toothdevelopment (1)

7/24/2019 ToothDevelopment (1)

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Tooth Development

(Odontogenesis)


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Dentition

Primary dentition develops duringprenatal period 20 teeth

Permanent dentition develops as the jawgrows and matures 32 teeth

period in etween during the preteenyears mi!ed dentition period


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T"#$# %$# &'TP# *T%+#* ,

TOOT" D#-#OP,T ut three major

ones a.tually

initiation stage /thto thwee1

ud stage thwee1

.ap stage th

to 40th

wee1s ell stage 44thto 42thwee1s

apposition stage vaires per tooth

maturation stage varies per tooth


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Tooth 5ormation

5irst signs o5 5ormation day 44

thi.1ening o5 the epithelium where tooth

5ormation will o..ur 6 on the 4stran.hial ar.h

more than 0 genes have een identi5ied in the

oral epithelium7 dental epithelium and dental

mesen.hyme88 so e!a.t signaling me.hanisms

remain un.lear


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Tooth 5ormation9 nitial stages

The initiation o5 tooth 5ormation starts around the 3th day o5 gestation:

Primary epithelial bands9 "orseshoe6shaped ands

that appear appro!imately around the 3th day o5

development7 one 5or ea.h jaw:

6there are two sudivisions9 vestibular laminaand

dental lamina

6the dental lamina grows deep into the mesen.hyme

6develops in the 5uture spot 5or the

dental arches6the ingrowths represent the 5uture sites

5or ea.h de.iduous tooth

6the vestiular lamina .ells rapidly enlarge and then

degenerate 5orms a .le5t that e.omes the

vestiule o5 the oral .avity

6involves the physiologi. pro.ess o5 indu.tion

6indu.tion o5 e.todermal tissues y the developing mesen.hyme

6me.hanisms remain un1nown

6at the /thwee1 the stomatodeum is lined with e.toderm outer portion is the

oral epithelium6this gives rise to the primary epithelial bands

6also is a developing mesen.hyme whi.h .ontains neural .rest .ells that have migrated

to the area

6a asement memrane separates the developing oral epithelium and mesen.hyme


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;ud *tage

mar1ed y the in.ursion o5 epithelium into the mesen.hyme

period o5 e!tensive proli5eration and growth o5 the dental lamina 5orms into tooth uds or oral masses that penetrate into the mesen.hyme ea.h tooth ud is surrounded y the mesen.hyme uds < mesen.hyme develop into the tooth germand the asso.iated

tissues o5 the tooth

4: Tooth ud

2: Oral epithelium

3: &esen.hyme


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=ap *tage .hara.teri>ed y .ontinuation o5 the ingrowth o5 the oral

epithelium into the mesen.hyme:

tooth ud o5 the dental lamina proli5erates une?ually in

di55erent parts o5 the ud 5orms a .ap shaped tissue atta.hed to the remaining

dental lamina

this stage mar1s the eginning o5 histodifferentiation

(di55erentiation o5 tissues)

the tooth germ also egins to ta1e on 5orm start o5

morphodifferentiation

a depression 5orms in the deepest part o5 ea.h tooth ud

and 5orms the .ap or enamel organ (or dental organ)

produ.es the 5uture enamel (e.todermal origin)

elow this .ap is a .ondensing mass o5 mesen.hyme

dental papilla produ.es the 5uture dentin and pulp

tissue (mesen.hymal origin)

the asement memrane separating the dental organ and

the dental papilla e.omes the 5uture site 5or the

dentinoenamel junction (DEJ)

remaining mesen.hyme surrounds the dental@enamel

organ and .ondenses to 5orm the dental sacor the dental

follicle


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=ap

stage together the enamel

organ < dental papilla< dental 5olli.le is.onsidered the

developing toothgerm

these germs are5ound in thedeveloping dental

ar.hes and willdevelop into theprimary dentition


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;ell *tage =ontinuation o5 histodi55erentiation and morphodi55erentiation .ap shape then assumes a more ell6li1e shape di55erentiation produ.es 5our types o5 .ells within the enamel@dental organ

1. inner enamel epithelium 2. outer enamel epithelium . stellate reticulum !. stratum intermedium

the dental papilla undergoes di55erentiation and produ.es two types o5 .ells 1. outer cells of the DP 5orms the dentin6se.reting .ells (odontolasts) 2. central cells of the DP 5orms the primordium o5 the pulp

dental [email protected] in.reases its .ollagen .ontent and di55erentiates at a later stage thanthe #O and DP


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Di55erentiation o5 the #namel@Dental organ

outer enamel epithelium ("EE) .uoidal

shape prote.tive arrier during enamel produ.tion may also e .alled the outer dental

epithelium

inner enamel epithelium (#EE) short7 .olumnar .ells

di55erentiates into the enamel se.reting .ells Aameloblasts separated 5rom the dental papilla elow it y

a asement memrane also may also e .alled the inner dental epithelium the ## and O## are .ontinuous region where they .onne.t .urved rim o5 the

#O A cervical loop

stellate reticulum

star6shaped .ells in many layers .enter o5 the enamel organ 5orms a networ1 A reticulum supports produ.tion o5 enamel

stratum intermedium inner layer o5 .ompressed 5lat to .uoidal

.ells supports produ.tion o5 enamel

.ervi.al loop

#EE

"EE


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;ell *tage

6the .ells in the .enter o5

the enamel organ egin to

synthesi>e and se.rete

+%+s

6this pulls water into the #O

6in.reasing amount o5 5luidin the #O 5or.es the .entral

.ells apart

6however7 they remain

.onne.ted via .ellular

pro.esses whi.h ma1es them

star shaped A stellate ret.

; A inner dental epithelium (inner enamel epithelium)


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;ell stage early .rown 5ormation

the dental papilla is separated 5rom theenamel organ y a asementmemrane

immediately elow this ;& is a region.alled the acellular $one

this is where the 5irst enamel proteinswill e laid down

the dental lamina egins to rea1 upinto dis.rete islands o5 epithelial .ells(epithelial pearls) separates the oralepithelium 5rom the developing tooth

the ## .ompletes its 5olding and you.an egin to identi5y the shape o5 the5uture .rown pattern


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Tooth development so 5ar


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=ap and ;ell stages B Permanent

teeth during the .ap stage thedevelopment o5 the permanent

dentition egins the primordia 5or these teeth

appears as an e!tension o55 thedeveloping dental lamina

its site o5 origin is .alled thesuccesional dental lamina

these permanent teeth are.alled succedaneous teeth(anterior teeth and the

premolars) teeth that 5orm with the primary

tooth uds (primaryprede.essors)


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%ppositional stage

se.retion o5 enamel7 dentin and

.ementum

these tissues are initially se.reted as a

matri! that is partially .al.i5ied serves as

a 5ramewor1 5or later .al.i5i.ation


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&aturation stage

.hara.teri>ed y the .ompletion o5

.al.i5i.ation


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%melolasts and Odontolasts ameloblasts

the .ells o5 the ## assume a more.olumnar shape or they elongate

di55erentiate into pre%ameloblasts the pre6%;s indu.e the .ells o5 the dentalpapilla to di55erentiate also

odontoblasts di55erentiation y the mesen.hyme o5 thedental papilla

o..urs a5ter di55erentiation o5 pre6%;segins

results e.ause the pre6%;s indu.edi55erentiation o5 the mesen.hymal .ellsalso

a5ter di55erentiation the ODs then startdentinogenesis


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%t 1the epithelium is separated 5rom thedental papilla y an a.ellular >one:

%t 2the .ells o5 the inner dentalepithelium have elongated7 and the

a.ellular >one egins to e eliminated asodontolasts di55erentiate 5rome.tomesen.hymal .ells in the tooth pulp:

%t 3the odontolasts retreat toward the.enter o5 the pulp7 leaving ehind 5ormeddentin:

%t 4the .ells o5 the inner dentalepithelium7 now amelolasts7 egin to

migrate outward and leave ehind5ormed enamel: e5ore dentin 5orms .ells o5 the #O

re.eive lood supply 5rom vessels o5 thedental lamina

as dentin 5orms7 it .uts o5 this papillarysour.e o5 lood@nutrients

this .auses a drasti. redu.tion in the

amount o5 nutrients that rea.h the #O ut the %;s re?uire e!tensive nutrients to

5orm enamel stellate reti.ulum.ollapses and invagination o5 the O## this rings in lood supply 5romperipheral vessels 5ound outside thetooth


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Dentinoenamel jun.tion

a5ter OD di55erentiation and theinitiation o5 dentinogenesis the;& etween the pre6%;s andODs disintegrates

this allows dire.t .onta.t etween

the pre6%;s and ODs results inthe .ompletion o5 pre6%;di55erentiation to mature %;s

%;s then egin amelogenesisapposition o5 enamel matri!

upon .onta.t o5 the enamelmatri! and dentin thedisintegrating ;& egins tominerali>e 5orms thedentinoenamel junction or DEJ

minerali>ation o5 the developingdentin and enamel is distin.t 5orea.h type o5 tissue


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&imetable for tooth development #ntire primary dentition initiated

etween / and wee1s o5

emryoni. development: *u..essional permanent teethinitiated etween 20th wee1 inutero and 40th month a5ter irth

permanent molars etween 20thwee1 in utero (5irst molar) and Cthyear o5 li5e (third molar)


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$OOT O$&%TO,

ta1es pla.e as the .rown is .ompletelyshaped and the tooth egins to erupt

there5ore the tooth 5orms 5rom the EtopdownF i:e: .rown to root root 5ormation is through the 5ormation o5

a cervical loop the = is the most .ervi.al portion o5 the

enamel@dental organ two layers.onsisting o5 ## and O##

the = egins to grow down into thedental sa.

it 5orms a 'ertigs root sheath

grows down to en.ompass all ut theasal portion o5 the pulp

this sheath shapes the root and indu.esdentin 5ormation in the root area y theODs o5 the dental papilla

this sheath la.1s the stellate reti.ulumand stratum intermedium is .apale o5 di55erentiating into ODs ;'T

,OT %;s

*+The root is eginning to 5orm as an e!tension o5

the inner and outer dental epithelia in the .ervi.al loop

region (circles)whi.h 5orm a ilayered stru.ture .alled

'ertig,s epithelial root sheath:

;: 5ormation o5 dentin y odontolasts aove the rootsheath


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-oot Dentin

The root o5 the tooth is .omposed y dentin and.ementum

dentin 5orms when the outer .ells o5 the dental

papilla are indu.ed to di55erentiation into ODs similar to what o..urs at the .rown area

in5luen.ed y "ertwigGs root sheath

the ODs then undergo dentinogenesis and

se.rete predentin a5ter dentin 5ormation the ;& disintegrates

along with the "ertwigGs sheath


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Periodontal ligament

the surrounding tissues o5 thetooth also develop as the .rownand root 5orm

the mesen.hyme o5 the dentalsa. .ondenses to 5orm theperiodontal ligament

5orms adja.ent to the new.ementum

ends o5 these 5iers insert intothe outer layer o5 .ementumand surrounding alveolar one

the .ells o5 the disintegrating ":root sheath develop intodis.rete islands o5 epithelial.ells e.ome epithelial rests of

/alasse$(5igure /622)

no 1nown 5un.tion they .an e identi5ied in the

periodontal ligament and areresponsile 5or thedevelopment o5 radicularcysts.


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&ultirooted teeth

anterior teeth7 premolars and molars all

egin as a single root root trun1

root o5 the posterior teeth divides 5rom the

trun1 into the .orre.t numer o5 root

ran.hes

di55erential growth o5 the ": root sheath

results in the division o5 the root trun1 into

two or three roots


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toothdevelopment (1)

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