This document provides an overview of the periodontal ligament (PDL), including its development, cells, extracellular components, fiber groups, and structures. The PDL is a specialized connective tissue that attaches teeth to alveolar bone. It contains fibroblasts that secrete collagen fibers, along with blood vessels, nerves, and progenitor cells. The principal fiber groups resist various forces on teeth. The PDL allows teeth to withstand chewing forces through its extracellular matrix and continual remodeling by synthetic and resorptive cells.

1. Guided by - Submitted by -
Dr. Prashant Bhusari Dr .Hitesh Mankad

2. INTRODUCTION
DEVELOPMENT OF PDL
CELLS OF PDL
EXTRACELLULAR SUBSTANCE
Fibers
Ground substance
STRUCTURES PRESENT IN CONNECTIVE TISSUE
Blood vessels
Nerves
Lymphatics
Cementicles
FUNCTIONS OF PDL
PERIODONTAL LIGAMENT HOMEOSTASIS
NORMAL CELL BIOLOGY
AGE CHANGES IN PDL
UNIQUE FEATURES OF PDL
CLINICAL CONSIDERATIONS
CONCLUSION

3. The PERIODONTIUM is a connective tissue organ, covered by epithelium
that attaches the teeth to the bone of the jaws and provides a continually adapting
apparatus for support of the teeth during function.
 It comprises of cementum ,periodontal ligament , alveolar bone .It is
attached to the dentin of the root of the tooth by cementum and to the bone of
the jaws by alveolar bone.
 PDL occupies the periodontal space which is located between the
cementum and the periodontal space of the alveolar bone , and extends
coronally to the most apical part of lamina propria of gingiva . At the apical
part foramen it is continuous with the dental pulp.
 The average width of periodontal ligament space is documented to
be about 0.2 mm, though considerable variation exists.

5. Immediately before tooth eruption and for sometimes thereafter, active
fibroblasts adjacent to cementum of the coronal third of root, appear to become
aligned in an oblique direction to long axis of the tooth .
 Later the first collagen fiber bundles of the ligament becomes discernible.
These are the precursors of the alveolar crest fibre bundle group.
 Cemental and alveolar fibers continue to elongate towards each , to meet and
fuse .
 As the first occlusal contact of the tooth occurs with its antagonist the
principal fibres around the coronal third of root, horizontal group are almost
completely developed .
 Oblique fibres are still being developed in middle third of root. With the
formation of apical fiber group, the definitive periodontal ligament architecture
is established.

7. CELLS
The principal cells of healthy, functioning periodontal ligament are
concerned with the synthesis and resorption of alveolar bone and
fibrous connective of the ligament and cementum . The cells of the PDL
may be divided as -
Synthetic
cells
Resorptive
cells
Progenitor
cells
Defence
cells
Cells rests
of malassez

8. The fibroblasts is the predominant cell in the pdl . These fibroblasts origin in part
of from the ectomesenchyme of investing layer of dental papilla and from the dental
follicle . Pdl contains a fibroblasts cell populations with different functional
characteristics .
 These fibroblasts are regularly distributed throughout the ligament and are
oriented with their long axis parallel to the direction of collagen fibrils .
 Fibroblasts of pdl generate an organizational pattern as they have ability to
both synthesize and shape the proteins of the extracellular matrix in which collagen
fibrils form bundles that insert into tooth and bone as SHARPEY’S fibers .
 Once embedded in the wall of alveolus or tooth , these fibers calcify to a certain
degree and are associated with an abundance of non collagenous proteins found in
the bone i.e. osteopontin and bone sialoprotein .

9. These cells covering the the periodontal surface of the alveolar bone constitute a
modified endosteum and not a periosteum .
A cellular layer but not an fibrous layer is present on the periodontal surface of the
alveolar bone . The surface of the bone is covered largely by osteoblasts in various
stages of differentiation . As well as by occasional osteoclasts .
These are the cells lining the tooth socket . These cells are cuboidal in shape with a
prominent round nucleus at the basal end of the cell . Rough endoplasmic
reticulum , mitochondria , and vesicles are abundant in active cells .
These cells appear basophilic due to the presence of abundant rough endoplasmic
reticulum . The cells contact one another through desmosomes and tight junctions
.

10. Its distribution is similar to that of osteoblasts on the bone surface . These cells
line the surface of cementum . They are cuboidal with a large vesicular nucleus ,
with one ore more nucleoli and abundant cytoplasm.
All the organelles are required for protein synthesis and secretion are present .
Cells actively depositing cellular cementum exhibit abundant basophilic cytoplasm
and cytoplasmic processes .

11. OSTEOCLASTS : - These resorb bone and tend to be large and
multinucleated but can also be small and mononuclear . Multinucleated
osteoclasts are formed by fusion of precursor cells similar to circulating monocytes.
These when viewed in light microscope are cells occupy bays in bone or surround
end of bone spicule .
The part of plasma membrane lying adjacent to bone that is being resorbed is
raised in characteristic folds and is termed the ruffled or striated border.

12. The ruffled border is separated from the rest of plasma membrane
by a zone of specialized membrane that is closely applied to the bone
the underlying cytoplasm of which tends to be devoid of organelles
and has been called the clear zone .
The area of bone that is sealed off by virtue of active pumping of
protons by the osteoclast into this environment .

13. FIBROBLASTS: - These cells show rapid degradation of collagen by fibroblast
phagocytosis and is the basis for fast turnover in periodontal ligament . Collagen
degradation was an extracellular event involving the activity of the enzyme
collagenase .
Intracellular collagen profiles are organelles present . These are associated with the
degradation of collagen that has been ingested from extracellular environment .
Some studies suggested that collagen degradation is intracellular .
The extracellular elements in degradation of collagenase involve Collagenase
which cleaves the triple helical portion of molecules within the fibrils .

14. INTRACELLULAR DEGRADATION - Fibroblasts are capable of
phagocytosing collagen fibrils from extracellular environment and
degrading them inside phagolysomal bodies . Collagenase is not
involved in the intracellular phase of degradation of collagen fibrils .
CEMENTOCLASTS: - These resemble osteoclasts and sometimes
found in normally functioning periodontal ligament . Cementum is
not remodeled in the fashion of alveolar bone and periodontal
ligament . Its origin is unknown bit it is conceivable that they arise in
the same manner as osteoclasts .

15. PROGENITOR CELLS : - All connective tissues including periodontal
ligament contain progenitors for synthetic cells that have the capacity to undergo
mitotic division .
If they were not present there would be no cells available to replace differentiated
cells lying at the end of their life span or as a result of trauma.
These cell populations within the ligament appear to be in highest concentrations
in locations adjacent to blood vessel and exhibit some of the classical cytological
features .

16. The ligament contains epithelial cells that are found close to the cementum . At the
time of cementum formation the continuous layer of epithelium that covers the
surface of newly formed dentin breaks into lacelike stands . The epithelial rests
persist as a network stands islands or tubelike structures near and parallel to the
surface of the root .
Their function is not clear but they could be involved in periodontal repair and
generation .
These cells rests can be distinguished from fibroblasts in pdl by the close packing
of their cuboidal cells and their nucleus stains more deeply . They are more
numerous in older individuals and more numerous in children . These cells may
proliferate to form cysts and tumors. These cells may undergo calcification to
become CEMENTICLES.

17. MAST CELLS – These are relatively small round or oval cell having a diameter
of about 12 to 15 um . Mast cells are often associated with blood vessels . These cells
are characterized by numerous cytoplasmic granules which frequently obscure the
small , round nucleus .
Mast cells histamine plays a role in the inflammatory reaction and have been
shown to de granulate in response to antigen – antibody reaction on their surface .
The release of histamine into the extracellular environment causes proliferation of
endothelial cells and mesenchymal cells .

18. MACROPHAGES- These are found in the ligament and are
predominantly located adjacent to blood vessels . The
wandering type are derived from blood monocytes has a
characteristic ultrastructure that permits it to be readily
distinguished from fibroblasts .
EOSINOPHILLS – These are seen in the periodontal ligament .
They posses granules that consist of one or more crystalloid
structures . These are capable of phagocytosis .

19. EOSINOPHILLS

20. EXTRACELLULAR SUBSTANCE
 Collagen Proteoglycans
 Elastic Glycoproteins
 Reticular
 Indifferent fiber plexus
 Oxytalan
GROUND SUBSTANCEFIBERS

21. The connective tissue fibers are mainly collagenous, but there may be small
amounts of oxytalan and reticulin fibers and in some species, elastin fibers.
The collagen is gathered to form bundles approximately 5 um in diameter. These
bundles are termed as principal fibers. Within each collagen bundle , subunits are
present called collagen fibrils.
These fibrils are formed by packing togather of individual tropocollagen
molecules . The diameter of collagen fibril is 45-55 nm .
COLLAGEN

22. The main types of collagen in the periodontal ligament are type I and type III.
More than 70 % of pdl is type I .
Type I is uniformly distributed in the ligament .
Type III collagen accounts for about 20 % of collagen fibers . The function of type
III
May be involved with collagen turnover , tooth mobility and collagen fibril
diameter .
Type IV and VII are associated with epithelial cell rests and blood vessels .
Type XIII collagen is believed to occur within the pdl only when ligament is fully
functional .

23. The principal fiber group is alveolodental ligament which
consists of 5 fiber groups -
Inter
radicular
Alveolar
crest
Apical
Horizontal
Oblique

24. 1. Alveolar crest : - These fibers extend obliquely from cementum just
beneath the junctional epithelium to the alveolar crest .These fibers resist
tilting, intrusive , extrusive and rotational forces .
2. Horizontal group : - These fibers run at right angles to the long axis of the
tooth from cementum to bone and are roughly parallel to the occlusal plane of
the arch. These are apical to the alveolar crest group .They resist horizontal and
tipping forces.
3. Oblique group : - These are most numerous and occupy nearby 2/3 rd of
ligament . These are inserted into alveolar bone at a position coronal to their
attachment to cementum . These fibers resist vertical and intrusive forces .

25. 4. Apical group : - From the cementum at the root tip , fibers radiate through
the periodontal space to become anchored into the fundus on bony socket. These
fibers resist the forces of luxation may prevent tooth tipping and probably protect
delicate blood and lymph vessels and nerves traversing and periodontal ligament
space at the root apex .
5. Interradicular group : - The principal fibers of this group are inserted into
the cementum from the crest of interradicular septum in multirooted teeth .
These fibers resist tooth tipping, torquing and luxation . These fibers are lost, if
age related gingival recession proceeds to the extent that the furcation area is
exposed.

27. SHARPEY’S FIBERS
Collagen fibers are embedded into cementum on one side of the periodontal space
and into the alveolar bone on other . These embedded fibers are termed Sharpey’s
fibers . These fiber’s are more numerous but smaller at their attachment into the
alveolar bone .
The mineralized parts of sharpey’s fibers in alveolar bone appear as projecting
stubs covered with mineral clusters. These fibers in primary acellular cementum
are mineralized fully , those in cellular cementum and bone are generally
mineralized.

28. Few fibers pass through the bone uninterruptedly through the bone
of alveolar process to continue as principal fibers of the adjacent
periodontal ligament or they may mingle bucally and lingually with
fibers of periosteum that covers the outer cortical plates of alveolar
process .
These fibers pass through the alveolar process only when the process
contains entirely of compact bone and contains no haversian system.

29. There are three types of elastic fibers which are histochemically and
ultrastructurally different . And are mature elastic fibers , eulanin fibers
and the oxytalan fibers
Eulanin fibers and oxytalan fibers have been described as immature
elastic fibers .
Mature elastic fibers consist of microfibrillar component surrounding an
amorphous core of elastin protein .
Elastin proteins contains a high percentage of glycine, proline, and
hydrophobic residues with little hydroxyproline . These fibers are observed
only in walls of afferent of blood vessels , where they constitute the elastic
laminae of larger arterioles .

30. Eulanin fibers are seen as bundles of microfibrils embedded in a relatively small
amounts of amorphous elastin .
These fibers may be found with the fibers of gingival ligament . Oxytalan fibers
appear to consist of microfibrillar component only .
The orientation of these fibers is different from that of collagen fibers. Instead of
running from bone to tooth they tend to run in axial direction one end being
embedded in cementum or possibly bone and the other end in wall of blood vessel.
Within the pdl they run longitudinally oriented crossing the fibers perpendicularly
. Its function is unknown.

32. INTERMEDIATE PLEXUS
Earlier it was believed that principal fibers frequently followed a wavy
course from cementum to bone and are joined in the mid region of the periodontal
space giving rise to a zone of district appearance the so called Intermediate plexus .
The plexus was considered to be an area of high metabolic activity .
But recent research suggests cemental fibers meet and fuse with osseous fibers no
such plexus remains .
Secondly the entire pdl is metabolically active , not just the middle or
intermediate zone .
The recent concept is that, fibers cross the entire width of periodontal space
but branch en route and join neighboring fibers to from a complex three
dimensional network .

33. RETICULAR FIBERS
These are immature collagen fibers with argyrophilic staining properties and are
related to basement membrane of blood vessels and epithelial cells which lie
within the periodontal ligament .
SECONDARY FIBERS
These are located between and among the principal fibers . These fibers are
relatively non – directional and randomly oriented . These are associated with
paths of vasculature and nervous elements .
INDIFFERENT FIBER PLEXUS
These fibers run in all directions forming a plexus .

34. Ground substance composed of glycoproteins and proteoglycans . Ground
substance has been estimated to contain 70 % water and is thought to have a
significant effect on the tooth ‘s ability to withstand stress loads .
Ground substance is a gel like matrix in which are embedded the cellular
components such as collagen . Berkovitz et al estimated that ground substance
accounted for 65 % of the volume in the pdl .
All anabolites reaching the cells from the microcirculation in the ligament and all
catabolites passing in the opposite direction must pass through the ground
substance . Its integrity is essential if the cells of ligament are to function properly .

35. The ground substance consists of mainly of hyaluronate ,
glycosaminoglycans , proteoglycans and glycoproteins . All
components are presumed to be secreted by fibroblasts .
Proteoglycans are compounds containing anionic polysaccharides
covalently attached to a protein .
Glycosaminoglycans are linear polymers of disaccharide repeat
sequence which contains a hexosamine,,heparin sulfate and
hexuronic acid .

36. Substrate adhesion molecules such as tenascin , osteonectin , laminin , undulin ,
and fibronectin have been identified in pdl .
INTERSTITIAL TISSUE
Some of blood vessels , lymphatics , and nerves of the pdl are surrounded by loose
connective tissue and can be readily recognized in light microscope .

37. The following discrete structures are present in connective tissue of pdl
 Blood vessels
 Lymphatics
 Nerves
 Cementicles
BLOOD VESSELS – The blood supply is derived from inferior and superior
alveolar arteries to the mandible and maxilla respectively and reach the pdl from
these sources –
1. Branches in the pdl from apical vessels that supply the dental pulp .
2. Branches from the intraalveolar vessels – These run horizontally penetrating
the alveolar bone to enter the pdl .
3 . Branches from gingival vessels – These enter the ligament from the coronal
direction .
The arterioles and capillaries of the microcirculation ramify in the pdl forming a
rich network of arcades that is more evident in the half of the periodontal space
adjacent to bone than that adjacent to cementum . There is a particularly rich
vascular plexus at the apex and in the cervical part of the ligament .

38. The interradicular arteries branch into vessels of lesser caliber to emerge from the
cribiform plate as perforating arteries and supply the pdl along most of the
coronoapical extent including the bifurcation and trifurcation arteries .
The interdental artery also exit the bone to supply the middle three fifth of the pdl
though most of the interdental arteries emerge from the crest of the alveolar
process and supply the coronal aspect of pdl .
The pdl has some specialized features in the vasculature namely the presence of
large number of fenestrations in the capillaries and a cervical plexus of capillary
loops .
VENOUS DRAINAGE- The venous channels accompanying their arterial
counterparts . The channels are larger in diameter with mean average of 28 um .
These channels receive blood from the capillary network and also specialized
shunts called glomera in the pdl . These shunts provides an arteriovenous
anastomosis .

40. LYMPHATIC DRAINAGE - A network of lymphatic vessels following
the path of the blood vessels , provides the lymph drainage of the pdl . The flow is
from the ligament toward and into the adjacent alveolar bone .
It may course apically through the substance of pdl to arise and pass through the
fundus of the socket or may through the cribiform plate . They finally enter into
larger channels after pursuing intraosseous path .
The flow is via the alveolar lymph channels which are joined by the dental and
interrradicular lymph channels .

41. NERVES – The pdl has functionally two types of nerve fibers sensory and autonomic
. The sensory fibers are associated with nociception and of mechanoception , with
touch , pressure , pain and proprioceptive sensations . The autonomic fibers are
associated with pdl vessels .
All pdl innervations are mediated by the dental branches of alveolar nerves which
enter through apical perforation of the tooth socket and perforating branches of
interalveolar nerves traversing the bone .
Nerves which usually are associated with blood vessels pass through foramina in the
alveolar bone including the apical foramen to enter the pdl . In the region of apex apex
they run toward the cervix whereas along the length of root they branch and run both
coronally and apically .
Nerve fibers are either of large diameter and myelinated or small diameter in which
case they may or not be myelinated .
.

42. The pdl is abundantly supplied with sensory nerve fibers capable of transmitting
tactile pressure and pain sensations by the trigeminal pathways . Nerve bundles
pass into pdl from the periapical area and through channels from the alveolar bone
that follow the course of the blood vessels .
The bundles divide into single myelinated fibers which ultimately loose their
myelin sheath and end in one of four types of neural termination
1. Free endings which have a tree like configuration and carry pain sensation
2. Ruffini – like mechanoreceptor located primarily in the apical area
3. Coiled Meissner’s corpuscle also mechanoreceptor found mainly in the
midroot region
4. Spindle like pressure and vibration endings which are surrounded by a fibrous
capsule and located primarily in the apex .

43. CEMENTICLES - Calcified bodies called cementicles , sometimes
found in the pdl . These bodies are seen in older individuals and they
may remain free in the connective tissue and may fuse into large
calcified masses or they may be joined with the cementum . As the
cementum thickens with advancing age it may envelop these bodies .
When they are adherent to the cementum they form excementoses.
The origin of these calcified bodies is not established . It is possible
that degenerated epithelial cells form the nidus for their calcification
.

44. The Periodontal ligament has the following functions : -
 Supportive
 Sensory
 Nutritive
 Homeostatic
 Eruptive
SUPPORTIVE : - When a tooth is moved in its socket as a result of forces
acting on it during mastication or through application of an orthodontic force part
of periodontal space will be narrowed and the periodontal ligament in these areas
will be compressed . Other parts will be widened .The compressed ligament
provides support for the loaded teeth .

45. The collagen fibers in the ligament in concert with water molecules and other
molecules bound to collagen act as a cushion for the displaced tooth . The pressure
of blood in the numerous vessels also provides a hydraulic cushion for the support
of the teeth .
Thus PDL behaves as suspensory ligament . Accordingly load on the PDL
is dissipated to alveolar bone thorough the principal fibers of PDL primarily ,
which is placed in tension and on release of load ,an elastic recoil of tissue enables
the tooth recovery to its resting position .

46. SENSORY : - The PDL provides a most efficient proprioreceptive
mechanism , allowing the organism to detect the application of most delicate
forces to the teeth and very slight displacement of the teeth .
Mechanoreception protects both supporting structures of the
tooth and the substances of the crown from excessive masticatory forces .
The responsive elements of stromal cells and actin dependent sensory system are
involved in the mechanical signal transduction . To survive a mechanically active
environment cells adapt to variations of applied membrane tension . This
involves sensing increase in intracellular tension maintaining contact with
extracellular matrix ligands and preventing irreversible membrane disruptions .

47. NUTRITIVE : - The ligament contains blood vessels , which provide anabolites
and other substances required by the cells of the ligament , by the cementocytes .
The blood vessels are also concerned with the removal of catabolties . Occlusion of
blood vessels leads to necrosis of cells in the affected part of ligament this occurs
when too heavy a force is applied to a tooth in orthodontic therapy .

48. HOMEOSTATIC : - Its is evident that the cells of pdl have the ability to
resorb and synthesize the extracellular substance of the connective tissue of the
ligament , alveolar bone and cementum .
Alveolar bone appears to be resorbed and replaced at a rate higher than other
tissue in jaws . Furthermore the collagen of pdl is turned over at a rate that may
be the fastest of all connective tissues in the body and the cells in the bone half of
ligament may be more active than those on the cementum side.
The mechanism whereby cells responsible for these processes of
synthesis and resorption are controlled are largely unknown .

49. PERIODONTAL LIGAMENT HOMEOSTASIS
A remarkable capacity of pdl is that it maintains its width more or less overtime
despite the fact that it is squeezed between two hard tissues . Studies indicate that
the population of cells within the pdl both during development and regeneration
secreate molecules that can regulate the extent of mineralization and prevent
fusion of tooth root with surrounding bone .
Various molecules have been proposed which plays a role in
maintaining an unmineralized pdl .
PERIODONTAL CELLS can inhibit mineralized bone nodule formation by
bone stromal cells and studies have reported that inhibition may be dependent on
prostaglandin production .
Msx2 prevents the osteogenic differentiation of pdl fibroblasts by
repressing Runx2 also known as cbfa 1 transcriptional activity . The balance
between the activities of bone sialoprotein and osteopontin may also contribute in
maintaining pdl region .

50. Matrix gla protein an inhibitor of mineralization is also present in periodontal
tissues . Studies suggest that it may play a role in preserving width of the ligament .
When the functional demand increases the width of pdl can increase by as much
as 50 % and fiber bundles also increase in thickness . Conversely reduction in
function leads to narrowing of ligament and decrease in number and thickness of
fiber bundles .

51. The production and destruction of tissue matix ( turnover ) in a healthy state , involves
interaction among a myriad of effector molecules that are synthesized and secreted by
resident cell of periodontal ligament . Growth factors and cytokines that are believed
to play a role in the pathogenesis of gingivitis and periodontitis .
Cytokines are a series of multifunctional polypeptides and glycoproteins that are
secreted by one or several cell types and act locally or systemically . These includes
Interleukins , cytotoxic factors , interferons , growth factors , colony stimulating factors
and intercrines .
Growth factors have been defined as substances capable of re – initiating
proliferation of cells that are in a quiescent state .
In vivo cytokines play an important role in numerous biological events , including
development , homeostasis , regeneration , repair , inflammation and neoplasia .
.

52. 1 . Fibroblast growth factors (FGF) - Two of seven isoforms of fibroblast
growth factors have been described in particular one is acidic and other basic .
Acidic fibroblast growth factors has effects on endothelial cell replication and
neovascularisation . It stimulates dna synthesis and cell replication , in bone tissue
cultures which results in increased protein synthesis especially type 1 collagen .
Basic fibroblast growth factors has angiogenic properties has highly chemotactic
and mitogenic for a variety of cell types . It stimulates bone cell replication and
increases the number of cells of osteoblastic lineage .
Fibroblast growth factor bind to heparin sulfate heparin and fibronectin in the
extracellular matrix . Its is potent stimulator of periodontal cell migration and
mitogenesis but its effect but is effect on matrix production is not clear .

53. 2 . Platelet derived growth factor ( PGDF ) This factor is potent growth
factor for various connective tissue cells and is released from the a – granules in
platelets in conjunction with blood coagulation .
PGDF is a promoter of cell migration and a potent mitogen for cells bearing PGDF
receptors . It acts synergistically with other growth factors as a competence factor .
PGDF stimulated type v collagen formation and a drop in type III production in
gingival fibroblasts .

54. 3 . Transforming Growth factor ( TGF ) : - These factors are polypeptides
isolated from normal and neoplastic tissues which are known to cause a change in
normal cell growth . TGF is of 2 types α and b according to relationship to EGF .
TGF – α similar biological effects acting through EGF receptor .
TGF – β was originally purified from human placenta , platelets and bovine
kidney . It stimulates the synthesis of connective tissue matrix components such as
collagen , fibronectin proteoglycan and glycosaminoglycans .
4 . Interleukin- 1 ( IL – 1 ) : - Interleukin – 1 is a polypeptide with a great number
of roles in immunity , inflammation , tissue breakdown and tissue homeostasis . It
is synthesized by various cell types including macrophages , monocytes ,
lymphocytes vascular cells brain cells skin cells and fibroblasts following cellular
activation . 2 types of IL are known interleukin – 1 α and 1β .
.

55. 5 . Interferon – Y : - It posses important immunomodulatory effect and thus
is a lymphokine as much as an interferon . Its production is modulated by other
cytokines such as interleukin – 1 . Many biological activities have been ascribed to
interferon like action on B and T lymphocytes , antibody production , natural killer
cells , macrophages and tumour cells .
6 . Matrix metalloproteinases and their tissue inhibitors : -
Connective tissue cells participate in both the formation and breakdown of
connective tissue matrix . Such cells are found to synthesize and secrete a family of
enzymes known as MMP’s .
MMP gene family encodes a total 24 homologous proteinases classified into
collagenases , gelatinases , stromelysins , membrane type MMP ‘s depending on
their susbstrate specificity and molecular structures .

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

57. UNIQUE FEATURES OF PERIODONTAL LIGAMENT
The periodontal ligament is made up of collagen fibers in a proteoglycans stroma
and many types of connective tissue cells as in any other soft fibrous connective
tissue elsewhere in the body . But it has cells that form and resorb cementum
and bone and the collagen fibers in a specific orientation connecting the two
mineralized tissues make it unique .
The tissue hydrostatic pressure is high . The tissue is extremely cellular with
fibroblast showing many intercellular contacts well innervated with many
mechanoreceptors and highly vascular unlike any other connective tissue in the
adult . The features being high cellularity, very high rates of turnover and with
significant amount of type III collagen.
The collagen fibers are also sharp with unimodal size and frequency . The ground
substance of pdl occupies large volume with high content of glucornate rich
proteoglycans and glycoprotein- tenascin and fibronectin .
Thus the pdl has structural , ultrastructural , and biochemical features like fetal
tissue . This has helped us to undertsand periodontal inflammatory diseases and
for evolving newer treatment modalities .

58. 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 .
1. 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 .
2. The adjacent alveolar bone is resorbed the pdl is widened and tooth becomes
loose . When trauma is eliminated repair usually takes place .
3. 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 .

59. 4. 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 .
5 . 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 .
6 . 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
defence mechanism destroy the pdl and the adjacent bone very frequently . This
leads to tooth mobility and further loss of tooth .
7 . 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 .

60. 8. 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 .
Osteoblasts , cementoblasts ,and periodontal ligament cells are then afforded the
new opportunity to regenerate a new periodontal attachment on the previously
diseased root surface .
Non resorbable materials have been used as barrier membranes including latex and
teflon . Resorbable materials include include polyglycolic acid , trimethlene
carbonate , bilayer porcine- derived collagen .

61. 9. Fusion of alveolar bone and cementum with obliteration of the periodontal
ligament is termed Ankylosis . Ankylosis occurs in teeth with cemental resorption
which suggests that it may represent a form of abnormal repair . Ankylosis also may
develop after chronic periapical inflammation , tooth implantaion and occlusal
trauma and around embedded teeth . Clinically ankylosed tooth sounds DULL or
WOODY on percussion. Before extraction such tooth require X-ray to fascilitate
surgical extraction.
10 . Osseointegration 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 .

62. The periodontal ligament is a fibrous connective tissue forming
important part of the periodontium . Without it tooth is
support less .Cell of the periodontal ligament are pluri-
potential and helps in the regeneration of all the components
of periodontium lost in the periodontal disease.
A better understanding of cell and molecular biology of
developing and regenerating periodontium offers newer
avenues to regenerate the pdl . Newer options of treatment are
made available from time to time yet safeguarding the integrity
of the pdl and alveolar bone is still one of the most important
challenge .

63. 1. Orban ‘s Oral histology and embryology - 12 th edition
2 . Tencate ‘s Oral histology – 6 th edition
3. Carranza’s clinical periodontology – 10 th edition
4. Satish chandra ‘s oral histology
5.. dental.pit / pdl
6.. wikipedia.com/ pdl
7. . Google.com/images / pdl