PERIODONTAL LIGAMENT (PDL)

1. PERIODONTAL
LIGAMENT
PRESENTED BY:
Dr. MANISHA DEOL
MDS 1st YEAR
DEPARTMENT OF
PERIODONTOLOGYAND ORAL
IMPLANTOLOGY

2. CONTENTS
• INTRODUCTION
• DEFINITION
• EVOLUTION
• SYNONYM
• EXTENT
• SHAPE
• AVERAGE WIDTH
• DEVELOPMENT OF PERIODONTAL LIGAMENT
• DEVELOPMENT OF PRINCIPLE FIBERS
• ORGANIZATION OF PERIODONTAL LIGAMENT

3. • MICROSCOPIC FEATURES
CELLS OF PERIODONTAL LIGAMENT
FIBERS OF PERIODONTAL LIGAMENT
• EXTRACELLULAR SUBSTANCE
• INNERVATION OF PERIODONTAL LIGAMENT
• AGE CHANGES IN PERIODONTAL LIGAMENT
• FUNCTIONS
• CLINICAL CONSIDERATIONS
• CONCLUSION
• REFERENCES

4. INTRODUCTION
The term “Periodontium” arises from Greek words
“Peri” meaning around
&
“Odont” meaning tooth
Periodontium is a connective tissue organ, covered by
the epithelium that attaches the teeth to the bones of
the jaws and provides a continually adapting
apparatus for the support of the teeth during function.

5. The attachment apparatus of the tooth
includes:
Periodontium
Gingiva
Periodontal
ligament
Alveolar
bone
Cementum

6. WHAT IS PERIODONTAL LIGAMENT ?
The Periodontal Ligament is the connective tissue that
surrounds the root & connects it to the bone. It is
continuous with the connective tissue of the gingiva
and communicates with the narrow spaces through
vasacular channels in the bone.
(Carranza 10th edition)
The Periodontal Ligament is the soft, richly vascular
and cellular connective tissue which surrounds the
roots of the teeth and joins the root cementum with
the socket wall.
( Lindhe 5th edition )

7. The Periodontal Ligament is that soft, specialized
connective tissue situated between the
cementum covering the roots of the tooth and
the bone forming the socket wall.
(Ten Cate`s 7th edition)
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 13th edition)

8. EVOLUTION
• A series of coordinated changes in the jaws have occurred
during an evolutionary step from reptiles to mammals.
• In reptiles, the teeth are ankylosed to the bone whereas in
mammals, the teeth are suspended in their sockets
ligaments.
• There is a radical reconstruction of the mandible from
reptiles to the mammals. In reptiles, the bones of the
mandible are joined by the sutures. The dentary, which is
the upper bone, carries the ankylosed teeth.
(EVOLUTION AND HISTORY OF THE PERIODONTAL LIGAMENT-A REVIEW. THE
INTERNET JOURNAL OF MEDICAL TECHNOLOGY 2012, VOL 6(1).)

9. • The growth of the mandibular height in reptiles, occurs in
mandibular sutures while in mammals the growth occurs at
the free margin of the alveolar process.
• In reptiles the teeth move with the bone to which they are
fused. while in mammals, the teeth move as a unit.
• This is because of remodeling of the periodontium. Thus,
during evolution from reptiles to the mammals, there is
replacement of the ankylosis of the tooth and bone to a
ligamentous suspension of the tooth.
• Because of this, movement of the mammalian teeth is made
possible, resulting in continual repositioning as required by
the jaw growth and also tooth wear.

10. SYNONYMS
1. Desmodont
2. Gomphosis
3. Pericementum
4. Dental periosteum
5. Alveolodental ligament
6. Periodontal
membrane

11. • "Periodontal membrane" and "periodontal ligament"
are the terms that are most commonly used.
It is neither a typical membrane nor a typical
ligament. However, because it is a complex soft
connective tissue providing continuity between two
mineralized connective tissues, the term
"periodontal ligament" appears to be the more
appropriate.

12. EXTENT
• In the coronal direction, it is continuous with
lamina propria of gingiva & is demarcated by
the alveolar crest fibres.
• At the root apex, it merges with dental pulp.
• It ranges in width from 0.15 -0.38mm.

13. AVERAGE WIDTH
 Depending on the age
 Depending on the functioning and functionless
teeth.
 Depending on the age
I. 11-16 years - 0.21 mm
II. 32 – 52 year - 0.18 mm
III. 51 – 67 years - 0.15 mm

14.  Depending on the functioning and
functionless teeth

15. SHAPE
• 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 -1.5 mm on radiographs i:e between the
radiopaque lamina dura of the alveolar bone
and cementum.

16. DEVELOPMENT OF PERIODONTAL LIGAMENT
Begins with root formation, prior to tooth eruption
Continuous proliferation of the internal and
external enamel epithelium forms the cervical loop
of the tooth bud.
Sheath of epithelial cells grows apically, in the form
of Hertwig's epithelial root sheath, between the
dental papilla and the dental follicle.
At this stage, the sheath forms circumferential
structure encompassing dental papilla separating it
externally from dental follicle cells.

17. Hertwigs root sheath separates, forming the
strand known as epithelial rest of malassez.
This separation permits the cells of dental
follicle to migrate to the external surface of
the newly formed root dentin.
These migrant follicle then differentiate into
fibroblast which synthesize the fibers and
ground substance of periodontal ligament.
These fibers of the periodontal ligament then
get embedded at one end into the newly
formed cementum laid by cementoblasts and
at the other end into the bone laid by
osteoblasts.

18. • The developing and mature PDL contain
undifferentiated stem cells that retain the
potential to differentiate into osteoblasts,
cementoblasts and fibroblasts.
• Studies suggest that, stem cells occupy
perivascular sites in the periodontal ligament
and in adjacent endosteal spaces.

19. DEVELOPMENT OF THE
PRINCIPAL FIBERS
• First, small , fine , brush –
like fibrils are detected
arising from the root
cementum and projecting
into periodontal ligament
space .
• At this stage the surface
of the bone is covered by
osteoblasts. From the
surface of the bone only a
small number of radiating,
thin collagen fibrils can
be seen.

20. • Later on, the number and
thickness of fibers
entering the bone
increase .
• These fibers radiate
towards the loose
connective tissue in the
mid-portion of the
periodontal ligament
area, which contains
more or less randomly
oriented collagen fibrils .

21. • The fibers originating
from the cementum are
still short while those
entering the bone
gradually become
longer.
• The terminal portions of
these fibers carry finger-
like projections.

22. • These fibers originating from
cementum subsequently increase in
length and thickness and fuse in the
periodontal ligament space with the
fibers originating from alveolar
bone.
• When the tooth , following eruption
, reaches contact in occlusion and
starts to function , the principal
fibers become organized in bundles
and run continuously from the bone
to the cementum .

23. SHARPEY`S FIBERS
• Collagen fibers are embedded into cementum on
one side of the periodontal space and into
alveolar bone on the other.
• The embedded fibers are termed Sharpey's
fibers. Sharpey's fibers are more numerous but
smaller at their attachment into cementum than
alveolar bone.

24. • The mineralized parts of Sharpey's fibers in alveolar bone appear as
projecting stubs covered with mineral clusters.
• The mineralization is at right angles to long axis of fibers, indicating
that in function, the fibers are subjected to tensional forces.
• Sharpey's fibers in primary acellular cementum are mineralized
fully, those in cellular cementum and bone are mineralized, partially
at their periphery.

25. • Few Sharpey's fibers pass uninterruptedly through the
bone of the alveolar process (termed Transalveolar fibers)
to continue as principal fibers of the adjacent periodontal
ligament.
• They may mingle buccally and lingually with fibers of the
periosteum that cover the outer cortical plates of the
alveolar process.
• These fibers pass through the alveolar process, only when
the process consists entirely of compact bone and contains
no haversian system.

26. Mature PDL can be subdivided into:-
1.A bone-related region – rich in cells and blood
vessels.
2.A cementum-related region - characterized by
dense ,well-ordered collagen bundles.
3.A middle zone – containing fewer cells and
thinner collagen fibrils.

27. ORGANIZATION OF THE
PERIODONTAL LIGAMENT
• The tooth bud is formed in a crypt of the
bone.
• The collagen fibers produced by the fibroblast
in the connective tissue around the tooth bud
are embedded , during the process of their
maturation, into the newly formed cementum
immediately apical to CEJ.

28. • These fiber bundle
oriented towards the
coronal portion of the
bone crypt will later form
the dentogingival fiber
group,the dentoperiosteal
fiber group and the
transeptal fiber group
which belong to the
oriented fiber of the
gingiva.

29. The true periodontal
ligament fiber, the
principal fibers, develop
in conjugation with the
eruption of tooth . First,
fibers can be identified
entering the most
marginal portion of the
alveolar bone.

30. • Later, more apically
positioned bundles of
oriented collagen fibers are
seen .
• The orientation of collagen
fiber bundles alters
continuously during the
phase of tooth eruption .

31. • First, when tooth has
reached contact in
occlusion and is functioning
properly , the fiber of the
periodontal ligament
associate into groups of well
oriented dentoalveolar
collagen fibers.
• These collagen structures
undergo constant
remodeling (i.e. resorption
of old fibers and formation
of new ones).

32. MICROSCOPIC FEATURES
PDL
Cells
Progenitor
cells
Differentiated
cells
Synthetic cells
Resorptive
cells
others
Extracellular
substances
Fibers
Ground
substances

33. CELLS OF PERIODONTAL
LIGAMENT
• The cells of the periodontal ligament may
be divided into:
1. Synthetic cells
• Osteoblasts
• Fibroblasts
• Cementoblasts
2. Resorptive cells
• Osteoclasts
• Fibroblasts
• Cementoclasts

34. 3. Progenitor cells
Undifferentiated mesenchymal cell
4. Epithelial cell rests of Malassez
5. Defense cells
• Mast cells
• Macrophages
• Eosinophils

36. SYNTHETIC CELLS
General cytologic criteria for protein synthesizing
and secreting cells are:
• Large open-faced nucleus
• Abundant cytoplasm
• Increase in no. of mitochondria
• Extensive rough endoplasmic
reticulum( RER)
• Increase in size of Golgi apparatus
• Presence of secretory granules

37. If Cells are found at the periodontal surface of
alveolar bone
– active osteoblasts
If lying in the body of the soft connective tissue
– active fibroblasts
If found at cementum – active cementoblats

38. FIBROBLASTS (synthetic and resorptive)
• The fibroblast is the predominant cell and most important
functionally in the periodontal ligament.
• Origin –
– Ectomesenchyme of investing layer of dental papilla and
– Dental follicle.
• The rapid degradation of collagen by fibroblast
phagocytosis is the basis for the very fast turnover of
collagen in the periodontal ligament.

39. • Sixty-five percent of the cells
in gingival connective tissue
are fibroblasts . The role of
this cell is to produce the
structural connective tissue
proteins, collagen and elastin,
as well as the glycoproteins
and glycosaminoglycans that
comprise the periodontal
ligament ground substance.
• Periodontal fibro- blasts also
secrete an active collagenase
as well as a family of enzymes
known collectively as matrix
metallo-proteinases

40. • These enzymes have the capacity to degrade the
extracellular matrix .
• All of the metalloproteinases are secreted by
fibroblasts in an inactive, precursor form.
• Also, even when activated, the
metalloproteinase family of enzymes is effectively
inhibited by a variety of tissue inhibitors .
• In addition to fibroblasts , metalloproteinases
and other enzymes that destroy periodontal
tissues are also produced by keratinocytes and
tissue macrophages.

41. • Periodontal ligament contains a variety of fibroblast cell
populations with different functional characteristics.
• For example, fibroblasts on the bone side of the ligament
show abundant alkaline phosphatase activity than those
on the tooth side.
• Another example: one subpopulation of cells may secrete
collagen at a high rate, and another synthesizes less
collagen but also produces considerable amounts of
collagenase. Different cell subpopulations probably are
responsible for the production of differing quantities of the
various collagen types as well. The theory is that clinical
normalcy is the result and sum of the particular mixture of
cell subpopulations within the healthy tissue.

42. • Developmental differences may
also exist. It has been
demonstrated that, the
fibroblasts near cementum are
derived from ectomesenchymal
cells of the investing layer of
dental papilla, while fibroblasts
near alveolar bone are derived
from perivascular mesenchyme.
• These fibroblasts are regularly
distributed throughout the
ligament, and are oriented with
their long axis parallel to the
direction of collagen fibrils.

43. • Proline is incorporated into collagen polypeptides in rough
endoplasmic reticulum.
• Sodek has demostrated that pdl incorporates proline at least
5 times faster than gingiva or alveolar bone and the biological
half-life of mature collagen was 20% and 17% less than found
in gingiva or alveolar bone respectively.
(SODEK J.A Comparison of collagen and non-collagenous protein metabolism in rat
molar and incisor periodontal ligament Arch Oral Biol 1978 : 23: 977 – 982)
• The fibroblasts of PDL have cilia.
• These cilia may be associated with control of the cell cycle or
inhibition of centriolar activity.

44. MORPHOLOGY
• The fibroblasts are large cells with extensive cytoplasm and
abundant organelles, associated with protein synthesis and
secretion.
• The nucleus occupies a large volume of the cell and
contains one or more prominent nucleoli.
• During development and initial formation of the
Periodontal ligament, the fibroblasts appear very active
with extensive network of rough endoplasmic reticulum,
well developed Golgi apparatus and abundant secretory
granules continent type I collagen molecules.

45. Principal cells
They are found between the fibers of the PDL.
RESTING - Elongated with little cytoplasm, flattened nucleus.
ACTIVE - Oval nucleus with extensive cytoplasm with abundance of organelles
associated with protein synthesis & secretion.

46. Differences between Periodontal Ligament Fibroblasts and
Gingival Fibroblasts
PDL FIBROBLASTS GINGIVAL FIBROBLASTS
ectomesenchymal in origin mesodermal in origin
Expression of alkaline Phosphatase and
cyclic AMP is more
Expression of alkaline phosphatase and
cyclic AMP is less
more proliferative less proliferative
can generate a force for tooth eruption as
they are motile and contractile
Less contractile
In culture synthesize and secrete
elevated quantities of chondroitin
sulfates A and C but lesser amounts
of hyaluronic acid and heparin
Comparatively less synthesis of chondroitin
sulfates, but higher hyaluronic acid and
heparin

47. PDL FIBROBLASTS GINGIVAL FIBROBLASTS
Periodontal ligament fibroblasts become
senescent in vitro more rapidly ,when
proliferation rates are compared
Gingival fibroblast become senescent
comparatively slowly
Attachment properties in vitro in response to
various factors such as fibronectin or extracts
from various mineralized oral tissues less as
compare to gingival fibroblast
Gingival cell attachment far outweigh that of
periodontal ligament-derived cells
(Perio 2000 vol 3;9-38)

48. CEMENTOBLAST
• The distribution of cementoblasts is similar to the
distribution of osteoblasts on the bone surface.
• Cells line the surface of cementum, but are not
regularly arranged as osteoblasts.
• These cells are often indistinguishable from
periodontal fibroblasts apart from their location
adjacent to cementum surface.

49. • Cementoblasts are almost cuboidal with a large
vesicular nucleus, with one or more nucleoli and
abundant cytoplasm.
• All the organelles required for protein synthesis and
secretion are present.
• Cementoblasts have abundant mitochondria and less
amounts of rough endoplasmic reticulum than PDL
fibroblasts.

50. • Cells actively depositing cellular cementum exhibit
abundant basophilic cytoplasm and cytoplasmic
processes and the nuclei are folded and irregularly
shaped.
• Cells depositing acellular cementum do not have
prominent cytoplasmic processes.
• Cell membrane shows gap junctions and desmosomes
and has receptors for growth hormone and EGF.

51. OSTEOBLAST
• The osteoblasts covering the periodontal surface
of the alveolar bone constitute a modified
endosteum and not a periosteum.
• A cellular layer, but not an outer fibrous layer, is
present on the periodontal surface of the alveolar
bone.

52. • The surface of the bone lining the dental
socket must therefore be regarded as an
interior surface of bone, akin to that lining
medullary cavities, and not an external
surface, which would be covered by
periosteum.
• The surface of the bone is covered largely by
osteoblasts in various stages of differentiation
as well as by occasional osteoclasts.

53. • Osteoblasts are bone forming cells lining the tooth
socket.
• These cells are :
- cuboidal in shape
-prominent round nucleus placed at the basal end of the
cell.
-Rough endoplasmic reticulum, mitochondria and vesicles
are abundant in active cells.

54. • The cells contact one another through
desmosomes and tight junctions.
• Osteoblasts are also in contact with
underlying osteocytes through cytoplasmic
processes.

55. RESORPTIVE CELL

56. OSTEOCLAST
• Osteoclasts are cells that
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.

57. • At a site of active bone
resorption, the osteoclast
forms a specialized cell
membrane, the "ruffled
border," that touches the
surface of the bone tissue.
The ruffled border, which
facilitates removal of the
bony matrix, is a
morphologic characteristic
of an osteoclast that is
actively resorbing bone. The
ruffled border increases
surface area interface for
bone resorption.

58. CEMENTOCLAST
• Cementoclasts resemble osteoclasts and are occasionally found in normal
functioning periodontal ligament.
• Cementum is not remodeled in the fashion of alveolar bone and PDL but
that it undergoes continual deposition during life.
• The origin of cementoclasts is unknown, but it is conceivable that they arise
in the same manner as osteoclasts.

59. PROGENITOR CELLS
• All connective tissues, including PDL, contain
progenitors for synthetic cells that have the
capacity to undergo mitotic division.
• some mesenchymal stem cells remain within the
periodontal ligament and are responsible for
tissue homeostasis, serving as a source of
renewable progenitor cells generating
cementoblasts, osteoblasts and fibroblasts
throughout adult life.

60. • Progenitor cells are present is evident from the
burst of mitoses that occurs after application of
pressure to a tooth as in orthodontic therapy or
after wounding, that stimulate proliferation and
differentiation of cells of PDL.
• Its populations within the PDL appear to be in
highest concentrations in locations adjacent to
blood vessels and also enter the periodontal
ligament through penetrations from adjacent
endosteal spaces.

61. Epithelial Cell Rest of Malassez
• The PDL contains epithelial cells that are found close to
the cementum.
• These cells were first described by Malassez in 1884 and
are the remnants of the epithelium of Hertwig's
epithelial root sheath.
• At the time of cementum formation, the continuous
layer of epithelium that covers the surface of the newly
formed dentin breaks into lacelike strands.
• The epithelial rests persist as a network, strands,
islands, or tubule-like structures near and parallel to the
surface of the root.
• They lie about 25 µm from the cementum surface.

62. • In cross-sections, they appear
cluster like. The cluster
arrangement appears like a duct
with the cells separated from the
surrounding connective tissue by
a basal lamina.
• These cell rests are abundant in
the furcation areas.
• These cell rests can be
distinguished from fibroblasts in
PDL by the close packing of their
cuboidal cells and the deeply
stained nucleus.

63. • Although there is no general agreement on the functions of epithelial cell rests of malassez,
accumulating evidence suggests that the putative roles of the epithelial cell rests of
malassez in adult periodontal ligament include:
• Maintaining periodontal homeostasis to prevent ankylosis.
• To maintain periodontal space.
• To prevent root resorption.
• To serve as a target during periodontal ligament innervation.
• To contribute to cemental repair.

64. • The distribution of these cells varies according to site and age.
• They are less numerous in older individuals and more numerous in
children.
• Up to the second decade, these cells are most commonly found in
apical region, later they are mainly located cervically in the gingiva
above the alveolar crest.
• These cells may proliferate to form cysts and tumors or may also
undergo calcification to become cementicles.

65. DEFENSE CELLS

66. MAST CELLS
• The mast cell is a relatively round or oval cell having a diameter
of about 12 to 15 µm.
• Mast cells are often associated with blood vessels.
• The cells are characterized by numerous cytoplasmic granules,
which frequently obscure the small, round nucleus.
• The granules stain with basic dyes but stain metachromatically
with metachromatic dyes such as azure A.
• They are also positively stained by the periodic acid-Schiff
reaction.
• The granules are dense, membrane bound vesicles
approximately 0.5 to 1µm diameter.

67. • When the cell is stimulated it degranulates.
• The granules have been shown to contain heparin and
histamine and, in some animals, serotonin .
• Mast cell histamine plays a role in the inflammatory reaction.
• Mast cells degranulate in response to antigen-antibody
reaction on their surface.
• Occasionally mast cells may be seen in the healthy
periodontal ligament.
• The release of histamine into the extracellular environment
causes proliferation of endothelial cells and mesenchymal
cells.

68. MACROPHAGES
• Macrophages are also
found in the PDL and are
predominantly located
adjacent to blood vessels.
• These defense cells are
derived from monocytes
and phagocytose
particulate matter and
invading microorganisms.

69. • In the periodontal ligament macrophages may
play a dual role:
(1) phagocytosing dead cells and
(2) secreting growth factors that regulate the
proliferation of adjacent fibroblasts.

70. EOSINOPHILS
• Eosinophils are occasionally
seen in the periodontal
ligament.
• They possess granules that
consist of one or more
crystalloid structures.
• The cells are capable of
phagocytosis.

71. Extracellular elements
Connective tissue Fibers
• Collagen fibers
• Oxytalan fibres
• Reticular fibers
• Elastic fibres
• Secondary fibres
• Indifferent fiber plexus
Ground substance
– Proteoglycans
– Glycosaminoglycans
– Glycoproteins

72. COLLAGEN
• Collagen is a protein composed of different
amino acids; the most important being glycine,
proline, hydroxylysine and hydroxyproline.
• The amount of collagen in a tissue can be
determined by its hydroxyproline content.
• The collagen is gathered to form bundles
approximately 5µm in diameter.
• These bundles are termed principal fibers.
• Within each collagen bundle, subunits are present
called collagen fibrils.

73. • These fibrils are formed by packing together of
individual tropocollagen molecules.
• The PDL fibrils are small and the diameter reflects the
mechanical demands put upon the connective tissue.
• Collagen fibrils have transverse striations with a
characteristic periodicity of 64 nm.
• These striations are caused by the overlapping
arrangement of the tropocollagen molecules.

74. • The collagen fibril diameters of the mammalian
periodontal ligament are small (45-55nm).
• The small diameter of the fibrils could be due to
– high rate of collagen turnover
– the absence of mature collagen fibrils.
• The main types of collagen in the periodontal ligament are
– type I (More than 70% )and
– type III.

75. • Type I collagen is uniformly distributed
– Contains
• Two identical α1(I) chains and
• One α2 chain.
• It is low in hydroxylysine and glycosylated hydroxylysine.

76. • Type III collagen accounts for about 20% of collagen
fibers.
– It consists of three identical αl(III) chains. It is high
in hydroxyproline, low in hydroxylysine and
contains cysteine.
– Type III collagen is covalently linked to type I
collagen throughout the tissue.
– It is found at the periphery of Sharpey's fiber
attachments into alveolar bone.
– The function of type III may be involved with
collagen turnover, tooth mobility and collagen fibril
diameter.

77. • Small amounts of type V and type VI collagens and traces of type IV and type VII collagen
are also found in the ligament.
• Type V collagen coats cell surfaces and other types of collagen. This collagen increases in
amount in periodontal inflammatory disease.
• Type VI is a short chain molecule that ramifies the extracellular matrix, but is not directly
associated with major banded collagen fibrils. It may play a role in maintaining the
integrity and elasticity of the extracellular matrix.

78. The principal fiber present in periodontal ligament include:
 Transseptal group
 Alveolar crest fiber group
 Horizontal group fibers
 Oblique fibers
 Apical group
 Interradicular group in multirooted teeth

79. TRANSSEPTAL FIBERS
• Transseptal fibers extend
interproximally over the
alveolar bone crest and are
embedded in the cementum
of adjacent teeth.
• They area remarkably
constant finding and
are reconstructed even after
destruction of the alveolar
bone has occurred in
periodontal disease.
• These fibers may be
considered as belonging to the
gingiva because they do not
have osseous attachment.

80. • Fibers 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 periosteum covering the
alveolar bone.
• These fibers resist tilting,
intrusive, extrusive and
rotational forces.
ALVEOLARCREST FIBERS
ALVEOLAR
CREST FIBRES
80

81. HORIZONTAL FIBERS
HORIZONTAL
FIBRES
81
• Horizontal fibers extend at right
angles to the long axis of the
tooth from the cementum to the
alveolar bone.

82. OBLIQUE GROUP
• Oblique fibers, the largest group in the
periodontal ligament, extend from the cementum
in a coronal direction obliquely to the bone.
• They bear the brunt of vertical masticatory
stresses and transform them into tension on the
alveolar bone.
OBLIQUE
GROUP
82

83. APICAL GROUP
• The apical fibers radiate in a rather irregular
manner from the cementum to the bone at the
apical region of the socket.
• They do not occur on incompletely formed
roots.
APICAL
GROUP
83

84. INTERRADICULAR FIBERS
• The interradicular fibers fan
out from the cementum to the
tooth in the furcation areas of
multirooted teeth.
INTERRADICULAR
FIBERS
84

85. Reticular fibers
• These are fine immature collagen fibers with argyrophilic staining
properties,
• Related to basement membrane of blood vessels and epithelial cells
which lie within the periodontal ligament.
• These fibers are composed of type III collagen.

86. Secondary fibers
• These are located between and among the principal fibers.
– relatively non-directional and randomly oriented.
– newly formed collagenous elements that have not yet been incorporated
into principal fiber bundles.
– appear to traverse the periodontal ligament space coronoapically and are
often associated with paths of vasculature and nervous elements.

87. ELASTIC FIBRES
• Although the periodontal ligament does not contain
mature elastin, two immature forms are found:
oxytalan and eluanin.
• The so-called oxytalan fibers run parallel to the root
surface in a vertical direction and bend to attach to
the cementum in the cervical third of the root.
• They are thought to regulate vascular flow.

88. OXYTALAN FIBERS
• Oxytalan fibers are a type of immature elastic fibers.
– consist of microfibrillar component only.
– demonstrated under the light microscope when the
section is oxidized strongly before staining with elastin
stains.
– not susceptible to acid hydrolysis.
– approximately 0.5-2.5µm diameter and appear to have
elastin and type IV collagen.

89.  Oxytalan fibers tend to run in an axial direction one end being embedded in cementum
or possibly bone, and the other often in the wall of a blood vessel(different from
collagen).
• In the cervical region, they follow the course of gingival and Transseptal fibers.
• Within the periodontal ligament proper, these fibers are longitudinally oriented,
crossing the oblique fibers perpendicularly.
• In the vicinity of the apex they form a complex network.

90. • The function of the oxytalan fibers is unknown, but it has been suggested
that they may play a part in supporting the blood vessels of the periodontal
ligament.
• They are thicker and more numerous in teeth that are subjected to high
loads, as in abutment teeth for bridges and teeth that are moved
orthodontically. Thus, these fibers may have a role in tooth support.

91. Elaunin fibers
• Elaunin fibers are seen as bundles of microfibrils
embedded in a relatively small amount of
amorphous elastin.
• These fibers may be found within the fibers of the
gingival ligament.
• An elastic meshwork has been described in the
PDL as being composed of many elastin lamellae
with peripheral oxytalan fibers and elaunin fibers.

92. Indifferent fiber plexus
• These fiber are small collagen fibers associated with the large principal collagen
fibers.
– Run in all directions, forming a plexus called indifferent fiber plexus.
– But some studies report that this plexus is seen in ground sections examined under
scanning electron microscope, but not under transmission electron microscope or light
microscope.
– Hence, some authors consider it to be an artifact produced by preparation.

93. INTERMEDIATE PLEXUS OF PDL
• The principal fibers frequently run a wavy course from
cementum to bone. It may appear as fibers arising from
cementum & bone are joined in the midregion of the PD space,
giving rise to a zone of distinct appearance, called intermediate
plexus.
• It was also considered to be an area of high metabolic activity.
• Research over the past few years demostrated that, once the
cemental fibres meet and fuse with osseous fibres no such
plexus exit.
• A specific type of waviness has been reported in collagenous
tissues including the pdl, called crimping. The crimp is
gradually pulled out when the ligament is subjected to
mechanical tension, until it disappears.

94. GROUND SUBSTANCE
• 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.
• Its a gel-like matrix present in every nook and cranny,
including the interstices between fibers and between
fibrils.
• It is important to understand that 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.

95. • Its integrity is essential, if the cells of the ligament have to
function properly.
• The other functions of ground substance are ion and water
binding and exchange, control of collagen fibrillogenesis
and fiber orientation and binding of growth factors.
• The ground substance consists mainly of hyaluronate,
glycosaminoglycans, proteoglycans and glycoproteins.
• All components of the ground substance are presumed to
be secreted by fibroblasts.

96. STRUCTURE PRESENT IN CONNECTIVE
TISSUE
The following discrete structures are present in
the connective tissue of the periodontal
ligament:
• Blood vessels
• Lymphatics
• Nerves
• Cementicles

97. ARTERIAL SUPPLY
• The blood supply is derived from the inferior and the
superior alveolar arteries to the mandible and maxilla
respectively and reach the PDL from three sources:
1.Branches in the periodontal ligament from apical vessels
that supply the dental pulp.
2.Branches from intra-alveolar vessels. These branches run
horizontally, penetrating the alveolar bone to enter the
periodontal ligament.
3. Branches from gingival vessels. These enter the periodontal
ligament from the coronal direction.

98. • Diagram of the major components of the
blood vascular system of the periodontium.
The periodontal ligament (l), the alveolar
process (2) and the gingiva (3) are supplied
primarily by 3 vascular sources.
• The vessels exhibit frequent arborization
and anastomoses. Within the periodontal
ligament the vascular network is especially
dense, taking on the appearance and
Character of a thickly woven net.
• Adjacent to the junctional epithelium the
vessels splay into a very dense plexus (A)
with numerous venules. The connective
tissue rete that occupy invaginations in the
basal epithelial surface contain abundant
capillary loops. The oral gingiva (B) is also
supplied by capillary loops within rete pegs.

99. VENOUS SUPPLY
• 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.
• The specialized shunts provide an arteriovenous anastomosis and
drainage by passing the capillaries.
• In some parts of the PDL, particularly around the apex a dense
venous network is generally seen.

100. LYMPH DRAINAGE
• A network of lymphatic vessels, following the path of the
blood vessels, provides the lymph drainage of the periodontal
ligament.
• The flow is from the ligament toward and into the adjacent
alveolar bone.
• The lymphatic vessels are like veins provided with valves.
• The lymph from the periodontal tissues drains into thelymph
nodes of head and neck.
• It may course apically through the substance of PDL to arise
and pass through the fundus of the socket or may through the
cribriform plate.
• They finally empty into larger channels after pursuing
intraosseous path.

101. Nerve supply
• The PDL has functionally two types of nerve
fibers: sensory and autonomic.
• The sensory fibers are associated with
nociception and mechanoception, with touch,
pressure, pain and proprioceptive sensations.
• The autonomic fibers are associated with PDL
vessels.

102. • 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 periodontal ligament.
• In the region of the apex, they run toward the cervix,
whereas along the length of the root they branch and run
both coronally and apically.

103. • The nerve fibers are either of large diameter and myelinated or of
small diameter, in which case they may or may not be myelinated.
• The small fibers appear to end in fine branches throughout the
ligament and the large fibers in a variety of endings, for example,
knob like, spindle like, and Meissner like, but these seem to vary
among the species.
• The large diameter fibers appear to be concerned with discernment
of pressure and the small diameter ones with pain.

104. • PDL mechanoceptors exhibit
directional sensitivity as they
respond to a force applied to
the crown in a particular
direction
1. FREE ENDING ,which have a tree like
configuration, carry pain sensation .
2. RUFFINI-LIKE MECHANORECEPTOR ,
located primarily in apical area .
3. COILED MESSINER’S CORPUSCLES ,
found mainly in mid root region.
4. SPINDLE LIKE PRESSURE AND
VIBRATION ENDING , located mainly
in the apex

105. CEMENTICALS
• Calcified bodies called cementicles are sometimes found in the periodontal
ligament.
• These bodies are seen in older individuals, and they may remain free in the
connective tissue.
• They 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.

106. AGE CHANGES IN PDL
• The PDL ages as in all other tissues of the body.
• The cell number and the cell activity decreases with
aging.
• One of the prominent age changes is seen in the
calcified tissues of the periodontium, the bone
(alveolar) 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.

107. • This remarkable change affects the supporting structures of
the teeth.
• With aging the activity of the PDL tissue decreases because
restricted diets and therefore normal functional stimulation
of the tissue is diminished.
• Any loss of gingival height related to gingival and
periodontal disease promotes destructive changes in the
PDL.
• The teeth becomes nonfunctional and the PDL width also
starts to dwindle.

108. FUNCTIONS OF PDL
• Supportive
• Sensory
• Nutritive
• Homeostatic
• Eruptive

109. 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 the
periodontal ligament space will be narrowed and
the periodontal ligament contained in these areas
will be compressed.
• Other parts of periodontal space will be widened.

110. • The compressed periodontal ligament
provides support for the loaded tooth.
• The collagen fibers in the compressed
ligament, in concert with water molecules and
other molecules bound to collagen, act as a
cushion for the displaced tooth.

111. • The pressure of blood in the numerous vessels
also provides a hydraulic cushion for the support
of the teeth.
• Its suggested that collagen fibers in the widened
periodontal space are extended to their limit
when a force is applied to a tooth and, being non-
elastic, prevent the tooth from being moved too
far.

112. SENSORY
• The PDL, through its nerve supply, provides a most
efficient proprioceptive mechanism.
• Allowing the organism to detect the application of the
most delicate forces to the teeth and very slight
displacement of the teeth.
• Mechanoprotection protects both supporting
structures of the tooth and the substances of the
crown from excessive masticatory forces.

113. NUTRITIVE
• The ligament contains blood vessels, which provide
anabolites and other substances required by the cells of the
ligament, by the cementocytes, and presumably by the
more superficial osteocytes of the alveolar bone.
• Experimental extirpation of the ligament results in necrosis
of underlying cementocytes. The blood vessels are also
concerned with removal of catabolites.
• Occlusion of blood vessels leads to necrosis of cells in the
affected part of the ligament; this occurs when too heavy a
force is applied to a tooth in orthodontic therapy.

114. HOMEOSTATICS
• The cells of the periodontal ligament have the
capacity to resorb and synthesize the
extracellular substances of the connective tissue
of the ligament, alveolar bone and cementum.
• The collagen of the periodontal ligament 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 the ligament may be more active
than those on the cementum side.

115. • The preservation of the PDL width throughout mammalian
lifetime is an important measure of PDL homeostasis.
• The ability of the PDL cells to synthesize and secrete a wide
range of regulatory molecules is an essential component of
tissue remodeling and PDL homeostasis.
• The failure of homeostatic mechanism to regulate PDL
width may lead to tooth ankylosis and / root resorption.

116. ERUPTIVE
• The cells, vascular elements and extracellular
matrix proteins of the PDL function collectively to
enable mammalian teeth of limited eruption to
adjust their position while remaining firmly
attached to the bone socket.
• The PDL provides space and acts as a medium for
cellular remodeling and hence continued
eruption and approximal shift occurs.

117. PHYSICAL FUNCTION
• The physical functions of the periodontal ligament entail the following:
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. Maintenance of the gingival tissues in their proper relationship to the teeth
5. Resistance to the impact of occlusal forces (shock absorption)
• RESISTANCE TO THE IMPACT OF OCCLUSAL FORCES
• Two theories relative to the mechanism of tooth support have been considered:
the tensional and viscoelastic system theories.

118. • The tensional theory of tooth support ascribes to the principal
fibers of the periodontal ligament the major responsibility in
supporting the tooth and transmitting forces to the bone.
• When a force is applied to the crown, the principal fibers first
unfold and straighten and then transmit force's to the alveolar
bone, causing an elastic deformation of the bony socket.
• Finally, when the alveolar bone has reached its limit, the load is
transmitted to the basal bone.

119. • The viscoelastic system theory considers the
displacement of the tooth to be largely controlled
by fluid movements, with fibers having only a
secondary role.
• When forces are transmitted to the tooth, the
extracellular fluid passes from the periodontal
ligament into the marrow spaces of bone through
foramina in the cribriform plate.

120. • These perforations of the cribriform plate link the periodontal
ligament with the cancellous portion of the alveolar bone and are
more abundant in the cervical third than in the middle and apical
thirds.
• After depletion of tissue fluids, the fiber bundles absorb the slack
and tighten. This leads to blood vessel stenosis.
• Arterial back pressure causes ballooning of the vessels, and passage
of blood ultrafiltrates into the tissues, thereby replenishing the
tissue fluids.

121. CLINICAL CONSIDERATIONS
• The primary role of the periodontal ligament 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.
• The fact that the periodontal ligament is thinnest in the
middle region of the root seems to indicate that the
fulcrum of physiologic movement is in this region.

122. • For the practice of restorative dentistry, the supporting
tissues of a tooth long out of function are poorly
adapted to carry the load suddenly placed on the tooth
by a restoration.
• This applies to bridge abutments, teeth opposing
bridges or dentures, and teeth used as anchorage for
removable bridges.
• This may account for the inability of a patient to use a
restoration immediately after its placement.

123. • Some time must elapse before the supporting tissues
become adapted again to the new functional demands.
• An adjustment period, likewise, must be permitted
after orthodontic treatment.
• Acute trauma to the periodontal ligament, accidental
blows, or rapid mechanical separation may produce
pathologic changes such as fractures or resorption of
the cementum, tears of fiber bundles, hemorrhage,
and necrosis.

124. • The adjacent alveolar bone is resorbed, the
periodontal ligament is widened, and the tooth
becomes loose.
• When trauma is eliminated, repair usually takes place.
• Occlusal trauma is always restricted to the intra-
alveolar tissues and does not cause changes of the
gingiva such as recession or pocket formation or
gingivitis.
• Orthodontic tooth movement depends on resorption
and formation of both bone and periodontal ligament.

125. • These activities can be stimulated by properly regulated
pressure and tension.
• The stimuli are transmitted through the medium of the
periodontal ligament.
• If the movement of teeth is within physiologic limits (which
may vary with the individual), the initial compression of the
periodontal ligament on the pressure side is compensated for
bone resorption, whereas on the tension side bone apposition
is seen.
• Application of large forces results in necrosis of periodontal
ligament and alveolar bone on the pressure side

126. • The periodontal ligament in the periapical area of the tooth is often
the site of a pathologic lesion.
• Inflammatory diseases of the pulp progress to the apical
periodontal ligament and replace fiber bundles with granulation
tissue.
• This lesion, called a periapical granuloma, may contain epithelial
cells that undergo proliferation and produce a cyst.
• The periapical granuloma and the apical cyst are the most common
pathologic lesions of the jaws.

127. • The commonest pathology related to the PDL is
chronic inflammatory periodontal disease.
• 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.
• Periodontal disease results because of
periodontic bacteria coupled with specific host
inflammatory response.

128. • Progression of the periodontal disease 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 (PDL and bone) to
their original form in such a way that
reattachment of PDL to the bone becomes
possible.

129. CONCLUSION
• A better understanding of cell and molecular biology of the
developing and regenerating periodontium offers newer avenues to
regenerate the PDL.
• The use of progenitor cells or the mesenchymal stem cells to
regenerate the PDL is being thought of.
• The PDL regeneration is said to be achieved by the activation of the
mesenchymal stem cells towards terminal differentiation, tissue
repair and degeneration.
• 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.

130. REFERENCES
• Arthur F.Hefti. Aspects of cell biology of the normal
periodontium. Periodontology2000,1993;3:64-75.
• Thomas M. Hassell. Tissues and cell of the
periodontium. Periodontology 2000,1993;3: 9-38.
• Carranza’s Clinical Periodontology, 10th edition by
Newman, Takei, Klokkevold and Carranza.
• Orban’s Oral Histology and Embryology, 13th edition,
by G.S.Kumar
• Oral Anatomy, Histology and Embryology, 4th edition,
by B.K.B.Berkovitz, G.R.Holland and B.J.Moxham
• Tencate’s Oral histology, 7th edition, by Antonio Nanci