This document provides an overview of the periodontal ligament (PDL). It describes the PDL's extent, shape, width and cellular components. The PDL contains principal collagen fibers that connect cementum to alveolar bone in different orientations. It is made up of fibroblasts, osteoblasts, cementoblasts and other cells. The PDL helps anchor teeth, withstand forces from chewing and allows limited movement.

1. Photo by Steve Snodgrass
• Presented by-
• ABHIJEET KAMBLE
FINAL YEAR

2. ContentsContents
 Introduction
 Extent and shape
 Average width
 Structure
 Biochemical composition
 Cellular elements
 Periodontal fibers

3.  Collagen
 Ground substance
 Functions of PDL
 Blood supply
 Venous drainage
 Lymphatic
 Nerve supply
 References

4. IntroductionIntroduction
 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.

5. Extent & shapeExtent & shape
 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.

6. Average widthAverage 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

7. StructureStructure
1. Synthetic Cells
a) Osteoblasts
b) Fibroblasts
c) Cementoblasts
2. Resorptive Cells
a) Osteoclasts
b) Cementoclasts
c) Fibroblasts
3. Progenitor Cells
4. Epithelial Cell rests of malassez
5. Connective Tissue cells
a) Mast cells
b) Macrophages

9. Cellular elementsCellular elements
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.

10. FibroblastsFibroblasts
 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.

11. Osteoblasts & cementoblastsOsteoblasts & cementoblasts
 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.

12. Resorptive cellsResorptive cells
 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.

13. Progenitor cellsProgenitor 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

14. Epithelial rests ofEpithelial rests of
MallassezMallassez
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.

15. 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.

16. Fig. shows the presence of clusters of epithelial cells (ER) in the
periodontal ligament. These cells, called the epithelial cell rests ofepithelial 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.

17. Defense CellsDefense Cells
 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.

18. MacrophagesMacrophages
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 cells
2. Secreting growth factors that regulate the proliferation of
adjacent fibroblasts

19. CementiclesCementicles
 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

20. Cemental Tears
 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.

21. Periodontal fibersPeriodontal fibers
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)

22. CollagenCollagen
 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.

23. Collagen…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

24. 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

25. 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.

26. Formation of collagenFormation of 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.

27. Collagen microfibrils, fibrils, fibers, and bundles

30. Principal fibers of PDLPrincipal fibers of PDL
 Trans septal
 Alveolar crest group
 Horizontal
 Oblique
 Apical
 Inter – radicular

31. Transseptal GroupTransseptal Group
 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.

32. Alveolar Crest GroupAlveolar Crest 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

33. 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.

34. 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.

35. Sharpey’s FibersSharpey’s Fibers
 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.
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

36. 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.

38. 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

39. Eulanin FibersEulanin Fibers
 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

40. Ground SubstanceGround Substance
 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

41. ProteoglycansProteoglycans
 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 adhesion
b. Cell-cell & cell- matrix adhesion
c. Cell repair
d. Binding to various growth factors

42. GlycoproteinGlycoprotein
 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.

43. Glycoproteins….
 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

44. Functions Of PDLFunctions Of PDL
1. Physical
2. Formative and Remodeling
3. Nutritive
4. Sensory
5. Regulation of periodontal ligament width

45. Physical FunctionsPhysical Functions
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

46. 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.

47. 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

48. Transmission Of OcclusalTransmission 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.

49. 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

50.  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)

51. 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.

52. NutritionalNutritional
 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

53. SensorySensory
 Periodontal ligament provides the most
efficient proprioceptive mechanism
 4 types of neural terminations are seen
1. Free nerve endings -pain
2. Ruffini like mechanoreceptors (apical
area)
3. Meissner’s corpuscles -
mechanoreceptors (middle 3rd
)
4. Spindle like pressure and vibration
endings (apex)

54.  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)

55.  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.

56. 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)

57. 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.

58. Blood supply….
 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.

59. Fenestrated CapillariesFenestrated Capillaries
 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.

60. 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

61. 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

62.  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

64. Venous drainageVenous drainage
 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).

65. Lymphatics
 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.

66. ReferencesReferences
 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