periodontal ligament.pdf

PERIODONTAL LIGAMENT
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Contents
INTRODUCTION
DEFINITION
COMPONENTS
PERIODONTAL FIBRES
CELLULAR ELEMENTS
FUNCTIONS OF PERIODONTAL LIGAMENT
TRANSMISSION OF OCCLUSAL FORCES TO BONE
BLOOD SUPPLY AND LYMPHATICS

Introduction
Periodontium
It is a dynamic structure composed
of the tissues supporting and investing
the teeth.
Peri – around
Odontos - tooth
Four principal components
Gingiva.
1.
Periodontal ligament.
2.
Cementum.
3.
Alveolar bone.
4.

Periodontal ligament
It is composed of complex vascular and highly cellular connective
tissue that surrounds the tooth root and connects it to the inner wall
of the alveolar bone.
Shape : Hourglass.
Other names:
Periodontal membrane
Pericemental membrane
Alveolo-dental ligament
Desmodent
Gomphosis

Periodontal ligament space = 0.2mm.
Decreased in teeth which are not in
function/unerupted teeth.
Increased in teeth subjected to
hyperfunction .

Components
Periodontal fibres
Cellular components
Ground substance

Periodontal fibers
Principal fibers collagenous.
1.
Non- collagenous fibres/elastic fibers.
2.
Indifferent fiber plexus.
3.

Collagen
Collagen molecule –
Tropocollagen -3 alpha chains.
Three helical alpha chains- coiled
around each other triple helix
rigid structure like rope.

3 amino acids per turn.
Sequence of tripeptides-
Gly-X-Y
Glycine- Every 3ʳᵈ
position, centre
X -Proline , Y- hydroxy
proline- 30% .

Most abundant amino acids present in
collagen:
Glycine
Proline
Hydroxylysine and
Hydroxyproline

Tensile strength of collagen greater than steel.
Unique combination of tensile strength and flexibility.

Types of collagen in PDL
Type I - Most abundant- 80%. Compose principal fibers
Type III- Compose reticular fibers
Type IV- Found in basal lamina/ basement membrane.
Type XII- help in the alignment and organization of
periodontal fibers during the tooth development
Type VI- Immunolocalized in pdl & gingiva

Principal fibers
They are composed of six groups
Transseptal group: Extend interproximally over the alveolar bone crest
and embedded in the cementum of adjacent teeth.
Reconstructed after destruction of alveolar bone.
Responsible for relapse of orthodontic treatment.

Alveolar crest group
From alv crest to cementum just beneath the junctional ep.
prevents extrusion of tooth)
incision of these fibres during periodontal sugery doesnt
lead to increase in mobility.

Horizontal group
Extent at right angles from cementum and bone
prevents lateral movement of tooth

Oblique group
Largest group
extent from cementum to bone obliquely in a coronal
direction.
Bear the brunt of vertical masticatory stresses

Apical group
Arranged in irregular fashion
prevent tooth tipping

Interradicular group
Interradicular fibres
Fan out in the furcation areas of multirooted
teeth

Sharpey’s fibres
Terminal portions of the
principal fibers
Calcify to a significant
degree
Associated with proteins :
osteopontin and
bone sialoprotein

Non collagenous fibers/elastic fibres:
Two immature forms found
are:-
oxytalan fibers
Eluanin fibers
Functions
Regulate vascular flow
Role in tooth support
Facilitate fibroblast attachment
and migration

Indifferent fiber plexus
Small collagen fibers along with large principal
fibers
Randomly oriented forming plexus.

Cellular elements
Connective tissue cells
Epithelial cells
Immune system cells
Cells associated with neuro- vascular
elements

Fibroblasts:
Most common cells
Ovoid, elongated or stellate str.
Oriented along principal fibers
Synthesize collagen
Connective tissue cells

Possess capacity to phagocytose
old collagen & degrade them – enzyme hydrolysis
Regulates collagen turnover

Epithelial rests of Malassez
Considered as remnants of hertwig’s
epithelial root sheath
Distributed close to cementum and
throughout the periodontal ligament of
most teeth.
Clinical considertaions
Periapical cyst
Lateral root cyst

Neutrophils
Lymphocytes
Macrophages
Mast cells
Eosinophils
Immune system cells

Ground substance:
Contains 70% water
Proteoglycans participates in various biological functions
like cell adhesion, cell-cell matrix interaction.
Glycosaminoglycans
Glycoprotein
Hyaluronic acid
Proteoglycans
Fibronectin
Osteopontin

CEMENTICLES
Calcified masses found adherent to or detached from the root
surfaces.
Develop from
Calcified epithelial rests
Small spicules of cementum
Alveolar bone traumatically displaced into pdl
Calcified sharpey’s fibers
Thrombosed vessels with in pdl

Functions
of
PDL
Physical
Formative
and
remodeling
Nutritional
Sensory

Physical Function
Protection- provide sof tissue casing for nerves
and vessels.
1.
Transmission of occlusal forces to the bone.
2.
Shock absorption: resistance to the impact of
occlusal forces.
3.
Attachment of the teeth to the bone.
4.
Maintenance of the gingival tissues in the
5.

Theories of shock absorption:
Tensional theory
Viscoelastic theory

Tensional theory
Forces are applied
principal fibers unfold & straighten
transmission of forces to alveolar bone
elastic deformation of the bony socket
transmitted to the basal bone

Viscoelastic theory
Extracellular fluid passes from pdl to marrow spaces of
bone
depletion of tissue
fluid
Fibers slacken & tighten
Blood vessels
stenosis
Forces are
applied
Arterial back pressure causes ballooning of vessels
& passage of blood into tissues, replenishing tissue

TRANSMISSION OF OCCLUSAL
FORCES TO THE BONE
When there is axial force-
oblique fibres become taut-
assume their full length -
sustain the force
When there is horizontal
force- the tooth rotates
around centre of rotation-
Area of compression- fibres
are compressed
Area of tension- fibres are
tensed

Helps in formation & resorption of
cementum and bone during physiologic tooth
movement.
Constantly undergoes remodeling.
Formative and Remodeling
Function

Supplies nutrients to cementum ,bone & gingiva
Abundantly supplied with sensory nerve fibers capable
of transmitting tactile ,pressure and pain sensation by
trigeminal pathway.
Nutritional and sensory function

Free nerve endings-pain sensation
Ruffini like mechano receptors-apical region
Meissner’s corpuscles(mechano receptors)-mid
root region
Spindle like(pressure,vibration nerve endings)-
apical region
4 TYPES OF NEURAL
TERMINATIONS :

Spindle like
endings
Meissner’s corpuscels
(tactile receptors

BLOOD SUPPLY
Inferior and superior alveolar
arteries
Branches from
Apical vessels
1.
Penetrating vessels from the
alveolar bone
2.
Anastomosing vessels from the
gingiva.
3.

Junctional epithelium
Periodontal ligament
Periapical region
Alveolar bone
Submaxillary lymph nodes
Lymphatics (PDL to bone)

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