ByHesham Dameer

The periodontal ligament is the dense fibrous connective tissue that occupies the periodontal space between the root of the tooth and the alveolus.

cells

Fibers,

Extracellular substances

Synthetic Synthetic

Resorptive Resorptive

ProgenitorProgenitor

Defensive Defensive

ground substancesground substances

blood vessels, blood vessels,

nerves & lymphatics.nerves & lymphatics.

Synthetic Synthetic cellscells

Resorptive Resorptive cellscells

Progenitor Progenitor cellscells

fibroblasts, osteoblasts fibroblasts, osteoblasts cementoblastscementoblasts..

cementoclasts , osteoclasts cementoclasts , osteoclasts fibroclasts.fibroclasts.

undifferentiated mesenchymal undifferentiated mesenchymal cellscells

Defensive Defensive cellscells

macrophage, lymphocytes and macrophage, lymphocytes and mast cellsmast cells

epithelial cells epithelial cells remnants of the epithelialremnants of the epithelial root sheath of Hertwigroot sheath of Hertwig

The fibers of the periodontal ligament are mainly collagen .They are divided into:A) The principal fibers.B) The accessory fibers.C) The oxytalan ( elastic ) fibers.

Extracellular substances

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.

1- Dentogingival group : extend from the cervical cementum into the lamina propria of the gingival.

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 and then incline apically between the periosteum of the alveolar bone to the lamina propria of the gingiva.

They hold the marginal gingiva against the tooth . They provide the marginal gingiva with enough rigidity to withstand the forces of mastication without distorting .

Functions of the gingival fibers

*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.

Dentin

Dentin

Bone

1-Alveolar crest group:

radiate from the crest of the alveolar process and attach 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

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.

Immature elastic fibers. Run in axial or oblique direction. One end being embedded in cementum or

bone and the other end in the wall of b.v. 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.

Oxytalan FibersOxytalan Fibers

Some of the b.vs., lymphatics, and nerves of the PDL are surrounded by loose C.T. These areas have termed interstitial tissue.

Fibroblasts histiocytes, UMC, and lymphocytes are also found in interstitial tissue.

Biological significance: unknown.

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

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

2- Branches from the 2- Branches from the intra-intra-alveolaralveolar vessels, these vessels, these branches run horizontally branches run horizontally and these constitue the and these constitue the main blood supply.main blood supply.

1- Branches from the 1- Branches from the gingival gingival vessels.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 formatina in the bone.

mechanoreceptorsmechanoreceptorslarge fiberslarge fibers

Small fibersSmall fibers pain sensationpain sensation

touch & pressuretouch & pressure

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 of the collagen fibers gradually straightening out

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

The periodontal ligament having the mechanoreceptor contributes to the sensation of touch and pressure on the teeth.

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.

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 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.

c- The nerves:By its mechanoreceptors nerves.

*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 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.

Dr. Hesham Dameer