PERIODONTAL LIGAMENT AND ALVEOLAR BONEdental.subharti.org/periodonotics/PERIODONTAL_LIGAMENT.pdfMost...

PERIODONTAL

LIGAMENT

Dr. Amit Wadhawan

Dr. Amit Wadhawan, Subharti Dental College, SVSU

DEFINITION

Connective tissue that surrounds the

root & connects it to the bone.

Continuous with the connective tissue of

gingiva & communicates with marrow

spaces of bone.

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GOMPHOSIS

Mammals

ANKYLOSIS

Reptiles, Pisces

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COMPOSITION

Periodontal fibers

Cellular elements

Extracellular matrix

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PERIODONTAL FIBERS

Principal Fibers: Collagenous in

nature, arranged in bundles & follow

a wavy course.

Sharpey’s Fibers: Terminal ends

which insert into bone & cementum.

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COLLAGEN

Protein composed of different amino acids: glycine, proline, hydroxylysine & hydroxyproline.

Synthesized by fibroblasts, chondroblasts, osteoblasts & odontoblasts.

Different types according to chemical composition, distribution, function & morphology.

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TYPES OF COLLAGEN

TYPE I - Bone

TYPE II - Cartilage

TYPE III, V - Granulation Tissue

TYPE IV,VI - Endothelial matrix

TYPE X - Hypertrophic cartilage

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COLLAGEN SYNTHESIS

TROPOCOLLAGEN

FIBRIL

FIBER

BUNDLE

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GROUPS OF PRINCIPAL

FIBERS

1) TRANSSEPTAL GROUP

2) ALVEOLAR CREST GROUP

3) HORIZONTAL GROUP

4) OBLIQUE GROUP

5) APICAL GROUP

6) INTERRADICULAR GROUP

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OTHER FIBER GROUPS

Oxytalan Fibers: Contain immature

forms of elastin – oxytalan & eluanin.

Direction : Run parallel to the root

surface in a vertical direction.

Function : Regulate blood flow.

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1) Connective tissue cells: Fibroblasts,

Cementoblasts, Osteoblasts

2) Epithelial rest cells

3) Immune system cells

4) Cells associated with neurovascular

elements.

CELLULAR ELEMENTS

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Most common cells in the Pdl.

Synthesize collagen & also

phagocytose "old" collagen fibers and

degrade them by enzyme hydrolysis –

regulate collagen turn-over.

Functions such as secretion of collagen

of different types or production of

collagenase.

FIBROBLASTS

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1) Connective tissue cells: Fibroblasts,

Cementoblasts, Osteoblasts

2) Epithelial rest cells

3) Immune system cells

4) Cells associated with neurovascular

elements.

CELLULAR ELEMENTS

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Osteoblasts

Osteoclasts

Cementoblasts

Odontoclasts

Seen in the cemental and osseous

surfaces of the periodontal ligament.

OTHER CELLS

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Appear as either isolated clusters of cells or

interlacing strands.

Are considered remnants of Hertwig's root

sheath, which disintegrates during root

development.

Distributed close to the cementum throughout

the periodontal ligament & are most numerous

in the apical and cervical areas.

EPITHELIAL RESTS OF

MALASSEZ

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CLINICAL SIGNIFICANCE

Diminish in number with age by

degenerating or undergoing calcification

to become cementicles.

Proliferate when stimulated and

participate in the formation of periapical

cysts and lateral root cysts.

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GROUND SUBSTANCE

Has a high water content (70%). 1.Proteoglycans (Glycosaminoglycans & Decorin, Biglycan),

2. Glycoproteins (Fibronectin & Laminin).

Calcified masses called cementicles, which

are adherent to or detached from the root

surfaces. May develop from :

Calcified epithelial rests;

Around small spicules of cementum or alveolar

bone traumatically displaced into the pdl;

Calcified Sharpey's fibers; &

Calcified, thrombosed vessels within the pdl.

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WIDTH & SHAPE

Normal width : 0.15 – 0.25 mm

Increases during hyperfunction.

Shape : Hourglass

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19 Dr. Amit Wadhawan, Subharti Dental College, SVSU

1) PHYSICAL FUNCTION

2) FORMATIVE & REMODELLING

FUNCTION

3) NUTRITIVE & SENSORY FUNCTION

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FUNCTIONS OF THE PERIODONTAL

LIGAMENT


1) PHYSICAL FUNCTION

1. Provision of a soft tissue "casing" to protect the vessels and nerves

2. Transmission of occlusal forces to the bone

3. Attachment of the teeth to the bone

4. Maintenance of the gingival tissues in their

proper relationship to the teeth.

5. Resistance to the impact of occlusal forces

(shock absorption) .

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RESISTANCE TO THE IMPACT OF

OCCLUSAL FORCES

1) TENSIONAL THEORY

2) VISCOELASTIC THEORY

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When a force is applied to the crown, the

principal fibers first unfold and straighten and

then transmit forces to the alveolar bone,

causing an elastic deformation of the bony

socket.

Finally, when the alveolar bone has reached its

limit, the load is transmitted to the basal bone.

TENSIONAL THEORY

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Considers the displacement of the tooth to be largely controlled by fluid movements, with fibers having only a secondary role.

The extra cellular fluid passes from the pdl into the marrow spaces of bone through foramina in the cribriform plate.

These perforations are more abundant in the cervical third than in the middle and apical thirds

VISCOELASTIC THEORY

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After depletion of tissue fluids, the fiber

bundles absorb the slack and tighten. This

leads to blood vessel stenosis.

Arterial back pressure causes ballooning of

the vessels, and passage of blood ultrafiltrates

into the tissues, thereby replenishing the

tissue fluids

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TRANSMISSION OF OCCLUSAL

FORCES TO THE BONE

The arrangement of the principal fibers is similar to a suspension bridge or hammock.

When an axial force is applied to a tooth, a tendency toward displacement of the root into the alveolus occurs.

The oblique fibers alter their wavy, untensed pattern; assume their full length; and sustain the major part of the axial force.

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When a horizontal or tipping force is applied :

The first is within the confines of the

periodontal ligament,

the second produces a displacement of the

facial and lingual bony plates.

The tooth rotates about an axis that may

change as the force is increased.

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The apical portion of the root moves in a direction opposite to the coronal portion.

In areas of tension, the principal fiber bundles are taut rather than wavy.

In areas of pressure, the fibers are compressed, the tooth is displaced, and a corresponding distortion of bone exists in the direction of root movement

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In single-rooted teeth, the axis of rotation is

located in the area between the apical third

and the middle third of the root .

The periodontal ligament, which is shaped

like an hourglass, is narrowest in the region

of the axis of rotation.

AXIS OF ROTATION

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31 Dr. Amit Wadhawan, Subharti Dental College, SVSU

In multirooted teeth, the axis of rotation is

located in the bone between the roots.

In compliance with the physiologic mesial

migration of the teeth, the periodontal

ligament is thinner on the mesial root

surface than on the distal surface.

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2) FORMATIVE AND REMODELING

FUNCTION

Cells of the pdl participate in the formation and resorption of cementum and bone :

physiologic tooth movement

in the accommodation of the periodontium to occlusal forces

in the repair of injuries.

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COLLAGEN TURNOVER

Radioautographic studies indicate a very

high turnover rate of collagen

The rate of collagen synthesis is twice as

fast as that in the gingiva and four times

as fast as that in the skin, as established

in the rat molar.

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3) NUTRITIONAL AND SENSORY

FUNCTIONS

The pdl supplies nutrients to the

cementum, bone, and gingiva by way

of the blood vessels and provides

lymphatic drainage .

The pdl is abundantly supplied with

sensory nerve fibers capable of

transmitting tactile, pressure, and pain

sensations by the trigeminal pathways.

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Pass into the pdl from the periapical area & through channels from the alveolar bone .

Divide into single myelinated fibers.

Four types of neural termination:

1.Free endings : carry pain sensation

2.Ruffini-like mechanoreceptors, located primarily in the apical area;

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3.Coiled Meissner's corpuscles, also mechanoreceptors, found mainly in the midroot region;

4.Spindle-like endings for pressure and vibration, which after chronic periapical inflammation, tooth replantation, and occlusal trauma and around embedded teeth

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