The periodontal ligament is a complex connective tissue that surrounds the tooth root and attaches the tooth to the alveolar bone. It is composed of collagen fibers, ground substance, blood vessels, nerves and cells. The principal collagen fibers resist various forces on the tooth and help transmit these forces to the bone. The periodontal ligament provides nutrition to surrounding structures, allows for remodeling and repair, and has proprioceptive functions through its nerve endings.

2. PERIODONTAL LIGAMENT

3. PERIODONTIUM
Cementum
Periodontal
ligament
Alveolar bone
Apical foramen
Pulp cavity
Enamel
Dentin
Gingiva
Root canal
Alveolar vessels
& nerves

4. DEFINITION
 Periodontal ligament is composed of soft complex
vascular and highly cellular connective tissue that
surrounds the tooth roots and connects it to the inner wall
of the alveolar bone.

5. 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

6. STRUCTURE
 In the coronal direction it is continuous with
lamina propria of gingiva & is demarcated by
the alveolar crest fibers.
 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.-beertsen
etal 1997

7. RADIOGRAPHICAPPEARANCE
 The interdental septum normally
present as a thin radiopaque
border that is adjacent to the PDL
& at alveolar crest is termed as
Lamina dura.
 Radiographic evaluation of bone
changes in periodontal disease is
mainly based on its appearance.
 Discontinuity of lamina dura
indicates pathological changes.

8. DEVELOPMENT

9. cells
COMPONENTS
The periodontal ligament is formed of :
Fibers
Extracellular
substances
Synthetic
Resorptive
Progenitor
Defensive
Ground substances
Blood Vessels,
Nerves & Lymphatics.
ECRM

13. EPITHELIALCELLRESTS 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.
13

14. cells
COMPONENTS
The periodontal ligament is formed of :
Fibers
Extracellular
substances
Synthetic
Resorptive
Progenitor
Defensive
Ground substances
Blood Vessels,
Nerves & Lymphatics.
ECRM

15. FIBERS
 Principal fibers
 Elastic-oxytalan
 Indifferent fiber plexus

16. COLLAGEN
 Synthesized by fibroblasts, chondroblasts, osteoblasts & other
cells
 Contain 2 unique amino acid hydroxy proline and hydroxy
lysine along with glycine & proline (Carneiro J, Fava de
Moraes F , 1955)
 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. Principal fibers ---- Type I
b. Basement membrane ---- Type IV
c. Reticular fibers ---- Type III
d. Tooth development ---- Type XII

17. PRINCIPAL FIBERS OF PDL
 Alveolar crest group
 Horizontal
 Oblique
 Apical
 Transeptal
 Inter – radicular

18. Alveolar crest group:
radiate from the cementum over the
alveolar crest & to the fibrous
layer of periosteum covering the
alveolar bone.
Function – prevents extrusion of the
tooth & resist lateral tooth
movement
Horizontal group:
The fiber bundles run from the
cementum to the bone at right
angle to the long axis of the
tooth.
Function - resists horizontal and
tipping forces
Bone Dentin

19. Oblique group:
The fiber bundles run obliquely.
Their attachment in the bone is
somewhat coronal
than the attachment in the
cementum.
The greatest number of fiber
bundles are found in this group.
Function
Resists vertical and intrusive forces
bone
dentin

20. Apical group
The bundles radiate from the
apical region of the root to
the surrounding bone
Function resists vertical
force
Interradicular group
The bundles radiate from the
interradicular septum to the
furcation of the multirooted
tooth.
Function resists vertical and lateral
forces.
Transeptal fibers
It extends interproximally
Reconstructed even after destruction of
bone due to periodontal disease
dentin
bone
dentin
bone

21. ELASTIN FIBERS
 PDL fibers do not contain mature elastin but two
immature forms are found oxytalan and eulanin
 Run in apico-coronal direction to bend and attach
at cervical third of root (Fulmer et al. 1974)
 Function
- regulate vascular flow
- play a role in tooth support
- guides cell migration

22. GROUND SUBSTANCE
 Fills the space between the fibers and cells
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
 cementicles

23. FUNCTIONS
• PHYSICAL
• FORMATIVE AND REMODELING
• NUTRITIVE
• SENSORY
• PDL HOMEOSTASIS

24. PHYSICAL
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

26. VISCOELASTIC THEORY

27. TRANSMISSION OF OCCLUSAL
FORCES TO BONE
 Arrangement is like suspension bridge or hammock.
 Axial force
 The oblique fibers alter their wavy pattern and attain full
length,sustain the major part of the axial force
 Horizontal force:
 Confines within pdl
 displacement
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.

28. 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

30. FORMATIVEAND REMODELING
 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.
Sodek (1977), Muhlemann; 1954)

31. NUTRITIVE
 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

32. SENSORY
 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)

33. BLOOD SUPPLY
Main blood supply
is from superior and
inferior alveolar
arteries. The blood
vessels are derived
from the following:

34. 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.

35. CLINICAL SIGNIFICANCE

36.  Replantation, transplantation
 Orthodontic tooth movement
 trauma from occlusion
 Regeneration

37. PICK UP THE ODD ONE OUT
 Cementum, bone, gingiva, pulp, periodontal ligament
 Apical fibers, horizontal fibers, circular fibers,oblique fi
 Fibroblast, osteoblast, osteoclast, ameloblast
 Physical, chemical, nutritive, sensory,

38. WHO AM I
 I am the largest group of fibers
 I resist extrusion of tooth
 I have 19 family members
 I connect cell and cell, cell and matrix
 I am present between mid third & apical third
of root