Dr. Mazood Ahamad
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The periodontal ligament is the connective
tissue that surrounds the root and connects it
with the bone.
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It is the soft
richly vascular and cellular
connective tissue which surround the tooth root
and connects it to the inner wall of the alveolar
bone.
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Average space or width: 0.25 mm (0.150.38 mm)
They are divided into:
A) The principal fibers.
B) The accessory fibers.
C) The oxytalan ( elastic ) fibers.
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The most important elements of the periodontal ligament
are the principal fibers, are collagenous,
are arranged in bundles, and follow a wavy course when(
longitudinal sections)
Terminal portions of the principal fibers that insert into
cementum and bone are termed Sharpey's fibers
Collagen Type 1 – Principal fibers
 Collagen type 3 – Reticular Fibers
 Collagen Type 4 
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Collagen is a protein composed of different amino acids,
the most important are glycine, proline,hydroxylysine, and
hydroxyproline.
Collagen biosynthesis occurs inside the fibroblasts to form
tropocollagen molecules.
These aggregate into microfibrils
that are packed together to form fibrils
these fibrils associate to form fibers,
the fibers associate to form bundles
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The principal fibers of the periodontal ligament are
arranged in six groups
1-Transseptal or interdental ligament.
2- Alveolar crest group.
3- Horizontal group.
4- Oblique group.
5-Apical group.
6- Interradicular group.
1-Transseptal or interdental ligament Transseptal fibers extend interproximally over the alveolar
bone crest and are embedded in the cementum of
adjacent teeth
 Reconstructed even after destruction of the alveolar bone
2- Alveolar crest group.
 Alveolar crest fibers extend obliquely from the cementum
just beneath the junctional epithelium to the alveolar
crest.
 The alveolar crest fibers prevent the extrusion of the tooth
and resist lateral tooth movements.
3- Horizontal group.
 Horizontal fibers extend at right angles to the long axis of
the tooth from the cementum to the alveolar bone.
4- Oblique group.
 The largest group , extend from the cementum in a
coronal direction obliquely to the bone
 They bear the brunt of vertical masticatory stresses and
transform them into tension on the alveolar bone.
5-Apical group.
 Fibers radiate in a rather irregular fashion from the
cementum to the bone at the apical region of the socket.
 They do not occur on incompletely formed roots.
6- Interradicular group.
 The Interradicular fibers fan out from the cementum to
the tooth in the furcation areas of multirooted teeth.
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1.
2.
3.
4.
Four types of cells have been identified in the periodontal
ligament:
Connective tissue cells,
Epithelial rest cells,
Immune system cells, and
Cells associated with neurovascular elements.
fibroblast
Synthetic
cells
cementoblast
oseoblast
osteoclast
Resorptive
cells
Connective
tissue cells
fibroblast
Epithelial cell
rests
Defense
cells
cementoclast
macrophages
Mast cells
Neurovascular
elements
eosinophils
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They represent the remnants of
epithelial root sheath.
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appear
as
either
isolated
clusters of cells or interlacing
strands
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most numerous in the apical and
cervical areas.
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Proliferate when stimulated
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It consists of two main components:
GLYCOSAMINOGLYCANS,such as hyaluronic acid and
proteoglycans,and
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GLYCOPROTEINS such as fibronectin and laminin.
It also has a high water content (70%).
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CEMENTICLES
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The periodontal ligament also may contain calcified
masses called cementicles,
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Cementicles may develop from calcified epithelial rests;
FUNCTIONS OF PDL
I.
Physical.
II.
Formative & Remodelling.
III.
Nutritional.
IV.
Sensory.
l. Provision of 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 the teeth to the bone
4. Maintenance of the gingival tissues in their proper
relationship to the teeth.
5. Resistance to the impact of occlusal forces (shock
absorption)
SHOCK ABSORPTION – 3 THEORIES
1.
Tensional Theory.
2.
Viscoelastic Theory.
3.
Thixotropic Gel Theory.
TENSIONAL THEORY
Force is applied to crown
Principal fibers unfold and straightens
Transmits forces to bone
Elastic deformation of bony socket
Alveolar bone reaches its limit
Load is transmitted to basal bone
VISCOELASTIC THEORY
Controlled by fluid movement.
Forces transmitted to tooth.
Extracellular fluid - from foramina in cortical
layer to marrow spaces
Fiber bundle absorb slack and tighten
Blood vessels stenosis
Passages of blood filtrates into tissues
THIXOTROPIC GEL THEORY
Behavior of Thixotropic Gel.
Physiologic response – changes in viscosity
of biologic system.
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The pdl is constantly undergoing remodelling.
PDL cells participate in formation and resorption.
Rate of formation & differentiation of fibroblasts affects
rate of collagen, cementum & bone.
Cementoblasts and osteoblasts are essential in building up
cementum and bone.
NUTRITIONAL & SENSORY
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The periodontal ligament supplies nutrients to the
cementum, bone, and gingiva by way of the blood vessels
and lymphatic drainage.
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The periodontal ligament is capable of transmitting
tactile, pressure, and pain sensations
THANK YOU