1. PERIODONTAL LIGAMENT
P R E S E N T E D B Y
D R . M A L V I K A T H A K U R
M D S I Y E A R 1/71
GUIDED BY:
DR.RUPINDER KAUR

2. CONTENTS
 Introduction
 Definition
 Synonyms
 Extent and Shape
 Average Width
 Development of PDL
 Structure
 Blood Supply
 Nerve Supply
 Lymphatics
 Functions of PDL
 Age changes in PDL
 Regulation of PDL width
 PDL relationship with Implants
 Conclusion
 References
2/71

3. INTRODUCTION
• The term periodontium arises
from greek words “peri”
meaning around and “odont”
meaning tooth. Tissues that
invest and support the teeth
are collectively termed
PERIODONTIUM.
3/71
Periodontium
Gingiva
Periodontal
Ligament
Alveolar
Bone
Cementum

4. DEFINITION
• According to Carranza & Bernard
“The periodontal ligament is the connective tissue that
surrounds the root & connects it to the bone. It is continous with
the connective tissue of the gingiva & communicates with the
marrow spaces through vascular channels in the bone.”
• According to Berkovitz , Holland & Moxham
“ It is the dense fibrous connective tissue that occupies the
periodontal space between the root of the tooth & the alveolus. It
is derived from the dental follicle above the alveolar crest is
continous with the connective tissues of the gingiva ; at the apical
foramen it is continous with the dental pulp.”
4/71

5. • According to Orbans
“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.”
5/71

6. SYNONYMS
1. Periodontal membrane
2. Alveolo-dental ligament
3. Desmodont
4. Pericementum
5. Dental periosteum
6. Gomphosis
6/71

7. EXTENT
• 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.
• It ranges in width from 0.15-
0.38mm (A.R Ten Cate)
7/71

8. • It is thinnest around the middle third of the root, with an
hour glass appearance.
• The ligament appears as a radiolucent area of 0.4- 1.5mm
between the radiopaque lamina dura of the alveolar bone
and cementum.(Orbans)
8/71
SHAPE

9. AVERAGE WIDTH
 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
9/71

10. DEVELOPMENT
• All the periodontal tissues are derived from dental follicle
• (Osborn 1984) proposed that mesenchyme deriving the
periodontium may have two different compartments
• Alveolar clade- fibroblasts and osteoblasts
• Cemental clade- fibroblasts and cementoblasts
10/71

11. • Begins with root formation & prior to tooth eruption. (Tencate et
al.,1972).
• At Late bell stage - when amelogenesis and dentinogenesis are well
advanced, the int and the ext enamel epithelium at the cervical loop of
enamel organs form a doubled layered epithelial root sheath which
proliferates apically map out the shape of future root.
11/71

12. 12/71
• HERS loses structural
continuity
• Epithelial rests of
Malassez.
• CT cells of dental
follicle to migrate to
the newly formed root
dentin.
DENTAL
FOLLICULAR
CELLS
FIBROBLLASTS CEMENTOBLASTS OSTEOBLASTS
remnants persist as
this separation permits

13. 13/71
As the root formation continues, cells in the
peri follicular mesenchyme gain their polarity,
cellular volume & become widely separated
Actively synthesize & deposit collagen fibrils
and glycoproteins in developing PDL
(Grant’s 1989; Ten Cate’s 1971)
Type I collagen is secreted
Assembles as collagen bundles on the bone and
cementum surface
Establish continuity across the ligament space

14. DEVELOPMENT OF PRINCIPAL
FIBERS
14/71
•The alveolar bone proper (ABP) is seen to the left, the periodontal
ligament (PL) is depicted in the center and the root cementum (RC)
is seen to the right

15. • Mature PDL can be sub divided into 3 region
15/71
Bone
related
region -
rich in cells
Cementum
related region
- dense and
ordered
collagen fibers
Middle zone-
few cells &
thinner
collagen
fibers

16. ORGANIZATION OF PDL
16/71
As the teeth begin to , erupt the orientation of ligament fibres changes
according to the stage of eruption. (Grant and Bernick 1972).

17. PERIODONTAL LIGAMENT HOMEOSTASIS
• PDL has the capacity to maintain its width overtime despite the
fact that its squeezed in between 2 hard tissues.
• Studies indicate that cells of PDL, both during development and
regeneration secrete molecules which regulate mineralization
and prevent ankylosis.
• Various molecules proposed:
1. PDL cells inhibit mineralized bone nodule formation by bone
stromal cells – dependent on prostaglandin production.
2. Msx2 prevents osteogenic differentiation of PDL fibroblasts
by repressing transcriptional activity of Runx2 .
3. Matrix Gla Protein – inhibitor of mineralization.
4. GAGs – maintain unmineralised state of PDL.
17/71

18. 5. Balance b/w activities of bone sialoproteins and osteopontin –
maintains unmineralized PDL region.
• PDL has capacity to adapt to functional changes:
18/71
Functional demand
increases
 Width of PDL increases
by as much as 50%
 Fiber bundle increses in
thickness
Functional demand
decreases
 Narrowing of PDL
 Decrease in number and
thickness of fiber
bundle

19. STRUCTURE
19/71
PDL
CELLS
EXTRACELLULAR
SUBSTANCES
3.Progenitor
cells
4.Epithelial
rests of
Malassez
1.Fibers
Collagen fibers
Oxytalan fibers
2.Ground substance
Glycosaminoglycans
Glycoproteins
1.Synthetic cells
Osteoblasts
Fibroblasts
Cementablasts
2.Resorptive cells
Osteoclasts
Fibroblasts
Cementaclasts
5.Defence cells
Mast Cells
Macrophages
Eosinophils

20. • Architect, builder and caretaker
• Predominant cell in the pdl .
• Origin:
Cementum surface: Ectomesenchyme of
investing layer of dental papilla and the
dental follicle
Alveolar bone: perivascular
mesenchyme.
20/71
1.)SYNTHETIC CELLS
FIBROBLASTS
• Oriented with their long axis parallel to the direction of
collagen fibers .
• Alligned along and between collagen fibers.
• Appearance governed by surrounding matrix.

21. 21/71
• Fibroblasts of PDL generate an
organizational pattern as they have
ability to both synthesize and shape
the proteins of the extracellular
matrix .
• Certain Fibril form bundles get
inserted into tooth and bone and
are known 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 .

22. 1) Synthesize Collagen (Esterl 1961)
2) Synthesize fibrils (Stallard 1963).
3) Organize fibrous network & generate force for tooth eruption.
4) Produce extracellular matrix of PDL (Sodek 1977).
5) Have capacity to give rise to cementobalsts and osteoblasts.
6) Maintain normal width of PDL.
7) Synthesize and shape the proteins of ECM in which collagen
fibrils form bundles and insert as Sharpey’s fibers.
8) Regulate collagen turnover by PHAGOCYTOSING old
collagen fibers.
30 minutes are taken for the intercellular degradation of
collagen.
22/71
FUNCTIONS OF FIBROBLASTS

23. • These cells covers the periodontal
surface of the alveolar bone.
• Line the tooth socket and are cuboidal
in shape with a prominent round
nucleus at the basal end of the cell.
• RER , mitochondria , and vesicles are
abundant in active cells.
• Microfilaments are prominent beneath
the cell membrane at secreting surface,
• The cells contact one another through
desmosomes and tight junctions.
23/71
OSTEOBLASTS

24. CEMENTOBLASTS
• 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 required for protein synthesis and secretion
are present.
24
• Cells actively depositing
cellular cementum exhibit
abundant basophilic
cytoplasm and
cytoplasmic processes.
• Acellular cementum- no
prominent cytoplasmic
processes.

25. 2. RESORPTIVE CELLS
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.
25/71
• 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.
• Are found against the bony surface
occupying shallow depression
called Howship’s lacunae.

26. • 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.
26/71

27. CEMENTOCLASTS
• As cementum does not remodel, Cementoclasts are not usually
found in the ligament.
• These cells only occur in certain pathologic conditions, during
resorption of deciduous teeth and when regressive forces are
applied on a tooth such as orthodontic therapy.
27/71
• These Cementoclasts resembles Osteoclasts and are located in
depressions in cementum resembling Howship’s lacuna.
• These cells not only resorb cementum, they can destroy dentin
and enamel as well thus they are also called Odontoclasts.

28. 3.PROGENITOR CELLS
• All connective tissues including PDL
contain progenitors cells that have the
capacity to undergo mitotic division .
• Are the undifferentiated mesenchymal
cells that have a perivascular location
within 5 micrometres of blood vessels.
• When stimulated appropriately, these
cells undergo mitotic division and can
differentiate into fibroblast, osteoblast or
cementoblast.
28/71

29. 4.EPITHELIAL CELL REST OF
MALASSEZ
• These were first described by Malassez in 1884 and are the
remnants of the epithelium of Hertwig’s epithelial root
sheath.
• The PDL contains epithelial cells that lie about 25 m
from the cementum surface.
• They persist as networks, strands, islands or tubule-like
structures near and parallel to the surface of the root.
29/71

30. 30/71
• Their function is not yet clear but they could be involved in
periodontal repair and regeneration .
•Most numerous in the apical area & cervical area.
(Xiong J, Gronthos S, Bartold PM )
• Presence: children – more numerous
old individuals – less
Dimnishes with age (Simpson HE)
•These cells may proliferate to form cysts and tumors.
•These cells may undergo calcification to become
CEMENTICLES.

31. 5.DEFENCE CELLS
31/71
MACROPHAGES
MAST CELLS EOSINOPHILS

32. EXTRACELLULAR SUBSTANCES
FIBERS
1.COLLAGEN
2.ELASTIC
3.RETICULAR
4.SECONDARY
5.INDIFFERENT FIBER
PLEXUS
6.OXYTALAN
32/71
GROUND SUBSTANCE
1.PROTEOGLYCANS
2.GLYCOPROTEINS

33. COLLAGEN
• The main types of collagen in the PDL 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, found in periphery of Sharpey’s fiber attachments
into alveolar bone.
• 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 . 33/71

34. • 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.
34/71

35. 35/71
Turnover Rate of the Collagen:
• The rate of turnover of collagen within the PDL is faster than all
other connective tissues.
• Sodek (1977) found collagen synthesis in PDL of adult rat to be
2 fold greater than that of gingiva
4 fold greater than that of skin
6 fold greater than that of bone.
• The rate appears to be highest towards the root apex.
• The collagen on the tooth side has low turnover rate than that on
the bone side where it shows high turnover rate.

36. PRINCIPAL PDL FIBERS
36/71
• The principle fibres of
Periodontal ligament (Holmstrup
1996).
• These are collagenous and follow
a wavy pattern when viewed in
longitudinal section .
• 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)
• The adult human PDL fibers : 54-
59 nm in diameter.

37. 37
Fibre Group Origin and insertion Supposed function
1) Alveolar crest Extend obliquely from the
cementum just beneath the
junctional epithelium to the alveolar
crest and to the fibrous layer of
the periosteum covering the
alveolar bone.
Retains tooth in the socket
Oppose lateral forces
Prevents extrusion & intrusion
of tooth.
Protects deeper periodontal
ligament structures
2) Horizontal group They extend from cementum to
alveolar bone in horizontal direction
at right angles to long axis of tooth.
Occupy 10-15 % of coronal root
surface.
Restrain lateral tooth
movements.
3) Oblique group Largest group of PDL fibers.
Occupy 80-85% of root surface.
Extend from cementum in a coronal
direction obliquely to the bone.
They bear the brunt of
vertical masticatory
stresses and transform them
into tension on alveolar bone
and resist intrusive forces.
4) Apical group The apical fibres radiate in a rather
irregular fashion from cementum to
the apical region of the socket They
donot occur in incompletely
formed roots.
Prevent tooth tipping
Resist luxation.
Protect blood, lymph
and nerve supplies to tooth.
5) Inter radicular group. They fan out from the cementum to
the tooth in the furcation areas of
multirooted teeth.
Aid in resisting tipping
torquing and luxation.

38. SHARPEYS FIBERS
38/71
• The collagen bundles of the periodontal
ligament embedded into cementum and
alveolar bone – are called as Sharpey’s
fibers.
• Orientation is similar to that of adjacent
periodontal ligament bundles.
• Are more numerous but smaller at their
attachment into cementum than alveolar
bone.
• Sharpey’s fibers in Acellular cementum-
fully mineralized. Cellular cementum &
AB – partially mineralized.
• Few Sharpey’s fibers pass
uninterruptedly through bone of alveolar
process – Transalveolar fibers.

39. INTERMEDIATE PLEXUS
Earlier it was believed
that principal fibers
follow a wavy course
from cementum to
bone and are joined in
the mid region of the
periodontal space
giving rise to a zone of
distinct appearance i.e
the Intermediate
plexus .
Research over past yrs
suggests that 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
(Thomas M. Hassel).
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 .
39/71

40. ELASTIC FIBERS
• There are three types of elastic fibers which are histochemically
and ultrastructurally different.
• 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 .
40/71

41. • 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 FIBERS
• Are micro fibrils
• Run in apico-coronal direction to bend and attach at cervical
third of root (Fulmer et al. 1974)
• Diameter – 0.5-2.5um
• Volume – 3%
• Function is unknown but they may play
a role in - supporting blood vessels of PDL.
- tooth support (abutments/
Orthodontically moved teeth) 41/71
Oxytalan fibers. (A) Cementum, (B)
Principal oxytalan fiber, (C) Oxytalan
tract, and (D) Periodontal vessel.

42. EULANIN FIBERS
• Are bundles of microfibrils embedded in a small amount of
amorphous 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
42/71

43. 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
• Represent the newly formed collagenous elements, not yet
incorporated into principal fiber bundle.
• Located between and among the principal fibers.
• These are relatively non-directional and randomly oriented.
• Appear to transverse the periodontal ligament space corono-apically
and are often associated with path of vasculature and nervous
elements.
43/71

44. INDIFFERENT FIBER PLEXUS
• Described by Shackleford, 1971
• Small Collagen fibers in association with the larger principal
collagen fiber
• Run in all directions forming a plexus.
• 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.
44/71

45. GROUND SUBSTANCE
• The ground substance is the gel like matrix synthesized
by the fibroblast family & fills the space between the
fibers and cells.
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
45/71

46. PROTEOGLYCANS
• Large group of anionic macromolecules that consists of a protein
core to which are attached hexose amine containing polysaccharides
called GAG chains.
46/71
1. Decorin – regulates growth
of collagen fibrils.
2. Versican – binds cell surface
glycoproteins to ECM.
3. Prelecan - binds to
fibronectin & helps anchor
fibroblast to ECM.
4. Syndecan - binds to collagen
& other glycoproteins.
5. CD44 – binds to
glycoproteins.

47. • With the exception of hyluronic acid, the other glycosamino
glycans are sulphated and covalently attached to the core proteins
at the reducing terminus of PG.
• The major GAGs are:
1. Chondroitin Sulphate
2. Dermatan Sulphate
3. Heparin Sulphate
4. Hyaluronic Acid
5. Keratan Sulphate
47/71

48. GLYCOPROTEINS
• Three distinctly related glycoprotiens of the extra cellular matrix
have been localized in the decalcified sections of human periodontal
ligament, namely:
• It promotes the attachment of cells to the substaratum especially
to collagen.
• It is expressed strongly along attachment sites of the PDL
collagen fibers to cementum but not bone.
• In addition to its function as an adhesion protein it is also
involved in blood coagulation, wound healing and chemotaxis.
1. FIBRONECTIN
48/71

49. 2. TENASCIN :
• Also known as cytotactin
• It is the other glycoprotein identified in the PDL .
• It is found mostly in healing wounds.
• Unlike fibronectin it is not uniformly distributed through out the
PDL.
• But is concentrated in between the less densely packed collagen
fibrils near cementum and alveolar bone.
• Present in the glycoproteins of periodontal ligament with a smaller
role in cell attachment and organization of basement membrane.
49/71

50. 3. LAMININ :
• Major glycoprotein component of basement membrane of
Epithelial cell rests of Mallassez..
• Implicated in variety of functions including.
Cell adhesion
Migration
Differentiation
• Other glycoproteins like
Entactin (Nidogen ) – dumb bell shaped glycoprotiens
Vitronectin
Thrombospondin
May also be present in the glycoproteins of PDL with a smaller
role in cell attachment and organization of basement membrane.50/71

51. BLOOD SUPPLY
51/71
Blood supply is derived mainly from
: Inferior and superior alveolar
arteries to mand. & max
respectively from 3 sources:
1. Apical vessels (Dental artery) –
supply dental pulp
2. Transalveolar vessels (rami
perforantes-penetrating vessels
from alveolar bone)
3. Intraseptal vessels
(anastomosing vessels from the
gingiva)
• Ramify and form a rich network of arcades more evident adjacent
to bone than cementum..
• Blood Supply: Posterior teeth > Anterior teeth
• Gingival third > Apical third > Middle third

52. Nerve sUPPLY
52/71
The nerve fibres supplying the PDL – 2 types
sensory
autonomic.
• 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 terminations :
Free endings with treelike ramifications :
• terminal branching of myelinated fibers
• 0.2-1 um in diameter
• fine, non myelinated fibers only type of ending in tooth
pulp → classic model of pure nociception.
•Located at regular intervals along the length of the root.

53. 53/71
Ruffini’s endings :
• Found around the root apex.
• Appear dendritic and end in terminal expansions among the PDL
fiber bundles.
• Are mechanoreceptors.
Meissner's corpuscles : mid-root, for tactile perception
Encapsulated spindle type : temperature receptor, associated with root
apex.

54. Lymphatic drainage
54/71
• Lymph vessels - Follow the course of blood vessels.
• 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.

55. Functions of pdl
55/71
I. PHYSICAL FUNCTION :
1) Provision of 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 the teeth to the bone.
4) Maintainence of the gingival tissues in their
proper relationship to the teeth.
5) Resistance to the impact of occlusal forces
(Shock absorption).

56. 56/71
When a
force is
applied to
the crown
Principal
fibers first
unfold and
straighten
Transmit
forces to
the alveolar
bone
Causes
elastic
deformation
of the bony
socket.
Finally, when
the alveolar
bone has
reached its
limit
The load is
transmitted
to the basal
bone.
TENSIONAL
THEORY
States that the principal
fibers of PDL are the
major factors in
supporting the tooth and
transmitting the forces to
the bone.
Many investigators find this
theory insufficient to explain
available experimental
evidence.

57. 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 into
the tissues
Lost fluid
replenished
VISCOELASTIC
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)
57/71

58. 58/71
THE
THIXOTROPIC
THEORY
However the
presence of
organized collagen
fibers make this
theory
unacceptable.
Claims that the PDL
has the rheologic
behaviour of a
thixotropic gel (i.e. the
property of becoming
gel when shaken or
stirred and then
becoming semisolid
again).

59. 59/71
II. FORMATIVE AND REMODELING FUNCTION :
• Cells of the PDL participate in the formation and resorption of
cementum and bone, which occur in
- physiologic tooth movement,
- accommodation of the periodontium to occlusal forces
- in the repair of injures.
• Remodeling : The 3-D organization of the fiber meshwork is
adapted to accommodate for positional changes of the tooth in
its socket or changes in functional state (such as hypofunction).
• It relates to adaptability of PDL tissues.
• Both these processes can occur simultaneously and may
therefore be indistinguishable.

60. • 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) 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.
60/71

61. 61/71
III. NUTRITIONAL:
• PDL supplies nutrients to the cementum , bone, and gingiva
by way of blood vessels and provides lymphatic drainage.
• The PDL contains blood vessels, which provide anabolites
and other substance to the cementum, bone and gingiva. &
removes catabolites.
IV. HOMEOSTATIC:
• Adaptability to rapidly changing applied forces and its
capacity to maintain its width at constant diameter
throughout life.
• 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

62. V. SENSORY FUNCTION
• The PDL is abundantly supplied with sensory nerve fibers
capable of the repair of transmitting tactile, pressure and pain
sensations by the trigeminal pathway.
• The PDL provides a most efficient proprioceptive mechanism.
• 4 types of neural terminations are seen
1. Free nerve endings –pain(at regular intervals along the
length of the root.
2. Ruffini like mechanoreceptors (apical area)
3. Meissner’s corpuscles - mechanoreceptors (middle 3rd)
4. Spindle like pressure and vibration endings (apex) 62/71

63. aGE CHANGES IN PDL
63/71
• Increase in the collagen fibrosis & decrease in cellularity (Grant
& Bernick 1972).
• Areas of hyalinization are present.
• Sporadic mineralization of the fibers also occurs.
• Decrease in the no of periodontal fibers (Grant et al 1973).
• Decrease in the cellularity & the formation of multinucleated
fibroblasts.
• Decrease in collagen synthesis (Johnson et al 1986).
• The surfaces of the periodontal alveolar bone are jagged &
uneven & an irregular insertion of fibers is seen.
• Replacement of some of the PDL space by interstitial areas &
fat cells.
• Structural organization of the ligament degenerates with age.

64. WIDTH OF THE PERIODONTAL LIGAMENT SPACE
• The width of the periodontal ligament space of
nonfunctioning teeth is narrower than that of functioning
teeth (Klein 1928, Kronfeld 1931).
• If, with increasing age, less teeth are present, the force acting
on the remaining teeth may increase and an increasing width
of the periodontal ligament space with age.
• On the other hand, it has also been noted that the masticatory
forces decrease with age (Helkins et al 1977, Herring 1977).
This could explain decrease in the periodontal ligament space
with age.
64/71

65. REGULATION OF PDL WIDTH
• 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)
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66. • 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)
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67. • 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.
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68. PDL RELATIONSHIP WITH
IMPLANTS
• Implants do not employ a gomphosis to provide support and
attachment to the jaw bones as does the PDL , but still it serves as
a replacement for natural teeth.
• The absence of PDL around implants – absence of resilient
connection between teeth and jaw bone thus any occlusal
disharmony will have repercussions at bone to implant interface.
• No intrusion or migration can compensate for the eventful
presence of a premature contact.
• Absence of PDL leads to : reduced tactile sensitivity & reduced
reflex function.
• Even if certain degree of perception is present – Osseoperception.
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69. CONCLUSION
• The periodontal ligament is a fibrous connective tissue
forming important part of the Periodontium.
• The PDL is a physically small, but functionally important
tissue in tooth support, proprioception and regulation of
alveolar bone volume.
• The PDL is an absolute requirement for rapid remodeling of
alveolar bone when forces are applied to teeth.
• Cell of the periodontal ligament are Pluri-potent and helps in
the regeneration of all the components of Periodontium lost in
the periodontal disease process.
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70. • A better understanding of cell and molecular biology of
developing and regenerating periodontium offers newer
avenues to regenerate the PDL.
• Yet safeguarding the integrity of the PDL and alveolar
bone is still one of the most important challenge .
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71. REFERENCES
1) Clinical Periodontology 10th edition. F.A. Carranza, M.G. Newman .
2) Clinical Periodontology and Implant Dentistry, 4th edition. Jan Lindhe,
Thorkild Karring, Niklaus P. Lang.
3) Tencate’s Oral histology, Development, Structure and function. 4th
edition.
4) Orbans Oral Histology And Embryology. 12th Edition
5) Dental embrology, histology and anatomy. Mary Bath- Balogh, Margret
J Ferhrenbach. 2nd edition.
6) Development and general structures of the periodontium. Periodontol
2000;24,2000;9-22.
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72. Perfection is not attainable
But
If we chase Perfection we
can achieve Excellence
72