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Dental germ. Morphological and biological characteristics of the tooth germ. Origin of teeth. Teeth have a dual origin: Ectodermal ; Mesodermal : Ectomesenchymal . EPITHELIUM-ECTOMESEMCHYME INTERACTION IN THE TOOTH DEVELOPMENT.

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Origin of teeth
Origin of teeth germ

  • Teeth have a dual origin:

    • Ectodermal;

    • Mesodermal:

    • Ectomesenchymal.


Epithelium ectomesemchyme interaction in the tooth development
EPITHELIUM-ECTOMESEMCHYME INTERACTION IN THE TOOTH DEVELOPMENT

  • Combine tissue type (neural crest cells + mesenchyme) is called ectomesenchyme.

  • In tooth development, an interaction occurs between oral ectoderm and ectomesenchyme to initiate the process.

  • Cellular interactions, between epithelium+ectomesenchyme:Formation of dentine, enamel and cementum as well as crown;


The processes involved in tooth development
The processes involved in tooth development DEVELOPMENT

  • Morphogenesis is stimulated by molecular signals that control:

    • Cell growth;

    • Migration;

    • Cell fate and differentiation.

  • For every developmental event a complex and intricate cascade of gene expression take place to direct the cells to the right place and onto the proper differentiation pathway;

  • Many of these pathways all result from epithelial-mesenchymal interactions in which essentially the same molecular mediators are implicated.


Embryonic terms to consider induction
Embryonic terms to consider DEVELOPMENTInduction

  • First process to occur during embryogenesis;

  • Interaction between developing embryonic cells.


Morphogenesis
Morphogenesis DEVELOPMENT

  • May also be called morphodifferentiation;

  • Development of form and specific tissues;

  • Results from migration of embryonic cells and inductive interactions between these cells.


Dental germ

  • Specification of the embryo through segmentation DEVELOPMENT;

  • Patterningisboth a spatialandtemporaleventasexemplifiedbyregionaldevelopment of incisors, canines, premolars, andmolars, whichoccursatdifferenttimesandinvolvestheclassicalprocesses of induction, competence, anddifferentiation.

  • Process of specialization of embryonic cells.

Patterning

Differentiation


Interstitial growth
interstitial growth DEVELOPMENT

  • Growth deep within a tissue of organ;

  • As opposed to appositional growth – growth at the periphery through the addition of additional cell layers;


Stages of development
Stages of development DEVELOPMENT

  • Initiation;

  • Proliferation;

  • Histodifferentiation;

  • Morphodifferentiation;

  • Apposition;

  • Maturation;

  • Eruption.


Initiation of tooth development
Initiation DEVELOPMENT of toothdevelopment


Iniciation of tooth development
Iniciation DEVELOPMENT of tooth development

  • The newly formed stomadeum is lined by a primitive two- or three-cell-thick layered epithelium covering an embryonic connective tissue that, because neural crest cells have migrated in it, is termed ectomesenchyme;

  • The ectomesenchyme consists of a few spindle-shaped cells separated by a gelatinous ground substance.


Phase 1 initiation phase
PHASE 1-initiation phase DEVELOPMENT

  • Formation of primary epithelial thickening, dental lamina, tooth bud & the cap, bell stage cannot take place in absence of dentally active ectomesenchyme which becomes concentrated in regions of presumptive tooth development;

  • Inner epithelium of enamel organ induces ectomesenchyme of dental papilla to become orientated towards the intervening basal lamina and differentiate into odontoblasts.


Iniciation of tooth development1
Iniciation DEVELOPMENT of tooth development

  • Thickening of the epithelium.


Stages of the initiation
Stages of the initiation DEVELOPMENT

  • Primary epithelial band;

  • Vestibular lamina;

  • Dental lamina.


Primary epithelial band
Primary epithelial band DEVELOPMENT

  • A continuous band of thickened epithelium forms around the mouth in the presumptive upper and lower jaws;

  • This bands are roughly horseshoe shaped and correspond in position of the future dental arches of the jaws;

  • Each band of epithelium quickly gives rise to two subdivisions:

    • The vestibular lamina and

    • The dental lamina just behind it.




Dental germ

Upper epithelial DEVELOPMENT

band

tongue

lower epithelial

band


Dental germ

U DEVELOPMENTpper and lower

epithelial bands


The reason for epithelial thickening
The reason for epithelial thickening DEVELOPMENT

  • The formation of these thickened epithelial bands is the result not so much of increased proliferative activity within the epeithelium as of a change in orientation of the mitotic spindle and clevage plane of dividing cells.


Dental germ

Sagittal DEVELOPMENT section through the head of an embryo.

A. Primary epithelial bands; B. The same structure at higher magnification; C The change in plane of clevage.


Development of the epithelial proliferation
Development of the epithelial proliferation DEVELOPMENT

Upper epithelial

band

Lower

Epithelial

band



Vestibular lamina
Vestibular Lamina DEVELOPMENT

  • Thefirstsubdivision of theprimaryepithelialbandisvestibularlamina;

  • The vestibule forms as a result of the proliferation of the vestibular lamina into ectomesenchyme;

  • Itscellsrapidlyenlargeandthendegenerate to form a cleftthatbecomesthevestibulebetweenthecheekandtooth-bearingarea.


Dental l amina
Dental DEVELOPMENT lamina

  • The othersubdivision of theprimaryepithelialbandisdentallamina;

  • Dental lamina is located orally to the vestibularlamina;

  • Withinthedentallamina, continuedandlocalizedproliferativeactivityleads to theformation of a series of epithelialoutgrowths intotheectomesenchymeatsitescorresponding to thepositions of thefuturedeciduousteeth.


F ormation of the vestibule of the vestibular lamina
F DEVELOPMENTormation of the vestibule of the vestibularlamina


Dental lamina vestibular lamina
Dental lamina, Vestibular lamina DEVELOPMENT

Dental lamina

  • Vestibular proliferationleads to the formation of the vestibular lamina;

  • Oral proliferation leads to the formation of the dental lamina.

Vestibular

lamina


Dental germ

tongue DEVELOPMENT

Vestibular

lamina

Dental

lamina


Next development of dental lamina
Next development of DEVELOPMENTdentallamina

  • Begin localized proliferations;

    • Early in the medial part - incisors;

    • Then in the lateral part - canines and molars;

  • In the upper and lower dental laminaareformed 10 proliferations;

  • The process is called “the formation of tooth bud”

  • This is the beginning of the toothdevelopment;


Initiation of tooth development1
Initiation DEVELOPMENT of toothdevelopment

  • Teethdevelopfromtwotyps of cells:

    • Oralepithelialcells;

    • Mesenchymalcellsfromthedentalpapilla;

    • Neuralcrestcells – ectomesenchymalcells;

  • Epithelialcellsare flat on the surface of theepitheliumand cylindrical immediately above to thebasallamina;

  • Theunderlyingectomesenchymalcellsaccumulatearoundtheepithelialautgrowths.


The flat and cylindrical epithelial cells basal lamina immediately below and ectomesenchymal cells
The DEVELOPMENTflatandcylindrical epithelialcells, basal lamina immediately below, andectomesenchymalcells

Flat cells

Cylindrical cells


Iniciaction of the tooth
Iniciaction DEVELOPMENT of thetooth


Dental germ

The controlling signals ( DEVELOPMENTBMP-7)in place of the thickened epithelium


Proliferation
Proliferation DEVELOPMENT

  • The proliferation is:

    • Multiplication of cells;

    • Increases the amount of tooth bud;

  • The proliferation is observed:

    • Intheepithelium;

    • Intheectomesenchym.


Dental germ

  • Certain DEVELOPMENTcells of thebasallayerbegin to proliferateat a morerapidratethendotheadjacentcells.

    Theseproliferatingcellscontaintheentiregrowthpotential of theteeth .


Toothe development proceeds in three stages
Toothe DEVELOPMENTdevelopmentproceedsinthreestages:

  • Dentalbud;

  • Dentalcap;

  • Dentalbell.

  • Thesetermsarediscriptive of themorphologybutwehave to describethesignificantfuctionalchangesthatoccurduringdevelopment, suchasmorphogenesisandhistodifferentiation;

  • Becausedevelopmentis a continuousprocess, cleardistinctionbrtweenthetransitionstagesisnotpossible.


Dental bud
Dental DEVELOPMENTbud

  • 1. Dental bud;

  • 2. Oral epithelium;

  • 3. Ectomesenchyme.


Histodifferentiation
Histodifferentiation DEVELOPMENT

  • Histological appearance of different cellswith:

    • Different form;

    • Different size;

    • Differentfunction;

  • Than are formed differentlayers of cells :

    • Intheepithelium;

    • Intheectomesenchym.


Dental lamina and vestibular lamina
Dental DEVELOPMENTLamina andVestibularLamina


Morphogenesis with morphodifferentiation
Morphogenesis DEVELOPMENTwithmorphodifferentiation

  • The differentiated cells shall be arranged under differentlayers;

  • Each layer acquires a separate function;

  • Each layer takes part in creating the structures of the tooth, in determining the shape and size of thetooth.




Elements of the tooth germ
Elements of DEVELOPMENTthetooth germ

  • Enamelorgan - epithelial;

  • Dentalpapilla:

    • Мesenchymal;

    • Ectomesenchymal;

  • Dentalfollicle:

    • Мesenchymal;

    • Ectomesenchymal.


Bud stage
Bud DEVELOPMENTstage


Bud stage1
Bud DEVELOPMENTstage


Bud stage of tooth development
Bud DEVELOPMENTstage of toothdevelopment

  • Proliferation of epithelial cells;

  • Mitotic cell division;

  • Increasing the cells number;

  • Increasing the size of the cells;

  • Still no cells differentiation.


B ud stage
B DEVELOPMENTudstage

  • Thebudstageisrepresentedbythefirst epithelialincursionintotheectomesenchyme of thejaw;

  • Theepithelialcellsshowlittleifanychangeinshapeorfunction;

  • Thesupportingectomesenchymalcellsarepacked closely and around theepithelialbud.



Ectomesenchylal cells arriving directly from neural crests
Ectomesenchylal DEVELOPMENTcells arriving directly from neural crests

  • Stem cells involved in the formation of thetooth bud;

  • This is pluripotent cell capable to become virtually any cell.


Dental bud1
Dental DEVELOPMENTbud

  • At this stage there is no cell differentiation;

  • There is onlycell division and cell mitotic activity;

  • The cells are identical in shape and size.


Dental lamina and dental bud
Dental DEVELOPMENTlaminaanddentalbud


Dental bud2
Dental DEVELOPMENTbud

  • Thetooth budnow is a ball of cells;

  • Thetooth bud grows rapidly in volume.


Bud to cap transition
Bud DEVELOPMENT to CapTransition

  • Thetransitionfrombud to capmarkstheonset of morphologicaldifferencesbetweentoothgermsthatgiverise to differenttypes of teeth;

  • Astheepithelialbudcontinues to proliferateintotheectomesenchyme, cellulardensityincreasesimmediatelyadjacent to theepithelialoutgrowth;

  • Thisprocessreferred to as a condensation of theectomesenchyme, resultsfrom a localgrouping of cellsthathavefailed to produceextracellularsubstanceandhavethusnotseparatedfromeachother.


Lateral lamina or gubernaculum dentis
Lateral DEVELOPMENTlaminaorGubernaculumdentis

  • Asthetoothbudgrowslarger, itdragsalongwithitpart of thedentallamina;

  • Sofromthatpointonthedevelopingtoothistethered to thedentallaminabyanextensioncalledgubernaculumdentis orlaterallamina.


The extension of the dental bud into the ectomesenchyme
The DEVELOPMENTextension of thedentalbudintotheectomesenchyme


The e xtension continues and can be seen condensing ectomesenchyme
The DEVELOPMENT extension continues and can be seen condensingectomesenchyme.


Transition from dental bud to dental cap there is condensed ectomesenchyme
Transition from DEVELOPMENTdentalbud to dentalcap.There is condensedectomesenchyme.


Model of mutual stimulation between the epithelial and ectomesenchymal growth factor s
Model of mutual stimulation between the DEVELOPMENTepithelialandectomesenchymalgrowth factors.

  • Separated from ectomesenchyme factors (red) stimulated epithelialcells (blue), which in turn cause the release of others in the ectomesenchyme(pink);

  • Immediately the bone morphogenetic protein (green) inhibits the further release of epithelialfactors (blue);

  • This is the starting signal for the cellsdifferentiation.


Crossing the bud stage in ca p stage
Crossing the DEVELOPMENTbudstage in cap stage



Cap stage
Cap DEVELOPMENTstage



P rocesses taking place in cap stage
P DEVELOPMENTrocesses taking place incapstage

  • Itisthe beginning of cellular differentiation;

  • Differentiated cells are arranged in layers;

  • Theformativeelements of thetoothare already visible:

    • Theepithelialoutgrowth, whichresemble a capsittingon a ball of condensedectomesenchyme, isreferredastheenamelorgan (itwillformtheenamel of thetooth);

    • Theball of condensedectomesenchymalcells, calleddentalpapilla, formsthedentinandpulp;

    • Thecondensedectomesenchymelimitingthedentalpapillaandencapsulatingtheenamelorgan – thedentalfollicleorsac – giverise to thesupportingtissues of thetooth.


C ap stage early and late
C DEVELOPMENTapstage – earlyandlate


Cup stage
Cup DEVELOPMENTstage

  • Because the enamel organ sits over the dental papilla like a cap, this stage of the tooth development is known as the cap stage.


The concavity of the enamel organ
The DEVELOPMENTconcavity of the enamel organ


Histodifferentiation of the cells of the enamel organ
Histodifferentiation DEVELOPMENT of thecells of theenamelorgan

  • Thecells that covering the enamel organareouterdental (orenamel) epithelium;

  • Thecells, which are covering the recess of the enamel organareinnerdentalepithelium;

  • Thecenter of theenamelorganistermedthestellareticulum:

    • Thecellsinthecenter of theenamelorgansynthesizeandsecreteglycosaminoglycansintotheextracellularcompartmentbetweentheepithelialcells;

    • Glycosaminoglycansarehydrophilicandsopullwaterintotheenamelorgan;

    • Theincreasingamount of fluidincreasesthevolume of theextracellularcompartement of theenamelorgan, andthecentralcellsareforcedapart;

    • Becausetheyretain connectionswitheachotherthroughtheirdesmosomalcontact, theybecomestarshaped.


The layers of the enamel organ in the cap stage
The DEVELOPMENTlayers of theenamelorganinthecapstage

  • You can see three separate cell layers :

    • Outer epithelium– a single row of cuboidal cells;

    • Inner epithelium- cuboid cells adjacent to dental papilla;

    • Stellate reticulum -star shapedcells.They arethe largest volume with large intercellular spaces.


Formation of three new structures
Formation of three new structures DEVELOPMENT

  • Enamelknots – arecluster of nondividingepithelialcells;

  • Enamelcord– enamelknotisextendsbetweentheinnerandouterepitheliaastheenamelcord;

  • Enamelniche- spaces between the epithelium of the dental laminaandouterenamelepithelium.


T ransition from the cap to the bell stage
T DEVELOPMENTransition from thecap to thebellstage

  • 1. Dentallamina

  • 2. Dentalfollicle

  • 3. Outerenamelepithelium;

  • 4. Stellatereticulum;

  • 5. Innerenamelepithelium;

  • 6. Dentalpapilla;

  • 7. Enamelcord - epithelial proliferation, which seemed to divide enamel organ into two parts;

  • 8. Enamel

  • 9. Blood vessels;

  • 10. Enamelniche;

  • 11.Permanenttoothbud


E namel knot
E DEVELOPMENTnamelknot

  • Enamelknotsareclusters of nondividingepithelialcells;

  • Thecurrentviewisthattheenamelknotrepresentsanorganizationalcenter, whichorchestratesmorphogenesis.


Enamel knot
Enamel DEVELOPMENTknot

  • Blue dots are the boundary between epithelial and ectomesenchymecells;

  • Red circles and arrows indicate enamel knot - the command center.


Enamel knot formation in tooth cap
Enamel knot formation in tooth cap DEVELOPMENT

  • The primary enamel knot is under the influence of beta-catenin;

  • The progression of a budin the cap is done undermesenchymal incentives that activate cells from the tip of the tooth bud to form enamel knot. This is the epithelial signaling center.

  • The enamel knot is an important regulator of tooth shape;

  • Induction of theenamelknotis required for the transition from bud to cap;


Enamel knot1
Enamel DEVELOPMENTknot

  • Enamel knot iscluster of nondividingepithelialcells.

  • If theenamelknot be removed, thetooth is not developing.


Dental germ

E DEVELOPMENTnamel knot - the expression of growth factors


E namel knot and enamel cord
E DEVELOPMENTnamelknotandenamelcord

  • Eachtoothgermhas a singleprimaryenamelknotandenamelcordatthecapstage, andasthesedisappear, secondaryenamelknotsappearatthetip of thefuturecuspsinmolars.


Enamel cor d
Enamel DEVELOPMENTcord

  • Localized group of cells in the enamel organ;

  • Enamel cord be located under the outer enamel epithelium;

  • It directs and binds to enamel knot;

  • The function of the enamel cord is obviously associated with theenamel knot.


Dental germ

E DEVELOPMENTnamel cord

Enamel

knot


Enamel niche
Enamel DEVELOPMENTniche

  • Thisstructureiscreatedbytheplane of sectioncuttingthrough a curvedlaterallaminasothatmesenchymeappears to besurroundedbydentalepithelium.


Bell stage
Bell DEVELOPMENTstage


Bell stage1
Bell DEVELOPMENTstage

  • Continuedgrowth of thetoothgermleads to thenextstage – bellstage, socalledbecausetheenamelorgancomes to resemble a bellastheundersurface of theepithelialcapdeepens;

  • Duringthisstage, thetoothcrownassumesitsfinalshape (morphodifferentiation);

  • Thecellsthatwillbemakingthehardtissues of thecrown (ameloblastsandodontoblasts) acquiretheirdistinctivephenotype (histodifferentiation).


Enamel organ has four layers of cells
Enamel DEVELOPMENTorganhas four layers of cells

  • Attheperiphery of theenamelorganthecellsassume a lowcuboidalshapeandformtheouterdentalepithelium;

  • Thecellsborderingonthedentalpapillaassume a shortcolumnarshape – innerdentalepithelium;

  • Thestar-shapedcellsformsstellatereticulum;

  • Inthebellstage, someepithelialcellsbetweentheinnerdentalepitheliumandthestellatereticulumdifferentiateinto a layercalledthestratumintermedium.


B ell stage of the enamel organ
B DEVELOPMENTellstage of theenamelorgan


B ell stage of the enamel orga n
B DEVELOPMENTellstage of theenamelorgan

  • Represents enlargement of the overall size of the tooth germ and deepening of its under surface;

  • Cells at the center secrete an acid mucopolysaccharide into the extracellular space between the epithelial cells covering the germ, (drawing in of the water cause enlargement of germ);

  • A zone of stretched but interconnected cells (stellate reticulum) produced at center of the germ;

  • Epithelial cells:

    • Next to the papilla develop into an enamel-producing layer of cells (inner dental epithelium);

    • Along leading edge of germ form the outer dental epithelium (dental cuticle).

    • The transition zone between outer and inner dental epithelia forms the cervical loop.


Outer enamel epithelium
Outer DEVELOPMENTenamelepithelium

  • Thislayercoverenamelorgan;

  • Thecellsarecuboidalshape;

  • They areconnected to dentallamina;

  • The function of this cell layeris to transport products from dental follicle to enamelorganand to limit the growth impulses of enamel organ.


Inner enamel epithelium
Inner DEVELOPMENTenamelepithelium

  • In the early bell stage theyhaveshortcolumnarshape;

  • Thecellsbecometallandcolumnar;

  • The cells are located directly above the basementmembrane, which separates them from the cells of the dental papilla;

  • They have highly developed intracellular organelles;

  • At this stage they receive nutrients from the dental papilla;

  • Cell nucleus is large and positioned above the basement membrane.


Inner epithelium
Inner DEVELOPMENTepithelium


Functions of the inner epithelium
Functions of the DEVELOPMENTinnerepithelium

  • These cells are called "pre ameloblasts”

  • Thefunctionsare:

    • They are differentiated for protein synthesis;

    • They are preparing for secretory function;

    • They stimulate the underlying ectomesenchyme ofthedentalpapilla;

    • They produce and secrete the enamel;

    • They determine the shape of the dental crown.


Stellate reticulum
Stellate DEVELOPMENTreticulum

  • Thestar-shapedcellsareconected to eachother, to thecells of theouterdentalepithelium, and to thestratumintermediumbyattachmentplaquesknownasdesmosomes;

  • Theircytoplasmcontainsall of theusualorganelles, butthesearedistributedsparsely;


S tellate reticulum
S DEVELOPMENTtellatereticulum


Functions of the stellate reticulum
Functions of the DEVELOPMENTstellate reticulum

  • This layer provides a space for the development of enamel;

  • It transports nutrients and incentives fortheameloblasts;

  • In the wide intercellular space theystored thenutrientsandwater;

  • There takes place transformation of the different substances.


Stratum intermedium
Stratum intermedium DEVELOPMENT

  • Thecells of stratumintermediumareconnected to eachotherand to thecells of thestellatereticulumandinnerepitheliumalsobydesmosomes;

  • Thereare openings between the cells;

  • These cells can to be further differentiate into the cells of the neighboring layers;

  • This is the reason this layer is called thegerminativelayer.


Stratum intermedium1
Stratum intermedium DEVELOPMENT


Two other important events occur during the bell stage
Two DEVELOPMENTotherimportanteventsoccurduringthebellstage:

  • First, thedentallamina (andlaterallamina) joiningthetoothgerm to theoralepitheliumbreaksupintodiscretislands of epithelialcells, thusseparatingthedevelopingtoothfromtheoralepithelium;

  • Second, theinnerdentalepitheliumcompletesitsfolding, makingitpossible to recognizetheshape of thefuturecrownpattern of thetooth.


Epithelial pearls
Epithelial DEVELOPMENTpearls

  • Fragmentation of thedentallaminaresultsintheformation of discreteclusters of epithelialcellsthatnormally degenerate, butsomemaypersistandaregiventhename of epithelialpearls;

  • Thesemayformsmallcysts (eruptioncysts) anddelayederuption;

  • Maygiverise to odontoma;

  • Ormaybeactivated to formsupernumeraryteeth.


D isintegration of the dental lamina
D DEVELOPMENTisintegration of thedentallamina


D isintegration of the dental lamina at higher magnification
D DEVELOPMENTisintegration of thedentallamina at higher magnification


Zone of reflexion or cervical loop
Zone DEVELOPMENT of reflexionorcervicalloop

  • Theregionwheretheinnerandouterdentalepitheliummeetattherim of theenamelorganisknownasthezone of reflexionor “cervicalloop”;

  • Thispointiswherethecellscontinue to divideuntilthetoothcrownattainsitsfullsizeandwhich, aftercrownformation, givesrise to epithelialcomponent of rootformation;

  • Laterepithelialcells of thecervicalloopproliferate to form a doublelayer of cellsknownasHertwig`sepithelialrootsheath.


Dental germ

C DEVELOPMENTervical

loops


Cervical loop
Cervical DEVELOPMENTloop


Dental germ

C DEVELOPMENTervicalloop


Hertwig s epithelial root sheath
Hertwig's epithelial root sheath DEVELOPMENT

  • Hertwig's epithelial root sheath (frequently abbreviated as "HERS") is a proliferation of epithelial cells located at the cervical loop of the enamel organ in a developing tooth.

  • Hertwig's epithelial root sheath initiates the formation of dentin in the root of a tooth by causing the differentiation of odontoblasts from the dental papilla.

  • The root sheath will further dictate whether the tooth will have single or multiple roots.


Functions of the herwig s epithelial root sheath
Functions of the DEVELOPMENTHerwig’sepithelialrootsheath

  • It stimulates the ectomesenchyme of thedental papilla to differentiation;

  • Itsimulatestheectomesenchyme of thedentalfollicle to differentiation;

  • It contains information on the number, size and shape of the dentalroot.


Formation of the permanent dentition
Formation DEVELOPMENT of thepermanentdentition

  • Sofar, onlytheinitialdevelopment of thedecidious (orprimary) dentitionhasbeendescribed;

  • Thepermanentdentitionalsoarisefromthedentallamina;

  • Thetoothgermsthatgivesrise to thepermanentincisors, canines, andpremolarsformas a result of furtherproliferativeactivitywithinthedentallaminaatitsdeepestextremity;

  • Thisincreasedactivityleads to theformationof anothertoothbudonthelingualaspect of thedeciduoustoothgerm, whichremainsdormantforsometime;


The molars of the permanent dentition
The DEVELOPMENTmolars of thepermanentdentition

  • Theyhavenotdeciduouspredecessors, sotheirtoothgermsdonotoriginateinthesameway;

  • Thedentallaminaburrowsposteriorlybeneaththeliningepithelium of theoralmucosaintotheectomesenchyme;

  • Thisbackwardextentionsuccessivelyformthetoothgerms of thefirst, second , andthirdmolars.


Crown pattern determination
Crown DEVELOPMENTPatternDetermination

  • Thecessation of mitoticdivisionwithincells of theinnerdentalepitheliumdeterminisetheshape of a tooth;

  • Whenthetoothgermisgrowingrapidlyduringthecap to bellstage, celldivisionoccursthroughouttheinnerdentalepithelium;

  • Divisionceasesat a particularpointbecausethecellsarebeginning to differentiateandassumetheireventualfunction of producingenamel;

  • Thepointatwhichinnerepithelialcelldifferentiationfirstoccursrepresentsthesite of futurecuspdevelopment, orthegrowthcenter.


Summary of crown pattern formation in the internal dental e pithelium
Summary DEVELOPMENT of crownpatternformationintheinternaldentalepithelium

Thezone of celldevisionisindicatedbythebrekenedareaintheinnerdentalepithelium, andthezonewherecellshavedifferentiatedbythewhitearea.


Toothe type determination
Toothe DEVELOPMENTtypedetermination

  • Thedetermination of specifictoothtypesattheircorrectpositionsinthejawsisreferred to aspatterning of thedentition;

  • Twohypothetical modelshavebeenproposed to explainhowthesedifferentshapesaredetermined, andevidenceexisttusupportboth:

    • Thefirstisthefieldmodel;

    • Thesecondistheclonemodel.


Field model
Field DEVELOPMENTmodel

  • Thefieldmodelproposesthatthefactorsresponsiblefortoothshaperesidewithintheectomesenchymeindistinctbutgradedfieldforeachtoothfamily;


F or example
F DEVELOPMENTor example:

  • There is a "incisal field" responsible for dentalshape of the incisors;

  • It is concentrated in the central incisal area;

  • The stimulation strongly reducedat the end of the field.


Dental germ

Presumptive DEVELOPMENT

incisor mesenchyme

Molar

field

Incisal field


Clone model
Clone DEVELOPMENTmodel

  • Theclonemodelproposesthateachtoothclassisderivedfrom a clone of ectomesenchymalcellsprogrammedbyepithelium to produceteeth of a givenpattern;


Dental germ

  • Clone DEVELOPMENTtheory

  • Themolarclonhasinducedthedentallamina to begintoothdevelopment. Atitsposteriorborderthecloneanddentallaminagrowposteriorlybymeans of progresszona.

  • B. When a clonereachesthecriticalsize, a toothbudisinitiatedatitscenter. A zone of inhibitionsurroundsthetoothbud.

  • C. Thenexttoothbudisnotinitiateduntiltheprogresszoneof theclonehasescapeditsinfluence.


Development of the dental papilla
Development DEVELOPMENT of thedentalpapilla

  • Thedentalpapillaisseparatedfromtheenamelorganby a basementmembrane;

  • Thecells of thedentalpapillaappearasundifferentiatedectomesenchymalcells, havinganuncomplicatedstructureswithalltheusualorganelles;

  • Bloodvesselsappearearlyinthedentalpapilla, initiallyinthecentralregionalongwithnervefibersassociatedwiththesevessels;

  • Thevesselsbringnutrition to therapidlygrowingorgan;

  • Asthepapillagrows, smallervesselsarealsoseenintheperiphery of thearea, bringingnutrition to theelongatingodontoblastsandameloblasts.


Dental germ

D DEVELOPMENTental

papille


F unctions o f the dental papilla
F DEVELOPMENTunctions ofthedentalpapilla

  • Theectomesenchyme of thedentalpapillaforms:

    • Preodontoblastsintheearlybellstage;

    • Odontoblastsinthelatebellstage;

    • Thepapillacellsarebelieved to besignificantinfurtheringenamelorganbudformationintothecapandbellstage;

    • Thiscelldensityismaintainedastheenamelorgangrows.

  • Dentalpapillagivesrise to thedentinanddentalpulp;


Dental follicle
Dental DEVELOPMENTfollicle

-Thedentalfollicleisdistinguishedclearlyfromthedentalpapillainthatmanymorecollagenfibrilsoccupytheextracellularspacesbetweenthefollicularfibroblasts;

-Thesegenerallyareorientedcircularyaroundthedentalorgananddentalpapilla;

-Clusters of bloodvesselsarefoundramifyingaroundthetoothgerminthedentalfollicleadjasent to theouterdentalepithelium


Dental follicle1
Dental follicle DEVELOPMENT

  • Dental follicle is dental sac with its enclosed developing tooth.

  • It gives rise to three important entities: cementoblasts, osteoblasts, and fibroblasts.

  • Cementoblasts form the cementum;

  • Osteoblasts form alveolar bone;

  • Fibroblasts form periodontal ligaments which connect teeth to the alveolar bone;

  • The dental follicle is formed partly from cells at the base of the dental papilla that flatten and migrate to enclose the whole of tooth germ.


Dental germ

D DEVELOPMENTental

follicle


The role of dental follicle in the development of tooth structure
The role of DEVELOPMENTdentalfollicle in the development of tooth structure

  • Dentalfolliclebringsnutrition to theenamelorgananddentalpapilla;

  • It limits their growth impulses;

  • After stimulation of the Herwig’sepithelialrootsheathdentalfollicleformscement, periodontium and alveolar bone.


T he role of the tooth germ elements in the formation of teeth
T DEVELOPMENThe role of thetooth germ elements in the formation of teeth

  • Enamel organ:

    • Forms enamel;

    • Furthered dental papilla and dental follicle;

  • Dental papilla:

    • Forms dentin and dental pulp;

  • Dental follicle:

    • Forms cement, periodontium and alveolar bone.


S tages of the dental germ development
S DEVELOPMENTtages of thedentalgermdevelopment