Cementum Periodontal Ligament Alveolar bone Gingiva facing the tooth

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

Different names: Desmodont, Gomphosis, Pericementum, Dental –periosteum, Alveolodental ligament, Periodontal

membrane .

PDLdevelopment:begins after separation of Hirtwigs epithelial root sheath.Differentiation of cells of perifollicular mesenchyme

Ranges in thickness between 0.15 and 0.38 mm and is thinnest in the middle portion of the root

The width decreases with age

Tissue with high turnover rate

Contains fibers, cells and intercellular substance

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 remnants of the epithelialepithelial

root sheath of root sheath of HertwigHertwig

The fibers of the periodontal ligament are mainly collagen .They are divided into:A) The principal fibers.B) The accessory fibers.C) The oxytalan ( immature 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 other fibers.4- Dentoperiosteal fibers: they extend from the cementum direct over the crest and then incline apically between the lamina

propria of the gingiva to periosteum of the alveolar bone .

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

Maintain proper relationship of teeth during mesial drift.

Cause postretention relapse of orthodontically positioned tooth.

1-Alveolar crest fibers: radiate from the crest of

the alveolar process and attach to the cervical part of the cementum.

2-Horizontal fibers: The fiber bundles run from the

cementum to the bone at right angle to the long axis of the tooth. Avoid intrusive movement and tipping

Bone Dentin

3- Oblique fibers: 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 intrusive movement by masticatory force.

bone

dentin

4- Apical fibers: The bundles radiate from the

apical region of the root to the surrounding bone.Avoid vertical movements.

5- Interradicular fibers: The bundles radiate from the

interradicular septum to the furcation of the multirooted tooth. Avoid vertical and lateral movements.

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 arteriols.arteriols.

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.

mechanoreceptorsmechanoreceptorslarge nerve f.large nerve f.

Small nerve f.Small nerve f. pain sensationpain sensation

touch & pressuretouch & pressure

Free nerve ending-along the root length Ruffinis corpuscles-around root apex Coiled form-at mid region Spindle like ending-at root apex

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 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.

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.

If the movement of teeth isn't within phsysiologic limits bone is resorbed ,the PDL is widened and tooth becomes loose .When trauma is eliminated repair usually takes place.

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 .

Dr. fatma ibrahim