PERIODONTAL LIGAMENT

A SEMINAR

Presented by: Dr. Abhishek Gakhar

Department of Periodontics

At

I.T.S DENTAL COLLEGE,HOSPITAL &RESEARCH

CENTRE,GREATER NOIDA

26th Sep 2012

Moderator - Dr. Kanwarjit Singh Asi

Introduction

1) Structure

2) Evolution

3) Development

4) Constituents of the pdl

5) Blood supply

6) Nerve supply

7) Functions

8) Clinical Corelations

9) Conclusion

10)References

Soft fibrous specialised connective tissue

present in periodontal space b/w cementum of

root &bone forming the socket wall.(1)

Other names

Gomphosis

Desmodent

Pericementum

Dental Periosteum

Alveo-dental ligament

Periodontal membrane

Hour-glass shaped

Widest cervically

Is the dense, fibrous connective tissue

Average width is 0.2mm

Nonfunctional ,unerupted

Bears Heavy occlusal stress

Thickness decreases with age

Reptiles teeth are ankylosed to bone & growth is

by sutures

Teeth fixed to bone

Mammals teeth are suspended by ligaments in sockets &

growth is by cartilage.

The teeth are independent of bone- individual tooth

movement

Hertwigs Epith Root Sheath

Epithelial Rests of Malassez

Cells of dental follicle migrate to root dentin

Migrated follicular cells - cementoblastlay cementum

Other cells of dental follicle differentiate into fibroblast, synthesize fibers & extra cellularsubstance of PDL(2)

PDL

Cells

Resorptive

Synthetic Progenitor

Defence

Extracellular substance

Fibers

Ground substance

The characteristic of synthetic cells are:

Should be actively synthesizing ribosomes.

Increase in rough endoplasmic reticulum and golgi

apparatus.

Large open faced or vesicular nucleus with

prominent nucleoli.(2)

Uninucleated cells

Cuboidal in shape

Basophilic cytoplasm

Numerous orgenelles

Get incorporated as osteocytes(2)

Synthesize both collagenous and

noncollagenous bone proteins.(3)

Osteoblasts also synthesize the enzyme

alkaline phosphatase, which is needed locally

for the mineralization of osteoid.

The precursor cell of the osteoblast is the

preosteoblast. (4)

Osteoblasts have all the characteristics of

hard tissue-forming cells.

When the bone is no longer forming, the

surfaces of the osteoblasts become inactive

and are called Lining cells.

Function:

Osteoblasts help in the synthesis of alveolar bone.

Constitute 65% of total cell population

Remodeling of collagen

Parallel to the collagen fibres

Well developed cytoskeleton

Interconnected by desmosomes.

Appear as elongated cells with pseudopodia like process.(5)

Extensive cytoplasm

Prominent nucleus- flat, disc shaped

Occupys 30% of cell space

Cell organelles-protein synthesis,

Numerous Cytoplasmic processes

Mitochondria numerous,

Lysosomes large , membrane bound vesicles

• The fibroblast is stellate shaped cell which produces:

1. COLLAGEN FIBERS

2. RETICULIN FIBERS

3. OXYTALAN FIBERS

• Various stages in the production of collagen fibers

are as follows:

The first molecule released by fibroblasts is

tropocollagen which contains three polypeptide chains

intertwined to form helix. Tropocollagen molecules are

aggregated longitudinally to form protofibrils, which

are subsequently laterally arranged parallel to

form collagen fibrils. (6)

FUNCTION:

PRODUCTION OF VARIOUS TYPES OF FIBERS & IS ALSO

INSTRUMENTAL IN THE SYNTHESIS OF CONNECTIVE TISSUE

MATRIX

Observed during phases of active cementum

deposition(7)

Oval to cuboidal shape

Basophilic due to high %membrane bound and free

ribosomes.

large nuclei

Structure depends on activity

After some cementum has been laid down, its

mineralization begins with the help of calcium and

phosphate ions.

FUNCTION:

Cementoblasts synthesize the organic

matrix of the cementum

Large & multinucleated gaint cells

Located in Howships lacunae.

Seen adjacent to the bone surface

Irregular distribution

Appear only in active resorption / deposition

Cytoplasm-vacuolated ,numerous mitochondria

Derived from a monocytic-macrophage

system, which are responsible for bone

resorbtion.(8)

They are multinucleated cells with fine,

fingerlike cytoplasmic processes and are rich

in lysosomes that contain tartrate-resistant

acid phosphatase (TRAP).(9)

Osteoclasts lie in resorbtion craters known

as Howship’s lacunae on bone surfaces or in

deep resorption cavities called cutting cones.

These bone cells can only resorb mineralized

bone matrix.

The surface of an osteoclasts which is in contact

with bone has a ruffled border.

Resorption occurs in two stages:

The mineral is removed at bone margins and

then exposed organic matrix disintegrates.

Cementoclasts are found in periodontal ligament

but not remodeled like alveolar bone and

periodontal ligament.

These are found on the surface of cementum.

Progenitor cells are the undifferentiated

mesenchymal cells, which have the capacity to

undergo mitotic division and replace the

differentiated cells

Located in perivasular region and have a small

cnucleus and little cytoplasm(5).

When cell division occurs, one of the daughter cells

differentiate into functional type of connective tissue

cells. The other remaining cells retain their capacity to

divide.

These cells are the remnants of the epithelium ofHertwig’s Epithelial Root Sheath close to cementum.

These cells exhibit monofilaments and are attached to eachother by desmosomes.

They are round to ovoid cells with central darkly stained nuclei.

Can develop into pathological cysts.

Normal function is unknown.

The epithelia cells are isolated from connective tissue by abasal lamina.

Although seen in longitudinal sections as

isolated cell clusters surrounded by a

basement membrane, which separates them

from the surrounding connective tissue, they

apparently form a continuous network

ensheathing the root at a certain distance.

Although the number of epithelial rests of

Malassez decreases with age, cell mitotic

Activity has also been observed. (2,4)

Periodontal ligament showing

epithelial cell rests of

malassez, indicated by arrows

MAST CELLS

Small round or oval.

Numerous cytoplasmic granules, which mask its small,

indistinct nucleus.

The diameter of mast cells is about 12 to 15 microns.

The granules contain heparin and histamine. The

release of histamine into the extracellular compartment

causes proliferation of the endothelial and

mesenchymal cells.

FUNCTION:

Degranulate in response to antigen- antibody formation

on their surface

MACROPHAGES

Derived from blood monocytes

Present near the blood vessels.

These cells have a horse-shoe shaped or kidney

shaped nucleus with peripheral chromatin and

cytoplasm contain phagocytosed material.

FUNCTION

1. Phagocytosis of dead cells .

2. Secretion of growth factor, which help to regulate

the proliferation of adjacent fibroblasts

Extra cellular substance comprises the following:

1. Fibers

a) Collagen b) Oxytalan

2. Ground Substance

a) Proteoglycans b) Glycoproteins

The most important element of periodontal ligament -principal fibers

The principal fibers are collagenous in nature and a arranged in bundles

Follow a wavy course

Dia-5 µm

Primarily composed of type I & III collagen fibrils.

COLLAGEN

Collagen is a high molecular weight protein.

Composed of 3 polypeptide α-chain coiled around each

other- Triple helix

Individual fibril diameter = 50 – 60 nm

Half life : 3 - 23 day

collagen imparts a unique combination of flexibility

and strength to tissue.

Vitamin C help in formation and repair of collagen

Collagen macromolecules are rod like and are

arranged in form of fibrils. Fibrils are packed side by

side to form fibers.

Alveolar crest group

Horizontal group

Oblique group

Apical group

Interradicular group

These fibers extend obliquely from the cementum over the

alveolar crest to alveolar crest.

The alveolar crest fibers prevent extrusion of tooth and resist

lateral tooth movements.

.These fibers resists vertical and intrusive forces

Horizontal fibers extend at right angles to long axis of

tooth from the cementum to alveolar bone.

These fibers are located apical to the level of alveolar

bone crest.

These fibers resists horizontal and tipping forces.

The main attachment of the tooth.

They run obliquely in coronal

direction.

These fibers mainly resists the

vertical and intrusive forces.

They bear the brunt of vertical

masticatory stresses and transfer

them on to the alveolar bone

The apical fibers radiate in a rather irregular manner fThey do not occur on incompletely formed roots. These fibers resist vertical forceps.

These fibers are seen mainly in multi-rooted teeth with bifurcations and trifurcations ,fanning out from cementum into bone.These fibers resists vertical and lateral movements

Do not have osseous attachment

Run from cementum to cementum

Reconstructed even after destruction

These are elastic fibres found in the PL

Restricted to the walls of the blood vessels.

They originate from cementun or bone & are embedded into walls

of the blood vessels.

Function- support blood vessels & regulate vascular flow

These oxytalan fibers run perpendicular to the collagen fibres .

Represents another form of elastic tissue consisting of

bundles of microfibrils embedded within a small quantity of

elastin.

They form a network together with oxytalan fibers,

extending from cementum to bone & sheathing the collagen

fibers of PDL.

It is a zone of loose not well oriented collagen fibers in the

center of the periodontal space.

In this zone the fiber radiating from bone and cementum

intermingle to form lattice network.

Earlier it was thought that this is zone of rapid remodeling

of fibers and necessary for tooth movement.

It is presently believed/ concluded that this is just an

artifact arising out of plane of section. In completely

erupted tooth these fibers are no longer exist.

Collagen fibers bundles are anchored in cementum at

one end of PDL space and alveolar bone at other end.

These fibers do not run in straight line but have a

wavy course.

It mainly consists of-

GAG’s such as hyaluronic acid

Proteoglycans

Glycoprotein i.e. fibronectin and tenascin.

It also consists of water 70%.

They are present between cells & fibers of the PDL.

Main blood supply is from superior and inferior

alveolar arteries. The blood vessels are derived

from the following:

1. BRANCHES FROM APICAL VESSELS

Vessels supplying the pulp.

2. BRANCHES FROM INTRA-ALVEOLAR

VESSELS:- Vessels run horizontally and penetrate

the alveolar bone to enter into the periodontal

ligament.

3. BRANCHES FROM GINGIVAL VESSELS:- The

arterioles and capillaries ramify and form a rich

network. Rich vascular plexus is found at the apex and

in cervical part of ligament.

Nerves pass through apical foramen to enter the PL.

Finer branches enter middle & cervical

portions of the PL through openings in the alveolar

bone

Nerves supplying the PDL are : Superior Alveolar

Nerve & Inferior Alveolar Nerve

• Branches of trigeminal nerve

These nerve fibers provide sense of touch, pressure,

pain and proprioception during mastication

There are four types of neural terminations in the PDL that

have been described:

1- Free endings- Sensory, pain perception

2- Ruffini’s Corpuscles- knob-like, mechanoreceptors

3- Tactile (meissner’s) corpuscles –mid root,

mechanoreceptors

4- Spindle type nerve endings -apex

Small calcified bodies

Remain free or fused into large calcified mass.

They may be joined with cementum to form

excementoses.

Degenerated epithelial cells form the nidus for their

calcification.

Old age

1. PHYSICAL FUNCTION

A) Provision of soft tissue ‘casing” in order to protect

the vessels and nerves from injury due to

mechanical forces.

B) Transmission of occlusal forces to bone.

Depending on type of force applied, axial force

when applied causes stretching of oblique fibers of

periodontal ligament.

C) Attaches the teeth to the bone.

D) Maintains the gingival tissues in their proper

relationship to the teeth.

E) “Shock absorption” resists the impact of occlusal

surfaces.

Two theories have been explained for mechanism

of tooth support.

A. TENSIONAL THEORY

B. VISCOELASTIC THEORY

• According to it, principal fibers play a major role

in supporting tooth and transmitting forces to

bone.

• When forces are applied to tooth, principal fibers

unfold and straighten and then transmit the

forces to alveolar bone, causing elastic

deformation of socket.

A. Tooth in a resting state

B. The periodontal ligament fibers are compressed in areas of pressure and stretched in area

of tension.

• According to it, the fluid movement largely controls the

displacement of the tooth, with fibers playing a secondary

role.

• When forces are transmitted to the tooth, the extracellular

fluid is pushed from periodontal ligament into marrow

spaces through the cribriform plate.

• After depletion of tissue fluids, the bundle fibers absorb

the shock and tighten.

• Cells of the periodontal ligament have the capacity

to control the synthesis and resorption of

cementum, ligament and alveolar bone.

• Periodontal ligament undergoes constant

remodeling, old cells and fibers are broken down

and replaced by new ones.

• Blood vessels of periodontal ligament provide nutrition

to the cells of periodontium, because they contain

various anabolites and other substances, which are

required by cells of ligament.

• Compression of blood vessels (due to heavy forces

applied on tooth) leads to necrosis of cells.

• Blood vessels also remove catabolites.

• The 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.

• The resorption and synthesis are controlled procedures.

• If there is a long term damage of periodontal ligament,

which is not repaired, the bone is deposited in the

periodontal space.

• This results in obliteration of space and ankylosis

between bone and the tooth.

• The quality of tissue changes if balance between

synthesis and resorption is disturbed.

• If there is deprivation of Vit. C which are essentialfor collagen synthesis, resorption of collagen willcontinue.

• So there is progressive destruction and loss ofextra cellular substance of ligament.

• This occurs more on bone side of ligament.

• Hence, loss of attachment between bone and toothand at last, loss of tooth.

The primary role of periodontal ligament is to support the tooth in the bony socket.

AGE CHANGES

The width of periodontal ligament varies from 0.15 to 0.38mm. The average width is:

- 0.21mm at 11 to 16 years of age. - 0.18mm at 32 to 50 years of age.- 0.15mm at 51 to 67 years

1. width of periodontal ligament decreases as age advances

2. Aging results in more number of elastic fibers and decrease in vascularity, mitotic activity, fibroblasts and in the number of collagen fibers and mucopolysaccharides.

PERIAPICAL LESIONS

Periapical area of the tooth is the main pathologic site.

Inflammation of the pulp reached to the apical periodontal

ligament and replaces its fiber bundles with granulation

tissue called as granuloma, which then progresses into

apical cyst.

Chronic periodontal disease can lead to infusion of

microorganisms into the blood stream.

The pressure receptors in ligament have a

protective role. Apical blood vessels are protected

from excessive compression by sensory apparatus of

the teeth.

The rate of mesial drift of tooth is related to health,

dietary factor and age. It varies from 0.05 to 0.7mm

per year

Trauma:

The trauma can be result from number of ways:

Abnormal occlusal function,Accidental blows.

Premature contacts from high points in restoration.

Excessive orthodontic forces.

All of the above leads to pulpal injury result in periapical

changes.

Over instrumentation during RCT causes profuse periapical

haemorrhage and dissemination of dentin debris beyond the

apical foramina. It result in edematous PDL, intense neutrophil

inflammatory infiltrate.

Surface resorption:

When there is very less damage to PDL – Adjacent PDL is

proliferates.

Inflammatory resorption: When there is infection is there –

inflammation of bone and PDL – which is replaced by

granulation tissue.

Replacement resorption : When there is severe damage to

PDL, resorption of bone, cementum, PDL it is replaced by the

bone. Results in ankylosis of tooth

Orthodontic tooth movement

Depends on resorbtion and formation of bone and periodontal

ligament (i.e. remodelling).

when a orthodontic force is applied through PDL to the tooth

there is a initial compression of PDL on pressure side followed

by the bone-resorbtion, whereas in tension side there is bone

apposition.

Application of large amount of force result in necrosis and

death of PDL

Carranza FA, and Saglie, 1984 :The PDL acts as a shock absorber & a means of transmitting occlusal forces to bone

GriffinCJ 1968:Presence of unnmyelinated nerve endings in the periodontal membrane

Grant DA, Stern, Listgarten,1988: PDL plays an active role in the resorption and formation of collagen and cementumand the fibroblasts of the PDL may develop into cementoblasts and osteoblasts.

ButlerWT,Birkedal-hansen,Beegle et al ,1975:studied the proteins in the periodontium,concluded with the identification of type I & III collagen.

Genco R, Goldman, HM., and Cohen, 1990: Periodontal regeneration is defined as restoration of the periodontal attachmentapparatus, which includes periodontal ligament, cementum, and alveolar bone, and gingival

Nyman S, Gottlow J, Karring T, et al. 1982:cells from the

periodontal ligament (PDL) are responsible for the

reestablishment of periodontal attachment.

A study done on Dogs by Isaka et. al. concluded that dogs

periodontal ligament cells retain capability to differentiate

into osteoblast lineage & may act in periodontal

regeneration of periodontal ligament with new cementum

formation .

The diseases of PDL are often irreversible once

destroyed the PDL is difficult to regenerate and

damage of PDL result in loss of tooth. So, all

operative procedures must be performed so as to

maintain and restore the PDL is optimum health and

function.

1) Glossary of Periodontal Terms

2) FerminA, Carranza, Newmann, Takei; clinical periodontology ;9thedition;45–51.

3)R.Tencate,AntonioNanci;oralhistology,development,structure&function;6thedition;111–143.

4)FerminA, Carranza, Newmann, Takei; clinical periodontology ;9thedition;45–51.

5)Junqueria LC, Carneiro J, Kelley RO: Basic Histology, ed6, Norwalk, Conn, 1989, Appleton & Lange.

6) Hagel-Bradway S, Dziak R: Regulation of bone cells metabolism, J Oral PatholMed 18:344,1989

7)Sicher H, DuBrul EL: Oral Anatomy, ed6, St Louis, 1975

8)Chambers TJ: The cellular basis of bone

resorption, Clin J Periodontal Res 1:120,

1966.

9)Bernard GW, Ko JS: Osteoclast formation

in vitro form bone marrow, mononuclear

cells in osteoclast-free bone, Am J Anat

161:415, 1981