PRESENTED BY:PRESENTED BY: DR SHILPA SHIV DR SHILPA SHIV I MDS I MDS DEPT OF PERIODONTOLOGYDEPT OF PERIODONTOLOGY

Introduction Definition Extent and shape Average width Evolution of PDL Development Orientation of PDL fibers Structure Biochemical composition Cellular elements Periodontal fibers

ContentsContents

Collagen Ground substance Functions of PDL Blood supply Venous drainage Lymphatic Nerve supply Age changes & Clinical considerations Healing after periodontal surgery Conclusion References

The normal periodontium is a unique and a complex

dynamic structure; each of its components having distinct functions that are capable of adaptation during the life of the structure.

PDL is the soft, richly vascular and cellular connective tissue which surrounds the roots of teeth and joins the root cementum with the socket wall.

Synonyms: Desmodont, Gomphosis, Pericementum, Dental –periosteum, Alveolodental ligament, Periodontal membrane.

IntroductionIntroduction

Periodontal ligament is composed of soft complex vascular and

highly cellular connective tissue that surrounds the tooth roots and connects to the inner wall of the alveolar bone (Mc Culloch CA, Lekic P, Mc Kee MD Periodontol 2000 24:56,2000)

It is that soft, specialized CT situated between the cementum covering the root of the tooth and bone forming the socket wall. (A.R.Tencate 1971)

It is a narrow and highly cellular CT that forms the interface between alveolar bone and cementum. (Periodontol 2000,vol.3,1993)

DefinitionDefinition

Soft, richly vascular and cellular connective tissue which

surrounds the roots of the teeth and joins the root cementum with the socket wall. (Jan Lindhe 5th ed)

The periodontal ligament occupies the periodontal space, which is located between the cementum and the periodontal surface of alveolar bone and extends coronally to the most apical part of the lamina propria of the gingiva. (Orban’s)

In the coronal direction it is continuous with lamina

propria of gingiva & is demarcated by the alveolar crest fibers.

At the root apex it merges with the dental pulp.

PDL has the shape of an hour glass and is narrowest at the mid root level.

It ranges in width from 0.15-0.38mm.

Extent & shapeExtent & shape

Depending on age

11-16 yrs - 0.21mm

32-52 yrs - 0.18mm

51-67 yrs - 0.15mm According to functional state of the tissues

Time of eruption - 0.1- 0.5mm

At function - 0.2-0.35mm

Hypo function - 0.1-0.15mm

Average widthAverage width

The evolutionary step from reptile to mammal included a

series of coordinated changes in the jaws.

The central point is the radical reconstruction of the mandible

In reptiles mandible consists of-Dentary

Mandibular articulation - Articulare and Quadratum

EvolutionEvolution

In mammals-

Fate of dentary- Forms the mandible Others were lost or changed into middle ear ossicles

Articulare- malleusQuadratum- incus

Dentary developed a condylar process which formed the new temporomandibular joint, that for some time functioned with old articulare-quadratum joint- Double jointed forms

Change from many boned to single boned mandible brings in a

radical change in mode of growth. Reptiles –Sutural Mammals- Cartilage of condyle

Growth of mandibular body height

Tooth movement during eruption. Teeth move as unit independent of bones, by remodeling of periodontium.

Growth changesGrowth changes

Begins with root formation

(Tencate et al.,1972)

& prior to tooth eruption.

Varies among species, tooth families

& between primary & secondary teeth.

DevelopmentDevelopment

The periodontal tissues are derived from dental follicle which

in turn originates from dental papilla.

It has also been proposed that the mesenchyme deriving periodontium may have two differentiation compartments

a. Alveolar clade --- Fibroblasts & osteoblasts b. Cementum clade --- fibroblasts & cementoblasts

The term dental follicle has been used by different authors to mean different things.

Development….

-

Closely related to root formation

Development of principal fibersDevelopment of principal fibers

Development….

Fig 2 Fig 1 Fig 3

Terminal portions of principal fibers that insert into

cementum and bone are termed as Sharpey’s fibers.

The principal fibers embedded in the cementum have a small diameter but are more numerous than those embedded in the alveolar bone proper.

In addition to these fiber types, small collagen fibers associated with larger principal fibers have been called as “Indifferent fiber plexus of Shefforfold”

Development…

Orientation of PDLOrientation of PDL

Mature PDL can be sub divided into 3 regions:

-Bone related region- rich in cells-Cementum related region- dense and ordered

collagen fibers-Middle zone- few cells & thinner collagen fibrils

CELLULAR ELEMENTS a. Connective tissue cells Synthetic Resorptive -Fibroblasts - Fibroblasts -Cementoblasts - Cementoclasts -Osteoblasts - Osteoclasts b. Epithelial cell rests c. Immune system cells d. Neuro-vascular elements• PERIODONTAL FIBERS• GROUND SUBSTANCE

Structure Structure

Basic properties Increased transcription of RNA and production of

ribosomes which is reflected by a large open faced or vesicular nucleus containing prominent nucleoli.

Development of large quantities of RER covered by ribosomes.

Large amounts of golgi saccules and vesicles (seen as clear unstained areas in light microscope).

Large numbers of mitochondria. Abundant cytoplasm.

Cellular elements Cellular elements

Most common cells in PDL

Occupies about 30% of the volume of the periodontal ligament space in rodents (Beertsen W, Brekelmans M, Everts V. 1978)

Appear as ovoid or elongated cells oriented along the principal fibers, exhibiting pseudopodia like processes.

In cross section, they may exhibit a stellate appearance

with cytoplasmic process segregating individual fiber bundles of collagen fiber.

FibroblastsFibroblasts

Phenotypically distinct & functionally different sub

populations of fibroblasts exist in adult PDL.

They may have different functions like secretion of different collagen types & production of collagenase.

Importantly in inflammatory situations, an increased expression of MMP occurs that aggressively destroys collagen.

Thus attractive therapies for controlling this may

include host modulators to inhibit MMP.

Fibroblasts…

The PDL fibroblasts are large cells with an extensive

cytoplasm containing in abundance, all organelles associated with protein synthesis and secretion.

They also have well developed cytoskeleton with a particularly prominent actin network.

ATTACHMENTS The fibroblasts of PDL are interconnected by gap

junctions or adherence type of junctions. The cells may attach to collagen via a fibro nexus type

of attachment plaque and are likely to have the capacity to orient extracellular matrix.

Fibroblasts…

The migratory and contractile activity of fibroblast

is because of the presence of contractile protein actin and myosin in their cytoskeleton.

It may: Remain stationary and pull on adjacent structures Crawl and cause the environment in which it lies

to wrinkle.

Fibroblasts…

Chemo attractants produced locally or by the hard tissues

bordering the ligament may have a role in this process. Directed migration of cells is associated with polarity of

organelles, the nucleus usually in the trailing portion of cell and golgi apparatus and centrioles are towards the leading edge of the cells.

They appear to be rich in alkaline phosphatase activity- an enzyme along outer plasma membrane that plays a key role in phosphate metabolism, probably in the mineralization process and in Acellular cementum formation.

Fibroblasts…

Although technically situated within the PDL, bone

and cementum cells are properly associated with the hard tissues they form.

Osteoblasts line the bone surface of the ligament and may be either functional or resting, depending on the functional state of the ligament.

Cementoblasts are responsible for formation of cellular cementum.

Osteoblasts & cementoblastsOsteoblasts & cementoblasts

Fibroblasts :

- Exhibit lysosomes that contain fragments of collagen that appear to be undergoing digestion.- Dual action

Osteoclasts & Cementoclasts: - Osteoclast cells resorb bone and tend to be large and multinucleated.- Cementoclasts resemble osteoclasts and are occasionally found in normal functioning PDL.

Resorptive cellsResorptive cells

Cell division ---- daughter cell ---- undifferentiated progenitor

CHARACTERISTICS Small cells Close faced nucleus Very little cytoplasm Highest concentrations' close to blood vessels Burst of mitosis occurs when pressure is applied

Progenitor cellsProgenitor cells

Mallassez – 1884

Remnants of HERS and are formed close to cementum

Most numerous in the apical area & cervical area. (Xiong J, Gronthos S, Bartold PM )

Form a lattice work and appear as either isolated cluster of cells or interlacing strands. They diminish in number with age and may undergo calcification to form cementicles.

Epithelial rests of MallassezEpithelial rests of Mallassez

ELECTRON MICROSCOPIC STRUCTURE Attached to one another by desmosomes Exhibit tonofilaments Isolated from CT cells by basal lamina & inter

connected by hemidesmosomes. Contain keratinocyte growth factors. Can proliferate and participate in formation of peri

apical cysts and lateral root cysts.

Fig. shows the presence of clusters of epithelial cells (ER) in the periodontal ligament. These cells, called the epithelial cell rests of epithelial cell rests of MallassezMallassez, represent remnants of the Hertwig's epithelial root sheathHertwig's epithelial root sheath. The epithelial cell rests are situated in the periodontal ligament at a distance of 15-75 μm from the cementum (C) on the root surface. A group of such epithelial cell rests is seen in a higher magnification.

Include neutrophils, lymphocytes, macrophages,&

eosinophil's. MAST CELLS Small round or oval cell; Diameter 12-15µm. Contain numerous cytoplasmic granules(0.5-1 µm) that

stain metachromatically with dyes like azure A and positively by PAS reaction.

Contain heparin & histamine. Role of heparin is not clear. Histamine plays a role in

inflammatory reaction. Occasionally seen in healthy PDL. It may cause proliferation of endothelial & mesenchymal cells.

Defense Cells Defense Cells

CHARACTERISTICS

Found adjacent to the blood vessels Nucleus has a regular contour and may be horse shoe or

kidney shaped with a dense peripheral layer of chromatin. Surface may be raised in microvilli. Sparse RER with widely spaced polysomes. Golgi apparatus is not well developed.DUAL ROLE

1. Phagocytosing dead cells2. Secreting growth factors that regulate the proliferation of

adjacent fibroblasts

MacrophagesMacrophages

Cementicles Cementicles

Calcified masses, adherent to or detached from the root surfaces

(O.J. Mikola, Wm.H. Bauer,1949) Represent dystrophic

calcification (example of regressive or degenerative change)

Develop from: calcified epithelial rests, calcified Sharpey’s fibers, Calcified, thrombosed vessels within the PDL, around small spicules of cementum or alveolar bone traumatically displaced into the PDL

Too small to be seen on IOPA, seldom being larger than

0.2-0.3 mm. in diameter.

No clinical significance.

Actually a variety of calcified bodies may occur in the PDL, not all of which have the morphologic characteristics of cementum. Nevertheless, they have all been commonly known as cementicles.

The pattern of calcification often gives the appearance of a circular lamellated structure.

Cementicles…

Small spicules of cementum torn from the root

surface or fragments of bone detached from the alveolar plate (Bosshardt DD, Selvig KA 1977)

If lying free in the PDL may resemble cementicles, particularly after they have undergone some remodeling through resorption & subsequent repair.

Cemental Tears

PRINCIPAL FIBRES

The most important elements of PDL are the principal fibers which are collagenous and follow a wavy pattern when viewed in longitudinal section.

They are associated with abundant non collagenous proteins typically found in bone and cementum like osteopontin and bone sialoprotein.

They are thought to contribute to the regulation of mineralization and to tissue cohesion at sites of increased biomechanical strain. (Mc Kee MD, Zalzal S, Nanci A 1996)

Periodontal fibers Periodontal fibers

The adult human PDL fibers are slightly thicker than other mammalian species and measure about 54-59 nm in diameter.

This relatively small diameter reflects the short half-life of ligament collagen, meaning that there is little time for continuous assembly.

Is derived from the French word collagene to

designate connective tissue constituents that produce glue.

Collagen molecule is rigid and resists stretching. Therefore it is utilized in tissues where mechanical forces should be transmitted without loss.

Organization of collagen depends upon the specific functional requirements in various tissues.

CollagenCollagen

STRUCTURE All collagens are composed of 3 polypeptide chains

coiled around each other to form the typical triple helix configuration.

Variations are brought about by Differences in assembly of the basic polypeptide

chains Different lengths of helix Various interruptions in helix Differences in the terminations of the helical mains

Collagen…

Made up of 3 polypeptide chains α chains that are left handed chains assembled into a triple

helix with a right handed twist. May be a homo-trimer or hetero-trimer.

Has a repeating gly-X-Y amino acid sequence in which X and Y are usually amino acid other than glycine.

Contain 2 unique amino acid hydroxy proline and hydroxy lysine along with glycine & proline (Carneiro J, Fava de Moraes F , 1955)

Collagen molecules are covalently linked through lysine derived intra and inter chain crosslink.

It is synthesized by fibroblasts, chondroblasts, osteoblasts & other cells.

UNIQUE STRUCTURAL PROPERTIES UNIQUE STRUCTURAL PROPERTIES THAT DISTINGUISH COLLAGEN THAT DISTINGUISH COLLAGEN

FROM OTHER PROTEINSFROM OTHER PROTEINS

The amount of collagen in a tissue is determined by its

hydroxy proline content. There are at least 19 recognized collagen species encoded

by at least 25 separate genes, dispersed among 12 chromosomes (Embery et al 2000)

Collagen classes a. Interstitial collagens ---- Type I,II,III b. Basement membrane type ---- Type IV,VI,VII c. Short chain collagens ---- Type IX,X

Collagen…

Type I, III, V, XII – Periodontal Ligament Type VI, II – cartilage Type IV - Basement membrane Type VI – Ligaments, skin, bone Type VII - Anchoring fibrils of basement

membrane Type IX - Cartilage Type X, XI - Cartilage, Bone Type XIII - Epidermis Cartilage

Collagen…

The ligament fibers and Sharpey’s fibers are composed of

interstitial collagen type III and I Collagen V is associated with these fibrils and is either

buried within these fibrils or is found in the spaces between the fiber bundles.

Type VI - microfibrillar component associated with oxytalan fiber system.

Type XII contribute to the construction of 3-dimensional fibril arrangement- hence closely associated with regeneration of PDL.

Collagen…

Synthesized by - Fibroblasts, chondroblasts,

osteoblasts, odontoblasts and other cells.

The steps involved in biosynthesis of collagen fiber involve- Intra cellular pro collagen synthesis- Extra cellular collagen biosynthesis & fibril/fiber formation.

Formation of collagenFormation of collagen

Shortened collagen molecules align as 5-unit, quater staggered microfibrils, which assemble in parallel fashion giving rise to a regular series of gaps or

holes within the fibril

The C-terminal extension and part of N-terminal ones are removed by action of C- and N- proteinases in the secretory granules

Secretory granules containing procollagen molecules formed at the transface of golgi complex

Transported to the golgi complex where glycosylation takes place to the O-linked galactose residues

Collagen microfibrils, fibrils, fibers, and bundles

Collagen Regulation Collagen Regulation

A variety of growth factors and cytokines regulate collagen production

The collagen mRNA levels may increase or decrease due to change in either the rate of collagen gene transcription or in mRNA stability.

TGF-β is an important mediator as it enhances the synthesis of collagen and other matrix components.

Interferon-γ suppress collagen gene expression. During inflammation and wound healing, these substances

are secreted by platelets, macrophages and other inflammatory cells.

1. Intracellular degradation - Selective ingestion of collagen

fibrils by fibroblasts.2. Extracellular degradation - Degradation by enzymes

secreted by cells Cleaving of polypeptide chain occurs at gly-iso-leucin and

gly-leu bonds in α1 and α2 chains respectively by enzymes collagenases.

These peptide bonds are located at approximately 1/4th of the length from C-terminal, thus fragments of 3/4th and 1/4th sizes are released.

These fragments are denatured and further degraded by other common tissue proteinases

Collagen DegradationCollagen Degradation

Principal fibers of PDLPrincipal fibers of PDL

Trans septal Alveolar crest group Horizontal Oblique Apical Inter – radicular

Extend Inter proximally over the alveolar bone crest

and are embedded in the cementum of adjacent tooth.

Are a remarkably constant finding and are reconstructed even after destruction of the alveolar bone has occurred in periodontal disease.

Considered as belonging to the gingiva because they do not have osseous attachment.

Transseptal GroupTransseptal Group

Extend obliquely from the cementum just beneath

the junctional epithelium to the alveolar crest.

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

Functions – 1. Prevent extrusion of tooth (Carranza, 1956) 2. Resist lateral tooth movement

Alveolar Crest GroupAlveolar Crest Group

HORIZONTAL GROUP (10-15%) Extend at right angles to the long axis of tooth from

cementum to the alveolar bone.

OBLIQUE GROUP (80-85%) Largest group in the PDL. Extend from the

cementum in a coronal directing obliquely to the bone.

Function - Bear the brunt of vertical masticatory stresses and transform them into tension on the alveolar bone.

APICAL GROUP Radiate in a rather irregular fashion from the cementum to

the bone at the apical region of the socket . Do not occur on incompletely formed roots. Resist forces of luxation, may prevent tooth tipping and

protect the delicate blood vessels, nerves and lymphs at the apex.

INTER RADICULAR FIBERS Fan out from cementum to the tooth in the furcation areas

of multi rooted teeth. Other well formed fiber bundles inter digitate at right

angles or splay around.

The terminal portion of principal fibers of periodontal

ligament, that are inserted into cementum and alveolar bone are called Sharpey’s fibers.

The number and size of sharpey’s fibers varies with functional status of the tooth.

Sharpey’s Fibers Sharpey’s Fibers

Functional stage

Pre-eruptive, eruptive stagePre-eruptive, eruptive stage

Normal functionNormal function

Completely embeddedCompletely embedded

Fixed bridge abutmentFixed bridge abutment

Density/100µ2 Diameter(µm)

53.453.4 3.03.0

2828 4.04.0

2.12.1 4.14.1

21.321.3 4.64.6

Elastin FibersElastin Fibers

Restricted to walls of blood vessels in humans

PDL fibers do not contain mature elastin but two immature forms are found oxytalan and eulanin.

Oxytalan FibersOxytalan Fibers

Are micro fibrils Run in apico-coronal direction to bend and attach at

cervical third of root (Fulmer et al. 1974) Diameter – 0.5-2.5mm Volume – 3% No cross banding seen Function - regulate vascular flow - play a role in tooth support - guides cell migration

Are immature elastic fibers consisting of micro fibrils

within small quantity of elastin

An elastic meshwork has been described in the PDL as being composed of many elastin lamellae with peripheral oxytalan & eulanin fibers

Functions- Regulate vascular flow- Role in tooth support- Facilitate fibroblast attachment and migration

Eulanin FibersEulanin Fibers

Small Collagen fibers in association with the larger

principal collagen fiber Run in all directions forming a plexus Described by Shackleford, 1971 Once the tooth has erupted into clinical occlusion such an

intermediate plexus is no longer demonstrable Intermediate plexus has been reinterpreted by Sloan as

representing merely an optical effect explained entirely by the arrangement of middle layer collagen into sheets rather than bundles.

Indifferent Fiber PlexusIndifferent Fiber Plexus

Fills the space between the fibers and cells Overlooked possibly because difficult to investigate and

not recognized in routine methods

COMPOSITION Consists of a biochemically complex, highly hydrated,

semisolid gel. Water content of 70% Glycosaminoglycan's – hyaluronic acid,

proteoglycans( versican , decorin ) Glycoproteins -- fibronectin , laminin , vibronectin ,

tenascin

Ground SubstanceGround Substance

Large group of anionic macromolecules that consists of a

protein core to which are attached hexose amine containing polysaccharide called gag chains.

Distribution in PDL is similar to gingival tissue.FUNCTIONS a. Cell adhesionb. Cell-cell & cell- matrix adhesion c. Cell repaird. Binding to various growth factors

ProteoglycansProteoglycans

The primary function of these molecules is to bind cells to

extracellular elements. Most widely studied is FIBRONECTIN

Exists in one form as an insoluble connective tissue matrix protein which promotes the attachment and subsequent spreading of cells that bind to a fibronectin – collagen complex.

The attachment and spreading of cells within the PDL collagen matrix is a pre requisite for both alignment of collagen fibers and for cell migration.

Glycoprotein Glycoprotein

TENASCIN is an adhesive glycoprotein synthesized

at specific times and location during embryogenesis.

In adult its distribution is specific and restricted.

It binds to fibronectin and to proteoglycans.

Its blocks the binding capacity of syndecan and thereby enables the cell to move freely

Glycoproteins….

1. Physical 2. Formative and Remodeling3. Nutritive4. Sensory5. Regulation of periodontal ligament width

Functions Of PDLFunctions Of PDL

1. Provision for a soft tissue ‘CASING’ to protect the vessels

and nerves from injury by mechanical forces .2. Transmission of occlusal forces to the bone 3. Attachment of teeth to bone.4. Maintenance of gingival tissues in their proper relationship

to the teeth.5. Resistance to impact of occlusal forces

SHOCK ABSORPTION : Tensional theory & Viscoelastic theory

Physical Functions Physical Functions

Tensional TheoryTensional Theory Ascribes the principal fibers of PDL the major responsibility in

supporting the tooth and transmitting the forces to the bone. Force is applied to the tooth

Principal fibers first unfold and straighten

Transmit force to the alveolar bone causing elastic deformation of the socket.

When alveolar bone has reached its limit, the force is transferred to underlying basal bone

Many investigators find this theory insufficient to explain available experimental evidence.

Viscoelastic TheoryViscoelastic Theory According to this, the displacement of tooth is largely

controlled by fluid movement, with fibers having only secondary role (Bien SM, 1966 and Birn H, 1966)

Force applied on tooth

Extra-cellular fluid from PDL escapes to marrow spaces

Depletion of fluid, Fibers absorb slack and tighten

Blood vessels stenosis

Arterial back pressure created

Ballooning of vessels

Passage of blood ultra filtrates

Lost fluid replenished

Transmission Of Occlusal Transmission Of Occlusal Forces to boneForces to bone

Arrangement is like suspension bridge or hammock. The oblique fibers alter their wavy pattern and

sustain the major part of the axial force

AXIS OF ROTATION Single rooted tooth at junction of middle and apical

3rd of the root. Multirooted tooth in the bone between the roots

below furcation.

Distribution of faciolingual forces (arrow) around the axis of rotation (black circle on root) in a mandibular premolar. The periodontal ligament fibers are compressed in areas of pressure

The apical portion of the root moves in a direction

opposite to the coronal portion.

Areas of tension→ Principal fiber bundles are taut rather than wavy.

Areas of pressure→ fibers are compressed, the tooth is displaced & a corresponding distortion of bone exists in a direction of root movement (Picton DC, 1967)

FORMATIVE & FORMATIVE & REMODELLINGREMODELLING

Cells have the capacity to resorb & synthesize the extracellular substance of the CT ligament, alveolar bone & cementum.

Participate in physiologic tooth movement & in repair of injuries.

PDL is constantly undergoing remodeling old cells and fibers are broken down and replaced by new ones.

Radio autographic studies indicate a very high turnover rate of collagen in PDL. A rapid turnover of sulfated GAGs in the cells and amorphous ground substances also occur.

Sodek (1977) has demonstrated that the periodontal

ligament incorporates proline at least 5 times faster than gingiva or alveolar bone and that the biological half-life of mature collagen was 20% and 17% less than found in gingiva and alveolar bone, respectively.

The PDL is constantly undergoing remodeling. Old cells & fibers are broken down & replaced by new ones, & mitotic activity can be observed in the fibroblasts & endothelial cells (Muhlemann; 1954)

Sodek ,1977 found collagen synthesis in PDL of adult rat

to be - two fold greater than that of gingiva, - four fold greater than that of skin, & - six fold greater than that of bone.

Almost all the newly synthesized collagen in the ligament was converted to mature cross linked collagen, whereas much less was converted in the gingiva & skin.

Collagen Turn Over RateCollagen Turn Over Rate

Half-life for collagen turnover: in ligament – 1 day, in bone – 6 days in gingiva - 5 days, in skin - 15 days

According to Rippin: half life in the apical areas 2.45 days, in the crestal areas 6.42days, fibers in mid-root region 5.7 days, transseptal fibers 8.4 days for dentogingival fibers 25 days.

PDL supplies nutrients to the cementum , bone, and gingiva by way of blood vessels and provides lymphatic drainage.

Rich vascular plexus at apex & in the cervical part of the ligament

Rich network of arcades are more evident in the PDL space adjacent to the bone than to cementum

Nutritional Nutritional

Periodontal ligament provides the most efficient

proprioceptive mechanism

4 types of neural terminations are seen1. Free nerve endings -pain2. Ruffini like mechanoreceptors (apical area)3. Meissner’s corpuscles - mechanoreceptors (middle

3rd)4. Spindle like pressure and vibration endings (apex)

Sensory Sensory

The extracellular signal-regulated kinase 1 and 2

(ERK-1/2) have been implicated in the inflammation dependent sensitization of nociceptors.

It is responsible for the neural regulation of blood vessels in the PDL (Korkmaz et al ,2009)

PDL contains calcitonin gene related peptide (CGRP) in nociceptors (Silverman JD, Kruger, 1987) and calretinin in mechanoreceptors (Maeda T et al , 1999)

Actin binding protein-280 plays an important role in

mechano protection by:

1. Reinforcing the membrane cortex thereby preventing force-induced membrane disruption

2. Increasing the strength of cytoskeletal links to the extracellular matrix

3. Desensitizing stretch activated ion channel activity.

An important measure of periodontal ligament

homeostasis.

The ability of periodontal ligament cells to synthesize and secrete a wide range of regulatory molecules is essential in accurately maintaining the width of the periodontal ligament in spite of high-amplitude physical forces during mastication and despite the presence of osteogenic cells within the whole width of the periodontal ligament. (McCulloch, 1983)

Regulation of PDL widthRegulation of PDL width

Transforming growth factor-β isoforms -synthesized by

periodontal ligament cells can dose-dependently down-regulate osteoblastic differentiation of periodontal ligament cells (Brady TA et al. 1998)

Prostaglandins - also produced by periodontal ligament cells, can inhibit mineralized bone nodule formation and prevent mineralization by periodontal ligament cells in vitro (Ogiso B, Hughes FJ, et al. 1991,1992)

Paracrine factors - inhibit bone resorption (Ginger MS, et al 1991)

Pro-inflammatory cytokine interleukin-1 (Shimizu N et al

1995) and one of the isoenzymes responsible for prostaglandin synthesis (cyclooxygenase 2 - Shimizu N et al 1998) are induced by applied mechanical force on periodontal ligament cells in vitro.

As prostaglandins and interleukin-1 can strongly induce matrix degradation, there is evidently an important relationship between mechanical forces, cytokine production and regulation of the periodontal ligament space.

Blood SupplyBlood Supply

Inferior & superior alveolar arteries to the mandible & maxilla - reaches the PDL from 3 sources:

1. Apical vessels (Dental artery)

2. Transalveolar vessels (rami perforantes-penetrating vessels from alveolar bone)

3. Intraseptal vessels (anastomosing vessels from the gingiva)

Blood supply….

Branches of the intraseptal vessels – perforate the lamina dura & enter the ligament.

After entering the PDL, perforating rami anastomose & form a polyhedral network which surrounds the root like a stocking.

Perforating channels are more abundant in the

maxilla than in the mandible, & more in the posterior than in the anterior teeth.

This dual supply allows the ligament to survive following removal of the root apex during certain endodontic procedures

Arteriole in PDL – diameter – 15 to 50 µm.

Blood supply….

Specialized feature of the PDL

Fenestrated capillary beds differ from continuous capillary beds in that the diffusion & filtration capabilities are greatly increased

Capillary fenestrations are related to the high metabolic requirements of the PDL & its high turnover rate.

Fenestrated CapillariesFenestrated Capillaries

Frohlich (1964) - diagonal symmetry of the

periodontal vessels If there is abundant vascularity palatally at the apical

area, there will be a similar abundance labially in the coronal area of the PDL.

This causes minute (0.5 µm) labiopalatal pulsation of teeth with each heart beat.

Palatolabial discrepancies Palatolabial discrepancies in vascularityin vascularity

Nerve SupplyNerve Supply

The nerve follow almost the same course as the blood vessels.

Nerve bundle divide

→ myelinated fibers → lose their myelin sheath → end in one of the 4 types of neural termination

1.Free nerve endings

- terminal arborization of thick/fine myelinated fibers - 0.2-1 um in diameter

- fine, nonmyelinated fibers only type of ending in tooth pulp → classic model of pure nociception.

2. Ruffini - like→ apical area

3. Meissner's corpuscles → mid-root, for tactile perception

4. Spindle shaped (Krause type end bulbs) → temperature receptor, present at apex of the tooth

development of a new technique in which the axons can

be radioactively labeled & visualized by radioautography

The PDL has double innervation: Axons arising both from the mesencephalic

nucleus- Unconscious reflex pathways &

proprioceptors – position control of the mandible Axons from the trigeminal ganglion

- Conscious sensation of touch, pain & temperature

The vast majority of the nerve endings –

unencapsulated, Ruffini-like mechanoreceptors & free nerve endings.

In experimental animals, innervation from the

trigeminal ganglion is very dense – tooth apex, circular & interdental ligaments.

Innervation from mesencephalic nucleus – most dense – subapical region, especially for the canines & incisors, with no innervation in the zone of the circular & interdental ligaments.

Absence of PDL around Absence of PDL around implantimplant

important clinical consequences

No resilient connection exists between teeth & jaw bone - any occlusal disharmony - repercussions at the bone-to-implant interface.

No intrusion or migration of teeth can compensate for the eventual presence of a premature contact.

Because the principal proprioception of the natural

dentition comes from the pdl, its absence in implants reduces tactile sensitivity & reflex function.

Accompany the arterial supply.

Venules receive the blood through the abundant capillary network. Also, arterio-venous anastomosis bypass the capillaries; these are seen most frequently in the apical & inter-radicular regions, & there significance is unknown.

They are somewhat larger in diameter – 28 µm (mean).

Venous drainage Venous drainage

Lymph vessels - originate as cul-de-sac in PDL

course apically - pass through the fundus of the socket or they may pass through the cribriform plate to empty into larger channels pursuing intraosseous paths.

Lymphatics

The cell number and cell activity decreases with aging. One of the prominent changes seen in the calcified tissues

of periodontium , the bone and the cementum is scalloping and the PDL fibers are attached to the peaks of these scallops than over the entire surface as seen in a younger periodontium.

This remarkable changes affect the supporting structures of the teeth.

Age changes in PDLAge changes in PDL

With aging the activity of the PDL tissue decreases

because of restricted diets and therefore normal functional stimulation of the tissue is diminished

Any loss of gingival height and periodontal disease promotes destructive changes in the PDL

The primary role of the periodontal socket is to support

the tooth in the bony socket . Its thickness varies in different individuals in different

teeth in the same person and in different locations on the same tooth .

Acute trauma to the periodontal ligament, accidental blows or rapid mechanical destruction may produce pathologic changes such as fractures or resorption of the cementum tears of fiber bundles , hemorrhage and necrosis .

Clinical considerationsClinical considerations

The adjacent alveolar bone is resorbed the PDL is

widened and tooth becomes loose .When trauma is eliminated repair usually takes place.

Orthodontic tooth movement depends on resorption and formation of tooth bone and periodontal ligament .

These activities can be stimulated by properly regulated pressure and tension.

If the movement of teeth is within phsysiologic limits the initial compression of PDL on the pressure side is compensated for by bone resorption whereas on the tension side bone apposition is seen.

Clinical considerations…Clinical considerations…

Application of large forces results in necrosis of PDL and

alveolar bone on the pressure side and movement of the tooth will occur after the necrotic bone has been resorbed by osteoclasts located on its endosteal surface.

Inflammatory diseases of the pulp progress to the apical periodontal ligament and replace its fiber bundles with granulation tissue .

This lesion is called a periapical granuloma may contain epithelial cells that undergo proliferation and produce a cyst .

Clinical Clinical

considerations…considerations…

Chronic inflammatory disease is common pathology

related to PDL . The toxins released from the bacteria in the dental plaque

and metabolites of the host’s defense mechanism destroy the PDL and the adjacent bone very frequently .

This leads to tooth mobility and further loss of tooth. To repair the existing destruction of PDL can be quite

challenging . It involves limiting the disease process and to regenerate

the host tissues to their original form in such a way that reattachment of PDL to bone becomes possible

Clinical Clinical

considerations…considerations…

Various surgical techniques like Guided Tissue

regeneration are being used for correction of Periodontal destruction .

Guided Tissue regeneration is based on principle that specific cells contribute to formation of specific tissues.

Important cells responsible for periodontal regeneration are derived from PDL.

Exclusion of the faster growing epithelium and connective tissue from a periodontal wound for 6 to 8 weeks allows the slower growing tissues to occupy the space adjacent to the tooth.

Clinical Clinical

considerations…considerations…

Fusion of alveolar bone and cementum with obliteration

of the periodontal ligament is termed Ankylosis. Occurs in teeth with cemental resorption which suggests

that it may represent a form of abnormal repair. May also develop after chronic periapical inflammation ,

tooth implantation and occlusal trauma and around embedded teeth.

Clinically ankylosed tooth sounds DULL or WOODY on percussion.

Before extraction such tooth require X-ray to facilitate surgical extraction.

Clinical Clinical

considerations…considerations…

Osseo integration is an intimate bone to implant contact

without presence of PDL in between. So this is not the ideal substitute for natural tooth

replacement. Future studies will be directed to regenerate PDL fibers

as an interface between bone and implant. Some fiber bundles are present which have a cuff like

circular orientation. The role of these fibers remains unknown but it appears

that there presence helps to create a soft – tissue seal around the implant .

Clinical Clinical

considerations…considerations…

Within physiologic limits, the PDL can accommodate

increased function with - an increase in width, - a thickening of its fiber bundles, and - an increase in diameter & number of Sharpey’s fibers Forces that exceed the adaptive capacity of the

periodontium produce injury called trauma from occlusion.

Slight excessive pressure: resorption of bone, widening of PDL space

Slight excessive tension: elongation of PDL fibers & apposition of bone

External forces & PDLExternal forces & PDL

To have any chance of success , it is essential to maintain the

viability of PDL . Avoid dehydration of PDL. Avoid loss of viability of its cell rests.

Transplantation Best results when unerupted tooth with partially formed

roots as there is less damage to PDL.

Replantation & Replantation & transplantationtransplantation

Cemento-ossifying fibroma – Middle age, mandible

(midbody), Women Predilection (slight) & Blacks, Well Circumscribed

Reactive fibro-cemento-osseous lesions of PDL origin:1.Periapical cemento-osseous dysplasia (PCD) – young-middle age, black female, apical area of anterior mandibular teeth.

2. Focal cemento-osseous dysplasia – women predilection, poster mandible.

3. Florid cemento-osseous dysplasia – Middle-elderly black women.

Neoplasms arising from Neoplasms arising from PDLPDL

Nishimura et al, 1998 - PDL cells - susceptible to hyper &

hypoglycemia & effects - mediated via the integrin system.

Hyperglycemia – increased expression of fibronectin receptor → results in reduced cellular adhesion & motility → probable tissue impairment.

Hypoglycemia – decreased expression of fibronectin receptor → lowers the viability & ultimately results in cell death & hence tissue impairment

Effect of hyper & hypo Effect of hyper & hypo glycaemia on PDLglycaemia on PDL

Thin radiolucent line interposed between the root &

lamina dura.

Occlusal Trauma → widened PDL space or funneling of coronal aspect of PDL space.

It can also widened in case of vertical fractures & progressive systemic sclerosis (Scleroderma).

PDL space RG appearancePDL space RG appearance

Gestrelium et al, 1997 studied effects of EMD on periodontal

ligament cell migration, attachment, proliferation, biosynthetic activity mineral nodule formation & ability to absorb a large range of polypeptide growth factors & cytokine.

In culture, EMD formed protein aggregates which appeared to provide ideal conditions for cell-matrix interactions.

Under these conditions EMD enhanced the proliferation of PDL cells, increased protein & collagen production of PDL cells & promoted mineral nodule formation by these cells.

However, no effect on migration, attachment & spreading of these cells nor did they absorb any of the growth factor or cytokine that were tested.

EMD & PDLEMD & PDL

PROGRESSIVE SYSTEMIC SCLEROSISRadio graphically ---- PDL widening up to 3mm thickeningCollagen ---- dense, mature & more hyalinized than normalOxytalan fibers increased.

Soft CT disorders & PDL Soft CT disorders & PDL

LATHYRISM Condition caused by drugs that inhibit cross linking in

collagen & elastin (cystamine) Fragile collagen fibers Retard eruption

DISUSE ATROPHY Narrowing of PDL & reduction in no. of principal fibers. Fibers oriented parallel to the long. Axis of root & PDL

shows reduced rate of collagen turn over.

FOOD TEXTURELittle correlation between the advent of soft, fiber deficient diet & dental health.

Significant factor in chronic inflammatory periodontal disease is loss of natural masticatory function, leading to accumulation of dental plaque.

Influences pattern of mastication & hence the mode of support offered by the PDL.

Nutrition & PDLNutrition & PDL

CARBOHYDRATES

Refined carbohydrates in the diet influence the severity of PDL disease in humans (Holloway et. Al 1963)

No direct evidence showing the direct effect of carbohydrates per se on PDL , though in some circumstances there could be an influence as a result of modifying the diet consistency.

PROTEINS Deficiency of protein might be expected to produce

changes within it. Reduction in PDL transseptal fibers (Stien & Ziskin 1949;

Ten Cate et al 1976) Reduction in cementoblasts, fibroblasts Occlusal trauma exacerbates these effects (Chawla &

Glickman 1951) Healing is delayed in rats fed on protein deficient diet.

REGENERATION is the reproduction or reconstitution of a

lost or injured part.

REPAIR is the healing of a wound by tissue that does not fully restore the architecture or the function of the part.

PERIODONTAL REGENERATION is defined histologically as regeneration of the tooth’s supporting tissues, including alveolar bone, periodontal ligament, and cementum over a previously diseased root surface.

Healing after periodontal Healing after periodontal therapytherapy

NEW ATTACHMENT is defined as the union of

connective tissue or epithelium with a root surface that has been deprived of its original attachment apparatus. This new attachment may be epithelial adhesion and/or connective tissue adaptation or attachment and may include new cementum.

Carranza’s Clinical Periodontology, 10th Edition Clinical Periodontology and Implantology by Jan Lindhe, 5th

edition Oral Histology and Embryology by Orban, 11th edition Tencate oral histology, 5th edition Fundamentals of Periodontics, 2nd Edition, by Thomas G.

Wilson, Kennath S. Kornman Hassel TM. Tissues and cells of periodontium. Periodontol

2000, Vol. 3, 1993, 9-38. The Periodontium - Hubert E Schroeder

References References

Bartold PM, Walsh LJ, Sampath Narayan A. Molecular and cell

biology of gingiva. Periodontol 2000, Vol. 24, 2000, 28–55. Cho MI, Garant PR. Development and general structure of

the periodontium, Periodontol 2000, Vol. 24, 2000, 9–27. Ertsenc W, Mcculloc HG , Sodek HJ. The periodontal ligament:

a unique, multifunctional connective tissue. Periodontol 2000. Vol. 13, 1997, 20-40.

Wright JM. Reactive, dysplastic and neoplastic conditions of periodontal ligament origin. Periodontol 2000, Vol. 21, 1999, 7-15.

Xiong J, Gronthos S, Bartold PM. Role of the epithelial cell

rests of Malassez in the development, maintenance and regeneration of periodontal ligament tissues. Periodontol 2000, Vol. 63, 2013, 217–233.

Bosshardt DD, Selvig KA.Dental cementum: the dynamic tissue covering of the root. Periodontol 2000 1997;13:41-75.

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