Periodontal ligament

 Periodontium : “peri” - “odont”
 In greek, Peri means Around & Odont means
tooth
 The PERIODONTIUM is a connective
tissue organ, covered by epithelium that
attaches the teeth to the bone of the
jaws and provides a continually adapting
apparatus for support of the teeth.

Periodontium
It consists of:
Two Hard tissues Two soft tissues
1. Cementum
2. Alveolar bone
1. Gingiva
2. Periodontal ligament

It is that soft, specialized CT situated between the cementum covering
the root of the tooth and bone forming the socket wall.
(A.R.Tencate 1971)
Periodontal ligament is the soft, richly vascular and cellular connective
tissue which surrounds the roots of the teeth and joins the root
cementum with the socket wall. (Jan Lindhe Clinical
Periodontology and Implant Dentistry , 6th ed)
The periodontal ligament occupies the periodontal space, which is located between the
cementum and the periodontal surface of alveolar bone and extends coronally to the
most apical part of the lamina propria of the gingiva. (Orban’s 12th Edition)
Periodontal membrane, Alveolo-dental ligament, Desmodont ,
Pericementum,Dental periosteum Gomphosis
Different names of PDL :
The periodontal ligament is composed of a complex vascular and highly cellular
connective tissue that surrounds the tooth root and connects it to the inner wall of
the socket. (Carranza’s Clinical Periodontology 12th Edition)

In the coronal direction it is continuous with
lamina propria of gingiva & is demarcated
by the alveolar crest fibers.
At the root apex it merges with the dental pulp.
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.
 Depending on age
11-16 yrs - 0.21mm
32-52 yrs - 0.18mm
51-67 yrs - 0.15mm
 According to functional state of the tissues
Time of eruption - 0.1- 0.5mm
At function - 0.2-0.35mm
Hypo function - 0.1-0.15mm

 Thin radiolucent line interposed between the
root & lamina dura.
 Occlusal Trauma → widened PDL space or
funneling of coronal aspect of PDL space.
 It can also widened in case of vertical
fractures & progressive systemic sclerosis
(Scleroderma).

 Begins with root formation
(Tencate et al.,1972)
& prior to tooth eruption.
 The periodontal tissues are derived from dental
follicle which in turn originates from dental papilla.

As the root formation continues, cells in
the peri follicular mesenchyme gain their
polarity, cellular volume &become
widely separated
Actively synthesize & deposit collagen
fibrils in developing PDL
(Grant’s 1989; Ten Cate’s 1971)
Type I collagen is secreted
Assembles as collagen bundles on
the bone and cementum surface
Establish continuity across the
ligament space

 Terminal portions of principal fibers that insert into
cementum and bone are termed as Sharpey’s fibers.
 The principal fibers embedded in the cementum
have a small diameter but are more numerous than
those embedded in the alveolar bone proper.
 In addition to these fiber types, small collagen
fibers associated with larger principal fibers have
been called as “Indifferent fiber plexus of
Shefforfold”

Periodontal
Ligament
Periodontal
Fibres
Cellular
Elements
Ground
Substance

PRINCIPAL FIBRES
 The most important elements of PDL are the principal
fibers which are collagenous and follow a wavy pattern
when viewed in longitudinal section.
 They are associated with abundant non collagenous
proteins typically found in bone and cementum like
osteopontin and bone sialoprotein.
 They are thought to contribute to the regulation of
mineralization and to tissue cohesion at sites of
increased biomechanical strain. (Mc Kee MD, Zalzal S,
Nanci A 1996)

 Collagen is synthesized by fibroblasts,
chondroblasts, osteoblasts, odontoblasts.
 Made up of 3 polypeptide chains
 Has a repeating gly-X-Y amino acid sequence in
which X and Y are usually amino acid other than
glycine.
 Contain 2 unique amino acid hydroxy proline and
hydroxy lysine along with glycine & proline
(Carneiro J, Fava de Moraes F , 1955)

Tropocollagen Microfibril Fibril

 The ligament fibers and Sharpey’s fibers are
composed of interstitial collagen type III and I
 Type IV is found in the Basal Lamina
 Collagen V : found in the spaces between the
fiber bundles.
 Type VI - microfibrillar component associated
with oxytalan fiber system.
 Type XII contribute to the construction of 3-
dimensional fibril arrangement- hence closely
associated with regeneration of PDL and also seen
during tooth development

 Trans septal
 Alveolar crest group
 Horizontal
 Oblique
 Apical
 Inter – radicular

 Extend Inter proximally over the alveolar
bone crest and are embedded in the
cementum of adjacent tooth.
 Are a remarkably constant finding and are
reconstructed even after destruction of the
alveolar bone has occurred in periodontal
disease.
 Considered as belonging to the gingiva
because they do not have osseous
attachment.

 Extend obliquely from the cementum just
beneath the junctional epithelium to the
alveolar crest.
 Functions –
1. Prevent extrusion of tooth (Carranza, 1956)
2. Resist lateral tooth movement

HORIZONTAL GROUP (10-15%)
 Extend at right angles to the long axis of tooth
from cementum to the alveolar bone.
OBLIQUE GROUP (80-85%)
 Largest group in the PDL. Extend from the
cementum in a coronal directing obliquely to the
bone.
 Function - Bear the brunt of vertical masticatory
stresses and transform them into tension on the
alveolar bone.

APICAL GROUP
 Radiate in a rather irregular fashion from the
cementum to the bone at the apical region of
the socket .
 Do not occur on incompletely formed roots.
 Resist forces of luxation, may prevent tooth
tipping and protect the delicate blood vessels,
nerves and lymphs at the apex.
INTER RADICULAR FIBERS
 Fan out from cementum to the tooth in the
furcation areas of multi rooted teeth.
 Other well formed fiber bundles inter digitate
at right angles or splay around.

 The terminal portion of principal fibers of
periodontal ligament, that are inserted into
cementum, on one side and alveolar bone, on the
other are called Sharpey’s fibers.
 The number and size of sharpey’s fibers varies
with functional status of the tooth.
 Calcification of Sharpey’s Fibre are related to the
non collagenous protein: Osteopontin & Bone
Sialoprotein

• A distinctly different zone
previously thought to be the junction
of PDL fibres from alveolar bone and
cementum.
• Previous Concept: Zone with
increased metabolic activity
• Current Concept: Fibres branching
and inter joining with each other
•Entire fibre metabolically active,
not just the mid portion
•Observed only in Longitudinal
Sections, not in cross sections

 Three histochemically and structurally
different fibres
 Elastin – Mature Fiber. High percentage of
Glycine, Proline & Hydroxyproline residues.
Observed in the walls of the afferent blood
vessels.
 Elaunin – Immanture Fibre. Found within the
fibres of gingival ligament
 Oxytalan- Immature elastic fibre. Oriented in
axial direction.
 Function : Load bearing, supporting blood vessels

 Reticular Fibre : Fine, immature collagen
fibres with argyrophillic staining
properties, related to basement
membranes of blood vessels and epithelial
cells within the PDL.
 Secondary Fibres: Newly formed collagen
fibre, relatively non directional and
randomly oriented among the principal
fibres.
 Indifferent Fibre Plexus: Small collagen
fibres associated with large collagen fibres
that run in all directions, forming a plexus
called Indifferent fibre plexus.

 Ground Substance: Gel like matrix, in
which the cellular matrix and fibrous
components such as collagen are
embedded.
 Berkovitz et al estimated that the ground
substance occupy 65% of the volume in the
PDL.
 GAGs, Glycoproteins, Proteoglycans,
Hyaluronate
 Substrate adhesion molecules- Tenascin,
Osteonectin, Undulin, Fibronectin,
Laminin.
 Function: Transport of metabolites,
Support

Cellular Elements
•Synthetic
•Resorptive
•Progenitor
•Epithelial cell rests of
Malassez
Extracellular
Substance
•Fibres ( Collagen,
Elasic, Reticular,
Secondary Fibres,
Indifferent fibre plexus,
Oxytalan
•Ground
Substance(Proteoglycan,
Glycoprotein)
Structures present
in Connective tissue
•Blood veseels
•Nerves
•Lymphatics
•Cementicles

 CELLULAR ELEMENTS
Synthetic Resorptive
-Fibroblasts - Fibroblasts
-Cementoblasts - Cementoclasts
-Osteoblasts - Osteoclasts
- Progenitor cells
- Epithelial cell rests of Malassez
- Defense cells – Mast cells, Macrophages , Eosinophils

Fibroblasts
Cementoblasts
Osteoblasts

Basic properties
 Increased transcription of RNA and production
of ribosomes which is reflected by a large
open faced or vesicular nucleus containing
prominent nucleoli.
 Development of large quantities of RER
covered by ribosomes.
 Large amounts of golgi saccules and vesicles
(seen as clear unstained areas in light
microscope).
 Large numbers of mitochondria.
 Abundant cytoplasm.

 Most common cells in PDL
 Appear as ovoid or elongated cells oriented
along the principal fibers, exhibiting
pseudopodia like processes.
 Phenotypically distinct & functionally different
sub populations of fibroblasts exist in adult PDL.
 The PDL fibroblasts are large cells with an
extensive cytoplasm containing in abundance, all
organelles associated with protein synthesis and
secretion.
 Importantly in inflammatory situations, an
increased expression of MMP occurs that
aggressively destroys collagen.

 Although technically situated within the PDL,
bone and cementum cells are properly
associated with the hard tissues they form.
 Osteoblasts line the bone surface of the
ligament and may be either functional or resting,
depending on the functional state of the
ligament.
 Cementoblasts are responsible for formation of
cellular cementum.

 Fibroblasts :
- Exhibit lysosomes that contain
fragments of collagen that appears to be
undergoing digestion.
- Dual action
 Osteoclasts & Cementoclasts:
- Osteoclast cells resorb bone and tend
to be large and multinucleated.
- Cementoclasts resemble osteoclasts
and are occasionally found in normal
functioning PDL.

 Mallassez – 1884
 Remnants of HERS and are formed close to cementum
 Most numerous in the apical area & cervical area.
(Xiong J, Gronthos S, Bartold PM )
 Form a lattice work and appear as either isolated
cluster of cells or interlacing strands. They diminish in
number with age and may undergo calcification to
form cementicles.

Fig. shows the presence of clusters of epithelial cells (ER) in the
periodontal ligament. These cells, called the epithelial cell rests of
Mallassez, represent remnants of the Hertwig's epithelial root sheath. The
epithelial cell rests are situated in the periodontal ligament at a distance of
15-75 μm from the cementum (C) on the root surface. A group of such
epithelial cell rests is seen in a higher magnification.

 Calcified masses, adherent to or
detached from the root surfaces
(O.J. Mikola, Wm.H. Bauer,1949)
 Represent dystrophic
calcification (example of
regressive or degenerative
change)
 Develop from: calcified epithelial
rests, calcified Sharpey’s fibers,
Calcified, thrombosed vessels
within the PDL, around small
spicules of cementum or alveolar
bone traumatically displaced into
the PDL

 Periodontal ligament stem cells were first
isolated in 2004. They are capable of developing
into adipocytes, osteoblasts & cementoblasts
like cells in vitro. As well as producing
cementum like and periodontal ligament like
tissues in vivo.
 Recent studies have also shown their ability to
differentiate into neuronal precursors
 PDL stem cells expresses an array of
cementoblasts and osteoblast markers as well as
STRO 1, CD146 Antigens, which are found in
Dental Pulp Stem Cells and Bone marrow
mesenchymal stem cells.

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

 Ascribes the principal fibers of PDL the major
responsibility in supporting the tooth and transmitting
the forces to the bone.
Force is applied to the tooth
Principal fibers first unfold and straighten
Transmit force to the alveolar bone causing elastic
deformation of the socket.
When alveolar bone has reached its limit, the force is
transferred to underlying basal bone
 Many investigators find this theory insufficient to
explain available experimental evidence.

 According to this, the displacement of tooth is largely
controlled by fluid movement, with fibers having only
secondary role (Bien SM, 1966 and Birn H, 1966)
Force applied on tooth
Extra-cellular fluid from PDL escapes to marrow spaces
Depletion of fluid, Fibers absorb slack and tighten
Blood vessels stenosis
Arterial back pressure created
Ballooning of vessels
Passage of blood ultra filtrates
Lost fluid replenished

 Arrangement is like suspension bridge or
hammock.
 The oblique fibers alter their wavy pattern
and sustain the major part of the axial force
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.

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

 The apical portion of the root moves in a
direction opposite to the coronal portion.
 Areas of tension→ Principal fiber bundles are
taut rather than wavy.
 Areas of pressure→ fibers are compressed,
the tooth is displaced & a corresponding
distortion of bone exists in a direction of
root movement (Picton DC, 1967)

 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.

 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

 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)

 Inferior & superior
alveolar arteries to the
mandible & maxilla -
reaches the PDL from 3
sources:
1. Apical vessels (Dental
artery)
2. Transalveolar vessels
(rami perforantes-
penetrating vessels
from alveolar bone)
3. Intraseptal vessels
(anastomosing vessels
from the gingiva)

 Branches of the
intraseptal vessels –
perforate the lamina
dura & enter the
ligament.
 After entering the PDL,
perforating rami
anastomose & form a
polyhedral network
which surrounds the root
like a stocking.

 Perforating channels are more abundant in
the maxilla than in the mandible, & more in
the posterior than in the anterior teeth.
 This dual supply allows the ligament to
survive following removal of the root apex
during certain endodontic procedures
 Arteriole in PDL – diameter – 15 to 50 µm.

 The nerve follow
almost the same
course as the blood
vessels.

 Accompany the arterial supply.
 Venules receive the blood through the
abundant capillary network. Also, arterio-
venous anastomosis bypass the capillaries;
these are seen most frequently in the apical
& inter-radicular regions, & there
significance is unknown.
 They are somewhat larger in diameter – 28
µm (mean).

 Lymph vessels - originate as cul-de-sac in PDL
 course apically - pass through the fundus of
the socket or they may pass through the
cribriform plate to empty into larger
channels pursuing intraosseous paths.

 The cell number and cell activity decreases
with aging.
 One of the prominent changes seen in the
calcified tissues of periodontium , the bone
and the cementum is scalloping and the PDL
fibers are attached to the peaks of these
scallops than over the entire surface as seen in
a younger periodontium.
 This remarkable changes affect the supporting
structures of the teeth.

 With aging the activity of the PDL tissue
decreases because of restricted diets and
therefore normal functional stimulation of
the tissue is diminished
 Any loss of gingival height and periodontal
disease promotes destructive changes in the
PDL

 The primary role of the periodontal socket is to
support the tooth in the bony socket .
 Its thickness varies in different individuals in
different teeth in the same person and in
different locations on the same tooth .
 Acute trauma to the periodontal ligament,
accidental blows or rapid mechanical
destruction may produce pathologic changes
such as fractures or resorption of the
cementum tears of fiber bundles , hemorrhage
and necrosis .

 The adjacent alveolar bone is resorbed the PDL is
widened and tooth becomes loose .When trauma is
eliminated repair usually takes place.
 Orthodontic tooth movement depends on
resorption and formation of tooth bone and
periodontal ligament .
 These activities can be stimulated by properly
regulated pressure and tension.
 If the movement of teeth is within phsysiologic
limits the initial compression of PDL on the
pressure side is compensated for by bone
resorption whereas on the tension side bone
apposition is seen.

 Application of large forces results in necrosis of
PDL and alveolar bone on the pressure side and
movement of the tooth will occur after the
necrotic bone has been resorbed by osteoclasts
located on its endosteal surface.
 Inflammatory diseases of the pulp progress to
the apical periodontal ligament and replace its
fiber bundles with granulation tissue .
 This lesion is called a periapical granuloma may
contain epithelial cells that undergo
proliferation and produce a cyst .

 Chronic inflammatory disease is common
pathology related to PDL .
 The toxins released from the bacteria in the
dental plaque and metabolites of the host’s
defense mechanism destroy the PDL and the
adjacent bone very frequently .
 This leads to tooth mobility and further loss of
tooth.
 To repair the existing destruction of PDL can be
quite challenging .
 It involves limiting the disease process and to
regenerate the host tissues to their original form
in such a way that reattachment of PDL to bone
becomes possible

 Various surgical techniques like Guided Tissue
regeneration are being used for correction of
Periodontal destruction .
 Important cells responsible for periodontal
regeneration are derived from PDL.

 Fusion of alveolar bone and cementum with
obliteration of the periodontal ligament is
termed Ankylosis.
 Occurs in teeth with cemental resorption
which suggests that it may represent a form
of abnormal repair.
 May also develop after chronic periapical
inflammation , tooth implantation and
occlusal trauma and around embedded teeth.
 Clinically ankylosed tooth sounds DULL or
WOODY on percussion.
 Before extraction such tooth require X-ray
to facilitate surgical extraction.

 important clinical consequences
 No resilient connection exists between teeth & jaw
bone - any occlusal disharmony - repercussions at
the bone-to-implant interface.
 No intrusion or migration of teeth can compensate
for the eventual presence of a premature contact.
 Because the principal proprioception of the natural
dentition comes from the pdl, its absence in
implants reduces tactile sensitivity & reflex
function.

 To have any chance of success , it is essential to
maintain the viability of PDL .
 Avoid dehydration of PDL.
 Avoid loss of viability of its cell rests.
Transplantation
 Best results when unerupted tooth with partially
formed roots as there is less damage to PDL.

 Nishimura et al, 1998 - PDL cells - susceptible to
hyper & hypoglycemia & effects - mediated via
the integrin system.
 Hyperglycemia – increased expression of
fibronectin receptor → results in reduced cellular
adhesion & motility → probable tissue
impairment.
 Hypoglycemia – decreased expression of
fibronectin receptor → lowers the viability &
ultimately results in cell death & hence tissue
impairment

 Carranza’s Clinical Periodontology, 12th Edition
 Clinical Periodontology and Implantology by Jan
Lindhe, 6th edition
 Oral Histology and Embryology by Orban, 11th
edition
 Tencate oral histology, 5th edition
 Fundamentals of Periodontics, 2nd Edition, by
Thomas G. Wilson, Kennath S. Kornman
 Hassel TM. Tissues and cells of periodontium.
Periodontol 2000, Vol. 3, 1993, 9-38.
 The Periodontium - Hubert E Schroeder

 Bartold PM, Walsh LJ, Sampath Narayan A.
Molecular and cell biology of gingiva.
Periodontol 2000, Vol. 24, 2000, 28–55.
 Cho MI, Garant PR. Development and
general structure of the periodontium,
Periodontol 2000, Vol. 24, 2000, 9–27.
 Ertsenc W, Mcculloc HG , Sodek HJ. The
periodontal ligament: a unique,
multifunctional connective tissue.
Periodontol 2000. Vol. 13, 1997, 20-40.
 Wright JM. Reactive, dysplastic and
neoplastic conditions of periodontal
ligament origin. Periodontol 2000, Vol. 21,
1999, 7-15.

 Xiong J, Gronthos S, Bartold PM. Role of the
epithelial cell rests of Malassez in the
development, maintenance and regeneration
of periodontal ligament tissues. Periodontol
2000, Vol. 63, 2013, 217–233.
 Bosshardt DD, Selvig KA.Dental cementum:
the dynamic tissue covering of the root.
Periodontol 2000 1997;13:41-75.

Periodontal ligament

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