Periodontal Ligament

Lec:10 ‫غادة موسى‬.‫د‬

The periodontium is the specialized tissues that both surround and

support the teeth, maintaining them in maxillary and mandibular bones. It
provides the support necessary to maintain teeth in function. It consists of
four principal components, namely
Gingiva ,Cementum, Periodontal ligament, Alveolar bone, 

Periodontal ligament (PDL):is a soft,fibrous specialized connective

tissue contain cellular, extracellular matrix,occupies the periodontal space
, which is located between the cementum and alveolar bone, coronally
extends to the lamina propria of the gingiva.
The PDL width :- ranges from 0.15 - 0.38mm, with its thinnest portion
around the middle third of the root.
Development:- It develops from dental follicles ,which consisted of
mesenchymal cells surrounds the developing enamel organ and dental
papilla. The cells that surround the dental follicle are called
perifollicular cells.

Follicular cells differentiate to:

Cementoblasts cells--------cementum
Osteoblasts cells--------alveolar bone
Fibroblasts cells--------collagen fiber and matrix of PDL .

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The PDL is a connective tissue supporting the teeth in their sockets and
also permitting them to withstand the considerable forces of mastication,
it has the important function ,in addition to attaching teeth to bone acting
as a sensory receptor for proper positioning of the jaws during normal
function.
Structures of PDL:-
*Cells divided into:
1-Synthetic cells [Cementoblasts, Osteoblasts, Fibroblasts]
A-These cells synthesis protein for secretion, and have large nucleus.
B-Have large quantites of Rough Endoplasmic Reticulum
C-Have large numbers of mitochondria

- Cementoblasts : lie on the surface of cementum

-Osteoblasts : on surface of alveolar bone
-Fibroblasts: lie in the body of PDL
-These cells synthesis collagen and ground substance and secrete protein.
2-Resorptive cells [Cementoclasts, Osteoclasts, Fibroblasts].

-Osteoclasts: Resorb bone, they are large multinucleated, develop from

fusion of circulatory monocytes, and have eosinophilic cytoplasm,
occupy bays in bone [Howship`s lacune]
-Cementoclasts: Resemble to osteoclast occasionally found in normal
functioning PDL.
-Fibroblast: mononuclear they resorb collagen fibril under physiological
conditions, fibroblast cells capable of both synthesis and resorption.

3-Progenitor cells: Undifferentiated connective tissue cells, retaining

capacity to divide to(differentiated to) above cells. (synthetic
cells).Production of new cells must be balanced by migration of cells out
of the ligament or cell death.

4-Epithelial rests of Malassez:

Remnant of epithelial R.sheath found close to cementum, as network or
strands, near and parallel to tooth surface, they proliferate under
pathogenic conditions and produce cysts and tumors in the jaw.
5-Mast cells and Macrophages (Defence cells)

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 Extra cellular substance:-
The extra cellular substance of periodontal ligament comprises the
following:

Fibers Ground substance

collagen proteoglycans
Elastic glycoprotein
* Collagen fibers: Predominantly type I & III and XII ,with individual
fibrils of PDL arrange in form of bundles having clear orientation relative
to P.D. spaces and these are termed [[principal fibers]]
1-The principal fibers of PDL are arranged in 3 particular groups:
a-Dentoalveolar groups:-
1-Alveolar crest group:
The fiber bundles radiate from crest of alveolar process attach to cervical
part of cementum.These fibers resist the various forces like tilting ,
vertical , intrusive and rotational forces.

2-Horizontal group:
Run at right angle to long axis of the tooth from cementum to the bone.
The fibers of this group resist the horizontal and tipping forces
.
3-Oblique group:
Run obliquely from cementum to the bone, are most numerous and
constitute the main attachment of tooth. The fibers of this group resist the
vertical and intrusive forces.

4-Apical group:
Bundles are irregularly arranged and radiate from apical region of root to
surrounding bone. These fibers resist the vertical force, prevent tipping
movement and protect the blood vessels, lymph and nerves.

5-Interradicular group:
From the furcation area of muli rooted teeth to the crest of interradicular
septum, the fibers of this group resist the resists vertical and lateral
forces and tipping forces.

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b-Gingival groups:- Other groups of collagen fs. are associated with
maintaining the functional integrity of the periodontium. These groups
are in the lamina propria of the gingiva, these five groups:
1-Dentogingival group2-Alveogingival group 3-circular group
4-Dentoperioosteal group
C-Transseptal fiber system: It connects two adjacent teeth.
*The ligament runs from the cementum of one tooth over the crest of the
alveolus to the cementum of the adjacent tooth

)
-Collagen fibers are embedded into Cementum. on one side of PDL and
into alveolar bone on the other, the embedded fibers are termed
)sharpey's fibers)
-The principal fibers run in a wavy course from cementum to bone, as
fibers arising from cementum and bone are joined in the mid-region of

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P.D. space giving rise to a zone of distinct appearance, it is so-called
((intermediate plexus)) it provides a site for rapid remodeling of fibers
occurs.
2- Accessory fiber: They are collagenous in nature and run from bone
to cementum in different planes, to prevent rotation of the tooth and
found in the region of the horizontal group
3--Elastic Fibers
The three types of elastic fibers are elastin ,oxytalan ,and elaunin. Only
oxytalan fibers are present within the PDL however, elaunin fibers also
may be found within fibers of the gingival ligaments.
*Oxytalan fibers:
Immature elastic fibers ,are bundles of microfibrils ,
The orientation of oxytalan fs. is an axial direction, one end being
embedded in cementum or possibly bone, other in the wall of blood
vessels (B.Vs)(arteries, veins and lymphatic),and with neural elements
also.
Functions: Play role in supporting B.Vs., they are thought to regulate
vascular flow in relation to tooth function

-Ground substance:-
The space between cells, fibers, blood vessels, and nerves in P.D. space is
occupied by ground substance, Ground substance is made up of 2 major
groups of substances (proteoglycans and glycoproteins) & water, also a
particular glycoproteins, (fibronectin), occurs in filamentous form in
PDL
-Interstitial tissue or space:-
Spaces between fibers bundles occupies by nerves, blood vessels,
lymphatic are surrounded by loose C.T. and these areas have been termed
interstitial tissue.

1. Dentin.
2. Mental dentin.
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3. Cementum.
4. Periodontal ligament.
5. Interstitial tissue.
6. Bundle bone.
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4

2 3

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Blood vesselsVs. : The arterial vs. of PDL, are derived from 3 sources:-
A- From apical vessels (vs.) that supply pulp.

B-From intra-alveolar vs. run horizontally penetrating the alveolar bone

to enter PDL

C-From gingival vessels : enter PDL from coronal direction.

*Arterioles and capillaries of microcirculation ramify in PDL forming
rich network is more evident in the side of bone than that adjacent to
cementum.
*There is a rich vascular plexus at apex and in the cervical part of
ligament.
-Lymphatics: Following the path of (B.Vs.), the flow from the ligament
toward and into the adjacent alveolar bone.

-Nerves :On the basis of function, nerve fibers of PDL are of the
following types.
A. Sensory fibers: Sensory are related with touch, pain, pressure and
proprioceptive sensation.,
B. Autonomic fibers: Are related with vessels of PDL .
The nerve fibers are sympathetic associated with BVs ,no evidence of a
parasympathetic supply.
The nerve fibers are either of large diameter and myelinated or small
(myelianted or not), the small end in fine branches through out the
ligament ,the large fibers in variety of endings ,for example knobe like
,spindle like ,meissner like.
Large diameter fibers concerned with pressure ,small-diameter with pain
-Cementicles: Calcified bodies found in PDL in older people fused into
large calcified masses or may be joined with cementum.(free, attached or
embeded cementicles),origin of cementicles from remnants of epith. Cells
.
Functions of PDL:-
1-Supportive: Possibly the most important function of the PDL is 
support of the teeth.
Failure of this function results in tooth loss .Every time the teeth are
clenched, as in mastication, the periodontal fibers are stretched and then
relaxed. This system is highly efficient to compensate for the thousands
of times this ligament is called into action.
2-Sensory: The PDL is supplied with abundant receptors and nerves that
sense any movement in function. Through this sensation protection the
supporting structures of tooth and the substance of crown from hard
object present in soft food

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3-Nutritive: The B.Vs. of ligament provide the essential nutrients for the
ligaments vitality and the hard tissue of cementum and alveolar bone. All
cells of PDL require nutrition which is carried by B.Vs. to the ligament.
B.Vs. also remove catabolites.

4-Homeostatic: Cells of PDL have capacity to resorb and synthesize

extra cellular substance of C.T. of PDL , alveolar bone and cementum.
Alveolar bone resorbed & replaced (i.e. remodeled), collagen of PDL is{
turn over} at a rate faster of all C.Ts. in the body
-If the balance between synthesis & resorption is disturbed, the quality of
tissues will be changed
.
Aging of the PDL :-

1-Decrease in cell number & cell activity.

2-The fiber bundles of the ligament are decreased in number.
3-Activity of the supporting structures of the teeth is decrease because of
restricted diets, so normal function is diminished.
4-Diseases of PDL increase with aging, gingival recession and chronic
periodontal diseases cause destruction of PDL .Due to reduced or non
functioning of some teeth PDL become weaker.
5-Cementicles are generally found in old age.