contents Introduction Development Homeostasis Contents of PDL Functions Age changes Clinical considerations Conclusion References

1. 1

2. M. RAVINDRA
I MDS
Dept of Oral Pathology & Microbiology
2

3.  Introduction
 Development
 Homeostasis
 Contents of PDL
 Functions
 Age changes
 Clinical considerations
 Conclusion
 Refferences
3

4.  PDL is an connective tissue
organ, covered by epithelium
which attaches the teeth to
the bones of jaw.
 And it provides continuously
adapting apparatus for support
of the teeth during function.
4

5.  The term ligament is used because of it is a complex
soft connective tissue, connecting two mineralized
tissues.
Definition:
 According to Caranza& Bernard:
“The periodontal ligament is the connective tissue that
surrounds the root & connects it to the bone. it is
continuous with the connective tissue of 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 continuous
with the connective tissues of gingiva; at the apical
foramen it is continuous with the dental pulp.
5

6.  SYNONYMS:
 Desmodont
 Gomphosis
 Pericementum
 Dental periosteum
 Alvelodental ligament
 Periodontal membrane
6

7.  Thickness of the PDL
0.15 to 0.38mm
 Radiographically
0.4 to 1.5 mm
 It is thinnest around the middle
third of the root, with an hour
glass appearance.
 Thickness of the PDL decreases
with age.
Young adult - 0.21mm
Mature adult - 0.18mm
Old adult - 0.15mm
7

8.  Develops from Dental Follicle.
 Development of PDL begins with root formation.
 Developing Hertwig`s epithelial root sheath separates
Dental papilla & dental follicle.
8

9. Dental follicle has 2 types of
cells.
 Dental follicle proper
 Perifollicularmesenchyme
9

10. 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
glycoprotiens in developing PDL
Type I collagen is secreted
Assembles as collagen bundles on the bone and
cememtum surface
Establish continuity across the ligament space
10

11. 11

12. Development of Principal Fibers:
 Periodontal fibers develop from mesenchymal cells of the PDL.
 First formed fibers are Alveolar crest fibers.
 Fibroblast in the coronal third, align in oblique direction to the
tooth long axis and start secreting alveolar crest group of
fibers.
12

13.  Microfibrils from cementum & alveolar bone grow towards
center to meet, intertwine and fuse to form remaining
groups of fibers.
 At the time of occulusal contact alveolar crest group and
horizontal group fibers are fully developed. Oblique &
Apilcal groups are under developing state.
13

14. 14

15.  Periodontal ligament maintains its width more or
less overtime.
 This is because of molecules secreted by
different cells in the PDL.
 These molecules can regulate the extent of
mineralization of the surrounding hard tissues
like bone and cementum.
 These factors can prevent the fusion of the root
and bone by preventing excess mineralization.
15

16. Some Factors maintaining homeostasis of PDL:
 Prostaglandins : Inhibit mineralized bone nodule
formation by bone stromal cells.
 Msx2 : Prevents Osteogenic differentiation of
fibroblasts by suppressing Cbfa1 (also
known as Runx2 ) transcriptional activity.
 Bone sialoprotien: Balance between these contributes to &
Osteopontin the unmineralized PDL.
 Matrix ‘GLA’ protein: Inhibitor of the mineralization.
 Glycosaminoglycans or
RGD-cementum attachment protein
16

17.  PDL has capacity to adapt to functional
changes:
Functional demand
increases
Width of PDL increases
by as much as 50%
Fiber bundle increases
in thickness
Functional demand
decreases
 Narrowing of PDL
Decrease in number
and thickness of fiber
bundle
17

18.  PDL consists of
 Cellular components
 Extracellular matrix
18

19. CELLS IN PDL
Mainly 5 types.
1. Synthetic cells
2. Resorptive cells
3. Progenitor cells
4. Epithelial cell rests of
Malassez
5. Defense cells.
19

20. Synthetic cells:
 Cells that are synthesizing proteins for secretion.
 Microscopically they appear as comparatively
large cells with large vesicular nucleus with
prominent nucleoli due to increased
transcription of RNA & production of ribosomes.
 And cytoplasm is also abundant, due to
increased activity of mitochondria, golgi
membrane and RER.
20

21. Three types
1. Osteoblasts
2. Fibroblasts
3. Cementoblasts
21

22. Osteoblasts:
 Secrete bone components.
 Cover the surface of the bone
Microscopic features:
Cuboidal in shape
Prominent round nucleus at
the basal end.
Abundant RER, mitochondria
and vesicles.
Basophilic due to RER
Pale juxtanuclear layer of
golgi membrane.
Microfilaments are present
beneath the cell membrane, at
the secretary surface.
22

23. Fibroblasts:
 Predominant cells in PDL
 Secret Fiber Components.
 Mainly secret
Collagen
Elastin
Glycoprotien
Glycosaminoglycans
Matrixmetalloprotinesases (MMP`s)
Responsible for the formation and remodeling of
PDL fibers & signaling system to maintain the
width and thickness of the PDL.
23

24.  Microscopic features
Fusiform in shape.
Large cells with large nucleus and one or
more prominent nucleoli.
Extensive RER Well developed golgi Complex
Abundant secretory granules containing type-
1 collagen.
Cytoplasmic extensions in secretory end that
form 3 dimensional veils which
compartmentalize collagen fibrils to fibers.
24

25. Cementoblasts:
 Secrete cementum.
 Arranged on the cementum.
 Microscopic features:
Often indistinguishable from PDL fibroblasts.
Cuboidal in shape.
Large nucleus with One or more nucleoli.
Abundant mitochondria & less RER.
Cellular cementum secreting cells have
cytoplasmic processes and the nucleoli are
folded and irregularly shaped.
Acellular cementum secreting cells don’t have
these cytoplasmic processes.
25

26. Resorptive cells:
Three types
 Osteoclasts
 Fibroblasts
 Cementoblasts
26

27. Osteoclasts:
 Responsible for bone
resorption.
 Microscopic features:
Large multinucleated but
sometimes small and mono
nucleated.
Have eosinophilic cytoplasm.
Abundant cytoplasam,
mitochondria,golgicomplex, free
ribosmomes, little RER.
Plasma membrane is folded in the
resorbing side- Ruffled boarder or
Striated boarder.
Under the ruffled boarder – Clear
zone.
Resorb bone by producing highly
acidic PH .
27

28. 28

29. Fibroblasts:
 Show rapid degeneration of collagen by
Phagocytosis, which results in fast turnover of
collagen.
 Collagen degradation is both
Extracellular
Intracellular
 Normally intracellular in healthy tissues, where
there is a controlled turnover& remodeling.
 Extracellular is seen in pathological conditions
where degeneration is rapid and involves whole
tissue, simultaneously.
29

30. Extracellular:
 Matrix metalloprotiens (MMP`s) secreted by fibroblasts
play an important role in extracellular collagen
degradation.
Removal of fibronectin & proteoglycans on fibril surface by
Stromelysin (MMP-III)
Collagenase (MMP-I)binding
Cleavage of triple helix portion of molecules
with in the fibril
Denaturation of collagen by MMP-IV
Prteolysis of the rest of the molecule by MMP-II (Gelatinase)
& MMP-V
30

31. Intracellular:
 Through Phagocytosis
 Intracellulrar collagen profiles – Special cell
organells for collagen degradation
 Collagenase is not involved
 Lysosomal cysterine protinesases are
involved.
31

32. Phagocytosis of collagen fibrils
Banded fibril is surrounded by Electron- lucent zone
Phagosome+ lysosome Phagolysosome
Enzymic degradation of fibrils
Electronlucent zone Electon dense zone
Fibrils loss their characeristic structure
32

33. Cementoclasts:
 They resembles osteoclasts and are located in
depressions in cementum resembling Howship`s
lacuna.
 As cementum does not remodel, Cementoclasts
are not usually found in the ligament.
 These cells only occur in some pathological
conditions, during resorption of deciduous teeth
and when regressive forces are applied on a
tooth such as orthodontic therapy.
 These cells not only resorb cementum, they can
destroy dentin and enamel as well thus they are
called Odontoclasts.
33

34. Progenitor cells:
 All connective tissues including PDL contain
progenitor cells that have the capacity to
undergo mitotic division.
 When stimulated appropriately, these cells
undergo mitotic division and can differentiate
into fibroblast, osteoblast or cementoblast.
34

35. Epithelial cell rests of
Malassez:
 These were first described by
Malassez in 1884 and are the
remnants of the epithelium of
Hertwig’s epithelial root
sheath.
 They persist as networks,
strands, islands or tubule-like
structures near and parallel to
the surface of the root.
35

36.  Their function is not yet clear
but they could be involved in
periodontal repair and
regeneration.
 These cells may proliferate to
form cysts and tumors.
 These cells may undergo
calcification to become
CEMENTICLES.
36

37. Defence cells:
 Mast cells
Eosinophills
Macrophages
 MAST CELLS – These are relatively small
round or oval cell having a diameter of about
12 to 15 um
Mast cells are often associated with blood
vessels .
These cells are characterized by numerous
cytoplasmic granules which frequently
obscure the small , round nucleus .
37

38. MACROPHAGES-
 These are found in the ligament and are
predominantly located adjacent to blood vessels
.
 The wandering type are derived from blood
monocytes has a characteristic ultrastructure
that permits it to be readily distinguished from
fibroblasts .
38

39. EOSINOPHILLS –
 These are seen in the periodontal ligament .
 They posses granules that consist of one or
more crystalloid structures .
 These are capable of phagocytosis .
39

40. EXTRACELLULAR SUBSTANCES
FIBERS
GROUND
SUBSTANCE
1.Collagen
2. Elastin
3. Reticular
4. Secondary
5. Indifferent
fiberplexus
6. Oxytalan
1. Proteoglycans
2. Glycoprotiens
40

41. FIBERS
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 .
 Within each collagen bundle , subunits are
present called collagen fibrils.
41

42. 42

43. PRINCIPAL PDL FIBERS :
 The collagen is gathered to form bundles
approximately 5 um in diameter. These bundles
are termed as PRINCIPAL FIBERS.
 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.
43

44.  Types of Principal fibers
Alveolar crest
Horizontal group
Oblique group
Apical group
Inter radicular group
44

45. Fiber group Origin & insertion 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 They extend from cementum to
alveolar bone in horizontal
direction at right angles to long
axis of tooth.
Restrain lateral tooth
movements.
3.Oblique Largest group of PDL fibers.
Occupy 80-85% of root surface.
Extend from cementum in a
coronal direction obliquely to
the bone.
They bear vertical
masticatory stresses and
transform them into
tension on alveolar bone
and resist intrusive forces.
4. Apical The apical fibres radiate in a
rather irregular fashion from
cementum to the apical region
of the socket
Prevent tooth tipping Resist
luxation. Protect blood,
lymph and nerve supplies
to tooth.
5. Interradicular They fan out from the cementum
to the tooth in the furcation
areas of multirooted teeth.
Aid in resisting tipping
torquing and luxation.
45

46. SHARPEYS FIBERS:
 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.
 Sharpey’s fibers in Acellular cementum- fully
mineralized.
 Cellular cementum & Alveolar Bone – partially
mineralized.
 Few Sharpey’s fibers pass uninterruptedly
through bone of alveolar process –
Transalveolar fibers.
46

47. 47

48. ELASTIN FIBERS :
 There are three types of elastic fibers which
are histochemically and ultrastructurally
different.
Mature Elastic fibers
Eulanin fibers
 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 .
48

49.  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
 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)
49

50. 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.
50

51. 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.
51

52. INDIFFERENT FIBER PLEXUS:
 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.
52

53. 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
53

54. Glycosaminoglycans:
PROTEOGLYCANS
 Large group of anionic macromolecules that
consists of a protein core to which are attached
hexose amine containing polysaccharides called
GAG chains.
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.
54

55. Glycoprotiens:
 Three distinctly related glycoprotiens of the
extra cellular matrix have been localized in
the decalcified sections of human
periodontal ligament, namely
Fibronectin
Tenascin
Laminin
Other glycoproteins like Entactin,
Vitronectin, Thrombospondin may also be
present in the glycoprotiens of PDL with a
smaller role in cell attachment and
organization of basement membrane.
55

56. I. Physical function
II. Formative & Remodeling
III. Nutritional
IV. Homeostatic
V. Sensory function.
56

57. I.PHYSICAL FUNCTION :
 Provision of a soft tissue ‘casing’ to protect the
vessels and nerves from injury by mechanical
forces.
 Transmission of occlusal forces to the bone.
 Attachment of the teeth to the bone.
 Maintainence of the gingival tissues in their
proper relationship to the teeth.
 Resistance to the impact of occlusal forces
(Shock absorption).
57

58. 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.
58

59.  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.
59

60. 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
60

61. 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)
61

62.  Increase in the collagen fibrosis & decrease in
cellularity .
 Areas of hyalinization are present.
 Sporadic mineralization of the fibers also occurs.
 Decrease in the no. of periodontal fibers
 Decrease in the cellularity & the formation of
multinucleated fibroblasts.
 Decrease in collagen synthesis.
 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.
62

63.  If gingivitis is not cured and supporting structure
become involved, the disease is termed as
periodontitis.
 There are few coccal cells and more motile rods
and spirochetes in the diseased site than in the
healthy site.
 The bacteria consists of gram-positive
facultative rods and cocci in healthy site while in
diseased site, gram-negative rods and anaerobes
are more in number.
 Resorption and formation of both bone and
periodontal ligament play an important role in
orthodontic tooth movement. If tooth movement
takes place, the compression of PDL is
compensated by bone resorption whereas on
tension side, apposition takes place.
63

64.  Inflammation of the pulp reached to the
apical periodontal ligament and replaces its
fiber bundles with granulation tissue called
as granuloma, which then progresses into
apical cyst.
 Chronic periodontal disease can lead to
infusion of microorganisms into the blood
stream.
 The pressure receptors in ligament have a
protective role. Apical blood vessels are
protected from excessive compression by
sensory apparatus of the teeth.
64

65. NEOPLASTIC INVOLVEMENT OF PDL:
 Mostly reactive rather than neoplastic.
 Oxytalan fibers are found in peripheral
odontogenic fibromas & Adenomatoid
odontogenic tumors
 Epithelial rests of malassez --- neoplastic
change
 Infiltration of PDL by primary or secondary
malignant tumors --- widening of PDL space--
- mobility –malignant loosening of teeth.
65

66. PERIODONTAL CYSTS :
 Inflammatory ---- Radicular cyst
 Developmental ---- Lateral periodontal cyst
PDL space Radiographic appearance :
 Thin radiolucent line interposed between the
root & lamina dura.
 Occlusal Trauma → widened PDL space or
funneling of coronal aspect of PDL space.
 It can also widened in case of vertical
fractures & progressive systemic sclerosis
(Scleroderma).
66

67.  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.
67

68.  Carranza’s Clinical Periodontology, 10th
Edition
 Clinical Periodontology and Implantology by
Jan Lindhe, 5th edition
 Oral Histology and Embryology by Orban,
13th edition
 Tencate oral histology, 5th edition
68

69. 69