PDL

Upload By : Ahmed Ali Abbas

Babylon University College of Dentistry

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The Periodontal Ligament

By :Ahmed Ali Abbas

Periodontium:Is the investing and supporting attachment system of the

teeth. It consists of:

Two soft tissues Two hard tissues

1- Gingiva

2- Periodontal Ligament

1- Cementum

2- Alveolar Bone :

Definition: The periodontal

ligament is the dense fibrous

connective tissue that occupies

periodontal space between the

of the tooth and the alveolus.

Inflammation from the

dental pulp and gingiva

could spread to involve the

PDL and other apical

supporting tissues.

Width of the periodontal ligament ranges from 0.15-0.21 mm.The narrowest area is at the mid-root ( Fulcrum ). The region at thealveolar crest is the widest area followed by the apical region.

DentinBone

The width generally reduced in:• Non-functional teeth. • Un-erupted teeth.

While increased in:• Teeth subjected to an occlusal stress within the physiological limits .• Deciduous teeth

Dental follicle consists of1-Dense fibrous and cellulartissues immediatelyencapsulate the developingtooth

(Cementum)

2-Perifollicular mesenchyme

(PDL ,Alveolar bone)

DevelopmentOf PDL:

cells

Histological structureThe periodontal ligament is formed of :

Fibers,

Intercellular

substances

Synthetic

Resorptive

Progenitor

Defensive

ground substances

blood vessels,

nerves & lymphatics.

a) Gingival fibers.

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.

A- The principal fibers:They are formed of collagen bundles, which are wavy

in course and are arranged in three groups.

1- Dento-gingival fibers: extend from thecervical cementum into the gingiva.

2- Alveolo-gingival group: extends from thealveolar crest into the gingiva.

3- Circular group: a small group of fibers thatencircles the tooth and interlaces with theouter fibers.

4- Dento-periosteal fibers: they extendfrom the cementum directed over thebone crest and then incline apicallybetween the periosteum of the alveolarbone and the gingiva.

A- The principal fibers:a- The gingival fibers:

Alveolo-

gingival

Dento-

gingival

Dento-

periosteal

Circular

fibers

Alveolar

bone

Function of gingival fibers:They form a rigid cuff around the tooth that can add stability and resist gingival displacement.

*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.

*Function:

Resists mesial and distal

tooth separation.

b- The transseptal ligament:

Dentin

Dentin

Bone

1-Alveolar crest group:

radiate from the crest of the alveolar process and attach themselves to the cervical part of the cementum.

Function: resists vertical and

intrusive forces.

2-Horizontal group:

The fiber bundles run from the

cementum to the bone at right

angle to the long axis of the

tooth.

Function: resists horizontaland tipping forces.

c- The alveolodental ligament:

Bone Dentin

3- Oblique group: The fiber bundles run obliquely.

Their attachment in the bone issomewhat coronal (higher) than the attachment in the cementum.

The greatest number of fiber bundles are found in this group.

Function:*Performs the main supportof the tooth against masticatoryforces.*Resists vertical and intrusive

forces.

bone

dentin

4- Apical group:

The bundles radiate from the

apical region of the root to

the surrounding bone

Function: resists vertical

force.

5- Interradicular group:

The bundles radiate from the

interradicular septum to the

furcation of the multirooted

tooth.

Function: resists vertical and lateral forces.

dentin

bone

dentin

bone

They are 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.

B- Accessory fibers:

These are immature elastic (pre-elastic) fibers.

They need special stains to be demonstrated.

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

At the apical region they form a complex network.

2- Oxytalan fibers

The functions of oxytalan fibers:

1-Support nerves.

2- Support blood vessels.

3- Help fibroblasts migration.

Epithelial cells

remnants of the epithelial

root sheath of Hertwig

Synthetic

cells

Resorptive

cells

Progenitor

cells

Defensive

cells

fibroblasts, osteoblasts and cementoblasts.

cementoclasts , osteoclasts and fibroclasts.

Note that fibroblasts perform both synthetic and resorptive activities.

undifferentiated mesenchymal

cells

macrophage, lymphocytes

and mast cells

Fibroblasts

Cementoblasts

Osteoblasts

Synthetic Cells of PDL

PDL Fibroblasts

• Oriented parallel to collagen fibers•Are motile due to contractile properties•Show numerous microtubules & microfilaments

•Assembles procollagen molecules•Perform fibroclastic function•Ingestion collagen fibers•Contains intracellular collagen profiles& vacoules

•Contains lysosomal system

Cementoblasts Osteoblasts

Both are rich in alkaline phosphatase activity.

Resorptive Cells of PDL

• osteoclasts• cementoclastsBoth are rich in acid phosphataseactivity.

Progenitor cellsU. M. C.

• Can undergo mitotic devision

• Can differentiate to different types of cells

• Have small, closed-face nucleus

• Little amount of cytoplasm

• Found close to blood vessels

Defensive Cells of PDL

Macrophages

lymphocytes

Mast cells

Note: There are no plasma cells.

Epithelial Cells: remnants of the epithelialroot sheath of Hertwig.

•They are separated from the

surrounding connective tissue by a

basal lamina.

•They show low cells turnover,

although they may proliferate to

form cysts or tumors.

Interstitial tissues

*They are found between the

fibers of the periodontal

ligament.

*They are areas that

contain some of the blood

vessels, lymphatic and

nerves.

*They are surrounded

by loose connective tissue.

Interstitial tissues

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

Blood supply

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

2- Branches from the intra-alveolarvessels, these branches run

horizontally and these constitute the

main blood supply.

1- Branches from the gingival vessels.

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 foramina in the bone.

Nerve supply:

(mechanoreceptors)

Large nerve fibers

Small nerve fibers pain sensation

touch & pressure

Are responsible for

Are responsible for

•Stimulation of the mechanoreceptors initiates a reflex

jaw opening.

•This reflex is a protective mechanism to prevent forces

applied to the teeth from reaching damaging levels.

Function of PDL

1- Supportive: [Through the collagen fibers and the blood

vessels.

*Periodontal ligament permits the teeth to withstand the considerable forces of mastication.

*As the force is applied on the teeth, the wavy course of the collagen fibers gradually straightening out and then acting as inelastic strings.

*Also periodontal fibers being non elastic prevent the tooth from being moved too far.

Functions of the periodontal ligament:

*Blood vessels and all the components of the ligament act together as a hydraulic damper or shock absorber with the ground substance and the tissue fluid.

Dental implants lack periodontal ligament fibers

and they have a rigid connection to bone

(Osseointegration).

Periimplant tissues

Titanium implant

Sulcular epithelium

Juunctional epithelium

Connective tissue

Bone

The periodontal ligament having the mechanoreceptors

contributes to the sensation of touch and pressure on

the teeth.

2- Sensory:

sudden overloadproprioceptive reflex

inhibition of the activity

of the masticatory muscles

Opening the mouth

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.

3- Nutritive:

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.

5- Protective

b- The blood vessels:The capillaries form a rich network, they are

arranged in form of a coil and attached to bone and cementum through the oxytalan 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.

*The periodontal ligament through aging shows

Vasuclarity

Cellularity

Thickness *It may contain cementicles.

The Age Changes of periodontal ligament

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

They have nidus favoring the deposition of concentric layers of calcosphrite 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.