periodontal ligament - development, structure and composition, cells and fibers of PDL, ground substance, nerve and blood supply of PDL

1. Periodontal Ligament
Synonyms:
Periodontal Membrane
Desmodont
Gomphosis
Pericementum
Dental Periosteum
Alveolodental Ligament

2. Periodontium
The word Periodontium refers to the
attachment apparatus of teeth and consists :
– Cementum
– Alveolar bone lining tooth socket
– Periodontal ligament
– Part of Gingiva facing the tooth

3. Periodontal Ligament
The space occupied
by PDL is called
Periodontal Space
Coronally :-
Continuous with
Gingiva
Apically :-
Continuous with
Pulp
Is the connective tissue which surrounds the roots of
the teeth and Attaches tooth root to the bony alveolus

4. The width of PDL ranges from 0.15
– 0.38mm
Thinnest around middle 1/3rd of
root and has “Hour-Glass”
appearance
Reduced in nonfunctional and
unerupted teeth.
Increased in teeth subjected to
heavy functional stresses.
Thicker in deciduous teeth than
permanent teeth.
The principal fibers run a wavy
course from Cementum to
alveolar bone

5. Periodontal Ligament consists of:
– Cells
– Extracellular substance:
Fibers
Ground substance
Structure and Composition

6. Cells
of
Periodontal Ligament

7. Cells in Periodontal Ligament
A – Alveolar Bone B - Cementum

8. The cells of Periodontal Ligament:
1. Synthetic cells:
Osteoblasts
Fibroblasts
Cementoblasts
2. Resorptive cells:
Osteoclasts
Fibroblasts
Cementoclasts
3. Progenitor cells
4. Epithelial Cell rests of Malassez
5. Defense cells:
Mast cells
Macrophages
Eosinophils

9. Synthetic cells
Unique characteristics of Synthesizing cells:
Vesicular nucleus containing prominent nuclei
Abundant cytoplasm containing numerous RER
and Increased Golgi bodies
Large numbers of Mitochondria
Cells with above description present on Alveolar
surface of PDL Osteoblasts
Such cells lying in body of soft connective tissue of
PDL Fibroblasts
Cells found on cemental surface Cementoblasts

10. Osteoblasts
Bone forming cells lining the alveolar bone of tooth
socket closely resembling cementoblasts
Cuboid in shape with prominent spherical and large
nucleus placed at basal end of cell
Large amounts of RER gives the cytoplasm of active
osteoblasts a slightly basophilic hue
Active osteoblast produces an enormous quantity of
collagen type-I
Alkaline phosphatase is present and is mostly found
on the apical cell membrane

12. Fibroblasts
A – Alveolar Bone
B – Fibroblasts
C – Cementum
D – Dentin

13. Fibroblasts
Predominant cells in PDL
Capable of Both Secretion and Degradation of
Collagen
Fibroblasts near cementum are derived from
investing layer of dental papilla and fibroblasts near
Alveolar bone are derived from Perivascular
Mesenchyme of Dental Follicle and show abundant
Alkaline phosphatase activity
Fibroblasts are large cells with extensive cytoplasm
and characteristics of synthesizing cells are seen
prominently

14. Fibroblasts are of various shapes:
– Fusiform
– Tripolar
– Stellate
Fibroblasts of PDL have Cilia and the Cilia is
associated with Control of Cell cycle or Inhibition of
Centriolar Activity
These cells produce growth factors and cytokines
such as IGF-1, BMP’s, PDGF, IL-1, etc
TGF-β stimulates synthesis of collagen and Inhibits the
synthesis of collagenase

16. Functions of Fibroblasts
To produce structural connective tissue proteins:
Collagen
Elastin
Proteoglycans
Glycoproteins
Glycosaminoglycans
Collagenolytic enzymes:
Matrix Metalloproteinases (MMP’s)
Fibroblasts are responsible for formation and
remodelling of PDL
They have a signaling system to maintain width of
PDL by preventing encroachment of bone or cementum
into the PDL space

17. Differences between
PDL Fibroblasts
Ectomesenchymal origin
Expression of Alkaline
phosphatase and cyclic
AMP is MORE
Motile and Contractile
and hence can generate a
force for tooth eruption
Gingival Fibroblasts
Mesodermal origin
Expression of Alkaline
phosphatase and cyclic
AMP is LESS
Non-contractile and no
role to play in tooth
eruption

18. Cementoblasts

19. Cementoblasts
Cuboidal cells with large vesicular nucleus
Active in cementum formation found adjacent to the
surface of cementum and show all the prominent
features of synthesizing cells
Cells depositing cellular cementum show abundant
basophilic cytoplasm and cytoplasmic processes and
nuclei are folded and irregularly shaped
Cells depositing - acellular cementum – DO NOT
SHOW prominent cytoplasmic processes

20. Cementoblsts

21. Resorptive Cells
Osteoclasts & Cementoclasts:
Found in areas of resorption.
Multinucleated
Originate from undifferentiated mesenchymal
cells in periodontal ligament.

22. Osteoclasts in
Howship’s
Lacunae
Osteoclasts
Howship’s Lacunae

23. Cytoplasm of the cells produce a
substance which dissolves the organic
components of bone and a chelating
agent capable of bringing calcium salts
into solution.
Where ever their cytoplasm comes
into contact with bone - hollows or
grooves called 'Howship's Lacunae' are
formed.
When bone resorption ceases - they
disappear.

24. Progenitor cells
These cells have the capacity to undergo
mitotic division.
They give rise to all of the specialized
synthetic cells.
Epithelial cell rests of Malassez:
Remanents of Hertwig’s Epithelial Root
Sheath.
Epithelial double strands and islands limited
by basement membrane of reticulin.

25. Cell
Rests of
Malassez

26. Mast cells
These are small round or oval cells.
12 - 15μm.
Characterized by numerous
cytoplasmic granules.
These granules contain heparin and
histamine.
Histamine plays and important role in
inflammatory reactions and also in
antigen antibody reaction.

28. Macrophages
These can be visualized by the presence
of phagocytosed material in their cytoplasm.
They are derived from blood monocytes.

30. Extracellular Substance
Comprises of:
–Fibers:
Collagen
Oxytalan.
–Ground substance:
Proteoglycans
Glycoproteins.

31. Fibers
of
Periodontal
Ligament

32. Fibers
Made up of collagen and Oxytalan.
Elastic fibers are restricted to the walls of blood
vessels.
The majority of fibers are collagen.
Mostly made up of type I collagen and some
amount of type III collagen.
The collagen fibers are gathered in bundles
having a clear orientation relative to the
periodontal space - “Principal fibers”.

33. Principal Fibers
Root
Alveolar Bone
Principal fibers

34. Principal Fibers
Arranged in five groups:
1. Alveolar crest group.
2. Horizontal group.
3. Oblique group.
4. Apical group.
5. Inter-radicular group.

35. Principal Fibers
1. Alveolar crest
2. Horizontal
3. Oblique
4. Apical
5. Interradicular

36. Principal Fibers
Alveolar Crest group:
They radiate from the crest of the
alveolar process and attach themselves to
the cervical part of the Cementum.
These fibers resist tilting, intrusive,
extrusive and rotational forces.
Most often confused with Dentoperiosteal
fibers

38. Horizontal group:
They run at right angles to long axis of
tooth from Cementum to Bone.
Roughly parallel to the occlusal plane of the
arch
They are found immediately apical to the
alveolar crest fiber group. They are limited
mostly to the coronal one-fourth of the
periodontal ligament space.
These fibers resist horizontal and tipping
forces.

39. Oblique group:
Most numerous and occupy
nearly 2/3rd of the ligament.
They are attached to
cementum apically from their
attachment to the bone
thereby resulting in their
oblique orientation within the
periodontal space
These fibers constitute the
main attachment.
These fibers resist vertical
and intrusive forces.

40. Apical group:
They radiate from the
cementum at the root tip to
become anchored into the
fundus of the bony socket.
The apical fibers resist the
forces of luxation, may
prevent tooth tipping and
protect delicate blood and
lymph vessels and nerves
traversing the PDL space at
the root apex.
These fibers are not seen on
incompletely formed roots.

41. Interradicular Group:
From the crest of
interradicular septum, bundles
extend to furcation of
multirooted teeth.
These fibers resist tooth
tipping, torquing and luxation.
These fibers are lost, if age-
related gingival recession
proceeds to the extent, that
the furcation area is exposed.
Total loss of these fibers
occurs in chronic
inflammatory periodontal
disease.

42. Oblique set

43. Inter-radicular

44. Elastic Fibers
There are three types of elastic fibers, which are
histochemically and ultrastructurally different.
They are, the mature elastic fibers, (elastin)
fibers, the elaunin fibers, and the oxytalan fibers.
Elaunin and oxytalan fibers have been described
as immature elastic fibers.
Mature elastic fibers consist of a microfibrillar
component surrounding an amorphous core of
elastin protein.

45. 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.

46. Oxytalan Fibers
These are immature elastic fibers.
Found in the periodontal ligament.
Largely restricted to the walls of blood vessels.
The orientation of these fibers is quite different.
They tend to run axially - one end being
embedded into cementum or possibly in bone
and the other - into the wall of a blood vessel.
In the vicinity of apex they form a complex
network.

47. Reticular Fibers
These are fine 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.
These fibers are composed of type III collagen.

49. Ground Substance
in
Periodontal Ligament

50. Ground Substance
Glycosaminoglycans:
– Hyaluronic acid
– Dermatan sulfate
– Chondroitin sulfate.
Carbohydrates, proteins, lipids and Glycoproteins.
Other Structures Present in connectinve tissue:
– Blood vessels
– Lymphatics
– Nerves and Cementicles.

51. Functions
1. Formative
2. Supportive
3. Sensory
4. Nutritive
5. Occlusion
6. Reparative
7. Protective

52. Branching Principal Fibers

53. Sharpey’s Fibers
A – Alveolar Bone B - Cementum

54. Sharpey's Fibers: The collagen fibers are
embedded into the cementum on one side of
the periodontal space and into alveolar bone
on the other.
Intermediate Plexus:
When examined under light microscope
the fibers appear to be joined in the mid
region of the periodontal space giving rise
to a zone of distinct appearance, so called
"Intermediate Plexus" – believed to be site for
rapid remodeling of fibers.

55. Intermediate Plexus

56. Blood Supply
&
Lymphatic Drainage

57. Blood Supply:
From three sources -
1. From the apical vessels supplying the
dental pulp.
2. Branches from intra-alveolar vessels.
3. Branches form gingival vessels.
Lymphatics:
Net work of lymphatic vessels following
the path of blood vessels.

58. Nerve Supply

59. Nerves are usually associated with blood vessels
Pass through foramina in the alveolar bone to
enter the periodontal ligament.
Myelinated or non myelinated.
Either large or small in diameter:
- larger diameter - concerned with touch.
- smaller diameter - concerned with pain.
Cementicles:
Calcified bodies.
Origin is probably from degenerated epithelial
cells – forming a nidus for calcification.

60. Nerve Bundles
A – Alveolar bone
B - Dentin