Periodontal

ligament

The periodontium

The periodontium includes:

The gingiva

Cementum

Periodontal ligament

Alveolar bone

Def: The periodontal

ligament is the

dense fibrous

connective tissue

that occupies the

periodontal space

between the root of

the tooth and the

alveolus.

The periodontal ligament characterized by:

1- The highest rate of turnover in the body.

2- Large volume of ground substance.

3- The presence of oxytalen fibers.

4- High cellularity.

Width of the periodontal ligament: It ranges from 0.15-0.21 mm.

The region at the alveolar crest is the widest followed by the (apical

region) and the narrowest area is at Fulcrum (midroot)

Dentin Bone

The space is reduced in

non-functional and

unerupted teeth,

while is increased in teeth

subjected to heavy occlusal

stress and in deciduous teeth

Development of periodontal ligament

•The periodontal ligament originates from the

progenitor cells of the dental sac surround the

enamel organ just after root formation.

•The innermost cells differentiate into

cementoblasts and lay down cementum.

•The outermost cells differentiate into

osteoblasts and lay down bone.

•The centrally located cells differentiate into

fibroblast that produce collagen fibers of the

P.L that their ends embedded inside the

cementum & bone .

1- Cells

3-Fibers,

2- Intercellular substances

Synthetic

Resorpative

Progenitor

Defensive

4- ground substances

5- blood vessels,

nerves & lymphatic.

Histological structure

The periodontal ligament is formed of:

Epithelial

epithelial cells

remnants of the epithelial

root sheath of Hertwig

The cells Synthetic

cells

Resorptive cells

Progenitor cells

Defensive cells

fibroblasts, osteoblasts ,cementoblasts.

cementoclasts , osteoclasts, fibroblasts.

undifferentiated mesenchymal cells (Stem Cells)

macrophage, lymphocytes and mast cells

- Epithelial rests of

Malassez:

**deeply stained

cuboidal cells

surrounded by basal

lamina.

** They may

proliferate to form

cysts or tumors.

II- The fibers

*The fibers of the periodontal ligament are mainly collagen.

They are divided into:

A) The principal fibers.

B) The accessory fibers.

C) The oxytalan fibers.

*Elastic fibers are restricted almost entirely to the

walls of blood vessels.

A- The principal fibers of periodontal ligament are

formed of collagen bundles, which are wavy in course

and are arranged mainly in three ligaments.

a) Gingival ligament.

b) Transseptal or interdental ligament.

c) Alveolodental ligament which is subdivided into the following five groups:

1- Alveolar crest group.

2- Horizontal group.

3- Oblique group.

4-Apical group.

5- Interradicular group.

1- The principal fibers: a- The gingival ligament:

1- Gingival fibers: extend from the cervical cementum into the lamina propria of the gingiva.

2- Alveologingival group: extends from

the alveolar crest into the lamina propria.

3- Circular group: a small group of

fibers that encircles the tooth and interlaces with the outer fibers & bone.

4- Dentoperiosteal fibers: they extend

from the cementum direct over the crest of the alveolar bone then inserted in periosteum of the labial surface of the alveolar bone.

Alveolo-gingival Dento-

gingival

Dento-periosteal

Circular fibers

Gingival fibers form a rigid cuff around the

tooth that can add stability.

b- The Transseptal fibers: *It connects two adjacent teeth

so it is called interdental group of fibers.

*The ligament runs from the cementum of one tooth over the crest of the alveolus to the cementum of the adjacent tooth.

* Responsible for the mesial shift of the teeth.

Dentin

Dentin

Bone

Transseptal Fibers

c- The alveolodental fibers:

1-Alveolar crest group:

radiate from the crest of the

alveolar process and attach

themselves to the cervical part

of the cementum.

2-Horizontal group:

The fiber bundles run from the

cementum to the bone at right

angle to the long axis of the

tooth.

Bone Dentin

3- Oblique group:

The fiber bundles run obliquely.

Their attachment in the bone is somewhat coronal than the attachment in the cementum.

It is the greatest number of fiber bundles found in this group.

They perform the main support of the tooth against masticatory force.

bone

dentin

4- Apical group:

The bundles radiate from the

apical region of the root to

the surrounding bone.

5- Interradicular group:

The bundles radiate from the

interradicular septum to the

furcation of the multirooted

tooth.

dentin

bone

dentin

bone

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B- Accessory fibers:

It is collagenous in nature and

run from bone to cementum

in different planes, more

tangentially to prevent

rotation of the tooth and

found in the region of the

horizontal group.

C- Oxytalan fibers

These are immature elastic (pre-elastic) fibers.

They need special stains to be demonstrated.

They tend to run in an axial direction, one end being embedded in bone or cementum and the other in the wall of blood vessels.

The function of the oxytalan fibers has been

suggested that they play a part in supporting the

blood vessels of the periodontal ligament during

mastication i.e., it prevents the sudden closure of the

blood vessels under masticatory forces.

Interstitial tissue

It is found between the fibers

of the periodontal ligament.

They are areas containing

some of the blood vessels,

lymphatics and nervs and

surrounded by loose

connective tissue.

Blood supply

The arterial blood supply of the periodontal ligament is derived from 3 sources:

3- Branches from the apical vessels that supply the dental pulp.

2- Branches from the intra-alveolar

vessels, these branches run horizontally

and these constitutes the main blood

supply.

1- Branches from the gingival vessels.

Nerve supply: The nerve supply of periodontal ligament comes from

either the inferior or superior dental nerves. 1- Bundles of nerve fibers run from the apical region of the

root towards the gingival margin. 2- Nerves enter the ligament horizontally through multiple

formatina in the bone.

mechanoreceptors

large fibers

Small fibers pain sensation

touch & pressure

Functions of the periodontal ligament:

1- Supportive: *periodontal ligament permits the teeth to withstand the

considerable forces of mastication.

*As the force is applied on the teeth, the wavy course

collagen fibers are transmitting tension to the wall of the

alveolus instead of pressure.

*Also periodontal fibers being non elastic to prevent the

tooth from being moved too far.

2- Sensory:

• The periodontal ligament having the

mechanoreceptor contributes to the

sensation of touch and pressure on the

teeth.

sudden overload proprioceptive reflex inhibition of the activity

of the masticatory muscles

Opening the mouth

3- Nutritive:

The blood vessels in the periodontal ligament provide nutrient supply required by the cells of the ligament and to the cementocytes and the most superficial osteocytes.

4- Formative: The fibroblasts are responsible for the formation of new

periodontal ligament fibers and dissolution of the old fibers

Cementoblasts and osteoblasts are essential in building up cementum and bone.

5- Protective:

The protective function of the periodontal ligament is achieved by:

a- The principal fibers.

b- The blood vessels.

c- The nerves.

a- The principal fibers:

The arrangement of the fiber bundles in the different groups is well adapted to fulfill the functions of the periodontal ligament.

The alveolodental ligament transforms the masticatory pressure exerted on the tooth into tension or traction on the cementum and bone.

If the exerted force on a tooth is transmitted as pressure this will lead to differentiation of osteoclasts in the pressure area and resorption of bone.

b- The blood vessels:

The capillaries form a rich network, they are arranged in the form of a coil and attached to bone and cementum through the oxytalen fibers.

This arrangement makes it possible when pressure is exerted on the tooth, the blood does not escape immediately from the capillaries and thus buffering the pressure action before it reaches the bone.

The behavior of the blood in the capillaries may be simulated to a hydraulic brake.

c- The nerves:

By its mechanoreceptors nerves.

Age Changes of periodontal ligament

The periodontal ligament through aging shows

• Vascularity

• Cellularity

• Thickness

*It may contain cementicles.

The cementicles appear near the surface of cementum may be free , attached or embedded in the cementum.

They have nidus favoring the deposition of concentric layers of calcospherite as degenerated cells, area of hemorrhage and epithelial rest's of Malassez.

Cementicles are usually seen in periodontal ligament by aging but in some cases they may be seen in a younger person after local trauma.

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