The periodontal Ligament

Periodontium:Is the investing and supporting attachment system of the teeth. It consists of:

Two soft tissues Two hard tissues

1 -Gingiva That part covers the neck of the tooth and part of the alveolar bone.

2 -Periodontal Ligament Strong ligament that attaches

the tooth to the alveolar bone

1 -Cementum

covers the anatomical root

2 -Alveolar Bone The bone of the jaw that surrounds the root of the tooth

Definition: The periodontal Definition: The periodontal ligament is the ligament is the dense dense fibrous connective tissuefibrous connective tissue that occupies the that occupies the periodontal space between periodontal space between the root of the tooth and the root of the tooth and the alveolus.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:It ranges from 0.15-0.21 mm.The narrowest area is at the mid-root ( Fulcrum ). The region at the alveolar crest is the widest area followed by the apical region.

Dentin

Bone

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

The periodontal ligament The periodontal ligament resembles immature, fetal-like resembles immature, fetal-like connective tissues in the connective tissues in the following features:following features:

1- High rate of turnover.1- High rate of turnover.

2- Large volume of ground substance.2- Large volume of ground substance.

3- The presence of oxytalan fibers.3- The presence of oxytalan fibers.

4- High cellularity.4- High cellularity.

5- Similar biomechanical propereties.5- Similar biomechanical propereties.

Knocked out toothKnocked out tooth

A tooth that is replaced within half an hour has a A tooth that is replaced within half an hour has a 90% chance of successful re-implantation.90% chance of successful re-implantation.

The The length of time before a tooth is reimplanted length of time before a tooth is reimplanted (within half an hour) and (within half an hour) and how it is transported to how it is transported to the dentist the dentist (in saline) are critical in successfully (in saline) are critical in successfully saving and re-implanting the tooth.saving and re-implanting the tooth.

The periodontal ligament will regenerate and revascularize.The periodontal ligament will regenerate and revascularize.

•Dental follicle consists of1-Dense fibrous and cellular tissues immediately encapsulate the developing tooth

(Cementum)

2-Perifollicular mesenchyme

(PDL ,Alveolar bone)

DevelopmentDevelopmentOf PDL:Of PDL:

cells

Histological structureHistological structureThe periodontal ligament is The periodontal ligament is

formed offormed of : :

Fibers,

Intercellular substances

Synthetic Synthetic

Resorptive Resorptive

Progenitor Progenitor

Defensive Defensive

ground substancesground substances

blood vessels, blood vessels,

nerves & lymphatics.nerves & lymphatics.

A- The principal fibers:A- The principal fibers: TheyThey are formed of collagen are formed of collagen

bundles, which are bundles, which are wavywavy in course in course and are arranged in and are arranged in threethree groups. groups.a)a) Gingival fibers.Gingival fibers.b)b) Transseptal or interdental ligament.Transseptal or interdental ligament.c)c) Alveolodental ligamentAlveolodental ligament which is subdivided which is subdivided

into the following five groups: into the following five groups:1- Alveolar crest group.1- Alveolar crest group.2- Horizontal group.2- Horizontal group.3- Oblique group.3- Oblique group.4-Apical group.4-Apical group.5- Interradicular group.5- Interradicular group.

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

1- Dento-g1- Dento-gingival fibersingival fibers: : extend from the cervical extend from the cervical cementum into the gingiva. cementum into the gingiva.

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

3- 3- Circular groupCircular group: : a small a small group of fibers that encircles group of fibers that encircles the tooth and interlaces with the tooth and interlaces with the outer fibers.the outer fibers.

4- 4- Dento-periostealDento-periosteal fibers: fibers: they extend from the they extend from the cementum directed over the cementum directed over the bone crest and then incline bone crest and then incline apically between the apically between the periosteum of the alveolar periosteum of the alveolar bone and the gingiva.bone and the gingiva.

Alveolo-gingival

Dento-gingival

Dento-periosteal

Circular fibers

Alveolarbone

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

b- The transseptal b- The transseptal ligament:ligament:**It connects two adjacent It connects two adjacent

teeth.teeth.*The ligament runs from the *The ligament runs from the

cementum of one tooth over cementum of one tooth over the crest of the alveolus to the crest of the alveolus to the cementum of the the cementum of the adjacent tooth.adjacent tooth.

*Function:*Function:Resists mesial and distalResists mesial and distaltooth separation.tooth separation.

Dentin

Dentin

Bone

c- The alveolodental c- The alveolodental ligament:ligament:1-Alveolar crest group: 1-Alveolar crest group: radiate from the crest of the radiate from the crest of the

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

Function: Function: resists vertical andresists vertical andintrusive forces.intrusive forces.2-Horizontal group: 2-Horizontal group: The fiber bundles run from the The fiber bundles run from the cementum to the bone at right cementum to the bone at right angle to the long axis of the angle to the long axis of the tooth. tooth. Function: Function: resists horizontal resists horizontal

and tipping forces.and tipping forces.

Bone Dentin

3- 3- Oblique group: Oblique group: The fiber bundles run The fiber bundles run obliquelyobliquely..

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

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

Function:Function:*Performs the *Performs the main supportmain support of the tooth against masticatory of the tooth against masticatory forces.forces.**Resists vertical and intrusive Resists vertical and intrusive

forces.forces.

bone

dentin

4- 4- Apical group: Apical group:

The bundles radiate from the The bundles radiate from the

apical region of the root to apical region of the root to

the surrounding bone the surrounding bone

Function: Function: resists vertical resists vertical

force.force.

5- Interradicular group: 5- Interradicular group:

The bundles radiate from the The bundles radiate from the

interradicular septum to the interradicular septum to the

furcation of the multirooted furcation of the multirooted

tooth. tooth.

Function: Function: resists vertical and resists vertical and lateral forces.lateral forces.

dentin

bone

dentin

bone

B- Accessory fibers:B- Accessory fibers:They are collagenous in nature and run They are collagenous in nature and run

from bone from bone

to cementum in different planes, more to cementum in different planes, more tangentially to tangentially to

prevent rotationprevent rotation of the tooth and of the tooth and found in the found in the

region of the horizontal group.region of the horizontal group.

22- Oxytalan fibers- Oxytalan fibersThese are These are immature elasticimmature elastic (pre- (pre-elastic) fibers.elastic) fibers.

They need They need special stainsspecial stains to be to be demonstrated. demonstrated.

They tend to run in an They tend to run in an axialaxial direction, one end being direction, one end being

embedded embedded in bone or cementum and the in bone or cementum and the other in the wall of blood vessels. other in the wall of blood vessels.

At the At the apical apical region they form a region they form a complex network. complex network.

The functions of oxytalan fibers:1-Support nerves. 2- Support blood vessels.3- Help fibroblasts migration.

cells

Histological structureHistological structureThe periodontal ligament is The periodontal ligament is

formed offormed of : :

Fibers,

Intercellular substances

Synthetic Synthetic

Resorptive Resorptive

Progenitor Progenitor

Defensive Defensive

ground substancesground substances

blood vessels, blood vessels,

nerves & lymphatics.nerves & lymphatics.

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

The cellsThe cellsSynthetic Synthetic

cellscells

Resorptive Resorptive cellscells

Progenitor Progenitor cellscells

Defensive Defensive cellscells

fibroblasts,fibroblasts, osteoblasts and osteoblasts and cementoblastscementoblasts..

cementoclasts , osteoclasts and cementoclasts , osteoclasts and fibroclasts.fibroclasts.Note that fibroblasts perform Note that fibroblasts perform both synthetic and resorptive both synthetic and resorptive activities.activities.undifferentiated undifferentiated mesenchymal cellsmesenchymal cells

macrophage, macrophage, lymphocytes and lymphocytes and mast cellsmast cells

Synthetic Cells of PDLSynthetic Cells of PDL

FibroblastsFibroblasts

CementoblastsCementoblasts

OsteoblastsOsteoblasts

PDL FibroblastsPDL 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

CementoblastsCementoblasts OsteoblastsOsteoblasts

Both are rich in alkaline phosphatase activity.

Resorptive Cells of Resorptive Cells of PDLPDL

• osteoclasts osteoclasts • cementoclastscementoclastsBoth are rich in acid Both are rich in acid phosphatase activity.phosphatase activity.

Progenitor cellsProgenitor cellsU. M. CU. 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 PDLDefensive Cells of PDLMacrophages

lymphocytes

Mast cells

Note: There are no plasma cells.

Epithelial Cells: remnants of the epithelial

root 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.

cells

Histological structureHistological structureThe periodontal ligament is The periodontal ligament is

formed offormed of : :

Fibers,

Intercellular substances

Synthetic Synthetic

Resorptive Resorptive

Progenitor Progenitor

Defensive Defensive

ground substancesground substances

blood vessels, blood vessels,

nerves & lymphatics.nerves & lymphatics.

Interstitial tissuesInterstitial tissues

*They are found between the *They are found between the fibers of the periodontal fibers of the periodontal ligament.ligament.*They are areas that *They are areas that contain some of the contain some of the blood blood vesselsvessels, , lymphatic lymphatic and and nerves.nerves. *They are surrounded *They are surrounded by loose connective tissue.by loose connective tissue.

Blood supplyBlood supplyThe arterial blood supply of the periodontal The arterial blood supply of the periodontal

ligament is derived from 3 sources:ligament is derived from 3 sources:

3- Branches from the 3- Branches from the apicalapical vessels that supply the dental pulp. vessels that 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 constitute the and these constitute the main blood supply.main blood supply.

1- Branches from the 1- Branches from the gingival gingival vessels.vessels.

Nerve supply:Nerve supply:The nerve supply of periodontal ligament The nerve supply of periodontal ligament comes from either the inferior or superior comes from either the inferior or superior dental nerves.dental nerves.

1- Bundles of nerve fibers run from 1- Bundles of nerve fibers run from the apical the apical regionregion of the root towards the gingival margin. of the root towards the gingival margin.

2- Nerves enter the ligament horizontally 2- Nerves enter the ligament horizontally through multiple foramina in the through multiple foramina in the bonebone. .

(mechanoreceptors)(mechanoreceptors)

Large nerve fibersLarge nerve fibers

Small nerve fibersSmall nerve fibers pain sensationpain sensation

touch & pressuretouch & 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.

Functions of the Functions of the periodontal ligament:periodontal ligament:

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

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

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

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

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

Dental implants lack periodontal ligament fibers and they have a rigid connection to bone (Osseointegration).

Periimplant tissuesPeriimplant tissues

Titanium implantSulcular epitheliumJuunctional epitheliumConnective tissue

Bone

2- Sensory:2- Sensory:The periodontal ligament having the The periodontal ligament having the

mechanoreceptorsmechanoreceptors

contributes to the sensation of touch and pressure on contributes to the sensation of touch and pressure on

the teeth. the teeth.

sudden overloadsudden overloadproprioceptive reflexproprioceptive reflex

inhibition of the inhibition of the activity activity of the masticatory of the masticatory musclesmuscles

Opening the mouthOpening the mouth

3- Nutritive:3- Nutritive:The blood vessels in the periodontal ligament provide The blood vessels in the periodontal ligament provide nutrient supply required by the cells of the ligament nutrient supply required by the cells of the ligament

and and to the to the cementocytescementocytes and the most superficial and the most superficial

osteocytesosteocytes..

4- Formative:4- Formative:The The fibroblastsfibroblasts are responsible for the formation of are responsible for the formation of

new new periodontal ligament fibers and dissolution of the old periodontal ligament fibers and dissolution of the old fibers fibers CementoblastsCementoblasts and and osteoblastsosteoblasts are essential in are essential in

building up cementum and bone.building up cementum and bone.

5- Protective5- ProtectiveThe protective function of the periodontal ligament is The protective function of the periodontal ligament is

achieved by:achieved by:a- The principal fibers.a- The principal fibers.b- The blood vessels.b- The blood vessels.c- The nerves.c- The nerves.a- The principal fibers:a- The principal fibers: The The arrangementarrangement of the fiber bundles in the different of the fiber bundles in the different

groups is well adapted to fulfill the functions of the groups is well adapted to fulfill the functions of the periodontal ligament. periodontal ligament.

The The alveolodentalalveolodental ligament transforms the masticatory ligament transforms the masticatory

pressure pressure exerted on the tooth into exerted on the tooth into tensiontension or traction on the cementum or traction on the cementum and bone.and bone.

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

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

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

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

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

c- The nerves:c- The nerves:By its mechanoreceptors nerves.By its mechanoreceptors nerves.

The Age Changes of The Age Changes of periodontal ligamentperiodontal ligament

*The periodontal ligament through aging *The periodontal ligament through aging

shows shows Vasuclarity Vasuclarity

Cellularity Cellularity

Thickness Thickness *It may contain cementicles.*It may contain cementicles.

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

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

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

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