CEMENTUMCEMENTUM

CEMENTUMCEMENTUM

It is calcified avascular It is calcified avascular mesenchymal tissue that mesenchymal tissue that forms the outer covering of forms the outer covering of anatomic rootanatomic root

1.Acellular( primary) 1.Acellular( primary) 2.cellular(secondary)2.cellular(secondary)

Types

Acellular cementum – first cementum formed before tooth reaches occlusal paneCovers cervical third or half of the root.Doesnot contain cells.Thickness – 30 to 230 usharpey’s fibres abundant and arranged irregularly or parallel to the surface

Cellular cementumCellular cementum – – formed after toothformed after tooth

reaches occlusal planereaches occlusal plane

More irregularMore irregular

Contains cementocytes in lacunae which Contains cementocytes in lacunae which communicates through canaliculicommunicates through canaliculi

Sharpey’s fibres occupy smaller portionSharpey’s fibres occupy smaller portion

Less calcifiedLess calcified

Rest periodsRest periods – both acellular and cellular – both acellular and cellular cementum are arranged in lamellae cementum are arranged in lamellae separated by incremental lines parallel to separated by incremental lines parallel to long axis of toothlong axis of tooth

More mineralized than adjacent cementumMore mineralized than adjacent cementum

According to schroeder, cementum According to schroeder, cementum can becan be classified as –classified as –Acellular afibrillar cementum :Acellular afibrillar cementum : No cellsNo cellsNo intrinsic or extrinsic collagen fibersNo intrinsic or extrinsic collagen fibersMineralised ground substancesMineralised ground substancesProduct of cementoblastsProduct of cementoblastsFound in coronal cementumFound in coronal cementumThickness 1 -15 uThickness 1 -15 u

Acellular extrinsic fiber Acellular extrinsic fiber cementumcementum

No cellsNo cells

Densely packed bundles of sharpey’s Densely packed bundles of sharpey’s fibersfibers

Product of cementoblasts and fibroblastsProduct of cementoblasts and fibroblasts

Found in cervical third of rootsFound in cervical third of roots

Thickness – 30 to 230 uThickness – 30 to 230 u

Cellular mixed stratified cementumCellular mixed stratified cementum

Contains cells Contains cells

Both intrinsic and extrinsic fibres presentBoth intrinsic and extrinsic fibres present

Co product of cementoblasts and fibroblastsCo product of cementoblasts and fibroblasts

Present in apical third, apices and furcation Present in apical third, apices and furcation areasareas

Thickness – 100 to 1000uThickness – 100 to 1000u

Cellular intrinsic fiber Cellular intrinsic fiber cementumcementumContains cellsContains cells

No extrinsic fibersNo extrinsic fibers

Formed by cementiblastsFormed by cementiblasts

Fills resorption lacunaeFills resorption lacunae

Intermediate cementumIntermediate cementumPoorly defined zone near cementodentinal Poorly defined zone near cementodentinal junctionjunction

Contains cellular remnants of root sheathContains cellular remnants of root sheath

CompositionComposition

Organic content - 50 to 55 %Organic content - 50 to 55 %

Type I collagen – 90 %Type I collagen – 90 %

Type III collagen – 5 %Type III collagen – 5 %

Sources of collagen include sharpey’s Sources of collagen include sharpey’s fibers (extrinsic ) and those belonging to fibers (extrinsic ) and those belonging to cementum produced by cementoblasts cementum produced by cementoblasts (intrinsic)(intrinsic)

Inorganic content – 45 to 50 %Inorganic content – 45 to 50 %

Consist of calcium and phosphorous in the Consist of calcium and phosphorous in the form of hydroxyapatiteform of hydroxyapatite

Trace elements in varying amountsTrace elements in varying amounts

Contains highest fluoride contentContains highest fluoride content

Cementoenamel junctionCementoenamel junction

Cementum at and immediately Cementum at and immediately subjacent to cementoenamel subjacent to cementoenamel junction is of great interest in root junction is of great interest in root planingplaning

three types of relationships three types of relationships existexistIn approx. 30% of all teeth cementum In approx. 30% of all teeth cementum meets the cervical end of enamelmeets the cervical end of enamelIn 10% cases enamel and cementum In 10% cases enamel and cementum donot meet which can cause accentuated donot meet which can cause accentuated sensitivity because of exposed dentinsensitivity because of exposed dentinIn about 60% cases cementum overlaps In about 60% cases cementum overlaps the cervical end of enamel the cervical end of enamel

Cementodentinal junctionCementodentinal junction

DefinitionDefinition – – the terminalthe terminal apical areaapical area of of cementum where it joins the internal root dentin cementum where it joins the internal root dentin is called cementodentinal junction or CDJis called cementodentinal junction or CDJ The obturating material should be at CDJ during The obturating material should be at CDJ during root canal treatmentroot canal treatmentWidth of CDJ is 2 to 3u and remains relatively Width of CDJ is 2 to 3u and remains relatively stable stable

Thickness of cementumThickness of cementum

Formation of cementum is continuous Formation of cementum is continuous process and its rate varies throughout the process and its rate varies throughout the life.life.

It is most rapid at apical regions.It is most rapid at apical regions.

At apical third it varies from 150 – 200uAt apical third it varies from 150 – 200u

At coronal portion it varies from 16 – 60uAt coronal portion it varies from 16 – 60u

It is thicker on distal surfaces than mesial It is thicker on distal surfaces than mesial because of following mesial migrationbecause of following mesial migration

Between 11 and 70 years of age the Between 11 and 70 years of age the thickness increases three fold and is more thickness increases three fold and is more on apical regionon apical region

At the age of 20 years the average At the age of 20 years the average thickness is 95u and at 60 years it is 215uthickness is 95u and at 60 years it is 215u

Abnormalities of cementum Abnormalities of cementum includesincludes

Cemental aplasia or Cemental aplasia or hypoplasiahypoplasia – – absenceabsence or paucity of or paucity of cellular cementumcellular cementum

Cemental hyperplasia or hypercementosis – excessive deposition of cementum

It can be –It can be –

LocalisedLocalised

GeneralisedGeneralised – – with nodular with nodular enlargement called cemental spikes enlargement called cemental spikes

It may be assosciated with situations like –It may be assosciated with situations like –

A. teeth without antagonist A. teeth without antagonist

B. teeth with pulpal and periapical B. teeth with pulpal and periapical infectionsinfections

Hypercementosis of entire dentition may Hypercementosis of entire dentition may be seen in patients with paget’s disease.be seen in patients with paget’s disease.

Other systemic disturbances include Other systemic disturbances include acromegaly,calcinosis,thyroid goitre etc.acromegaly,calcinosis,thyroid goitre etc.

Cementum resorption and Cementum resorption and repairrepair

Causes of cementum resorption are –Causes of cementum resorption are –

1.1.local causes local causes ––a.trauma from a.trauma from occlusion occlusion

B. orthodontic movementB. orthodontic movement

C. pressure from erupting teeth C. pressure from erupting teeth

D. cyst and tumoursD. cyst and tumours

E. Teeth without functional antagonistE. Teeth without functional antagonist

2.2.systemic causessystemic causes – – A.calcium A.calcium deficiencydeficiency

B. hereditary fibrous osteodystrophyB. hereditary fibrous osteodystrophy

C. hypothyroidismC. hypothyroidism

d,. Paget’s diseased,. Paget’s disease

Resorption occurs most commonly in Resorption occurs most commonly in apical third then middle third followed apical third then middle third followed by gingival thirdby gingival third

3. 3. idiopathicidiopathic

MicroscopicallyMicroscopically, 1.bay like concavities , 1.bay like concavities seen in root surfaces.seen in root surfaces.

2. presence of multinuclear giant cells and 2. presence of multinuclear giant cells and large mononuclear macrophages.large mononuclear macrophages.

3. several sites coalesce to form large 3. several sites coalesce to form large areas of destructionareas of destruction

It may extend into even to pulp and is It may extend into even to pulp and is painlees.painlees.

Cementum resorption may alternate with Cementum resorption may alternate with repair and deposition of new cementum.repair and deposition of new cementum.

Newly formed cementum is demarcated Newly formed cementum is demarcated from the root by an irregular deep staining from the root by an irregular deep staining line called line called reversal line.reversal line.

Remodelling requires the presence of Remodelling requires the presence of viable connective tissue and may occur viable connective tissue and may occur even in non vital teeth.even in non vital teeth.

ANKYLOSISANKYLOSIS

Definition – Definition – fusion of cementum and fusion of cementum and alveolar bone and obliteration of the alveolar bone and obliteration of the periodontal ligament is called ankylosis.periodontal ligament is called ankylosis.

This condition is uncommmon.This condition is uncommmon.

Occurs in teetgh with cemental resorption.Occurs in teetgh with cemental resorption.

It represents a form of abnormal repair.It represents a form of abnormal repair.

Can also occur after Can also occur after

- chronic periapical infection- chronic periapical infection

- tooth reimplantation- tooth reimplantation

- occlusal trauma- occlusal trauma

- around embedded teeth.- around embedded teeth.

More common in primary dentitionMore common in primary dentition

Results in resorption of root and its Results in resorption of root and its replacement by bone tissue.replacement by bone tissue.

Propriception is lost because pressure Propriception is lost because pressure receptors in periodontal ligament are receptors in periodontal ligament are altered or donot function correctly.altered or donot function correctly.

Physiologic drifting and eruption cannot Physiologic drifting and eruption cannot occur.occur.

Clinically Clinically , ,

1.lack of physiologic mobility which isDiagnostic sign of ankylotic resorption.2.Teeth have special metallic percussion sound.3. If the process continues teeth will be in

infraocclusion.

Radiographically,Radiographically,

Resorption lacunae are filled with bone.Resorption lacunae are filled with bone.

periodontal ligament space is missing.periodontal ligament space is missing.

Treatment-Treatment- Treatment ranges from Treatment ranges from conservativeconservative approach approach such as restorative such as restorative intervention to intervention to surgical extraction surgical extraction of of toothtooth

Exposure of cementum to Exposure of cementum to oral environmentoral environment

Occurs in case of gingival recession and Occurs in case of gingival recession and loss of attachment in pocket formation.loss of attachment in pocket formation.

Becomes permeable to bacteria, organic Becomes permeable to bacteria, organic substances, and inorganic ions resulting in substances, and inorganic ions resulting in cemental caries.cemental caries.

FUNCTIONS OF CEMENTUMFUNCTIONS OF CEMENTUM

1. it is medium for attachment of collagen 1. it is medium for attachment of collagen fibres that bind the tooth to alveolar bone. fibres that bind the tooth to alveolar bone.

2. serves as a reparative tissue for root 2. serves as a reparative tissue for root surfaces.surfaces.

Damage to roots such as resorption and Damage to roots such as resorption and fractures can be repaired by depsition of fractures can be repaired by depsition of new cementum.new cementum.

– 3. Makes functional adaptation of teeth3. Makes functional adaptation of teeth

possible.possible.

– Deposition in apical region can Deposition in apical region can compensate for tooth loss from occlusal compensate for tooth loss from occlusal wear.wear.

Definition Definition

It is that portion of the maxilla and It is that portion of the maxilla and

mandible mandible that forms and supports the tooth that forms and supports the tooth

sockets sockets (alveoli).(alveoli).

It forms when the tooth erupts to provide It forms when the tooth erupts to provide

the osseous attachment to the the osseous attachment to the

forming forming periodontal ligament; it disappears periodontal ligament; it disappears

gradually after the tooth is lost. gradually after the tooth is lost.

Since the alveolar processes develop & Since the alveolar processes develop & undergo remodeling with the tooth formation and undergo remodeling with the tooth formation and eruption, they are tooth dependent bony structureseruption, they are tooth dependent bony structures

Therefore, the size, shape, location & function Therefore, the size, shape, location & function

of of the teeth determine their morphology. the teeth determine their morphology.

Although the growth and development of the Although the growth and development of the

bones bones of the teeth, a certain degree of of the teeth, a certain degree of

repositioning of repositioning of teeth can be accomplished through teeth can be accomplished through

occlusal forces occlusal forces & in response to orthodontic & in response to orthodontic

procedure that rely on procedure that rely on the adaptability of the the adaptability of the

alveolar bone & associated alveolar bone & associated periodontal tissues. periodontal tissues.

PARTS OF ALVEOLAR PROCESS 1.1. An externalAn external plate of cortical bone formed plate of cortical bone formed

by by haversian bone & compacted bone haversian bone & compacted bone

lamellae.lamellae.

2.2. Inner socket Inner socket of thin, compact bone called of thin, compact bone called

alveolar bone proper. Histologically, it alveolar bone proper. Histologically, it

contains a series of openings (cribriform contains a series of openings (cribriform

plate) through which neurovascular bundles plate) through which neurovascular bundles

link the periodontal ligament with the central link the periodontal ligament with the central

component of alveolar bone, cancellous bonecomponent of alveolar bone, cancellous bone. .

Shape of roots and surrounding bone distribution in transverse section in maxilla and mandible at mid root level.

3.3. Cancellous Trabeculae Cancellous Trabeculae between these 2 between these 2

compact layers, which acts as supporting compact layers, which acts as supporting

alveolar bone. The interdental septum alveolar bone. The interdental septum

consists of cancellous supporting bone consists of cancellous supporting bone

enclosed within a compact border.enclosed within a compact border.

4. In addition, bones of jaw include basal bone which is the 4. In addition, bones of jaw include basal bone which is the

portion of jaw located apically, but unrelated to teeth.portion of jaw located apically, but unrelated to teeth.

5.5. Most of the facial & lingual portions of the sockets are Most of the facial & lingual portions of the sockets are

formed formed by compact bone aloneby compact bone alone

The dotted line indicates separation between the basal bone and alveolar bone.

COMPOSITION OF ALVEOLAR BONE

It has 2 basic constituentsIt has 2 basic constituents::

a)a)The cells consist of The cells consist of

•osteoblasts, osteoblasts,

•osteoclastsosteoclasts

• osteocytes osteocytes

b)b)Extra cellular matrix consists of Extra cellular matrix consists of

•65% inorganic 65% inorganic

• 35% organic matrix.35% organic matrix.

CELLS:-

Osteoblasts differentiate from pleuripotent Osteoblasts differentiate from pleuripotent

follicle cells.follicle cells.

Alveolar bone is formed during fetal Alveolar bone is formed during fetal

growth by growth by intra membranous ossification and intra membranous ossification and

consists consists of a calcified matrix with osteocytes of a calcified matrix with osteocytes

enclosed enclosed within spaces called lacunae. within spaces called lacunae.

Osteocytes extend processes into Osteocytes extend processes into

canaliculi canaliculi that radiate from the lacunae. that radiate from the lacunae.

The canaliculi form an anastomizing The canaliculi form an anastomizing

system system through the intercellular matrix of the through the intercellular matrix of the

bone, bone, which brings oxygen and nutrients to which brings oxygen and nutrients to

the the osteocytes and removes metabolic waste osteocytes and removes metabolic waste

products.products.

Bone growth occurs by apposition of an Bone growth occurs by apposition of an

organic matrix that is deposited by organic matrix that is deposited by

osteoblasts. osteoblasts.

Haversian systems (osteons) are the Haversian systems (osteons) are the

internal internal mechanisms that bring a vascular mechanisms that bring a vascular

supply to supply to bones too thick to be supplied only bones too thick to be supplied only

by surface by surface vessels.vessels.

These are found primarily in the outer These are found primarily in the outer

cortical cortical plates & alveolar bone proper. plates & alveolar bone proper.

Extra Cellular MatrixExtra Cellular Matrix

– It consists of:It consists of:

2/32/3rdrd inorganic matter inorganic matter

1/31/3rdrd organic matter. organic matter.

Inorganic matter is composed of minerals Inorganic matter is composed of minerals

- Calcium & Phosphate - Calcium & Phosphate

- Hydroxyl - Hydroxyl

- Carbonate - Carbonate

- Citrate - Citrate

Trace amounts of other ions like sodium, Trace amounts of other ions like sodium,

magnesium and fluorine.magnesium and fluorine.

Mineral salts are in the form of Mineral salts are in the form of

hydroxyapatite hydroxyapatite crystals and constitute 2/3crystals and constitute 2/3rdrd of of

bone structure.bone structure.

The The organic matrixorganic matrix consists mainly of consists mainly of

collagen type-I (90%) and small amounts of collagen type-I (90%) and small amounts of

noncollagenous proteins such as noncollagenous proteins such as

-- Osteonectin Osteonectin

-- Bone morphogenetic proteinBone morphogenetic protein

-- Phosphoproteins Phosphoproteins

-- Proteoglycans Proteoglycans

Osteopontin and bone sialoprotein are cell Osteopontin and bone sialoprotein are cell

adhesion proteins which are important for adhesion proteins which are important for

adhesion of osteoclasts and osteoblasts.adhesion of osteoclasts and osteoblasts.

In addition factors including In addition factors including

-- CytokinesCytokines

- Chemokines Chemokines

- Growth factors are also found Growth factors are also found

REMODELLING AND RESORPTION

Although, alveolar bone tissue is constantly Although, alveolar bone tissue is constantly changing in its internal organisation, it changing in its internal organisation, it

retains retains approximately the same form from approximately the same form from childhood childhood through adult life. through adult life.

Bone deposition by osteoblasts is balanced by Bone deposition by osteoblasts is balanced by resorption by osteoclasts during tissue remodelling resorption by osteoclasts during tissue remodelling and renewal.and renewal.

RemodellingRemodelling

Is major pathway of bony changes in shape ,Is major pathway of bony changes in shape ,resistance to forces, repair of wounds and resistance to forces, repair of wounds and

calcium & phosphate homeostasis in the body. calcium & phosphate homeostasis in the body.

It involves the coordination of activities of It involves the coordination of activities of

cells cells from 2 distinct lineages – osteoblasts and from 2 distinct lineages – osteoblasts and

osteoclasts, which form & resorb the mineralised osteoclasts, which form & resorb the mineralised

connective tissue of the bone.connective tissue of the bone.

Regulation of bone remodelling is a complex Regulation of bone remodelling is a complex

process process involving hormones and local factors on involving hormones and local factors on

the the generation and activity of differentiated bone generation and activity of differentiated bone

cells.cells.

Bone contains 90% of body’s calcium & is thus Bone contains 90% of body’s calcium & is thus

the the major source for calcium release when blood major source for calcium release when blood

calcium calcium levels decrease, this is monitored by levels decrease, this is monitored by

parathyroid parathyroid glands. glands.

This interdependency of osteoclasts & osteoblasts This interdependency of osteoclasts & osteoblasts

is is called called coupling.coupling.

Bone matrix that is laid down by osteoblasts is Bone matrix that is laid down by osteoblasts is

non-non- mineralised osteoid. mineralised osteoid.

While new osteoid is being deposited, older While new osteoid is being deposited, older

osteoid osteoid located below the surface becomes located below the surface becomes

mineralized mineralized as the mineralization front advances.as the mineralization front advances.

Bone resorption is a complex process Bone resorption is a complex process

morphologically related to the appearance of eroded morphologically related to the appearance of eroded

bone surfaces & large, multinucleated cells. bone surfaces & large, multinucleated cells.

Ten Cate described the following sequence of events Ten Cate described the following sequence of events during bone resorption. during bone resorption.

1.1. Attachment of osteoclasts to the mineralised Attachment of osteoclasts to the mineralised surface of the bone.surface of the bone.

2.2. Creation of a sealed acidic environment which Creation of a sealed acidic environment which demineralises the bone and exposes the demineralises the bone and exposes the

organic organic matrix. matrix.

3.3. Degradation of exposed organic matrix by the Degradation of exposed organic matrix by the action of enzymes like acid phosphatase and action of enzymes like acid phosphatase and cathepsin.cathepsin.

4.4. Sequestering of mineral ions & amino acids Sequestering of mineral ions & amino acids within within the osteoclasts. the osteoclasts.

SOCKET WALLSOCKET WALL

Socket wall consists of Socket wall consists of

dense,lamellated dense,lamellated bone, some of which bone, some of which

is arranged in is arranged in haversian systems & haversian systems &

bundle bone. bundle bone.

Bundle boneBundle bone is the term given to a is the term given to a

bone bone adjacent to the periodontal adjacent to the periodontal

ligament that ligament that contains a great no. of contains a great no. of

sharpey’s fiberssharpey’s fibers..

It is characterised by thin lamellae arranged It is characterised by thin lamellae arranged

in layers parallel to the root. in layers parallel to the root.

Socket Wall

The cancellous portion of the alveolar bone The cancellous portion of the alveolar bone

consists of trabeculae that enclose consists of trabeculae that enclose

irregularly shaped marrow spaces lined irregularly shaped marrow spaces lined with a with a

layer of thin, flattened endosteal cellslayer of thin, flattened endosteal cells

Cancellous bone is found predominantly in Cancellous bone is found predominantly in

the inter-radicular and interdental spaces the inter-radicular and interdental spaces

and in limited amounts facially or lingually, and in limited amounts facially or lingually,

except in the palate in the adult human, except in the palate in the adult human,

more cancellous bone exists in the maxilla more cancellous bone exists in the maxilla

than in the mandible. than in the mandible.

BONE MARROWBONE MARROW

In the embryo and newborn the cavities In the embryo and newborn the cavities

of of all bones are occupied by red all bones are occupied by red

hematopoietic marrow.hematopoietic marrow.

Red marrow gradually undergoes a Red marrow gradually undergoes a

physiologic change to the fatty or yellow physiologic change to the fatty or yellow

inactive type of marrow.inactive type of marrow.

In the adult the marrow of the jaw is In the adult the marrow of the jaw is

normally of latter type & red marrow is normally of latter type & red marrow is found found

only in the ribs, sternum, vertebrae, only in the ribs, sternum, vertebrae, skull skull

and humerus. and humerus.

The foci of red bone marrow are The foci of red bone marrow are

occasionally occasionally seen in the jaws, often seen in the jaws, often

accompanied by accompanied by resorption of bony trabeculae.resorption of bony trabeculae.

Common locations are the maxillary Common locations are the maxillary

tuberosity, maxillary and mandibular molar tuberosity, maxillary and mandibular molar

and premolar areas and the mandibular and premolar areas and the mandibular

symphysis and ramus angle, which will be symphysis and ramus angle, which will be

visible radiographically as zones of visible radiographically as zones of

radiolucency. radiolucency.

PERIOSTEUM & ENDOSTEUM PERIOSTEUM & ENDOSTEUM

Layers of differentiated osteogenic Layers of differentiated osteogenic

connective connective tissue cover all the bone surfaces.tissue cover all the bone surfaces.

The tissue covering the outer surface of The tissue covering the outer surface of

bone bone is termed periosteum.is termed periosteum.

The periosteum consists of an inner layer The periosteum consists of an inner layer

composed of osteoblasts surrounded by composed of osteoblasts surrounded by

osteoprogenitor cells, which have the potential osteoprogenitor cells, which have the potential

to differentiate into osteoblasts and an outer to differentiate into osteoblasts and an outer

layer rich in blood vessels and nerves and layer rich in blood vessels and nerves and

composed of collagen fibres and fibroblasts. composed of collagen fibres and fibroblasts.

Bundles of periosteal collagen fibres Bundles of periosteal collagen fibres

penetrate penetrate the bone, binding the periosteum to the bone, binding the periosteum to

the bone. the bone.

The endosteum is composed of a single The endosteum is composed of a single

layer layer of osteoblasts and sometimes a small of osteoblasts and sometimes a small

amount amount of connective tissue. of connective tissue.

Cellular events at the periosteum modulate Cellular events at the periosteum modulate

bone size throughout an individual’s life bone size throughout an individual’s life

span span and change in bone size is probably the and change in bone size is probably the

result result of the balance between periosteal of the balance between periosteal

osteoblastic osteoblastic and osteoclastic activities. and osteoclastic activities.

INTERDENTAL SEPTUM INTERDENTAL SEPTUM

The interdental septum consists of The interdental septum consists of

cancellous cancellous bone bordered by the socket wall bone bordered by the socket wall

cribriform cribriform plates (lamina dura or alveolar bone plates (lamina dura or alveolar bone

proper) of proper) of approximating teeth and the facial and approximating teeth and the facial and

lingual lingual cortical plates. cortical plates.

If the interdental space is narrow, the If the interdental space is narrow, the

septum septum may consist of only the cribriformmay consist of only the cribriform

plate. plate.

If roots are too close together, an irregular If roots are too close together, an irregular

“window” can appear in the bone between “window” can appear in the bone between

adjacent roots. adjacent roots.

Boneless window between adjoining close roots of molars

The mesiodistal and faciolingual The mesiodistal and faciolingual

dimensions & dimensions & shape of the interdental shape of the interdental

septum are governed septum are governed by the size and by the size and

convexity of the crowns of the convexity of the crowns of the

approximating teeth, as well as by the position approximating teeth, as well as by the position

of the teeth in and their degree of eruption. of the teeth in and their degree of eruption.

OSSEOUS TOPOGRAPHY OSSEOUS TOPOGRAPHY

The bone contour normally conforms to the The bone contour normally conforms to the

prominence of the roots, with intervening prominence of the roots, with intervening

vertical depressions that taper toward the vertical depressions that taper toward the margin.margin.

Alveolar bone anatomy varies among patients. Alveolar bone anatomy varies among patients.

The height & thickness of the facial and The height & thickness of the facial and

lingual lingual bony plates are affected by the bony plates are affected by the

alignment of the alignment of the teeth, angulations of the root to teeth, angulations of the root to

the bone and the bone and occlusal forces. occlusal forces.

On teeth in labial version, the On teeth in labial version, the margin of the margin of the labial bone is located labial bone is located farther apically than on teeth in proper farther apically than on teeth in proper alignment. alignment.

The bone margin is thinned to a The bone margin is thinned to a knife-edge and knife-edge and presents an presents an accentuated arc in the direction of accentuated arc in the direction of the apex.the apex.

On teeth in lingual version, the On teeth in lingual version, the facial bony plate is thicker than facial bony plate is thicker than normal. normal.

The margin is blunt, rounded and horizontal The margin is blunt, rounded and horizontal than accurate. than accurate.

The cervical portion of the alveolar plate is The cervical portion of the alveolar plate is sometimes considerably thickened on the sometimes considerably thickened on the facial surface, apparently as reinforcement facial surface, apparently as reinforcement against occlusal forces. against occlusal forces.

A BVariation in the cervical portion of buccal alveolar plate:

A:- Shelf like conformation

B:- Comparatively thin buccal plate

FENESTRATIONS AND DEHISCENCE FENESTRATIONS AND DEHISCENCE

Isolated areas in which the root is denuded of Isolated areas in which the root is denuded of

bone and the root surface is covered only by bone and the root surface is covered only by

periosteum and the overlying gingiva are periosteum and the overlying gingiva are termed termed

as fenestrations.as fenestrations.

In these areas marginal bone is intact. In these areas marginal bone is intact.

Fenestrations Fenestrations

FENESTRATION & FENESTRATION & DEHISCENCEDEHISCENCE

Dehiscence

Fenestration

When the denuded areas extend through the When the denuded areas extend through the

marginal bone, the defect is called dehiscence.marginal bone, the defect is called dehiscence.

Such defects occur on approximately 20% of Such defects occur on approximately 20% of

the teeth. the teeth.

They occur more often on the facial bone They occur more often on the facial bone

than than on the lingual bone. on the lingual bone.

They are more common on anterior teeth They are more common on anterior teeth

than than on posterior. on posterior.

The cause of these defects is not clear. The cause of these defects is not clear.

DehiscenceDehiscence

PREDISPOSING FACTORS PREDISPOSING FACTORS

Prominent root contourProminent root contour

MalpositionMalposition

Labial protrusion of the root combined Labial protrusion of the root combined

with a thin bony plate.with a thin bony plate.

Fenestrations and dehiscence Fenestrations and dehiscence

are important as the my are important as the my

complicate the outcome of complicate the outcome of

periodontal surgery.periodontal surgery.

REMODELLING OF ALVEOLAR BONE REMODELLING OF ALVEOLAR BONE

Local influences include Local influences include • Functional requirements on the tooth Functional requirements on the tooth

•Age related changes in bone cells Age related changes in bone cells

Systemic influences Systemic influences -Calcitonin -Calcitonin

-Vit D3-Vit D3

The remodeling of alveolar bone affects itsThe remodeling of alveolar bone affects its

-- Height Height - Contour - Contour

- Density - Density

& this is manifested in the following 3 areas.& this is manifested in the following 3 areas.

Adjacent to periodontal ligament Adjacent to periodontal ligament

In relation to the periosteum of the facial In relation to the periosteum of the facial

and and lingual plates. lingual plates.

and along the endosteal surface of the and along the endosteal surface of the marrow marrow

spaces. spaces.

Age changes in the alveolar boneAge changes in the alveolar bone

Osteoporosis Osteoporosis

Decreased vascularity Decreased vascularity

Reduction in metabolic rate and healing Reduction in metabolic rate and healing

capacity. capacity.

Resorption activity is increased and the rate Resorption activity is increased and the rate

of of bone formation is decreased. bone formation is decreased.

Greater irregularity in the surface of Greater irregularity in the surface of

alveolar alveolar bone. bone.

PERIODONTAL PERIODONTAL

LIGAMENTLIGAMENT

INTRODUCTIONINTRODUCTION

Periodontal ligament is an integral part of

periodontium. The periodontium is an

attachment apparatus of the teeth. It is a

connective tissue organ, which is covered

by epithelium on top surface. Teeth are

attached to the bone of the jaws by

periodontium.

It consists of 4 connective tissues:-It consists of 4 connective tissues:-

Cementum Cementum

Periodontal ligament Periodontal ligament

Alveolar bone Alveolar bone

Deeper part of Deeper part of

gingivagingiva

Two of these tissues are mineralized and two are

fibrous. The cementum and alveolar alone are

mineralized tissue while the periodontal ligament

and part of gingiva are fibrous tissues. On one side,

the periodontium is attached to the dentine of root

of teeth by cementum while on other side it is

attached to the bone of jaws by alveolar bone.

Definition Definition

The periodontal ligament is a soft, fibrous The periodontal ligament is a soft, fibrous specialized connective tissue which is present in specialized connective tissue which is present in

the periodontal space, which is situated the periodontal space, which is situated between between the cementum of root of the tooth and the cementum of root of the tooth and the bone the bone forming the socket wall.forming the socket wall.

The periodontal ligament extends coronally up to The periodontal ligament extends coronally up to the most apical part of connective tissue of the most apical part of connective tissue of gingiva.gingiva.

Because the collagen fibers are attached to the Because the collagen fibers are attached to the cementum and alveolar bone, the ligament cementum and alveolar bone, the ligament provides soft tissue continuity between the provides soft tissue continuity between the mineralized connective tissues of mineralized connective tissues of periodontium.periodontium.

Other terms which were previously used

for periodontal ligament are:-

1. Desmondont

2. Gomphosis

3. Pericementum

4. Dental Periosteum

5. Alveolodental ligament

6. Periodontal membrane

“Periodontal ligament” and “Periodontal

membrane” are the terms that are now most

commonly used. Neither term describes structure nor

function adequately. It is neither a typical membrane

nor a typical ligament. However, because it is a

complex connective tissue providing continuity

between two mineralized connective tissues, the term

“periodontal ligament” appears to be more

appropriate.

DEVELOPMENTDEVELOPMENT

Shortly after the beginning of root formation and formation of out dentinal

layer of root, the periodontal ligament is formed. The external and internal

dental epithelia proliferate from the cervical loop of dental organ to form

“Hertwigs Epithelial root sheath” This sheath is double layered. Because of

growth changes, the root sheath is stretched and then it fragments to form

the discrete cluster of epithelial cells called as “epithelial cell rests of

malassez”.

Now the periodontal ligament formation

occurs. The enamel organ and hertwig

epithelial root sheath are surrounded by

dental sac that is formed by condensed cells.

A thin layer of these cells lie adjacent to

dental organ. This is known as “Dental

Follicle”.

The cells of Dental Follicle divide and The cells of Dental Follicle divide and differentiate into:differentiate into:

FibroblastsFibroblasts

CementoblastsCementoblasts

OsteoclastsOsteoclasts

STRUCTURE STRUCTURE The periodontal ligament has the shape of an

“HOUR GLASS” and is narrowest at the midroot

level. The width of periodontal ligament is

approximately 0.15-0.38mm.

CELLULAR COMPOSITION CELLULAR COMPOSITION The cells of periodontal ligament are

categorised as:

1. Synthetic Cells

a) Osteoblasts

b) Fibroblasts

c) Cementoblasts

2) Resorptive Cells

a) Osteoclasts

b) Cementoclasts

c) Fibroblasts

3) Progenitor Cells

4) Epithelial Cell rests of malassez

5) Connective Tissue cells

i) Mast cells

ii) Macrophages

SYNTHETIC CELLSSYNTHETIC CELLS

The characteristic of synthetic cells are:

1. Should be actively synthesizing ribosomes.

2. Increase in the complement rough endoplasmic

reticulum and golgi apparatus.

3. Large open faced or vesicular nucleus with

prominent nucleoli.

The osteoblasts covers the periodontal surface of

alveolar bone. Alveolar bone constitute a modified

endosteum and not a periosteum. A periosteum

comprises at least two distinct layers:

1. An Inner – CELLULAR LAYER

2. An Outer – FIBROUS LAYER

A cellular, but not an outer fibrous layer is present on

the periodontal surface of alveolar bone.

A) OSTEOBLASTS

Function:

Osteoblasts help in the synthesis of alveolar bone.

Fibroblasts are the most common cells in periodontal ligament. They constitute about 65% of total population. They appear as ovoid or elongated cells with psuedopodia like process. They consist of subtypes with distinct phenotypes

and found to synthesize higher quantities of chondroitin sulphate and lesser quantities of heparin sulphate and hyaluronic acid. The main function of fibroblasts is the production

of various types of fibers and is also instrumental in the synthesis of connective tissue matrix.

B) FIBROBLASTS

The fibroblast is stellate shaped cell which produces:

1. COLLAGEN FIBERS

2. RETICLUIN FIBERS

3. OXYTALAN FIBERS

Various stages in the production of collagen fibers are

as follows:

The first molecule released by fibroblasts is

tropocollagen which contains three polypeptide chains

intertwined to form helix. Tropocollagen molecules are

aggregated longitudinally to form protofibrils, which are

subsequently laterally arranged parallel to form collagen

fibrils.

Collagan fibers are bundle of collagen fibrils. Because of

exceptionally high turnover of collagen in the ligament, any inter

reference with fibroblats function by disease may produce a loss

of supporting tissue of the tooth.

Importantly in inflammatory situations such as those

associated with periodontal diseases, an increased expression of

matrix metalloproteinase's occurs that aggressively destroys

collagen. Thus attractive therapies for controlling tissue

destruction may include host-modulators that have the capacity to

inhibit metalloproteinases.

The damaged periodontal fibers are replaced and

remodeled by newly formed fibers. The “RENEWAL

CAPABILITY” is an important characteristic of periodontal

ligament.

FUNCTIONS Cementoblasts synthesize collagen and protein polysaccharides, which make up the organic matrix of cementum. After some cementum has been laid down, its mineralization begins with the help of calcium and phosphate ions Connective tissue fibers from the periodontal ligament

pass between cementoblasts into the cementum. These fibers are embedded in the cementum and serve to attach the tooth to the surrounding bone and are known as

“Sharpey’s Fibers”. Each “Sharpey’s fibers” is composed of numerous collagen fibrils.

C) CEMENTOBLASTS

a) OSTEOCLASTSa) OSTEOCLASTS

RESORPTIVE CELLSRESORPTIVE CELLS

FUNCTIONS

Multinucleated osteoclasts are the cells which resorb bone.

The surface of an ostoclasts which is in contact with bone

has a ruffled border.

Resportion occurs in two stages

- The mineral is removed at bone margins and then

exposed organic matrix disintegrates. The

osteoclasts demineralise the inorganic part as well

as disintegrates the organic matrix.

b) FIBROBLASTS b) FIBROBLASTS

Fibroblasts are capable of both synthesis and resorption. They exhibit lysosomes, which contain collagen fragments undergoing digestion. The presence of collagen resorbing fibroblasts in a normal functioning periodontal ligament indicates resorption of fibers occurring during remodeling of periodontal ligament.

C) CEMENTOCLASTS C) CEMENTOCLASTS

Cementoclasts are found in periodontal ligament but not remodeled like alveolar bone and periodontal

ligament. These are found on the surface of cementum.

PROGENITOR CELLS PROGENITOR CELLS

FUNCTIONFUNCTION

Progenitor cells are the undifferentiated mesenchymal Progenitor cells are the undifferentiated mesenchymal

cells, which have the capacity to undergo mitotic cells, which have the capacity to undergo mitotic division division

and replace the differentiated cells dying at and replace the differentiated cells dying at the end of their the end of their

life span. life span.

These cells are located in perivascular region and have These cells are located in perivascular region and have

a small close faced nucleus and little cytoplasm. a small close faced nucleus and little cytoplasm.

When cell division occurs, one of the daughter cells When cell division occurs, one of the daughter cells

differentiate into functional type of connective tissue differentiate into functional type of connective tissue

cells. The other remaining cells retain their capacity to cells. The other remaining cells retain their capacity to

divide. divide.

These cells are the remnants of the epithelium of These cells are the remnants of the epithelium of

Hertwig’s Epithelial Root Sheath and are found close to Hertwig’s Epithelial Root Sheath and are found close to

cementum.cementum.

These cells exhibit monofilaments and are attached to These cells exhibit monofilaments and are attached to

each other by desmosomes.each other by desmosomes.

The epithelia cells are isolated from connective tissue The epithelia cells are isolated from connective tissue

by a basal lamina. by a basal lamina.

FUNCTION FUNCTION

The physiologic role of these cells is not known but The physiologic role of these cells is not known but

cells of epithelial rests can undergoe rapid cells of epithelial rests can undergoe rapid

proliferation and can produce a variety of cysts and proliferation and can produce a variety of cysts and tumors tumors

when certain pathologic conditions are present.when certain pathologic conditions are present.

EPITHELIAL CELL RESTS OF MALASSEZEPITHELIAL CELL RESTS OF MALASSEZ

Periodontal ligament showing Periodontal ligament showing

epithelial cell rests of malassez, epithelial cell rests of malassez,

indicated by arrows. indicated by arrows.

Mast cells are small round or oval. These Mast cells are small round or oval. These cells cells

are characterized by numerous cytoplasm, are characterized by numerous cytoplasm,

which mask its small, indistinct nucleus.which mask its small, indistinct nucleus.

The diameter of mast cells is about 12 to 15 The diameter of mast cells is about 12 to 15

microns. microns.

MAST CELLS MAST CELLS

The granules contain heparin and histamine. The granules contain heparin and histamine.

The release of histamine into the extracellular The release of histamine into the extracellular

compartment causes proliferation of the compartment causes proliferation of the

endothelial and mesenchymal cells.endothelial and mesenchymal cells.

FUNCTIONFUNCTION

Mast cells play an important role in regulating Mast cells play an important role in regulating

the endothelial and fibroblasts cell populations. the endothelial and fibroblasts cell populations.

These cells degranulate in response to antigen- These cells degranulate in response to antigen-

antibody formation on their surface. antibody formation on their surface.

Macrophages are derived from blood monocytes and are Macrophages are derived from blood monocytes and are present near the blood vessels.present near the blood vessels.

These cells have a horse-shoe shaped or kidney shaped These cells have a horse-shoe shaped or kidney shaped nucleus with peripheral chromatin and cytoplasm nucleus with peripheral chromatin and cytoplasm

contain phagocytosed material. contain phagocytosed material. FUNCTIONFUNCTION Macrophages help in phagocytosing dead cells and Macrophages help in phagocytosing dead cells and secreting growth factor, which help to regulate the secreting growth factor, which help to regulate the proliferation of adjacent fibroblasts.proliferation of adjacent fibroblasts.

MACROPHAGES MACROPHAGES

Extra cellular substance comprises the following:Extra cellular substance comprises the following:

1.1. Fibers Fibers

a) Collagen a) Collagen b) Oxytalan b) Oxytalan

2.2. Ground SubstanceGround Substance

a) Proteoglycans a) Proteoglycans b) Glycoprotein'sb) Glycoprotein's

PERIODONTAL FIBRES PERIODONTAL FIBRES

The most important element of periodontal ligament The most important element of periodontal ligament

has principal fibres, the principal are fibres are has principal fibres, the principal are fibres are

collagenous in nature and a arranged in bundles and collagenous in nature and a arranged in bundles and

follow a wavy course. follow a wavy course.

-- Collagen is a high molecular weight protein. Collagen is a high molecular weight protein.

EXTRA CELLULAR SUBSTANCE EXTRA CELLULAR SUBSTANCE

Collagen macromolecules are rod like and are arranged in Collagen macromolecules are rod like and are arranged in

form of fibrils. Fibrils are packed side by side to form form of fibrils. Fibrils are packed side by side to form

fibers. fibers.

Vitamin C help in formation and repair of collagen. Vitamin C help in formation and repair of collagen.

Half life of collagen fibers is between 3 to 23 days Half life of collagen fibers is between 3 to 23 days and and

collagen imparts a unique combination of flexibility and collagen imparts a unique combination of flexibility and

strength to tissue.strength to tissue.

The principal fibers of periodontal ligament are The principal fibers of periodontal ligament are

arranged in six particular groups. These are:arranged in six particular groups. These are:

Development of principal fibers of periodontal ligament Development of principal fibers of periodontal ligament

1.1. TRANSEPTAL GROUPTRANSEPTAL GROUP

These fibers extend interproximally over alveolar bone These fibers extend interproximally over alveolar bone

crest and are embedded in the cementum of adjacent crest and are embedded in the cementum of adjacent

teeth. teeth.

-- They are reconstructed even after the destruction They are reconstructed even after the destruction

of alveolar bone resulting from periodontal disease. of alveolar bone resulting from periodontal disease.

-- These fibers may be considered as belonging to the These fibers may be considered as belonging to the

gingiva because they do not have osseous gingiva because they do not have osseous

attachment. attachment.

2.2. ALVEOLAR CREST GROUPALVEOLAR CREST GROUP

These fibers extend obliquely from the cementum just These fibers extend obliquely from the cementum just

beneath the junctional epithelium to alveolar crest. beneath the junctional epithelium to alveolar crest.

-- Fibers also run from the cementum over the Fibers also run from the cementum over the

alveolar crest and to fibrous layer of periosteum alveolar crest and to fibrous layer of periosteum

covering alveolar bone. covering alveolar bone.

-- The alveolar crest fibers prevent extrusion of tooth The alveolar crest fibers prevent extrusion of tooth

and resist lateral tooth movements. and resist lateral tooth movements.

-- The incision of these fibers during periodontal The incision of these fibers during periodontal

surgery does not increase tooth mobility unless surgery does not increase tooth mobility unless

significant attachment loss has occurred. significant attachment loss has occurred.

3.3. HORIZONTAL GROUPHORIZONTAL GROUP

Horizontal fibers extend at right angles to long axis of Horizontal fibers extend at right angles to long axis of

tooth from the cementum to alveolar bone.tooth from the cementum to alveolar bone.

4.4. OBLIQUE GROUPOBLIQUE GROUP

Oblique fibers, the largest group in periodontal ligament, Oblique fibers, the largest group in periodontal ligament,

extend from cementum in a coronal direction obliquely to extend from cementum in a coronal direction obliquely to

bone. They bear the brunt of vertical masticatory stresses bone. They bear the brunt of vertical masticatory stresses

and transfer them into tension on the alveolar bone.and transfer them into tension on the alveolar bone.

5.5. APICAL GROUPAPICAL GROUP

The apical fibers radiate in a rather irregular manner from The apical fibers radiate in a rather irregular manner from

the cementum to bone at apical region of the socket. They the cementum to bone at apical region of the socket. They

do not occur on incompletely formed roots. do not occur on incompletely formed roots.

6.6. INTERRADICULAR FIBERS INTERRADICULAR FIBERS

The interradicular fibers fan out from the The interradicular fibers fan out from the

cementum to the tooth in furcation areas of multirooted cementum to the tooth in furcation areas of multirooted

teeth. teeth.

Some fibers arising from the cementum and bone Some fibers arising from the cementum and bone

are joined in the mid-region of periodontal space. This are joined in the mid-region of periodontal space. This

gives rise to a distinct zone called as “intermediate gives rise to a distinct zone called as “intermediate

plexus”. The remodeling of fibers take place in plexus”. The remodeling of fibers take place in

intermediate plexus. This allows adjustments in the intermediate plexus. This allows adjustments in the

ligament, which accommodate small movements of ligament, which accommodate small movements of

tooth.tooth.

OXYTALAN OXYTALAN

These are immature elastic fibers restricted to These are immature elastic fibers restricted to

walls of blood vessels and are oriented in an axial walls of blood vessels and are oriented in an axial

direction. direction.

-- The function is to support the bloods vessels in The function is to support the bloods vessels in

the periodontal ligament. the periodontal ligament.

GROUND SUBSTANCE GROUND SUBSTANCE

Ground substance is present between cells and fibers Ground substance is present between cells and fibers

of periodontal ligament. of periodontal ligament.

The cell surface proteoglycans participate in The cell surface proteoglycans participate in

several biologic functions including cell-adhesion, several biologic functions including cell-adhesion,

cell-cell and cell-matrix interactions, binding to cell-cell and cell-matrix interactions, binding to

various growth factors as co-receptors and cell various growth factors as co-receptors and cell

repair.repair.

A fibronectin, glycoprotein occur in filamentous A fibronectin, glycoprotein occur in filamentous

form in periodontal ligament. It contain a chemical form in periodontal ligament. It contain a chemical

group that gets attached to surface of the group that gets attached to surface of the

fibroblast, to the collagen, proteoglycans and fibroblast, to the collagen, proteoglycans and fibrin.fibrin.

The ground substance has 70% water in The ground substance has 70% water in

periodontal ligament. periodontal ligament.

The function of ground substance is transporting The function of ground substance is transporting

the food to cells and waste products from cells to the food to cells and waste products from cells to

blood vessels. blood vessels.

STRUCTURES PRESENT IN THE STRUCTURES PRESENT IN THE CONNECTIVE TISSUE CONNECTIVE TISSUE

1. BLOOD VESSELS1. BLOOD VESSELS

Main blood supply is form superior and inferior Main blood supply is form superior and inferior

alveolar arteries. The blood vessels are derived alveolar arteries. The blood vessels are derived

from the following:from the following:

Branches from apical vesselsBranches from apical vessels

Vessels supplying the pulpVessels supplying the pulp

Branches from intra-alveolar vessels Branches from intra-alveolar vessels

Vessels run horizontally and penetrate the alveolar Vessels run horizontally and penetrate the alveolar

bone to enter into the periodontal ligament. bone to enter into the periodontal ligament.

Branches from gingival vessels Branches from gingival vessels

The arterioles and capillaries ramify and form a The arterioles and capillaries ramify and form a

rich network. Rich vascular plexus is found at the rich network. Rich vascular plexus is found at the

apex and in cervical part of ligament. apex and in cervical part of ligament.

2.2. LYMPHATICSLYMPHATICS

Lymphatic drainage is from the ligament to Lymphatic drainage is from the ligament to

alveolar bone. alveolar bone.

Lymphatic vessel network follows the path of blood Lymphatic vessel network follows the path of blood

vessels. vessels.

3.3. NERVES NERVES

Nerves found in ligament pass through foramina in Nerves found in ligament pass through foramina in

alveolar bone. alveolar bone.

The nerves are the branches of second and third The nerves are the branches of second and third

division of fifth cranial nerve (trigeminal nerve) division of fifth cranial nerve (trigeminal nerve)

and follow same path as blood vessels. and follow same path as blood vessels.

These nerve fibers provide sense of touch, pressure, These nerve fibers provide sense of touch, pressure,

pain and proprioception during mastication. pain and proprioception during mastication.

4.4. CEMENTICLES CEMENTICLES

Cementicles are small calcified bodies present in Cementicles are small calcified bodies present in

the periodontal ligament. the periodontal ligament.

They may form into large calcified bodies and fuse They may form into large calcified bodies and fuse

within cementum or remain free. These are found within cementum or remain free. These are found

in old age. in old age.

The degenerated epithelial cells form a nidus for The degenerated epithelial cells form a nidus for

calcification. calcification.

FUNCTIONS FUNCTIONS

The periodontal ligament has many functions, The periodontal ligament has many functions,

important among them are as follows:important among them are as follows:

1.1. PHYSICAL FUNCTIONPHYSICAL FUNCTION

A)A) Provision of soft tissue ‘casing” in order to protect Provision of soft tissue ‘casing” in order to protect

the vessels and nerves from injury due to the vessels and nerves from injury due to

mechanical forces.mechanical forces.

B)B) Transmission of occlusal forces to boneTransmission of occlusal forces to bone

Depending on type of force applied, axial force Depending on type of force applied, axial force

when applied causes stretching of oblique fibers of when applied causes stretching of oblique fibers of

periodontal ligament. periodontal ligament.

Transmission of this tensional force to alveolar Transmission of this tensional force to alveolar

bone encourages bone formation rather then bone bone encourages bone formation rather then bone

resorption.resorption.

But when horizontal or tipping force is applied, But when horizontal or tipping force is applied,

the tooth rotates around the axis.the tooth rotates around the axis.

When a greater force is applied, displacement of When a greater force is applied, displacement of

facial and lingual plates may occur.facial and lingual plates may occur.

The axis of rotation in a single rooted tooth is The axis of rotation in a single rooted tooth is

located in area between the apical and middle third located in area between the apical and middle third

of root. of root.

In multirooted tooth, axis of rotations is located In multirooted tooth, axis of rotations is located

at furcation area. at furcation area.

C)C) Attaches the teeth to the bone. Attaches the teeth to the bone.

D)D) Maintains the gingival tissues in their proper Maintains the gingival tissues in their proper

relationship to the teeth.relationship to the teeth.

E)E) “Shock absorption” resists the impact of occlusal “Shock absorption” resists the impact of occlusal

surfaces. Due to its property of shock absorption surfaces. Due to its property of shock absorption

the teeth are slightly more mobile in early morning the teeth are slightly more mobile in early morning

than in evening. than in evening.

A. The periodontal ligament fibers A. The periodontal ligament fibers

are compressed in areas of pressure are compressed in areas of pressure

(a) and stretched in area of tension (a) and stretched in area of tension

(b) . (b) . B.B. Same tooth in a resting state. Same tooth in a resting state.

2 Theories have been explained for mechanism of 2 Theories have been explained for mechanism of

tooth support. tooth support.

A.A. TENSIONAL THEORY TENSIONAL THEORY

B.B. VISCOELASTIC THEORY VISCOELASTIC THEORY

According to it, principal fibers play a major role in According to it, principal fibers play a major role in

supporting tooth and transmitting forces to bone. supporting tooth and transmitting forces to bone.

When forces are applied to tooth, principal fibers When forces are applied to tooth, principal fibers

unfold and straighten and then transmit the forces to unfold and straighten and then transmit the forces to

alveolar bone, causing elastic deformation of socket. alveolar bone, causing elastic deformation of socket.

A.A. TENSIONAL THEORYTENSIONAL THEORY

According to it, the fluid movement largely controls the According to it, the fluid movement largely controls the

displacement of the tooth, with fibers playing a displacement of the tooth, with fibers playing a

secondary role. secondary role.

-- When forces are transmitted to the tooth, the When forces are transmitted to the tooth, the

extracellular fluid is pushed from periodontal ligament extracellular fluid is pushed from periodontal ligament

into marrow spaces through the cribriform plate. After into marrow spaces through the cribriform plate. After

depletion of tissue fluids, the bundle fibers absorb the depletion of tissue fluids, the bundle fibers absorb the

shock and tighten. This leads to blood vessel stenosis – shock and tighten. This leads to blood vessel stenosis –

arterial lack pressure – ballooning of vessels – tissue arterial lack pressure – ballooning of vessels – tissue

replenishes with fluids. replenishes with fluids.

B.B. VISCOELASTIC THEORYVISCOELASTIC THEORY

FORMATIVE AND REMODELING FUNCTION FORMATIVE AND REMODELING FUNCTION

Cells of the periodontal ligament have the capacity Cells of the periodontal ligament have the capacity

to control the synthesis and resorption of to control the synthesis and resorption of

cementum, ligament and alveolar bone.cementum, ligament and alveolar bone.

Periodontal ligament undergoes constant Periodontal ligament undergoes constant

remodeling, old cells and fibers are broken down remodeling, old cells and fibers are broken down

and replaced by new ones. and replaced by new ones.

NUTRITIONAL FUNCTION NUTRITIONAL FUNCTION

Blood vessels of periodontal ligament provide Blood vessels of periodontal ligament provide

nutrition to the cells of periodontium, because they nutrition to the cells of periodontium, because they

contain various anabolites and other substances, contain various anabolites and other substances,

which are required by cells of ligament.which are required by cells of ligament.

Compression of blood vessels (due to heavy Compression of blood vessels (due to heavy

forces applied on tooth) leads to necrosis of cells. forces applied on tooth) leads to necrosis of cells.

Blood vessels also remove catabolites. Blood vessels also remove catabolites.

SENSORY FUNCTION SENSORY FUNCTION

The nerve bundles found in periodontal ligament, divide into single myelinated nerve, which later on lose their myelin sheath and end in one of the four types of nerve termination. Free endings, carry pain sensations. Ruffini like mechanoreceptors located in the apical area. Meissener’s corpuscles are also mechanoreceptors located primarily in mid-root region. Spindle like pressure endings, located mainly in apex.

- Pain sensation is transmitted by small diameter nerves, temperature by intermediate type;

pressure by large myelinated fibers.

HOMEOSTATIC MECHANISM HOMEOSTATIC MECHANISM

The resportion and synthesis are controlled The resportion and synthesis are controlled

procedures. If there is a long term damage of procedures. If there is a long term damage of

periodontal ligament, which is not repaired, the periodontal ligament, which is not repaired, the

bone is deposited in the periodontal space. This bone is deposited in the periodontal space. This

results in obliteration of space and ankylosis results in obliteration of space and ankylosis

between bone and the tooth. between bone and the tooth.

The quality of tissue changes if balance between The quality of tissue changes if balance between

synthesis and resorption is disturbed. synthesis and resorption is disturbed.

If there is deprivation of Vit C which are essential for If there is deprivation of Vit C which are essential for

collagen synthesis, resorption of collagen will collagen synthesis, resorption of collagen will

continue. So there is progressive destruction and loss continue. So there is progressive destruction and loss

of extra cellular substance of ligament. This occurs of extra cellular substance of ligament. This occurs

more on bone side of ligament. Hence, loss of more on bone side of ligament. Hence, loss of

attachment between bone and tooth and at last, loss of attachment between bone and tooth and at last, loss of

tooth. The connective tissue cells of the periodontal tooth. The connective tissue cells of the periodontal

ligament are turned over and old cells are replaced by ligament are turned over and old cells are replaced by

new ones that are provided by cell division of new ones that are provided by cell division of

progenitor cells. progenitor cells.

CLINICAL CONSIDERATION CLINICAL CONSIDERATION

The primary role of periodontal ligament is to support The primary role of periodontal ligament is to support

the tooth in the bony socket. the tooth in the bony socket.

The width of periodontal ligament varies from The width of periodontal ligament varies from

0.15 to 0.38mm. The average width is:0.15 to 0.38mm. The average width is:

-- 0.21mm at 11 to 16 years of age. 0.21mm at 11 to 16 years of age.

-- 0.18mm at 32 to 50 years of age0.18mm at 32 to 50 years of age

-- 0.15 mm at 51 to 67 years of age0.15 mm at 51 to 67 years of age

So, the width of periodontal ligament decreases as So, the width of periodontal ligament decreases as

age advances. age advances.

In the periodontal ligament, aging results in more In the periodontal ligament, aging results in more

number of elastic fibers and decrease in number of elastic fibers and decrease in vascularity, vascularity,

mitotic activity, fibroplasia and in the number of collagen mitotic activity, fibroplasia and in the number of collagen

fibers and mucopolysaccharides. fibers and mucopolysaccharides.

If gingivitis is not cured and supporting structure become If gingivitis is not cured and supporting structure become

involved, the disease is termed as periodontitis.involved, the disease is termed as periodontitis.

There are few coccal cells and more motile rods and There are few coccal cells and more motile rods and

spirochetes in the diseased site than in the healthy site. The spirochetes in the diseased site than in the healthy site. The

bacteria consists of gram-positive facultative rods and bacteria consists of gram-positive facultative rods and

cocci in healthy site while in diseased site, gram-negative cocci in healthy site while in diseased site, gram-negative

rods and anaerobes are more in number.rods and anaerobes are more in number.

Trauma to the ligament due to mechanical separation Trauma to the ligament due to mechanical separation

can produce pathologic changes such as fracture or can produce pathologic changes such as fracture or

resorption of cementum, tear of fiber bundles, resorption of cementum, tear of fiber bundles,

haemorrhage and necrosis. These result in resorption of haemorrhage and necrosis. These result in resorption of

bone and periodontal ligament is widened, so that the bone and periodontal ligament is widened, so that the

teeth become loose. If trauma is eliminated, repair will teeth become loose. If trauma is eliminated, repair will

take place.take place.

Resorption and formation of both bone and periodontal Resorption and formation of both bone and periodontal

ligament play an important role in orthodontic tooth ligament play an important role in orthodontic tooth

movement. If tooth movement takes place, the movement. If tooth movement takes place, the

compression of PL is compensated by bone resorption compression of PL is compensated by bone resorption

whereas on tension side, apposition takes place.whereas on tension side, apposition takes place.

Periapcial area of the tooth is the main pathologic site. Periapcial area of the tooth is the main pathologic site.

Inflammation of the pulp reached to the apical Inflammation of the pulp reached to the apical

periodontal ligament and replaces its fiber bundles with periodontal ligament and replaces its fiber bundles with

granulation tissue called as granuloma, which then granulation tissue called as granuloma, which then

progresses into apical cyst. progresses into apical cyst.

Chronic periodontal disease can lead to infusion of Chronic periodontal disease can lead to infusion of

microorganisms into the blood stream. microorganisms into the blood stream.

The pressure receptors in ligament have a protective The pressure receptors in ligament have a protective

role. Apical blood vessels are protected from excessive role. Apical blood vessels are protected from excessive

compression by sensory apparatus of the teeth.compression by sensory apparatus of the teeth.

The rate of mesial drift of tooth is related to health, The rate of mesial drift of tooth is related to health,

dietary factor and age. It varies from 0.05 to 0.7mm per dietary factor and age. It varies from 0.05 to 0.7mm per

year. year.

AGING OF LIGAMENT AGING OF LIGAMENT

Aging occurs in all tissues of body including all Aging occurs in all tissues of body including all

ligaments. If general and dental health is good, ligaments. If general and dental health is good,

periodontium may remain healthy even in advanced periodontium may remain healthy even in advanced

age. age.

So, always motivate the patients to maintain good So, always motivate the patients to maintain good

oral hygiene and to have regular dental visits to have oral hygiene and to have regular dental visits to have

life long good oral health. life long good oral health.