The document discusses the periodontal ligament (PDL), which is the soft connective tissue that surrounds tooth roots and attaches cementum to alveolar bone. It defines PDL and describes its extent, average width, development from the dental follicle, orientation of collagen fibers, cellular elements including fibroblasts, cementoblasts, osteoblasts, and epithelial rests of Mallassez. The document also covers the biochemical composition and ground substance of PDL, as well as its blood supply, nerve supply, age-related changes, and role in healing after periodontal surgery.

2. PRESENTED BY:PRESENTED BY:
DR SHILPA SHIVDR SHILPA SHIV
I MDSI MDS
DEPT OF PERIODONTOLOGYDEPT OF PERIODONTOLOGY

3.  Introduction
 Definition
 Extent and shape
 Average width
 Evolution of PDL
 Development
 Orientation of PDL fibers
 Structure
 Biochemical composition
 Cellular elements
 Periodontal fibers
ContentsContents

4.  Collagen
 Ground substance
 Functions of PDL
 Blood supply
 Venous drainage
 Lymphatic
 Nerve supply
 Age changes & Clinical considerations
 Healing after periodontal surgery
 Conclusion
 References

5.  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.
IntroductionIntroduction

6.  Periodontal ligament is composed of soft complex vascular and
highly cellular connective tissue that surrounds the tooth roots
and connects to the inner wall of the alveolar bone (Mc Culloch
CA, Lekic P, Mc Kee MD Periodontol 2000 24:56,2000)
 It is that soft, specialized CT situated between the cementum
covering the root of the tooth and bone forming the socket wall.
(A.R.Tencate 1971)
 It is a narrow and highly cellular CT that forms the interface
between alveolar bone and cementum. (Periodontol
2000,vol.3,1993)
DefinitionDefinition

7. 
 Soft, richly vascular and cellular connective tissue which
surrounds the roots of the teeth and joins the root
cementum with the socket wall. (Jan Lindhe 5th ed)
 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)

8. 
 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.
Extent & shapeExtent & shape

9. 
 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
Average widthAverage width

10. 
 The evolutionary step from reptile to mammal included a
series of coordinated changes in the jaws.
 The central point is the radical reconstruction of the
mandible
 In reptiles mandible consists of-
Dentary
Mandibular articulation - Articulare and Quadratum
EvolutionEvolution

11. 
 In mammals-
 Fate of dentary- Forms the mandible
 Others were lost or changed into middle ear ossicles
Articulare- malleus
Quadratum- incus
 Dentary developed a condylar process which formed the
new temporomandibular joint, that for some time
functioned with old articulare-quadratum joint- Double
jointed forms

12.  Change from many boned to single boned mandible brings in a
radical change in mode of growth.
 Reptiles –Sutural
 Mammals- Cartilage of condyle
 Growth of mandibular body height
 Tooth movement during eruption. Teeth move as unit independent
of bones, by remodeling of periodontium.
Growth changesGrowth changes

13. 
 Begins with root formation
(Tencate et al.,1972)
& prior to tooth eruption.
 Varies among species, tooth families
& between primary & secondary teeth.
DevelopmentDevelopment

14. 
 The periodontal tissues are derived from dental follicle which
in turn originates from dental papilla.
 It has also been proposed that the mesenchyme deriving
periodontium may have two differentiation compartments
a. Alveolar clade --- Fibroblasts & osteoblasts
b. Cementum clade --- fibroblasts & cementoblasts
 The term dental follicle has been used by different authors to
mean different things.
Development….

15. 
-

16. 
 Closely related to root formation
Development of principal fibersDevelopment of principal fibers

17. 
Development….
Fig 2Fig 1 Fig 3

18. 
 Terminal portions of principal fibers that insert into
cementum and bone are termed as Sharpey’s fibers.
 The principal fibers embedded in the cementum have a
small diameter but are more numerous than those
embedded in the alveolar bone proper.
 In addition to these fiber types, small collagen fibers
associated with larger principal fibers have been called as
“Indifferent fiber plexus of Shefforfold”
Development…

20. 
Orientation of PDLOrientation of PDL

21.  Mature PDL can be sub divided into 3 regions:
-Bone related region- rich in cells
-Cementum related region- dense and ordered
collagen fibers
-Middle zone- few cells & thinner collagen fibrils

22. 
 CELLULAR ELEMENTS
a. Connective tissue cells
Synthetic Resorptive
-Fibroblasts - Fibroblasts
-Cementoblasts - Cementoclasts
-Osteoblasts - Osteoclasts
b. Epithelial cell rests
c. Immune system cells
d. Neuro-vascular elements
• PERIODONTAL FIBERS
• GROUND SUBSTANCE
StructureStructure

23. 

24. 
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.
Cellular elementsCellular elements

25.  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.
FibroblastsFibroblasts

26.  Phenotypically distinct & functionally different sub
populations of fibroblasts exist in adult PDL.
 They may have different functions like secretion of
different collagen types & production of collagenase.
 Importantly in inflammatory situations, an increased
expression of MMP occurs that aggressively destroys
collagen.
 Thus attractive therapies for controlling this may
include host modulators to inhibit MMP.
Fibroblasts…

27. 
 The PDL fibroblasts are large cells with an extensive
cytoplasm containing in abundance, all organelles
associated with protein synthesis and secretion.
 They also have well developed cytoskeleton with a
particularly prominent actin network.
ATTACHMENTS
 The fibroblasts of PDL are interconnected by gap
junctions or adherence type of junctions.
 The cells may attach to collagen via a fibro nexus type
of attachment plaque and are likely to have the
capacity to orient extracellular matrix.
Fibroblasts…

28. 
 The migratory and contractile activity of fibroblast
is because of the presence of contractile protein actin
and myosin in their cytoskeleton.
 It may:
 Remain stationary and pull on adjacent structures
 Crawl and cause the environment in which it lies
to wrinkle.
Fibroblasts…

29.  Chemo attractants produced locally or by the hard tissues
bordering the ligament may have a role in this process.
 Directed migration of cells is associated with polarity of
organelles, the nucleus usually in the trailing portion of
cell and golgi apparatus and centrioles are towards the
leading edge of the cells.
 They appear to be rich in alkaline phosphatase activity-
an enzyme along outer plasma membrane that plays a
key role in phosphate metabolism, probably in the
mineralization process and in Acellular cementum
formation.
Fibroblasts…

30. 
 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.
Osteoblasts & cementoblastsOsteoblasts & cementoblasts

31. 
 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.
Resorptive cellsResorptive cells

32. 
 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
Progenitor cellsProgenitor cells

33. 
 Mallassez – 1884
 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.
Epithelial rests of MallassezEpithelial rests of Mallassez

34. 
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.

35. 
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.

36.  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.
Defense CellsDefense Cells

37. 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
MacrophagesMacrophages

38. 
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

39. 
 Too small to be seen on IOPA, seldom being larger than
0.2-0.3 mm. in diameter.
 No clinical significance.
 Actually a variety of calcified bodies may occur in the
PDL, not all of which have the morphologic
characteristics of cementum. Nevertheless, they have all
been commonly known as cementicles.
 The pattern of calcification often gives the appearance of
a circular lamellated structure.
Cementicles…

40. 
 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.
Cemental Tears

41. 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)
Periodontal fibersPeriodontal fibers

42. 
 The adult human PDL fibers are slightly thicker than other
mammalian species and measure about 54-59 nm in diameter.
 This relatively small diameter reflects the short half-life of
ligament collagen, meaning that there is little time for
continuous assembly.

43. 
 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
CollagenCollagen

44. 
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
Collagen…

45. 
 Made up of 3 polypeptide chains
 α chains that are left handed chains assembled into a triple
helix with a right handed twist. May be a homo-trimer or
hetero-trimer.
 Has a repeating gly-X-Y amino acid sequence in which X
and Y are usually amino acid other than glycine.
 Contain 2 unique amino acid hydroxy proline and hydroxy
lysine along with glycine & proline (Carneiro J, Fava de
Moraes F , 1955)
 Collagen molecules are covalently linked through lysine
derived intra and inter chain crosslink.
 It is synthesized by fibroblasts, chondroblasts, osteoblasts
UNIQUE STRUCTURAL PROPERTIESUNIQUE STRUCTURAL PROPERTIES
THAT DISTINGUISH COLLAGENTHAT DISTINGUISH COLLAGEN
FROM OTHER PROTEINSFROM OTHER PROTEINS

46. 
 The amount of collagen in a tissue is determined by its
hydroxy proline content.
 There are at least 19 recognized collagen species encoded
by at least 25 separate genes, dispersed among 12
chromosomes (Embery et al 2000)
Collagen classes
a. Interstitial collagens ---- Type I,II,III
b. Basement membrane type ---- Type IV,VI,VII
c. Short chain collagens ---- Type IX,X
Collagen…

47. 
 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
Collagen…

48. 
 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.
Collagen…

49. 
 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.
Formation of collagenFormation of collagen

51. Shortened collagen molecules align as 5-unit, quater staggered microfibrils,
which assemble in parallel fashion giving rise to a regular series of gaps or
holes within the fibril
The C-terminal extension and part of N-terminal ones are removed by
action of C- and N- proteinases in the secretory granules
Secretory granules containing procollagen molecules formed at the
transface of golgi complex
Transported to the golgi complex where glycosylation takes place to
the O-linked galactose residues

52. Collagen microfibrils, fibrils, fibers, and bundles

53. 
Collagen RegulationCollagen Regulation
 A variety of growth factors and cytokines regulate collagen
production
 The collagen mRNA levels may increase or decrease due to
change in either the rate of collagen gene transcription or in
mRNA stability.
 TGF-β is an important mediator as it enhances the synthesis
of collagen and other matrix components.
 Interferon-γ suppress collagen gene expression.
 During inflammation and wound healing, these substances
are secreted by platelets, macrophages and other
inflammatory cells.

54. 1. Intracellular degradation - Selective ingestion of collagen
fibrils by fibroblasts.
2. Extracellular degradation - Degradation by enzymes
secreted by cells
 Cleaving of polypeptide chain occurs at gly-iso-leucin and
gly-leu bonds in α1 and α2 chains respectively by enzymes
collagenases.
 These peptide bonds are located at approximately 1/4th of
the length from C-terminal, thus fragments of 3/4th and
1/4th sizes are released.
 These fragments are denatured and further degraded by
other common tissue proteinases
Collagen DegradationCollagen Degradation

57. 
Principal fibers of PDLPrincipal fibers of PDL
 Trans septal
 Alveolar crest group
 Horizontal
 Oblique
 Apical
 Inter – radicular

58. 
 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.
Transseptal GroupTransseptal Group

59. 
 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
Alveolar Crest GroupAlveolar Crest Group

60. 
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.

61. 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

62.  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.
Sharpey’s FibersSharpey’s Fibers
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

64. 
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.

66. 
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

67.  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
Eulanin FibersEulanin Fibers

68. 
 Small Collagen fibers in association with the larger
principal collagen fiber
 Run in all directions forming a plexus
 Described by Shackleford, 1971
 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.
Indifferent Fiber PlexusIndifferent Fiber Plexus

69.  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
Ground SubstanceGround Substance

70.  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
ProteoglycansProteoglycans

71.  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.
GlycoproteinGlycoprotein

72. 
 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
Glycoproteins….

73. 
1. Physical
2. Formative and Remodeling
3. Nutritive
4. Sensory
5. Regulation of periodontal ligament width
Functions Of PDLFunctions Of PDL

74. 
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
Physical FunctionsPhysical Functions

75. 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.

76. 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

77. 
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.

78. 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

79. 
 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)

80. 
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.

81. 
 Sodek (1977) has demonstrated that the periodontal
ligament incorporates proline at least 5 times faster
than gingiva or alveolar bone and that the biological
half-life of mature collagen was 20% and 17% less
than found in gingiva and alveolar bone,
respectively.
 The PDL is constantly undergoing remodeling. Old
cells & fibers are broken down & replaced by new
ones, & mitotic activity can be observed in the
fibroblasts & endothelial cells (Muhlemann; 1954)

82. 
 Sodek ,1977 found collagen synthesis in PDL of adult rat
to be
- two fold greater than that of gingiva,
- four fold greater than that of skin, &
- six fold greater than that of bone.
 Almost all the newly synthesized collagen in the
ligament was converted to mature cross linked collagen,
whereas much less was converted in the gingiva & skin.
Collagen Turn Over RateCollagen Turn Over Rate

83. 
 Half-life for collagen turnover: in ligament – 1 day,
in bone – 6 days
in gingiva - 5 days,
in skin - 15 days
 According to Rippin: half life
in the apical areas 2.45 days,
in the crestal areas 6.42days,
fibers in mid-root region 5.7 days,
transseptal fibers 8.4 days
for dentogingival fibers 25 days.

84. 
 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
NutritionalNutritional

85. 
 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)
SensorySensory

86. 
 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)

87.  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.

88. 
 An important measure of periodontal ligament
homeostasis.
 The ability of periodontal ligament cells to synthesize
and secrete a wide range of regulatory molecules is
essential in accurately maintaining the width of the
periodontal ligament in spite of high-amplitude
physical forces during mastication and despite the
presence of osteogenic cells within the whole width
of the periodontal ligament. (McCulloch, 1983)
Regulation of PDL widthRegulation of PDL width

89.  Transforming growth factor-β isoforms -synthesized by
periodontal ligament cells can dose-dependently down-
regulate osteoblastic differentiation of periodontal ligament
cells (Brady TA et al. 1998)
 Prostaglandins - also produced by periodontal ligament
cells, can inhibit mineralized bone nodule formation and
prevent mineralization by periodontal ligament cells in
vitro (Ogiso B, Hughes FJ, et al. 1991,1992)
 Paracrine factors - inhibit bone resorption (Ginger MS, et al
1991)

90.  Pro-inflammatory cytokine interleukin-1 (Shimizu N et al
1995) and one of the isoenzymes responsible for
prostaglandin synthesis (cyclooxygenase 2 - Shimizu N et
al 1998) are induced by applied mechanical force on
periodontal ligament cells in vitro.
 As prostaglandins and interleukin-1 can strongly induce
matrix degradation, there is evidently an important
relationship between mechanical forces, cytokine
production and regulation of the periodontal ligament
space.

91. 
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)

92. 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.

93. 
 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.
Blood supply….

94. 
 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.
Fenestrated CapillariesFenestrated Capillaries

95. 
 Frohlich (1964) - diagonal symmetry of the
periodontal vessels
 If there is abundant vascularity palatally at the apical
area, there will be a similar abundance labially in the
coronal area of the PDL.
 This causes minute (0.5 µm) labiopalatal pulsation of
teeth with each heart beat.
Palatolabial discrepanciesPalatolabial discrepancies
in vascularityin vascularity

96. 
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

97. 
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

98.  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

99. 
 The vast majority of the nerve endings –
unencapsulated, Ruffini-like mechanoreceptors &
free nerve endings.
 In experimental animals, innervation from the
trigeminal ganglion is very dense – tooth apex,
circular & interdental ligaments.
 Innervation from mesencephalic nucleus – most
dense – subapical region, especially for the canines &
incisors, with no innervation in the zone of the
circular & interdental ligaments.

101. 
Absence of PDL aroundAbsence of PDL around
implantimplant
 important clinical consequences
 No resilient connection exists between teeth & jaw
bone - any occlusal disharmony - repercussions at
the bone-to-implant interface.
 No intrusion or migration of teeth can compensate
for the eventual presence of a premature contact.
 Because the principal proprioception of the natural
dentition comes from the pdl, its absence in implants
reduces tactile sensitivity & reflex function.

102. 
 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).
Venous drainageVenous drainage

103. 
 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.
Lymphatics

104.  The cell number and cell activity decreases with aging.
 One of the prominent changes seen in the calcified tissues
of periodontium , the bone 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.
 This remarkable changes affect the supporting structures
of the teeth.
Age changes in PDLAge changes in PDL

105. 
 With aging the activity of the PDL tissue decreases
because of restricted diets and therefore normal
functional stimulation of the tissue is diminished
 Any loss of gingival height and periodontal disease
promotes destructive changes in the PDL

106. 
 The primary role of the periodontal socket 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 .
 Acute trauma to the periodontal ligament, accidental
blows or rapid mechanical destruction may produce
pathologic changes such as fractures or resorption of the
cementum tears of fiber bundles , hemorrhage and
necrosis .
Clinical considerationsClinical considerations

107.  The adjacent alveolar bone is resorbed the PDL is
widened and tooth becomes loose .When trauma is
eliminated repair usually takes place.
 Orthodontic tooth movement depends on resorption and
formation of tooth bone and periodontal ligament .
 These activities can be stimulated by properly regulated
pressure and tension.
 If the movement of teeth is within phsysiologic limits the
initial compression of PDL on the pressure side is
compensated for by bone resorption whereas on the
tension side bone apposition is seen.
Clinical considerations…Clinical considerations…

108.  Application of large forces results in necrosis of PDL and
alveolar bone on the pressure side and movement of the
tooth will occur after the necrotic bone has been resorbed
by osteoclasts located on its endosteal surface.
 Inflammatory diseases of the pulp progress to the apical
periodontal ligament and replace its fiber bundles with
granulation tissue .
 This lesion is called a periapical granuloma may contain
epithelial cells that undergo proliferation and produce a
cyst .
ClinicalClinical
considerations…considerations…

109.  Chronic inflammatory disease is common pathology
related to PDL .
 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 .
 This 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 to their original form in such a way that
reattachment of PDL to bone becomes possible
ClinicalClinical
considerations…considerations…

110.  Various surgical techniques like Guided Tissue
regeneration are being used for correction of Periodontal
destruction .
 Guided Tissue regeneration is based on principle that
specific cells contribute to formation of specific tissues.
 Important cells responsible for periodontal regeneration
are derived from PDL.
 Exclusion of the faster growing epithelium and connective
tissue from a periodontal wound for 6 to 8 weeks allows
the slower growing tissues to occupy the space adjacent to
the tooth.
ClinicalClinical
considerations…considerations…

111.  Fusion of alveolar bone and cementum with obliteration
of the periodontal ligament is termed Ankylosis.
 Occurs in teeth with cemental resorption which suggests
that it may represent a form of abnormal repair.
 May also develop after chronic periapical inflammation ,
tooth implantation and occlusal trauma and around
embedded teeth.
 Clinically ankylosed tooth sounds DULL or WOODY on
percussion.
 Before extraction such tooth require X-ray to facilitate
surgical extraction.
ClinicalClinical
considerations…considerations…

112. 
 Osseo integration is an intimate bone to implant contact
without presence of PDL in between.
 So this is not the ideal substitute for natural tooth
replacement.
 Future studies will be directed to regenerate PDL fibers
as an interface between bone and implant.
 Some fiber bundles are present which have a cuff like
circular orientation.
 The role of these fibers remains unknown but it appears
that there presence helps to create a soft – tissue seal
around the implant .
ClinicalClinical
considerations…considerations…

113.  Within physiologic limits, the PDL can accommodate
increased function with
- an increase in width,
- a thickening of its fiber bundles, and
- an increase in diameter & number of Sharpey’s fibers
 Forces that exceed the adaptive capacity of the
periodontium produce injury called trauma from occlusion.
 Slight excessive pressure: resorption of bone, widening of
PDL space
 Slight excessive tension: elongation of PDL fibers &
apposition of bone
External forces & PDLExternal forces & PDL

114. 
 To have any chance of success , it is essential to maintain the
viability of PDL .
 Avoid dehydration of PDL.
 Avoid loss of viability of its cell rests.
Transplantation
 Best results when unerupted tooth with partially formed
roots as there is less damage to PDL.
Replantation &Replantation &
transplantationtransplantation

115.  Cemento-ossifying fibroma – Middle age, mandible
(midbody), Women Predilection (slight) & Blacks, Well
Circumscribed
 Reactive fibro-cemento-osseous lesions of PDL origin:
1.Periapical cemento-osseous dysplasia (PCD) – young-
middle age, black female, apical area of anterior
mandibular teeth.
2. Focal cemento-osseous dysplasia – women predilection,
poster mandible.
3. Florid cemento-osseous dysplasia – Middle-elderly
black women.
Neoplasms arising fromNeoplasms arising from
PDLPDL

116.  Nishimura et al, 1998 - PDL cells - susceptible to hyper &
hypoglycemia & effects - mediated via the integrin system.
 Hyperglycemia – increased expression of fibronectin
receptor → results in reduced cellular adhesion & motility →
probable tissue impairment.
 Hypoglycemia – decreased expression of fibronectin
receptor → lowers the viability & ultimately results in cell
death & hence tissue impairment
Effect of hyper & hypoEffect of hyper & hypo
glycaemia on PDLglycaemia on PDL

117. 
 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).
PDL space RG appearancePDL space RG appearance

118.  Gestrelium et al, 1997 studied effects of EMD on periodontal
ligament cell migration, attachment, proliferation,
biosynthetic activity mineral nodule formation & ability to
absorb a large range of polypeptide growth factors &
cytokine.
 In culture, EMD formed protein aggregates which
appeared to provide ideal conditions for cell-matrix
interactions.
 Under these conditions EMD enhanced the proliferation of
PDL cells, increased protein & collagen production of PDL
cells & promoted mineral nodule formation by these cells.
 However, no effect on migration, attachment & spreading
of these cells nor did they absorb any of the growth factor
or cytokine that were tested.
EMD & PDLEMD & PDL

119. 
PROGRESSIVE SYSTEMIC SCLEROSIS
Radio graphically ---- PDL widening up to 3mm
thickening
Collagen ---- dense, mature & more hyalinized than
normal
Oxytalan fibers increased.
Soft CT disorders & PDLSoft CT disorders & PDL

120. LATHYRISM
 Condition caused by drugs that inhibit cross linking in
collagen & elastin (cystamine)
 Fragile collagen fibers
 Retard eruption
DISUSE ATROPHY
 Narrowing of PDL & reduction in no. of principal fibers.
 Fibers oriented parallel to the long. Axis of root & PDL
shows reduced rate of collagen turn over.

121. FOOD TEXTURE
Little correlation between the advent of soft, fiber deficient
diet & dental health.
Significant factor in chronic inflammatory periodontal
disease is loss of natural masticatory function, leading to
accumulation of dental plaque.
Influences pattern of mastication & hence the mode of
support offered by the PDL.
Nutrition & PDLNutrition & PDL

122. CARBOHYDRATES
 Refined carbohydrates in the diet influence the severity of
PDL disease in humans (Holloway et. Al 1963)
 No direct evidence showing the direct effect of
carbohydrates per se on PDL , though in some
circumstances there could be an influence as a result of
modifying the diet consistency.

123. PROTEINS
 Deficiency of protein might be expected to produce
changes within it.
 Reduction in PDL transseptal fibers (Stien & Ziskin 1949;
Ten Cate et al 1976)
 Reduction in cementoblasts, fibroblasts
 Occlusal trauma exacerbates these effects (Chawla &
Glickman 1951)
 Healing is delayed in rats fed on protein deficient diet.

124. REGENERATION is the reproduction or reconstitution of a
lost or injured part.
REPAIR is the healing of a wound by tissue that does not
fully restore the architecture or the function of the part.
PERIODONTAL REGENERATION is defined histologically
as regeneration of the tooth’s supporting tissues, including
alveolar bone, periodontal ligament, and cementum over a
previously diseased root surface.
Healing after periodontalHealing after periodontal
therapytherapy

125. 
 NEW ATTACHMENT is defined as the union of
connective tissue or epithelium with a root surface
that has been deprived of its original attachment
apparatus. This new attachment may be epithelial
adhesion and/or connective tissue adaptation or
attachment and may include new cementum.

126.  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
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