C. Circular of Circumferential fibres– continuous around the neck of the tooth.

D. Transseptal fibres– these fibers extend from the cervical cementum of one tooth to the cervical cementum of the other.

Dentogingival group and alveologingival group fibers embed in attached gingiva and free gingiva, hence, also called attached gingival group and free gingival group fibers.

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Elastic fibres

Apart from principal fibres additional fine fibres appear in the periodontal ligament that are called oxytalan fibres.

These fibres support the principal fibres system and are considered to be part of the indifferent fibre plexus.

They are elastic-like and appear around the vessel walls.

Other elastic fibers are elastin and elaunin fibers.

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Vascular and Nerve supply

There are spaces between the fibre bundles called the interstitial spaces.

The interstitial spaces contain blood vessels, lymph channels, and nerves.

These structures help maintain the vitality of the periodontal ligament.

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