03 amelogenesis - english

8/12/2019 03 Amelogenesis - English

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Enamel: Composition,Formation, and Structure


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EnamelEnamel has involved as an epithelial derivedprotective covering for teeth;

The cells that are responsible for formation ofenamel, the ameloblasts, are lost as the tootherupt, and hence enamel cannot renew itself;


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Compensation

To compensate for this inherent limitation,enamel has acquired a complex structuralorganization and a high degree ofmineralization.These characteristics reflect the unusuallife cycle of the enamel-forming cells, theameloblasts.


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Amelogenesis

This is the process of enamel

formation


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Morphological stages of tooth

developmentBud stage;Cap stage;Bell stage;Early crown stage;

Late crown stage;Early development of the tooth root;Late development of the tooth root.


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The functional stages of life cycle

of the ameloblastsInitiation;Proliferation;Morphogenesis;Organization and differentiation;

Secretion;Maturation;Protection.


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There is a correlation betweenmophological and physiological

stages of the tooth development.


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The development of tooth structure is theresult of complex and continuous mutualstimulation between the epithelial andectomesenchymal cells.


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The stages of the amelogenesis

Amelogenesis, or enamel formation, istwo-step process.The first step produces a partial

mineralized (30%) enamel.The second step (when the full width ofthis enamel has been deposited) involves

significant influx of additional mineralcoincident with the removal of organicmaterial and water to attain greater than96% mineral content.


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Ameloblasts

Ameloblasts secrete matrix proteins andare responsible for creating extracellularenvironment favorable to mineraldeposition;

Ameloblasts exhibits a unique life cyclecharacterized by progressive phenotypicchanges that reflect its primary activity atvarious times of enamel formation.


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ameloblastsThe ameloblasts areectodermally derivedcells;In the process oftooth formation, theydifferentiate as a nice

neat row of cellsaround the future"outside" of the tooth The ameloblastsrequire an inductivestimulus from theembryonic connectivetissue just at the topof this field.


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The chronologicalchanges in

ameloblasts

The histologicalstructure of secretoryameloblasts ;

Flattened

ameloblasts thatmake contact withthe odontoblasts;


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The enamel organcells during

amelogenesis

Amelogenesis is divided intothe secretory stage and thematuration stage, beingseparated by a short period ofmorphological and functionaltransitions of ameloblasts(transitional stage).During the long-lasting procesof enamel maturation,ameloblasts cyclically changestructure and functionbetween ruffle-endedameloblasts (RA) and smooth-ended ameloblasts (SA).Here the enamel organ alsocomprises the papillary layer(PL) being deeply invaginatedby a capillary network.


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A l bl ll hi h
http://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Cell_(biology)


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Ameloblasts arecells whichsecrete the enamel proteins enamelin and amelogenin which will later mineralize toform enamel on teeth, thehardest substance in thehuman body.[1] Eachameloblast is approximately 4

micrometers in diameter, 40micrometers in length and hasa hexagonal cross section.The secretory end of theameloblast ends in a six-sidedpyramid-like projection knowas the Tomes' process
http://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Tooth_enamelhttp://en.wikipedia.org/wiki/Proteinshttp://en.wikipedia.org/wiki/Enamelinhttp://en.wikipedia.org/wiki/Amelogeninhttp://en.wikipedia.org/wiki/Tomes'_processhttp://en.wikipedia.org/wiki/File:Enamelmineralization11-17-05.jpghttp://en.wikipedia.org/wiki/Tomes'_processhttp://en.wikipedia.org/wiki/Amelogeninhttp://en.wikipedia.org/wiki/Enamelinhttp://en.wikipedia.org/wiki/Proteinshttp://en.wikipedia.org/wiki/Tooth_enamelhttp://en.wikipedia.org/wiki/Cell_(biology)


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Life cycle of ameloblastsconsists of six stages :

Morphogenic stageOrganizing stageFormative (secretory)stage(Tome's processesappear in secretorystage)Maturative stageProtective stage

Desmolytic stage


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Apex to apex junctionbetween theouter enamelepithelium

and the innerenamelapithelium orameloblasts


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Phases of the amelogenesis:

Amelogenesis has been described in asmany as six phases but generally issubdivided into three main functionalstages:Presecretory stage;Secretory stage;aturation stage.


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Presecretory stageDifferentiating ameloblasts acquire theirphenotyp, change polarity, develop anextensive protein synthetic apparatus, andprepare to secrete the organic matrix ofenamel.

M h i Ph f h


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Morphogenetic Phase of thePresecretory Stage

During the bell stage the shape of thecrown is determined.Cells of inner epithelium are separatedfrom dental papilla by a basementmembrane;The cells are cuboidal or low columnar,with large, centrally located nuclei, poorlydeveloped Golgi elements in the proximalportion of the cells (facing the stratumintermedium).


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Differentiation Phase of the

Presecretory Stage As the cells of the inner epitheliumdifferentiate into ameloblasts, theyelongate and their nuclei shift proximallytoward the stratum intermedium;The basement membrane is fragmented

by cytoplasmic projections anddisintegrates during mantle predentinformation;


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In each cell the Golgi complex and rough

endoplasmic reticulum increases andmigrated distally;

A second junctional complex develops atthe distal extremity of the cell, dividingthe ameloblast into body and a distalextention called Tomesprocess, ag ainstenamel forms;


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The cell nucleusmoved to the oppositeend towards stratumintermedium;

Thus ameloblastbecomes a polarizedcell, with the majorityof its organellessituated in the cellbody distal to thenucleus


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It's early enough infetal developmentthat no actualcalcification of theenamel has yetoccurred, hence it'slabeled "pre-

enamel." Similarly,there is no "dentin"yet, just pre-dentin.


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Changes in the Dental PapillaSuperficial cells differentiated into odontoblasts;The odontoblasts secrete an organic matrix;

They mineralize it to form the first layer ofdentin;


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Tall columnarameloblasts like

cells showing nuclearpalisading,.


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Presecretory stage .


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Vascular

supply

Compensation forthis distantvascular supply isachieved by bloodvesselsinvaginating theouter dentalepithelium;

And by the loss ofintervening stellatereticulum, whichblings ameloblastscloser to the bloodvessels.


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The Dentinoenamel junction is forming;

A small dentinal loyer is formed;Invagination of the outer dental epithelium.


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Ameloblasts;The cell nucleus moved towards stratum intermedium ;

omes`processes develop.

A l bl t


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AmeloblastThe ameloblasts elongateand are ready to becomeactive secretory cells;

Short conicalTomes`process developsat the apical end;

Junctional complexescalled the terminal barapparatus appear at the

junction of the cell bodiesand Tomes`processesand maintain contactbetween adjasent cells.

Hand points indicating Tome's


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Hand-points indicating Tome'sprocess ofameloblasts .

The content of thesecretory granulesis released againstthe newly formedmantle dentin

along the surfaceof the process;

S


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Secretory stage As the ameloblast differentiates, the matrix is

synthesized within the RER, which then migratesto Golgy`s apparatus, where it is condensed andpackaged in membrane-bound granules;

Vesicles migrate to the apical end of the cell,where their contents are exteriorized and aredeposited first along the junction of the enameland dentin;This first enamel deposition on the surface ofthe dentin establishes the dentino-enamel

junction;


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The disintegration of the basement membrane allowsthe preameloblasts to come into contact with the newlyformed predentin.This induces the preameloblasts to differentiate

into ameloblasts. Ameloblasts begin deposition ofenamel matrix


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Structureless enamel has

formed on the mantel dentinThe inicial layer ofenamel does not

contain enamel rods;Little if any timeelapses between thesecretion of enamelmatrix and itsmineralization.


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Junctional complexes called the terminal bar apparatusappear;The sites where enamel proteins are released

extracellulary can be identified by the presence ofabundant membrane infolding.


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Tomes`process


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The ameloblasts elongate; As the inicial


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The ameloblasts elongate; As the inicialenamellayer is formed, ameloblasts migrat

away from dentin.

S


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Secretory stageSecretion of enamelmatrix becomes to two sites:

The first site is on the proximal part of the process,close to the junctional complex, around the periphery ofthe cell;Secretion from this site along with that from ameloblasts,results in the formation of enamel portion that delimit apit in which resides the distal portion of Tomes`process.This is a continuum throught the enamel loyer calledinterrod enamel ;Secretion fromthe second site (along the face of thedistal portion of the Tomes`process) later fills this pit withmatrix that regulates formation of the so-calledrodenamel .


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The ameloblasts develop the distal portion of Tomes`processas an outdrowth of the proximal portion.

Rod

enamelInterrodenamel

Rod and interrod enamel


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Formation of interrod enamel is always a step ahead because the interrodenamel must delimit the cavity into which rod enamel is formed;

At both sites the enamel is of identical composition, and rod and interrodenamel differ only in the orientation of their crystallites;The distal Tomes`process , creating a narrow space along most of thecircumference between rod and interrod enamel that fills with organicmaterial and forms the rod sheath.

Rod and interrod enamel


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The proximal portion of Tomes`process

(ppTP) extends from the junctionalcomplex to the surface of the enamellayer, whereas the more distal portion

(dpTP) penetrates into enamel Interrod enamel (IR)


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( )surrounds the forming rod (R)and the distal portion ofTomes`process (dpTP);This portion is the continuatioof the proximal portion (ppTRinto the enamel loyer;The interrod (IGS) and rod(RGS) growth sites areassociated with membraneinfolding (im) on the proximaand distal portion of TP;

These foldings represent thesites where secretory granules(sg) release enamel proteins.

The way of enamel and dentin formation


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The way of enamel and dentin formationThe enamel is formed in the space provided by the enamel organ;The dentin is formed in the space provided by dental papilla.


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Tooth enamel formation

Forming celllayer (blue);

Enamel yellow.


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Appositional stage of tooth development .During this stage of tooth development, bothenamel and dentin are actively secreted until

the crown is complete


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Enamel matrix

Present in small quantities.Its difficult to investigate.

As gel-like which crystal is deposited.It composed large variety of amino acid.It can flow under pressure from the growing

crystal.

e na ure o ename ma r x

E l l i i


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e na ure o ename ma r xEarly enamel matrix contain :65% of water;Proteoglycans (small amount);Glycosaminoglycans;Lipid;Citrate;

Inorganic ion (small percentage);The organic material forms a heterogeneous mixture,divided into two :

Amelogenins have large amount of histidine, proline,

leucine, glutamic acid and absent hydroxyproline,hydroxylysine, and cystine.Enamelins contain less proline, glutamic acid, andhistidine compared to amelogenins, while it contain

greater glycine (enamel is devoid of both collagen andkeratin .

Enamel proteins


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Enamel proteinsThe organic matrix of enamel is made from noncollagenous proteins only and contains severalenamel proteins and enzymes.Enamel proteins are :

Amelogenins;

Ameloblastins;namelin;uftelin.

Other macromolecules sulfated glycoprotein,dentin phosphoprotein, dentin sialoproteinEnzymes metalloproteinase, serine proteinase,phosphatase.


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Vesicles in theameloblasts filled withamelogenin;

The red areas containamelogenin.


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melogenins 90% of the enamel proteins are aheterogeneous group of low-molecular-weightproteins known as amelogenins;

Amelogenins are hydrophobic proteins rich inproline, histidine, and glutamine;They accumulate during the secretory stage;Undergo minor short-term and major long-termdegradation;Regulate growth in thickness and width;May also nucleate crystals.

f l


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Taftelin

This is a new, previously unknown acidicenamel protein;

Believed to play an important role inenamel mineralization;In the C-terminal sites have theirstructures facilitating self-assembly andcrystal formation.Self-assembly to form the supramolecularstructural framework

Th j ll l


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The major extracellular events

involved in enamel formation are:(a) delineation of space by the secretoryameloblasts and the dentino-enamel junction;

(b) self-assembly of amelogenin proteins to formthe supramolecular structural framework;(c) transportation of calcium and phosphate ionsby the ameloblasts resulting in a supersaturatedsolution;(d) nucleation of apatite crystallites; (e) elongated growth of the crystallites.


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During the maturation step:

Rapid growth and thickening of thecrystallites take place, which is

concomitant with progressive degradationand eventual removal of the enamelextracellular matrix components (mainly

amelogenins).This latter stage during which physicalhardening of enamel occurs is perhapsunique to dental enamel.


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Maturation stageStarting with the initial mineralization:

Formation of crystals; Arranged in prisms;

Forming enamel prisms cross-architecture;Mineralization continues:Increasing amounts of minerals;Increasing the size of the crystals;Maturation of crystals.

Maturation of the organic matrix.

Mi li i f h l


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Mineralization of the enamel

matrix As enamel matrix is completed and amelogeninis deposited, the matrix begins to mineralize;

As soon as the small crystals of mineral aredeposited, thay begin to grow in lenght anddiameter;The initial deposition of mineral amounts toaproximately 25% of total enamel;The other 70% of mineral in enamel is result ofgrowth of the crystals (5% of enamel is water).

Mineralization and


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Mineralization andmaturation of enamel.

Two mineralization occurred :-Primary mineralization : deposited enamelmatrix, needle shaped crystals appear afterdeposition of thickness, 50 nm of matrix initiallythin widespread dispersed, rapidly increase insize and become hexagonal.Secondary mineralization : occurs at amelo-

dentinal junction, rapid process, cannot be easilydistinguish from initial phase, enamel aretransformed from soft material into hardsubstance, large quantities inorganic materialdeposited in matrix The time between enamel matrix deposition

d i i li i i h
http://dc401.4shared.com/doc/-xrLlLXq/preview.htmlhttp://dc401.4shared.com/doc/-xrLlLXq/preview.html


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and its mineralization is short;

The first matrix deposited is the first enamelmineralized, occurring alonge thedentinoenameljunction;

Matrix formation and mineralization continueperipherally to the tips of the cusps and thenlaterally on the sides of the vrowns, followiong

the enamel incrementqal deposition pattern;

Finally, the cervical region of the crownmineralized.


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Incremental pattern of enamel and dentinformation from initiation to completion

Initialdentin

deposition

Enamelincrement

Dentin

increment


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Summary of enamel mineralization stages. A initial enamel isformed; B initial enamel is calcified as further enamel isformed; C More increments are formed; D Matrix depositionand mineralization proceeds; E and F Matrix is formed on the

side s and cervical areas of the crown.


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A. Enamel crystals to a distal portion of Tomes`process. Theelongating extremity of the rod crystals aobut the infolded

membrane (im) at the secretory surface; B In cross section,newly formed crystals appear as small, needle-like structures

surrounded by granular organic matrix. Secretory granules (sg


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Initial mineralization

Arrangement ofcrystals in the prisms;

Lengthwise jointing ofthe crystals;Crossing the prisms.


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Mineralization After the initialprimary mineralizationstarts fast secondaryand tertiarymineralization;Mineralization startsfrom the top of thecrown and go laterallyto the cervix.

Maturation of the matrix


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Maturation of the matrix After the full thickness of immature enamel hasformed, ameloblasts undergo significant changessignificant morphologic changes in preparationfor their next functional role, that of maturingenamel;

At this stage, they change shape and size; A brief transitional phase involving a reduction in height anddecrease in their volume and organelle contenrt occurs;They lose Tomes`process;During this stage, ameloblasts undergo programingcell death (25% during the transitional phase and25% die as enamel maturation proceeds;The initial ameloblast population thus is reduced byroughly half during amelogenesis.

M t ti P


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Maturation ProperThe ameloblasts become involved in the remouval of water aorganic material from the enamel;

Additional inorganic material is introduced;The dramatic activity of ameloblasts is modulation, the cyclicreation, loss, and recreation of a highly invaginated ruffle-ended apical surface;The modulation seem to be related to calcium transport andalterations in permeability of the enamel organ;This process continuously alkalize the enamel fluid to prevenreverse demineralization of the growing crystallites andmaintain pH conditions optimized for functioning of the matrdegrading enzymes.


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After the mineralization occurs : Ameloblast undergo various change.Maturation of enamel is remarked by loss of water frommatrix.Final stage of maturation :

Loss of Tomes process;Mitochondria aggregate will increase in acid phosphateactivity;Many enzyme found in osteoclast undergo catabolicactivity;

Ameloblast degrade material which is selectivewithdrawn from maturing enamel;

Alkaline phosphatase activity as indication of transportmineral salt across cell membrane as part of finalmaturation enamel.

Ameloblasts in the maturation


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Ameloblasts in the maturation

Its terminal bar apparatusdesappears, and the surfaceenamel becomes smooth;This phase is signaled byachange in the appearance ofthe cell as well as by changein the function of theameloblasts;The apical end of this cellbecomes ruffled along theenamel surface.


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1. Ruffle-endedmaturation

stage;2. Smooth-

endedmaturation

stage.


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Final function of the ameloblasts

The ameloblasts shorten and contact thestratum intermedium and outer

epithelium, which fuse together to formthe reduced enamel epithelium;This cellular organic covering remains on

the enamel surface until the tooth eruptsinto the oral cavity.

Reduced enamel epithelium


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pand enamel cuticle.

Last phase of ameloblast. A homogenous layer found between dedifferentiation and enamelsurface. It described asthin layer of unmineralized enamel matrixcalled primary enamel cuticle.Secondary enamel cuticle occur before tooth eruption. A basallamina type junctional region between inactive ameloblast andenamel surface. After eruption, it known as internal basal lamina orattachment of lamina.

After enamel formation completed, before tooth erupts, ameloblastshorten to cuboidal cell form the inner component of reducedenamel epithelium calledNasmyths membrane.

Reduced enamel epithelium


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educed e a e ep t e uprotective stage of ameloblasts

When the enamel iscompleted, the enamel organis collapsed;There is only reducedenamel epithelium;These are reducedameloblasts and outerepithelium;

Among the outer epitheliumare seen blood vessels of thedental follicle.


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Different stagesof developmentof the enamel1.morphogenetic

stage; 2.histodifferentiation

stage; 3. initialsecretory stage (noTP); 4. secretory

stage (TP); 5. ruffle-ended ameloblast; 6.

smooth-endedameloblast; 7.protective stage.


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Ruffled border of ameloblasts attaches tothe basal lamina by means of

hemidesmosomes (HD)


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Four phases of enamel mineralization.


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Immature enamel

The red areasindicate partially

mineralizedenamel.

Theories for the mineralization of


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Theories for the mineralization ofthe enamel

Various theories which explainsmechanism of mineralisation:

1. Booster mechanism;2. Seeding mechanism/nucleation theory;3. Matrix vesicle concept.

Epitaxy theoryNanosphere theory 1994 . - Fincham;Confirmed by Du and Fallini in1998.;

Booster mechanism


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Booster mechanism

According to this mechanism, due to theactivity of certain enzymes the

concentration of calcium and phosphateions would raise further leadingto precipitation.

The earliest At this stage only one-third toone-half of the eventual crownform has been laid down yet


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The earlieststage

form has been laid down, yetthe enamel next to theamelodentinal junction shows

a bandof high radiopacity, indicating adegree of mineralization.This highly mineralized zone atthe amelodentinal junctionappears soon after the matrixis laid down. It is seen to be present in allrecently formed enamel suchas the growing cervical margin

and the thin occlusal part ofthe developing enamel joiningthe cusps in molars.

Theradiopaque zone occupies the

In the next stage the zone of highmineralization spreads out towardthe outer border of the tip or cusp


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radiopaque zone occupies thegreater part of the enamel overthe cusp and extends along the

amelodentinal junction.

the outer border of the tip or cuspof the tooth

At the same time this zone spreadsout from the amelodentinal junction along the whole length ofthe enamel.This occurs both labially andlingually and, in the molars acrossthe occlusal enamel as well.The direction of spread is irregulaand the border of the zoneappears in some places to beparallel to the amelodentinal

junction and in others parallel tothe enamel surface.

o nsons a a ne p osp a asetheory based on


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p ptheory based on

Booster mechanismThe discovery of enzymealkaline phosphates in mineralizing tissues

suggests that this enzyme is responsiblefor mineralisation.


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Mechanism

Alkaline phosphatase releasesinorganic phosphates from organic phosphate

(hexose phosphates) and thus raise locally thconcentration of phosphate ions in the tissuefluid which reacts with calcium ions in tissuefluid leading to precipitation of insolublecalcium phosphate.This theory is not well accepted.


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2. Seeding mechanism

According to this mechanism, there arecertain substances called seeding or

nucleating having resemblance to apatite.These substances act as mold or templateupon which crystals are laid down, after

which crystallization proceedsautomatically.This process is known asepitaxy.


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Matrix vesicle conceptMatrix vesicles were discovered simultaneous

by Anderson and Ermanno Bonucci;Matrix vesicles (MV) are organelles of cellula

origin that can be observed in the ameloblasts;Histochemical and biochemical studies haveshown that matrix vesicle contain most of thesubstances that are believed to play a role incalcification process, esp AlkPh and relatedenzymes.

Nanosphere theory of


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Nanosphere theory ofmineralization of enamel

Enamel biomineralization involves

secretion of the enamel specificamelogenin proteins that through self-assembly into nanosphere structures

provide the framework within which theinitial enamel crystallites are formed.

l


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Amelogenins

Amelogenins have the remarkablespontaneous self-assembly and

hierarchical organization of amelogenin microribbons and their ability to facilitateoriented growth of apatite crystals.


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E l t i


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Enamel matrix

Amelogenins areorganized in"nanospheres"


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Self-assemblyandhierarchical

organizationof amelogenin

in microribbons and

orientedgrowth of

apatitecrystals.

Fi f l l


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First occurrence of enamel crystals


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Structural and OrganizationalFeatures of Enamel

M h l f l


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Morphology of enamelEnamel rods;Enamel interrod space;Rod sheath;

Striae of Retzius;Bands of Hunter and Schreger;Cross-striation of the rods;

Gnarled enamel;namel Tufts and lamellae;Dentinoenamel junction and enamel spindles;

Enamel surface


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C ti f th d


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Cross-section of the rods rod a package oftightly arranged crystals;

Interrod space -

packaged crystals lose theirshape and go in differentdirections;

Tail of the rod;D Head of the rod.


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One ameloblast (1)forms the rodhead

And the tai is formed

by four ameloblasts(1,2, 3, 4); A part of twoameloblasts forms theneck (2 and 3)

C t l i t ti f th d


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Crystal orientation of the rodsIn the rods longitudinally;In the tail - diagonallyor perpendicular (lower

mineralization);The rod sheats - theleast mineralized place.There the crystals aremeeting with differentdirections.The rod has keyhole-shape form.

The rod is columnar in its long


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The rod is columnar in its longaxis

The head is the broadest part at 5 mwide;

Elongated thinner portion, or tail, is about1 m wide;The rod, including both head and tail, is 9

m long;The rod is about the same size as a redblood cell.

L it di l ti f th l


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Longitudinal section of the enamel

- A cross section of thecrystals forming theinterrod space;- longitudinally arangedcristals in the rod core;

Enamel rods interlock to prevent fracture


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Enamel rods interlock to prevent fractureand splitting of the tooth

Enamel rod groups alsointertwined, therebypreventingseparation;The rod direction in thecrown is normallyperpendicular to theenamel surface whichprovides additionalsupport in preventing

Diff t g f i g i


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Different groups of crossing prisms

Cross section of the rods


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Cross section of the rods

Enamel rods appearwavy;It can be seen keyhol-shape form of therods.


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- The surface of each rod isknown as the rod sheath;

- The rod center is thecore;- The rod sheath contains

slightly more organicmatter than the rod core.


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- The diagramshows orientationof crystals in

the forming rodHead and tail;

- And formingcrystals pack in

the rod fromthe cell complex.

One rodis pulled out


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is pulled outto illustrate

how individual

enamel rodsinterdigitate

with neighboringrods


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Orientation ofcrystals in a mature

enamel rod asindicated by crosssection and side ofcut rod.


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Head TailNeck


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Striae of Retzius in a cross


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sectionIn cross section theyappear as concentricrings;

Neonatal lineWhen present, is anenlarged striae of


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Neonatal line gRetzius thatapparently reflectsthe great physiologicchanges occuring atbirth;

Accentuatedincremental lines alsoare produced bysystematicdisturbances thataffect amelogenesis.

Lungitudinal section of enamel


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Lungitudinal section of enamel

The enamel rods andstriae of Retzius areseen.

Cross Striations


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Cross StriationsHuman enamel isknown to form at arate of approximately4m per day;

Ground sections ofenamel reveal whatappear to be periodicbands or cross

striations at 4-mintervals across so-called rods.

Undulating (wavy) rods


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Undulating (wavy) rods

In the cross section ofthe rods they aredifferently cuted becausetheir wavy course;One part is cutlongitudinally, another transversely;Photomicrograph of

enamel taken by reflectedlight illustratesphenomena of light anddark Hunter-Schrege rbands.

Enamel rods cross section


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of the rods

longitudinalsection of the

rods

Gnarled enamel


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Near the D-E junctionespecially in the cuspalregions, the enamel rodsform intertwining bundles

( A); This arrangement ofenamel rods, close totheir origin at the D-E

junction, is referred to asgnarled enamel.

Bands of Hunterand Schreger


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and Schreger

They are opticalphenomenonproduced by changesin direction betweenadjacent groups ofrods;

Thay are seen mostclearly in longitudinalsections viewed in theinner thirds of the

enamel


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Bands of Hunterand Schreger

Dentinoenamel junction


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Dentinoenamel junctionThe junction betweenthese two hard tissues asa scalloped profile incross section;The shape and nature ofthe junction preventshearing of the enamelduring function.

namellamellae


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Enamel tufts

Dentinoenemael junction

Enamelspindles


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Dentinoenamel Junction


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Enamel tufts


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Enamel tufts

Enamel tufts;

dentinoenamel junction;

Dentin.

namel l ll

namel lamellae.They are faults ind l t f


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lammellae development ofenamel and extendfor varing depthsfrom the surface ofthe enamel;

They are consist oflinear, longitudinallyoriented defects filledwith organic material; namel tufts; Neonatal line.


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namel lamellae;

namel tufts.

Enamel spindles


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Enamel spindles - Enamel spindles

Odontolastprocess in dentin.

Enamel spindles


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Enamel spindles

- enamel spindle odontoblast processesextend through the DEJinto the enamel;

Branched odontoblastprocesses in the dentin;

Enamel rod.


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Final enamel


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Final enamel

Final enamel providesgreater resistance ofthe enamel surface.


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Enamel surfase

Chemical composition of teeth


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Chemical composition of teethIn the permanent teeth inorganic phase of theenamel is 96% ;In the deciduous teeth is 93%;The mineral composition of enamel is:

Hydroxyapatite Ca10 (PO4)6(OH)2;Fluorapatite -Ca10(PO4)6F2;Carbonate Apatite;

In the intercrystalline spaces there are: Amorphous calcium carbonate;Manganese (Mn), zinc (Zn), copper (Cu), magnesium(Mg), aluminum (Al) and etc.

patite crystals


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patite yThe height of the crystal is - 1600 ;The crystal width is 200 ;

A single crystal portrayed as a ;carpenter-shaped pencil configuration;Ribbons;Needles;Hexagonal.

The water in the enamel is in two forms:Loosely connected;Firmly attached to the apatite crystal.

Organic matter


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g

Soluble in acids - 2/3;Insoluble in acids - 1/3;

Organic matter of the enamel is highlyorganized and similar to the keratin;It contains enamelin, tuftelin and

Carbohydrate-protein complexes.

Ionic exchange in the enamel


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Ion exchange in enamel is weak and slow;Ions in the crystal may undergo ionic exchange withions in the environment - saliva;One third of the ions in apatite can exchanged by

replacement of defferent ions heteroionicexchange; It is possible for one ion to be replaced by another othe same kind isoionic exchange.

Structure of the crystal

The inside of the crystal is a mosaic of


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The inside of the crystal is a mosaic of

mutually neutralize electrical charges;On the crystal surface there are electricalasymmetry;

The crystal is covered with a double waterlayer of Helmholtz.

Electrical double layer (EDL)f H l h l
http://en.wikipedia.org/wiki/Helmholtzhttp://en.wikipedia.org/wiki/Helmholtz


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of Helmholtz The DL refers to two parallel layers of chargesurrounding the enamel crystals. The first layer, thesurface charge (either positive or

negative), comprises ionsadsorbed directly onto theobject due to a host of chemical interactions. The second layer is composed of ions attracted to thesurface charge via the coulomb force, electricallyscreening the first layer. This second layer is looselyassociated with the object, because it is made of freeions which move in the fluid under the influence ofelectric attraction and thermal motion rather than beingfirmly anchored. It is thus called thediffuse layer .

Ionic exchange in the enamel

1. The first stage of the ionic exchange is
http://en.wikipedia.org/wiki/Surface_chargehttp://en.wikipedia.org/wiki/Adsorbedhttp://en.wikipedia.org/wiki/Electromagnetismhttp://en.wikipedia.org/wiki/Thermal_motionhttp://en.wikipedia.org/wiki/Thermal_motionhttp://en.wikipedia.org/wiki/Electromagnetismhttp://en.wikipedia.org/wiki/Adsorbedhttp://en.wikipedia.org/wiki/Surface_charge


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g greversible the ions diffuse into the superficialhydration layer;

2. The second stage is easily reversible theions enter into subsurface layer of absorbed ionsand neutralize their charges;

3. The third stage is difficult to reversed - the

ions are included in the surface of the crystal;

03 amelogenesis - english

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