INTRODUCTION TO PERIODONTAL LIGAMENT- DR. ARUN TOM

Periodontal ligament is an integral part of periodontium. The periodontium is an attachment apparatus of the teeth. It is a connective tissue organ, which is covered by epithelium on top surface. Teeth are attached to the bone of the jaws by periodontium.

1. PERIODONTAL LIGAMENT
1
PROF. DR. ARUN TOM
DEPT OF ORAL AND MAXILLOFACIAL
PATHOLOGY

2. INTRODUCTION
•Periodontal ligament is an integral part of
periodontium.
•The periodontium is an attachment
apparatus of the teeth. It is a connective
tissue organ, which is covered by
epithelium on top surface.
•Teeth are attached to the bone of the jaws
by periodontium.
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3. The periodontal ligament is a soft, fibrous specialized
connective tissue which is present in the periodontal
space, which is situated between the cementum of
root of the tooth and the bone forming the socket wall.
The periodontal ligament extends coronally up to
the most apical part of connective tissue of gingiva.
Because the collagen fibers are attached to the
cementum and alveolar bone, the ligament provides
soft tissue continuity between the mineralized
connective tissues of periodontium.
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4. Other terms which were previously
used for periodontal ligament are:-
1.Desmondont
2.Gomphosis
3.Pericementum
4.Dental Periosteum
5.Alveolodental ligament
6.Periodontal membrane
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5. STRUCTURE
•The periodontal ligament has the shape of an
“HOUR GLASS” and is narrowest at the
midroot level.
• The width of periodontal ligament is
approximately 0.15-0.38mm.
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6. CELLULAR COMPOSITION
The cells of periodontal ligament are categorized as:
1.Synthetic Cells
a) Osteoblasts
b) Fibroblasts
c) Cementoblasts
2.Resorptive Cells
a) Osteoclasts
b) Cementoclasts
c) Fibroblasts
3.Progenitor Cells
4.Epithelial Cell rests of malassez
5.Connective Tissue cells
a) Mast cells
b) Macrophages
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7. The characteristic of synthetic cells are:
•Should be actively synthesizing ribosomes.
•Increase in the complement rough
endoplasmic reticulum and golgi apparatus.
•Large open faced or vesicular nucleus with
prominent nucleoli.
SYNTHETIC CELLS
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8. OSTEOBLASTS
The osteoblasts covers the periodontal surface of
alveolar bone. Alveolar bone constitute a modified
endosteum and not a periosteum. A periosteum
comprises at least two distinct layers:
1. Inner – CELLULAR LAYER
2. Outer – FIBROUS LAYER
A cellular, but not an outer fibrous layer is present
on the periodontal surface of alveolar bone.
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9. Function:
Osteoblasts help in the synthesis of alveolar bone.
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10. FIBROBLASTS
•Fibroblasts are the most common cells in
periodontal ligament. They constitute about 65% of
total population.
•They appear as ovoid or elongated cells with
pseudopodia like process.
•They consist of subtypes with distinct phenotypes and
found to synthesize higher quantities of chondroitin
sulphate and lesser quantities of heparin sulphate and
hyaluronic acid.
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11. FUNCTION:
PRODUCTION OF VARIOUS TYPES OF FIBERS & IS ALSO
INSTRUMENTAL IN THE SYNTHESIS OF CONNECTIVE
TISSUE MATRIX.
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12. •The fibroblast is stellate shaped cell which produces:
1.COLLAGEN FIBERS
2.RETICULIN FIBERS
3.OXYTALAN FIBERS
•Various stages in the production of collagen fibers
are as follows:
The first molecule released by fibroblasts is
tropocollagen which contains three polypeptide chains
intertwined to form helix. Tropocollagen molecules are
aggregated longitudinally to form protofibrils, which
are subsequently laterally arranged parallel to form
collagen fibrils.
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13. •Importantly in inflammatory situations such
as those associated with periodontal
diseases, an increased expression of matrix
metalloproteinase's occurs that
aggressively destroys collagen.
•Thus attractive therapies for controlling
tissue destruction may include host-
modulators that have the capacity to inhibit
metalloproteinases.
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14. •The damaged periodontal fibers are replaced
and remodeled by newly formed fibers.
• The “RENEWAL CAPABILITY” is an
important characteristic of periodontal
ligament.
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15. CEMENTOBLASTS
•Cementoblasts synthesize collagen and
protein polysaccharides, which make up the
organic matrix of cementum.
•After some cementum has been laid down,
its mineralization begins with the help of
calcium and phosphate ions.
•Sharpey’s fibers
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16. RESORPTIVE CELLS
OSTEOCLASTS
•Resorb bone.
•The surface of an osteoclasts which is in contact with bone
has a ruffled border.
•Resorption occurs in two stages:
•The mineral is removed at bone margins and then exposed
organic matrix disintegrates. The osteoclasts demineralise
the inorganic part as well as disintegrates the organic
matrix.
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17. 17

18. FIBROBLASTS
•Fibroblasts are capable of both synthesis and
resorption.
•They exhibit lysosomes, which contain collagen
fragments undergoing digestion.
•The presence of collagen resorbing fibroblasts in a
normal functioning periodontal ligament indicates
resorption of fibers occurring during remodeling of
periodontal ligament.
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19. CEMENTOCLASTS
• Cementoclasts are found in periodontal
ligament but not remodeled like alveolar
bone and periodontal ligament.
•These are found on the surface of
cementum.
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20. PROGENITOR CELLS
•Progenitor cells are the Progenitor cells are the undifferentiated undifferentiated
mesenchymal cellsmesenchymal cells, which have the capacity to , which have the capacity to
undergo mitotic undergo mitotic division and replace the division and replace the
differentiated cells dying at differentiated cells dying at the end of their life the end of their life
span. span.
•These cells are located in These cells are located in perivascular region perivascular region and and
have have a a small close faced nucleus small close faced nucleus and little and little
cytoplasm. cytoplasm.
•When cell division occurs, one of the daughter cells When cell division occurs, one of the daughter cells
differentiate into functional type of connective tissue differentiate into functional type of connective tissue
cells. The other remaining cells retain their capacity cells. The other remaining cells retain their capacity
to to divide. divide.
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21. EPITHELIAL CELL RESTS OF MALASSEZ
•These cells are the These cells are the remnants of remnants of the epithelium of the epithelium of
Hertwig’s Epithelial Root Sheath Hertwig’s Epithelial Root Sheath and are found and are found
close to cementum.close to cementum.
•These cells exhibit These cells exhibit monofilamentsmonofilaments and are attached and are attached
to to each other by desmosomes.each other by desmosomes.
•The epithelia cells are isolated from connective The epithelia cells are isolated from connective
tissue by a tissue by a basal lamina.basal lamina.
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22. Periodontal ligament showing epithelial Periodontal ligament showing epithelial
cell rests of malassez, indicated by cell rests of malassez, indicated by
arrows. arrows.
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23. MAST CELLS
•Mast cells are small round or oval. These cells are Mast cells are small round or oval. These cells are
characterized by numerous cytoplasm, which mask its characterized by numerous cytoplasm, which mask its
small, indistinct nucleus.small, indistinct nucleus.
•The diameter of mast cells is about 12 to 15 microns.The diameter of mast cells is about 12 to 15 microns.
•The granules contain The granules contain heparin and histamineheparin and histamine. The . The
release of histamine into the extracellular compartment release of histamine into the extracellular compartment
causes causes proliferation of the endothelial and proliferation of the endothelial and
mesenchymal cells.mesenchymal cells.
•Degranulate in response to antigen- antibody Degranulate in response to antigen- antibody
formation on their surface.formation on their surface.
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24. 24

25. MACROPHAGES
•Macrophages are Macrophages are derived from blood monocytes derived from blood monocytes
and are present near the blood vessels.and are present near the blood vessels.
•These cells have a These cells have a horse-shoe shaped or kidney horse-shoe shaped or kidney
shaped nucleusshaped nucleus with peripheral chromatin and with peripheral chromatin and
cytoplasm contain phagocytosed material.cytoplasm contain phagocytosed material.
•Macrophages help in Macrophages help in phagocytosing dead cellsphagocytosing dead cells and and
secreting growth factorsecreting growth factor, which help to regulate the , which help to regulate the
proliferation of adjacent fibroblasts.proliferation of adjacent fibroblasts.
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26. 26

27. EXTRACELLULAR SUBSTANCE
•Extra cellular substance comprises the Extra cellular substance comprises the
following:following:
1.1.Fibers Fibers
a) Collagen a) Collagen b) Oxytalan b) Oxytalan
2.2.Ground SubstanceGround Substance
a) Proteoglycans a) Proteoglycans b) Glycoproteinsb) Glycoproteins
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28. PERIODONTAL FIBERS
•The most important element of periodontal ligament The most important element of periodontal ligament
has principal fibers, the principal fibers are has principal fibers, the principal fibers are
collagenouscollagenous in nature and a arranged in bundles and in nature and a arranged in bundles and
follow a follow a wavy coursewavy course. .
•Collagen is a high molecular weight protein.Collagen is a high molecular weight protein.
•Collagen macromolecules are Collagen macromolecules are rod like rod like and are and are
arranged in form of fibrils. Fibrils are packed side by arranged in form of fibrils. Fibrils are packed side by
side to form fibers. side to form fibers.
•Vitamin CVitamin C help in formation and repair of collagen. help in formation and repair of collagen.
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29. •Half life Half life of collagen fibers is between of collagen fibers is between 3 to 23 days 3 to 23 days
and collagen imparts a unique combination of and collagen imparts a unique combination of
flexibility and strength to tissue.flexibility and strength to tissue.
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30. TYPES OF PERIODONTAL LIGAMENT FIBERS
1. TRANSEPTAL GROUP
•These fibers extend interproximally over alveolar These fibers extend interproximally over alveolar
bone crest and are embedded in the cementum of bone crest and are embedded in the cementum of
adjacent teeth.adjacent teeth.
•They are They are reconstructedreconstructed even after the destruction even after the destruction
of alveolar bone resulting from periodontal disease.of alveolar bone resulting from periodontal disease.
•These fibers may be considered as belonging to the These fibers may be considered as belonging to the
gingiva because they gingiva because they do not have osseous do not have osseous
attachment. attachment.
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32. ALVEOLAR CREST GROUP
•These fibers extend obliquely from the cementum These fibers extend obliquely from the cementum
just beneath the junctional epithelium to alveolar just beneath the junctional epithelium to alveolar
crest. crest.
•Fibers also run from the cementum over the alveolar Fibers also run from the cementum over the alveolar
crest and to fibrous layer of periosteum covering crest and to fibrous layer of periosteum covering
alveolar bone. alveolar bone.
•The alveolar crest fibers The alveolar crest fibers prevent extrusion of tooth prevent extrusion of tooth
and and resist lateral tooth movements. resist lateral tooth movements.
•The incision of these fibers during periodontal The incision of these fibers during periodontal
surgery does not increase tooth mobility unless surgery does not increase tooth mobility unless
significant attachment loss has occurred. significant attachment loss has occurred.
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34. 3. 3. HORIZONTAL GROUP HORIZONTAL GROUP
Horizontal fibers extend at Horizontal fibers extend at right angles to long axis of tooth right angles to long axis of tooth
from the cementum to alveolar bone.from the cementum to alveolar bone.
4.4.OBLIQUE GROUP OBLIQUE GROUP
Oblique fibers, Oblique fibers, the largest group the largest group in periodontal ligament, in periodontal ligament,
extend from cementum in a coronal direction obliquely to bone. extend from cementum in a coronal direction obliquely to bone.
They They bear the brunt of vertical masticatory stresses bear the brunt of vertical masticatory stresses and and
transfer them into tension on the alveolar bone.transfer them into tension on the alveolar bone.
5.5.APICAL GROUP APICAL GROUP
The apical fibers radiate in a rather irregular manner from the The apical fibers radiate in a rather irregular manner from the
cementum to bone at apical region of the socket. They cementum to bone at apical region of the socket. They do not do not
occur on incompletely formed roots. occur on incompletely formed roots.
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36. INTER-RADICULAR FIBERS
•The interradicular fibers fan out from the The interradicular fibers fan out from the
cementum to the tooth in furcation areas of cementum to the tooth in furcation areas of
multirooted teeth.multirooted teeth.
•The remodeling of fibers take place in The remodeling of fibers take place in
intermediate plexusintermediate plexus. This allows adjustments . This allows adjustments
in the ligament, which in the ligament, which accommodate small accommodate small
movements of tooth.movements of tooth.
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38. OXYTALAN FIBERS
•These are These are immature elastic fibers immature elastic fibers restricted to restricted to
walls of blood vessels and are oriented in an walls of blood vessels and are oriented in an
axial direction. axial direction.
•The function is to The function is to support the bloods vessels support the bloods vessels
in in the periodontal ligament.the periodontal ligament.
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39. STRUCTURES PRESENT IN THE
CONNECTIVE TISSUE
BLOOD VESSELSBLOOD VESSELS
Main blood supply is from Main blood supply is from superior and inferior superior and inferior
alveolar arteriesalveolar arteries. The blood vessels are derived . The blood vessels are derived
from the following:from the following:
1. 1. BRANCHES FROM BRANCHES FROM APICAL VESSELSAPICAL VESSELS
Vessels supplying the pulp.Vessels supplying the pulp.
2. 2. BRANCHES FROM BRANCHES FROM INTRA-ALVEOLAR INTRA-ALVEOLAR
VESSELS:- VESSELS:- Vessels run horizontally and penetrate Vessels run horizontally and penetrate
the alveolar bone to enter into the periodontal the alveolar bone to enter into the periodontal
ligament.ligament.
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40. 3. BRANCHES FROM 3. BRANCHES FROM GINGIVAL VESSELSGINGIVAL VESSELS :- The :- The
arterioles and capillaries ramify and form a rich arterioles and capillaries ramify and form a rich
network. Rich vascular plexus is found at the apex network. Rich vascular plexus is found at the apex
and in cervical part of ligament. and in cervical part of ligament.
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41. NERVE SUPPLY
•Nerves found in ligament pass through foramina in Nerves found in ligament pass through foramina in
alveolar bone. alveolar bone.
•The nerves are the branches of The nerves are the branches of second and third second and third
division of fifth cranial nerve (trigeminal nerve) division of fifth cranial nerve (trigeminal nerve)
and follow same path as blood vessels. and follow same path as blood vessels.
•These nerve fibers provide sense of These nerve fibers provide sense of touch, pressure, touch, pressure,
pain and proprioception pain and proprioception during mastication.during mastication.
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42. CEMENTICLES
•Cementicles are small calcified bodies present in the Cementicles are small calcified bodies present in the
periodontal ligament.periodontal ligament.
•They may form into large calcified bodies and fuse within They may form into large calcified bodies and fuse within
cementum or remain free.cementum or remain free.
• These are found in old age.These are found in old age.
•The degenerated epithelial cells form a nidus for The degenerated epithelial cells form a nidus for
calcification. calcification.
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43. •Intermediate plexus : principal fibers frequently
follow a wavy course from cementum to bone and
are joined in the mid region of periodontal space
giving rise a zone of distinct appearance called
intermediate plexus
•Indifferent fiber plexus: small collagen fibers
associated with large principal collagen fibers .
These fibers run in all directions these form a
plexus called indifferent fiber plexus
•Crimping : a specific waviness have been reported
in collagenous tissues including the periodontal
ligament called crimping.

44. FUNCTIONS
1.PHYSICAL FUNCTION
A)A)Provision of Provision of soft tissue ‘casing” soft tissue ‘casing” in order to in order to
protect protect the vessels and nerves from injury the vessels and nerves from injury
due to mechanical forces.due to mechanical forces.
B)B)Transmission of occlusal forces to bone.Transmission of occlusal forces to bone.
Depending on type of force applied, axial Depending on type of force applied, axial
force when applied causes stretching of force when applied causes stretching of
oblique fibers of periodontal ligament. oblique fibers of periodontal ligament.
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45. •Transmission of this Transmission of this tensional force tensional force to alveolar to alveolar
bone encourages bone formation rather then bone bone encourages bone formation rather then bone
resorption.resorption.
•But when But when horizontal or tipping force horizontal or tipping force is applied, is applied,
the tooth rotates around the axis.the tooth rotates around the axis.
•When a greater force is applied, displacement of When a greater force is applied, displacement of
facial and lingual plates may occur.facial and lingual plates may occur.
•The The axis of rotation axis of rotation in a single rooted tooth is in a single rooted tooth is
located in area between the apical and middle third located in area between the apical and middle third
of root. of root.
•In multirooted tooth, axis of rotations is located In multirooted tooth, axis of rotations is located
at furcation area.at furcation area.
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46. C) Attaches the teeth to the bone.C) Attaches the teeth to the bone.
D) Maintains the gingival tissues in their proper D) Maintains the gingival tissues in their proper
relationship to the teeth.relationship to the teeth.
E) E) “Shock absorption” “Shock absorption” resists the impact of resists the impact of
occlusal surfaces. Due to its property of shock occlusal surfaces. Due to its property of shock
absorption the teeth are slightly more mobile in absorption the teeth are slightly more mobile in
early morning than in evening. early morning than in evening.
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47. •Two theories have been explained for Two theories have been explained for
mechanism of tooth support. mechanism of tooth support.
A.A.TENSIONAL THEORY TENSIONAL THEORY
B.B.VISCOELASTIC THEORY VISCOELASTIC THEORY
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48. A. TENSIONAL THEORY
•According to it, principal fibers play a major According to it, principal fibers play a major
role in supporting tooth and transmitting forces role in supporting tooth and transmitting forces
to bone.to bone.
• When forces are applied to tooth, principal When forces are applied to tooth, principal
fibers fibers unfold and straighten unfold and straighten and then transmit and then transmit
the forces to alveolar bone, causing elastic the forces to alveolar bone, causing elastic
deformation of socket. deformation of socket.
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49. A. Tooth in a resting stateA. Tooth in a resting state
B. The periodontal ligament fibers are compressed in B. The periodontal ligament fibers are compressed in
areas of pressure and stretched in area of tension.areas of pressure and stretched in area of tension.
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50. VISCOELASTIC THEORY
•According to it, the fluid movement largely controls According to it, the fluid movement largely controls
the displacement of the tooth, with fibers playing a the displacement of the tooth, with fibers playing a
secondary role.secondary role.
•When forces are transmitted to the tooth, the When forces are transmitted to the tooth, the
extracellular fluid is pushed from periodontal extracellular fluid is pushed from periodontal
ligament into marrow spaces through the cribriform ligament into marrow spaces through the cribriform
plate.plate.
• After depletion of tissue fluids, the bundle fibers After depletion of tissue fluids, the bundle fibers
absorb the shock and tighten.absorb the shock and tighten.
• This leads to blood vessel stenosis This leads to blood vessel stenosis  arterial lack arterial lack
pressure pressure  ballooning of vessels ballooning of vessels tissue tissue
replenishes with fluidsreplenishes with fluids..
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51. 2. FORMATIVE & REMODELLING
FUNCTION
•Cells of the periodontal ligament have the Cells of the periodontal ligament have the
capacity capacity to control the synthesis and to control the synthesis and
resorption of cementum, ligament and alveolar resorption of cementum, ligament and alveolar
bone.bone.
• Periodontal ligament undergoes constant Periodontal ligament undergoes constant
remodeling, old cells and fibers are broken remodeling, old cells and fibers are broken
down and replaced by new ones.down and replaced by new ones.
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52. 3. NUTRITIONAL FUNCTION
•Blood vessels of periodontal ligament provide Blood vessels of periodontal ligament provide
nutrition to the cells of periodontium, because they nutrition to the cells of periodontium, because they
contain contain various anabolites and other substances, various anabolites and other substances,
which are required by cells of ligament.which are required by cells of ligament.
•Compression of blood vessels (due to heavy forces Compression of blood vessels (due to heavy forces
applied on tooth) leads to necrosis of cells. applied on tooth) leads to necrosis of cells.
•Blood vessels also Blood vessels also remove catabolites.remove catabolites.
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53. 4. SENSORY FUNCTION
•The nerve bundles found in periodontal ligament, divide
into single myelinated nerve, which later on lose their
myelin sheath and end in one of the four types of nerve
termination:
1. Free endings, carry pain sensations.
2. Ruffini like mechanoreceptors located in the apical
area.
3.Meissener’s corpuscles are also mechanoreceptors
located primarily in mid-root region.
4. Spindle like pressure endings, located mainly in apex.
Pain sensation is transmitted by small diameter nerves,
temperature by intermediate type; pressure by large
myelinated fibers.
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54. HOMEOSTATIC MECHANISM
•The resorption and synthesis are controlled The resorption and synthesis are controlled
procedures. procedures.
•If there is a long term damage of periodontal If there is a long term damage of periodontal
ligament, which is not repaired, the ligament, which is not repaired, the bone is bone is
deposited in the periodontal space.deposited in the periodontal space.
• This results in obliteration of space and ankylosis This results in obliteration of space and ankylosis
between bone and the tooth. between bone and the tooth.
•The quality of tissue changes if balance between The quality of tissue changes if balance between
synthesis and resorption is disturbed. synthesis and resorption is disturbed.
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55. •If there is deprivation of If there is deprivation of Vit. C Vit. C which are which are
essential for collagen synthesis, resorption of essential for collagen synthesis, resorption of
collagen will continue. collagen will continue.
•So there is So there is progressive destruction and loss progressive destruction and loss
of extra cellular substance of ligament. of extra cellular substance of ligament.
•This occurs more on This occurs more on bone side of ligament. bone side of ligament.
•Hence, Hence, loss of attachment loss of attachment between bone and between bone and
tooth and at last, loss of tooth.tooth and at last, loss of tooth.
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56. CLINICAL CONSIDERATIONS
•The primary role of periodontal ligament is to support The primary role of periodontal ligament is to support
the tooth in the bony socket.the tooth in the bony socket.
•The width of periodontal ligament varies The width of periodontal ligament varies from 0.15 to from 0.15 to
0.38mm. 0.38mm. The average width is:The average width is:
-- 0.21mm at 11 to 16 years of age. 0.21mm at 11 to 16 years of age.
-- 0.18mm at 32 to 50 years of age.0.18mm at 32 to 50 years of age.
-- 0.15mm at 51 to 67 years of 0.15mm at 51 to 67 years of
age.age.
•So, the So, the width of periodontal ligament decreases as width of periodontal ligament decreases as
age advances. age advances. 56

57. • In the periodontal ligament, In the periodontal ligament, aging results in more aging results in more
number of elastic fibersnumber of elastic fibers and decrease in vascularity, and decrease in vascularity,
mitotic activity, fibroplasia and in the number of collagen mitotic activity, fibroplasia and in the number of collagen
fibers and mucopolysaccharides. fibers and mucopolysaccharides.
•If If gingivitisgingivitis is not cured and supporting structure become is not cured and supporting structure become
involved, the disease is termed as involved, the disease is termed as periodontitis.periodontitis.
•There are few coccal cells and more motile rods and There are few coccal cells and more motile rods and
spirochetes in the spirochetes in the diseased site diseased site than in the healthy site. than in the healthy site.
The The bacteria consists of gram-positive facultative rods bacteria consists of gram-positive facultative rods
and cocci in healthy site while in diseased site, and cocci in healthy site while in diseased site, gram-gram-
negative rods and anaerobes are more in number. negative rods and anaerobes are more in number.
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58. •Resorption and formation of both bone and Resorption and formation of both bone and
periodontal ligament play an important role in periodontal ligament play an important role in
orthodontic tooth movementorthodontic tooth movement. If tooth movement . If tooth movement
takes place, the takes place, the compression of PDL is compensated compression of PDL is compensated
by bone resorption whereas on tension side, by bone resorption whereas on tension side,
apposition takes place.apposition takes place.
•Periapical area Periapical area of the tooth is the of the tooth is the main pathologic main pathologic
site.site. Inflammation of the pulp reached to the apical Inflammation of the pulp reached to the apical
periodontal ligament and replaces its fiber bundles periodontal ligament and replaces its fiber bundles
with granulation tissue called as with granulation tissue called as granuloma,granuloma, which which
then progresses into then progresses into apical cyst. apical cyst.
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59. •Chronic periodontal disease Chronic periodontal disease can lead to can lead to infusion infusion
of microorganisms into the blood stream. of microorganisms into the blood stream.
•The The pressure receptors pressure receptors in ligament have a in ligament have a
protective role. protective role. Apical blood vessels Apical blood vessels are protected are protected
from excessive from excessive compression by sensory compression by sensory
apparatus of the teeth.apparatus of the teeth.
•The The rate of mesial drift rate of mesial drift of tooth is related to of tooth is related to
health, dietary factor and age. It varies from health, dietary factor and age. It varies from 0.05 0.05
to 0.7mm per to 0.7mm per year. year.
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60. THANK YOU