PERIODONTAL LIGAMENT
1
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.
2
 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.
3
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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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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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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SYNTHETIC CELLS
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.
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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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Function:
Osteoblasts help in the synthesis of alveolar bone.
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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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FUNCTION:
PRODUCTION OF VARIOUS TYPES OF FIBERS & IS ALSO
INSTRUMENTAL IN THE SYNTHESIS OF CONNECTIVE
TISSUE MATRIX.
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• 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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• 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 hostmodulators that have the capacity to inhibit
metalloproteinases.
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• 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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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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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
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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CEMENTOCLASTS
• Cementoclasts are found in periodontal
ligament but not remodeled like alveolar
bone and periodontal ligament.
• These are
cementum.
found
on
the
surface
of
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PROGENITOR CELLS
• Progenitor
cells
are
the
undifferentiated
mesenchymal cells, which have the capacity to
undergo mitotic division
and
replace
the
differentiated cells dying at the end of their life
span.
• These cells are located in perivascular region and
have
a small close faced nucleus and little
cytoplasm.
• When cell division occurs, one of the daughter cells
differentiate into functional type of connective tissue
cells. The other remaining cells retain their capacity
to divide.
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EPITHELIAL CELL RESTS OF MALASSEZ
• These cells are the remnants of the epithelium of
Hertwig’s Epithelial Root Sheath and are found
close to cementum.
• These cells exhibit monofilaments and are attached
to each other by desmosomes.
• The epithelia cells are isolated from connective
tissue by a basal lamina.
21
Periodontal ligament showing epithelial
cell rests of malassez, indicated by
arrows.
22
MAST CELLS
• Mast cells are small round or oval. These cells are
characterized by numerous cytoplasm, which mask
its small, indistinct nucleus.
• The diameter of mast cells is about 12 to 15 microns.
• The granules contain heparin and histamine. The
release of histamine into the extracellular
compartment causes proliferation of the
endothelial and mesenchymal cells.
• Degranulate in response to antigen- antibody
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formation on their surface.
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MACROPHAGES
• Macrophages are derived from blood monocytes
and are present near the blood vessels.
• These cells have a horse-shoe shaped or kidney
shaped nucleus with peripheral chromatin and
cytoplasm contain phagocytosed material.
• Macrophages help in phagocytosing dead cells and
secreting growth factor, which help to regulate the
proliferation of adjacent fibroblasts.
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EXTRACELLULAR SUBSTANCE
• Extra cellular
following:
substance
comprises
1. Fibers
a) Collagen
b) Oxytalan
2. Ground Substance
a) Proteoglycans
b) Glycoproteins
the
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PERIODONTAL FIBERS
• The most important element of periodontal ligament
has principal fibers, the principal fibers are
collagenous in nature and a arranged in bundles and
follow a wavy course.
• Collagen is a high molecular weight protein.
• Collagen macromolecules are rod like and are
arranged in form of fibrils. Fibrils are packed side by
side to form fibers.
• Vitamin C help in formation and repair of collagen.
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• Half life of collagen fibers is between 3 to 23 days
and collagen imparts a unique combination of
flexibility and strength to tissue.
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TYPES OF PERIODONTAL LIGAMENT FIBERS
1. TRANSEPTAL GROUP
• These fibers extend interproximally over alveolar
bone crest and are embedded in the cementum of
adjacent teeth.
• They are reconstructed even after the destruction
of alveolar bone resulting from periodontal disease.
• These fibers may be considered as belonging to the
gingiva because they do not have osseous
attachment.
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DIAGRAM OF PRINCIPAL FIBER GROUPS
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ALVEOLAR CREST GROUP
• These fibers extend obliquely from the cementum
just beneath the junctional epithelium to alveolar
crest.
• Fibers also run from the cementum over the alveolar
crest and to fibrous layer of periosteum covering
alveolar bone.
• The alveolar crest fibers prevent extrusion of tooth
and resist lateral tooth movements.
• The incision of these fibers during periodontal
surgery does not increase tooth mobility unless
significant attachment loss has occurred.
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3.
HORIZONTAL GROUP
Horizontal fibers extend at right angles to long axis of tooth
from the cementum to alveolar bone.
4.
OBLIQUE GROUP
Oblique fibers, the largest group in periodontal ligament,
extend from cementum in a coronal direction obliquely to bone.
They bear the brunt of vertical masticatory stresses and
transfer them into tension on the alveolar bone.
5.
APICAL GROUP
The apical fibers radiate in a rather irregular manner from the
cementum to bone at apical region of the socket. They do not
occur on incompletely formed roots.
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INTER-RADICULAR FIBERS
• The interradicular fibers fan out from the
cementum to the tooth in furcation areas of
multirooted teeth.
• The remodeling of fibers take place in
intermediate plexus. This allows adjustments
in the ligament, which accommodate small
movements of tooth.
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OXYTALAN FIBERS
• These are immature elastic fibers restricted to
walls of blood vessels and are oriented in an
axial direction.
• The function is to support the bloods vessels
in the periodontal ligament.
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STRUCTURES PRESENT
CONNECTIVE TISSUE
IN
THE
 BLOOD VESSELS
Main blood supply is from superior and inferior
alveolar arteries. The blood vessels are derived
from the following:
1.
BRANCHES FROM APICAL VESSELS
Vessels supplying the pulp.
2.
BRANCHES FROM INTRA-ALVEOLAR
VESSELS:- Vessels run horizontally and penetrate
the alveolar bone to enter into the periodontal
ligament.
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3. BRANCHES FROM GINGIVAL VESSELS:- The
arterioles and capillaries ramify and form a rich
network. Rich vascular plexus is found at the apex
and
in
cervical
part
of
ligament.
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NERVE SUPPLY
• Nerves found in ligament pass through foramina in
alveolar bone.
• The nerves are the branches of second and third
division of fifth cranial nerve (trigeminal nerve)
and follow same path as blood vessels.
• These nerve fibers provide sense of touch, pressure,
pain and proprioception during mastication.
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CEMENTICLES
• Cementicles are small calcified bodies present in the
periodontal ligament.
• They may form into large calcified bodies and fuse within
cementum or remain free.
• These are found in old age.
• The degenerated epithelial cells form a nidus for
calcification.
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FUNCTIONS
1. PHYSICAL FUNCTION
A) Provision of soft tissue ‘casing” in order to
protect the vessels and nerves from injury due
to mechanical forces.
B) Transmission of occlusal forces to bone.
 Depending on type of force applied, axial
force when applied causes stretching of
oblique fibers of periodontal ligament.
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• Transmission of this tensional force to alveolar
bone encourages bone formation rather then bone
resorption.
• But when horizontal or tipping force is applied, the
tooth rotates around the axis.
• When a greater force is applied, displacement of
facial and lingual plates may occur.
• The axis of rotation in a single rooted tooth is
located in area between the apical and middle third
of root.
• In multirooted tooth, axis of rotations is located at
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furcation area.
C) Attaches the teeth to the bone.
D) Maintains the gingival tissues in their proper
relationship to the teeth.
E) “Shock absorption” resists the impact of
occlusal surfaces. Due to its property of shock
absorption the teeth are slightly more mobile in
early morning than in evening.
42
• Two theories have been
mechanism of tooth support.
explained
for
A. TENSIONAL THEORY
B. VISCOELASTIC THEORY
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A. TENSIONAL THEORY
• According to it, principal fibers play a major
role in supporting tooth and transmitting forces
to bone.
• When forces are applied to tooth, principal
fibers unfold and straighten and then transmit
the forces to alveolar bone, causing elastic
deformation of socket.
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A. Tooth in a resting state
B. The periodontal ligament fibers are compressed in
areas of pressure and stretched in area of tension.
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VISCOELASTIC THEORY
• According to it, the fluid movement largely controls
the displacement of the tooth, with fibers playing a
secondary role.
• When forces are transmitted to the tooth, the
extracellular fluid is pushed from periodontal
ligament into marrow spaces through the cribriform
plate.
• After depletion of tissue fluids, the bundle fibers
absorb the shock and tighten.
• This leads to blood vessel stenosis  arterial lack
pressure  ballooning of vessels tissue
replenishes with fluids.
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2.
FORMATIVE
&
FUNCTION
REMODELLING
• Cells of the periodontal ligament have the
capacity to control the synthesis and resorption
of cementum, ligament and alveolar bone.
• Periodontal ligament undergoes constant
remodeling, old cells and fibers are broken
down and replaced by new ones.
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3. NUTRITIONAL FUNCTION
• Blood vessels of periodontal ligament provide
nutrition to the cells of periodontium, because they
contain various anabolites and other substances,
which are required by cells of ligament.
• Compression of blood vessels (due to heavy forces
applied on tooth) leads to necrosis of cells.
• Blood vessels also remove catabolites.
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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
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myelinated fibers.
HOMEOSTATIC MECHANISM
• The resorption
procedures.
and
synthesis
are
controlled
• If there is a long term damage of periodontal
ligament, which is not repaired, the bone is deposited
in the periodontal space.
• This results in obliteration of space and ankylosis
between bone and the tooth.
• The quality of tissue changes if balance between
synthesis and resorption is disturbed.
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• If there is deprivation of Vit. C which are
essential for collagen synthesis, resorption of
collagen will continue.
• So there is progressive destruction and loss
of extra cellular substance of ligament.
• This occurs more on bone side of ligament.
• Hence, loss of attachment between bone and
tooth and at last, loss of tooth.
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CLINICAL CONSIDERATIONS
• The primary role of periodontal ligament is to support
the tooth in the bony socket.
• The width of periodontal ligament varies from 0.15 to
0.38mm.
The
average
width
is:
0.21mm at 11 to 16 years of age.
0.18mm at 32 to 50 years of age.
0.15mm at 51 to 67 years of age.
• So, the width of periodontal ligament decreases as
age advances.
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• In the periodontal ligament, aging results in more
number of elastic fibers and decrease in vascularity,
mitotic activity, fibroplasia and in the number of collagen
fibers and mucopolysaccharides.
• 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.
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• 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.
• Periapical area of the tooth is the main pathologic
site. 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.
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• 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.
• The rate of mesial drift of tooth is related to
health, dietary factor and age. It varies from 0.05
to 0.7mm per year.
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