ENAMEL

Introduction

Enamel forms a protective covering of variable thickness over the entire

surface of the crown.

On the cusp of molars and premolars the enamel attains a maximum

thickness of about 2 to 2.5 mm, thinning down to almost a knife edge at the

cervical region.

The shape and contour to the cusps receive their final modeling in the

enamel.

It is the hardest calcified tissue in the human body because of its high

content of mineral salts and their crystalline arrangement.

Physical characteristics

Because of high mineral content, enamel is extremely hard, a properly

that enambles it to withstand the mechanical forces applied during its

functioning, this hardness also makes it brittle, therefore an underlying layer of

more resilient dentine is necessary to maintain its intergrity.

The specific gravity of enamel is 2.8 another physical property of

enamel is its permiability. It has been found with radisactive tracers and dyes

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that the enamel acts like semipermeable membrane, permitting complete or

partial passage of certain molecules like c-labeled urea etc.

Enamel is translucent are varies in color from light yellow to grayish

white, because the various in thickness that 2 to 2.5 mm the colour also

changes i.e. the underlying dentine is seen through the enamel.

- Incisal areas may have a bluish finge where the thin edge consists only of a

double layer of enamel.

Chemical properties

Enamel consists of 96% of inorganic materials and 4% organic

materials and water.

The inorganic content of enamel consists of a crystalline calcium

phosphate known as hydroxyapatite which is also found in bone, calcified

cartilage, dentine and cementum.

Various ions – Introtium, magnesium, lead and fluoride, the ions are

incorporated into or absorbed by the hydroxyapatite crystals if there ions are

present during enamel formations.

A fine lacy network of organic material appears between the densely

packed hydroxyapatite crystals.

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The bulk of the organic material consists of the TRAP (Tyrosine rich

amelogenin protein) peptide highly bound to the hydroxyapatite crystal as well

as nonnuelogenin proteins.

Structure of Enamel

Enamel in prepared ground sections can be studied under the light

microscope by means transmitted light, such sections show it to be composed

primarily of elongated structure termed rods.

Structures

Rods the enamel is impact of enamel rods or prisms rod sheets and in

some regims a cementing interprismatic sultanae.

The number of enamel rods has been estimated as ranging from 5 mm

in lower laterals in users to 12 millem in to upper first molars.

From to dentinoenamel for the rods run tortuous cause ofward to the

surface of the fork. The length of most rods is grater than the thickness of the

enamel because of the oblique direction and tortuous course of the rods. The

rods located in cusps the thicker part of the enamel are longer than those at the

cervical areas of the teeth. The diameter of the rods averages 4mm, the

diameter of the rods increases from DE in towards the surface of the tooth at

ratio of 1:2.

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Enamel rods have a crystalline appearance permitting light to pass

through them, under light microscope they appear henogonal round or oral.

In cross section they appear – as “Fish Scales”.

Submicroscopic structure

The rods are cylindrical in shape in made of apatite crystals whose long

axis rods parallel to the layitudanal axis of rod, this is applicable to crystals in

the cervical axis of the rod, the crystals flare laterally to an involved degree as

they approach the rod periphery.

The inter rod regions is an area Surrounding such rod is which crystals

are oriented in a different directions from the those making up the rods.

Rod sheath: the boundary where crystals of the rod must those of the

interod regions at sharp analysis.

A more common pattern in a keyhole pattern or paddle shaped prism in

human enamel, when cut longitudinally, section through the head or bodies of

one ow of rods and to “tails” of an adjacent row. This interrod substance.

These rods measure about 5mm in breath and 9mm in length. The bodies of

the rods are nearer occlusal or incisaly whereas the tails point cervically.

Striations: Each enamel rod is built up of segments separated by chak lines

that give it straighten appearance. These striations demarcate the rods, the

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striations are more pronounced in enamel that is insufficient calcified. The

rods are segmented became the enamel matrix is formed in a rythemic manner.

In humans there segments seem to be uniform length of about 4mm.

Directions of rods

Generally the rods are oriented at right angles to dentine surface. The

cervical and central part of it crown of Deciduous tooth they are approximately

horizontal. Near the incisal edge cusp tip they change gradually to an

increasingly oblique direction until they are they are almost vertical.

The permanent teeth is similar in the overall two thirds of the crown. In

the cervical region however, the rods deviate from the horizontal in an apical

direction (way course mention).

Deviation: Example it the middle part of the crown in divided into thin

horizontal disc, the rods in the adjacent discs bend in opposite directions, i.e. if

an discs start from the dentine in a oblique directions and bend more or less

sharply to the left side, whereas it adjacent disc the rods bend towards the

right. This alternating clock wire deviation from radial direction can be

observed at all levels of the crown if the discs are cut in the places of like

general rod direction.

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If discs in cut in oblique plane especially near the dentine in the regions

of cusp tips or incisal edges, the rod aggregate appears more complicated, to

bundles of rods seen to interwine more irregularly.

This appearance of enamel is called Gnarled enamel.

The enamel rods forming the developmental fissure and patients

concern in their outward course.

Hunter schileger bands

Change in directions of rods in responsible for the appearance of the

hunter schreger bands. There are alternative dark and light strips of varying

widths (seen in longitudinal sections and oblique reflected light). They

originate at DE/n and pass outward ending at some distance from out enamel

surface.

Some investigators claims that variations is calcification of the enamel

that coinside with the distribution of the bands of hunter schreger. Hunter

Schreger bands are composed of alternative zones having a slightly different

permeability and a different content of organic material.

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Incremental lines of Retzices

Appear as brownish bands in ground sections of the enamel,

incremental pattern of the ename. That is successive apposition of layers of

enamel during formation of the crown.

The incremental line have been attributed to periodic bending of the

enamel rods, to variations in basic organic structure, or to a physiologic

calcification rhythem.

Incremental lines if prevent in moderate intensity are considered normal

due to metabolic disturbance during formation of enamel broading of the

incremental line take place and reading them more prominent.

Surface structure

A relatively structures layer of enamel approximately 30 mm thick is

seen 70% permit teeth and all deciduous teeth, seen monthly over cusp tips

and cervical area, in this layer prism outline are visible and all apatite crystals

are parallel to one pillar and perpendicular. To strike of Retzines, it hevily

mineralized area.

Other microscopic details seen are like newly erupted teeth as

1. Prikymata

2. Rod ends.

3. Cracks (lamellae)

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Perikymata are transverse, wave like grooves, believed to be to external

manifestation of the strike of Retzines.

They are continues mound the tooth and usually lie prallel to each other

and to the cemetoenamel.

Enamel rod ends are concave and vary in depths and shape, they are

shallowest in the cervical regions and depth near the incisal or occlusal

edges.

Cracks are the outer edges of lamellae and a right angles to DE for.

Enamel lamellae are their leaf like structures the extended from the

enamel surface towards a dentin enamel for and also may penetrate dentin.

The consist of organic material but with little mineral intent.

Lamellae may develop in planes of tensins, where rods cross such

plane, a short segment of rods may not calcify, if it distribution in more seven

a crack may develop.

3 types of lamellae are seen.

Type A – Lamellae composed of poorly calcified rod segments.

Type B – Lamellae caristing of degradation colds.

Type C – Lamellae arising in erupted teeth where be cracks are filled with

organic matter.

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If has suggested that enamel lamellae may be a site of crack in a tooth

and may form a road of entry for bacteria that initate caries.

Neonatal lini or Neoratal ring

The enamel of the deciduous teeth develops partly before and partly

after birth, the boundary between the two portions of enamel in deciduous

teeth in marked by an accentuated incremental line of Rotizices, it is as a result

of abrupt change in the environment and nutritions of the newborn infront.

Enamel criticle

A delicate membrane called Nasmyth’s membrane, or primary enamel

cuticle careers covers the entire crown of the newly erupted tooth but a

probably soon removed by masticators. This membrane in a typical buccal

lamina found beneath most epithelia.

(Re basal lamellae is secrated by the endoblast when enamel formation

is completed)

Enamel tufts

Enamel tufts are at dentinoenamel for to the enamel to about one fifths

to one 3rd of its thickness, they are narrow, ribbon like structure and resemble

tufts of grass, so they are named enamel tufts.

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Tufts consists of hypocalcified enamel rods and inter prismatic

stubstance.

Dentinoenamel function

The surface of dentine is pitted at dentioenamel function, shallow

depression of the dentine facing to dentine fit round enamel projections, in

assure to form hold of enamel cap into the dentine.

In microradiograph of ground sections a hypominerlized zone about

30mm thick can sometimes be demonstrated at DE/n.

Odontoblast process and Enamel spindles

Occlusally odontoblast process pass across to dentino enamel functions

into enamel there are formed as enamel spindles.

The direction of the odontoblast process and spindles in the enamel

corresponds to the original directions of ameloblast – i.e. at right angles to the

surface of the dentine.

Age Changes

1. Most apparent age change is wear of occlusal surface and proximal contact

point as a result of mastications.

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2. Surface of unerrupted and recently erupted teeth are covered completely

with proximal rod ends and perikymata and later gingival loss of the rod

ends and perikymata disappear completely.

3. Localized the certain elements such as nitrogen and fluorine have been

found into superficial enamel layers of older teeth.

4. As the results of age changes in to organic portions of enamel, their

resistance to decay may be increased.

5. Enamel become harder with age (eg. Of reduced permeability of old teeth).

Clinical Considerations

1. Cavity cutting

Unsupported enamel rods are not lift at the margins, they would break and

produce leakage.

2. Brittleness of Enamel

Enamel is brittle and does not withstand forces in thin layers or in areas

where there is no underlying dentine.

3. Deep enamel fissures

Although these are not considered pathological, food lodgenet and difficult

clear it area may lead to dental caries, caries penetrate the floor of fissures

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rapidly become to enamel in there areas is very this. As the destructure

process reaches the dentin, it spread along to DE/n under rising to enamel.

4. Dental lamellae – may also be predisposing locations for caries because

they contain much organic materials.

Fluoride

There has been a reduction by 40% or more in the incidence of caries in

children after topical application of Sodium fluoride

Stannous fluoride

Incorporate of fluoride containing dentifrice’s.

Fluoride containing mixtures such as stannous fluoride parts, sodium

fluoride rinse are used to alter the surface of enamel for more substance to

caries.

Adjustment of fluoride level in commercial water supply to 1 parts per

millimeters.

5. Cervical region

Should be kept smooth and well polished, if it rough, food debris bacterial

plaque accurately and gingiva coming with this cause may lead to gingival

inflammation and progress to even severe periodontal disease.

6. Glue of pit and fissure sealents.

Histological clinical considerations

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Hypoplasia

Manifested by pitting, following or even total absence of enamel and

hypo-calcifications in form of opaque or chalky areas.

This may due to

1. Systems

2. Local

3. Genetic

Systemic inflame

Nutritional deff.

Endocarinopathies

Febrile eliseases

Chemical intoxication’s

Dentist should exert has inflame as his patient to ensure sound

nutritional practices. Recommended immunization procedure during

periods of gestations and postnatal endogessor.

Hypoplasia and hypocalcification

If matrix formation is affected, enamel hypoplasia will ensure. If

maturation is lacking or incomplete hypocalcifications results.

1. Systemic origin hypoplasia is termed as chronologic hypoplasia.

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2. Hypoplasia due to congenital synthesis.

Hutchisons teeth in anterior

Mulberry molars

3. Enamel hypoplasia due to hypocalcemia

Developed level of calcium in blood (mainly U / D) it caries molar pitting

variety of hypoplasia.

4. Hypoplasia due to berter injuries

Caries traumatic birth

prematurity born children

children who suffer from treatment hemolytic disease at birth.

5. Hypoplasia due to fluoride

Mottled enamel (ingestion of fluoride coating deficiency molar during to

time of tooth formation may result melted enamel.

Canal – distribution of the anelo blasts during formation stage of tooth

development.

There can be white spotting on enamel, white opaque areas, pitting and

brownish staining corroded appearance.

If is different o retain restoration in such teeth.

They wear and even fracture easily.

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Treatment:

For cosmetic rains – bleady

In race heredity disturbances of the enamel orgats caled odontodysplasia,

apposition and maturation of the enamel are disturbed such teeth have both

eater appearance (poorly calcified teeth).

Tetracycline stains

Deposition it mainly on the dentin, a small ansent of drug may be

deposited on enamel. (composite can be used).

Amelogenesis Imperfeeta

(Hereditary brown enamel, Heriditary Enamel Dysplasia)

it is a endodermal disturbance.

3 bacillus types

1) Hypolactice type defective formation of matrix.

2) Hypominaralization type defective mineralization of the formed matrix.

3) Hypomaturation type when enamel crystallation remains inmature.

C/F if may be present as

1. Discoloration

2. Total absence of enamel.

3. Numerous parallel wrinkles or grooves.

4. Chipped a show depression.

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5. Open contact points between teeth.

6. Overall surface or incisal edge abraded.

Treatment no 4 except of cosmetic improvement.

Tooth Development

At certain points along the dental lamina, each representing the location

of one of the 10 mandibular and 10 maxillary deriduous teeth, the ectodermal

cells multiply still more rapidly and from knobs that grow into the underlying

mesenchyme.

Each of there little downgrowths from the dental lamina represents the

beginning of the enamel organ.

As cells proliferation continues, each enamel organ increases in size

and changes in shape.

Stages

Bud stage

Cap stage

Bell stage

Advanced bell stage

Enamel development starts from the cap stage.

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Cap stage – As the tooth bud starts to proliferates if it does not expand

uniformly, instead unequal growth in different parts of the tooth bud leads to

the cap stage.

The peripheral cells of the cap stage are cuboidal cover to convexity of

the “cap” and are called the outer enamel epithelium, the cells into concavity

of the cap become face, columnar cells and represents the inner enamel

epithelium.

Bud stage – The inner enamel epithelium consists of a single layer of cells that

differentiate prior to amelogenesis into fall columnar cells called anelsblasts.

There cells are 4 to 5 mm in diameter and 40 mm high, there cells are

attached to one another by junctional complexes literary and to cells in to

stratum intermedium by dismosorces.

Stratum intermedium – A few layers of squamous cells form the statum

intermedium between the inner enamel epithelium and stellate reticulum there

cells are closely attached by desmosorces and gap functions.

Stellate reticulum – Before enamel formation begins the stellate reticulum

collapics, reducing the distance between the centrally situated ameloblasts and

the nutrient capillaries near the outer enamel epithelium, this changes begins at

the heights of the cusp or incisal edge and forgives cervically.

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Outer enamel epithelium – The cells of the outer enamel epithelium flatter to

low aiboidal form, at end of the bell stage and during the enamel formation the

surface of outer enamel epithelium is laid into folds, between to folds form

papillae that contains capillary loops which provides a rich nutritional supply

for the intense metabolic activity of vascular enamel organ.

Dental lamina – In all teeth except permanent molars in proliferates at its deep

and give rise to enamel organs of the permanent teeth.

Advanced bell stage: During the advanced bell stage the boundary

between, inner enamel epithelium and odentoblasts outline form future DE/n

and in addition the cervical portion of the enamel organ gives rise to epithelial

root sheath of hertwig.

Life cycle of ameloblasts

Ameloblasts life cycle starts in the inner enamel epithelus or

omeloblastic layer, and the near through ameloblasts in six stages

1. Morphologic stage

2. Organizing stage

3. Formation stage

4. Maturation stage

5. protractive stage

6. dismolytic stage

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Morphologic stage

The cells are short columnar with large oral nuclei that almost fill to

cell body.

High apparatus and controls are located in the proximal end of the cell,

into enclria are evenly disappeared throughout cytoplasm.

Organizing stage

Cells become longer and majorities of the contribute and golgi regimes

from proximal ends to into dental ends of to cell.

Formation stage

Cells retain same size and arranged as previous stage, blunt cell process

or to endoblast cell surface which penetrate the basal lamina enter the

predentine, in the stage intiation of secreature of enamel matrix tube place.

Maturative stage

Enamel maturation occurs after most of the thickness of the enamel

matrix has been formed in the occlusal or incisal area, in the cervical parts of

the crown, enamel matrix formation is still progressing at this fine.

Cells are slightly reduced in size in length and are closely attached to

enamel matrix.

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Ameloblasts display microvilli at their distal extremities cytoplasmic

vacuoles containing material resembling enamel matrix are present.

Protective stage

When the enamel has completely developed and has fully calcified, the

endoblasts leave to the arranged in a well defined layer and can no longer be

differentiated from to cells of stratrum intermedium and outer enamel

epithelium.

There are layer form a satisfied epithelial covering of the enamel called

reduced enamel epithelium.

Function is to protect the mature enamel by separating it from the

connective tissue unit tooth erupts, if connective tissue come in contact with

the enamel anomalies may develop.

Desmolytic stage

In this stage the reduced enamel epithelium proliferates and seems to

induce atrophy of connective tissue, epithelial cells elaborate enzymes that

destroy connective tissue fibers by clesmolysis.

Amelogenis

On the basis of ultrastructure and composition two process are involved

in the development of enamel.

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1. Organic matrix formation

2. Mineralization

Formation of the enamel matrix

Ameloblasts begin their secretary activity when a small amount of

dentine has been laid down.

Ameloblast lose the profection which had penetrated the basal lamina

separating from the predentine.

A thin layer of enamel forms along the dentin. This has been termed the

dentinenamel membrane, the presence of membrane shows that the distal ends

of enamel rods are not in direct contact with dentin.

Development of tomes process

The surfaces of the ameloblasts facing the developing enamel are not

smooth, this is became the long axis ameloblasts are not parallel to the long

axis of rod.

The profections of the ameloblasts into the enamel matrix in called

tomes processes.

They also contain typical secretion granules as well as rough

endoplasmic reticules and mitochondria.

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Distal terminal bars

When the tomes process begin to form, terminal bars appear at the

distal ends of ameloblasts, separating T.P. from the cell proper.

Structurally the terminal bars are localized condensations of

lytoplasmic substance closely associated with thickness code membrane.

The function is unknown.

Ameloblasts covering maturing enamel

Ameloblasts over maturing enamel are considerably shorter than the

ameloblast over in completely formed enamel, these short ameloblasts have a

villous surface near the enamel, and the ends of the tell are packed with

mitochondria.

Their morphology is typical of absorption cells, organic components and

water are lost in minerlization due to the obsorptive property of

ameloblasts.

Mineralization and Maturation of enamel matrix

Mineralization takes place in two stages

1. Immediate partial mineralization.

2. Maturation

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Immediate partial mineralization occur in those matrix segment

and inter prismatic substance as they are laid down. ( this amount to 25%

to 30% of total mineral content).

First mineral actually is in the form of crystalline apatite.

Maturation – is the gradual completion of mineraliztion,

maturation process starts from the height of the crown and progress

cervicaly.

The incisal and occlusal regims reach maturity ahead of the

cervical regims.

Maturation is characterized by growth of the crystal seen an primary

phase, crystal increase in thickness more rapidly than width, same time

organic matrix gradually become thinned and widely spaced to make room for

the growing crystals. This loss of volume of organic matrix is caused by with

drawn of substantial amount of protein as well as water.

Cervical loop

At the free border of the enamel organ the outer the outer and inner

enamel epithelial layer are continuous and reflected into on outer as the

cervical loop.

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When the crown has been formed the cells of this portion given rise to

Hertwig’s epithelial root sheath.

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