oral histology (تم الحفظ تلقائيًا)

8/2/2019 oral histology ( )

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If you remember last time we talked about the

development of the oral region and we started talking

about branchial arches , we said these branchial arches

are structures that appear in the lower part of the face andalso the neck , starting from the end of week three and

they appear as arches , as we said they appear as arches

so this is the head of the embryo and this is the lower jaw ,

we can see the first branchial arches , the second

branchial arch and third branchial arch and so on

These are six arches , each arch is separate from the arch

below it by a groove.

For example these groove is called the branchial cleft ,

from inside if you look at theses groove from inside the

embryo also you will see grooves but these grooves are

called branchial pouches , so the groove is called pouch if

it is from inside , it is called cleft if it's from outside , the

arch itself is called branchial arch and we have six arches

, it is not necessary to see all the arches at the same time

but what you do actually you see , for example arch

number one and two and three maybe but when you start


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see arch number four arch number one is disappear

because arch number one will have added to the

development of the lower part of the face

arches

arch number 4

arch number one

arch

Last time we said that each arch has skeletal elements ,

nervous elements , muscular elements and vascular

elements and we said skeletal elements of face arch aremeckels cartilage and so on , the nervous elements are

trigeminal nerve for first , facial nerve for second ,

glossopharngeal for third and from four to six we have the

vagus nerve and also if you remember , each muscle that

is supplied by one of these nerves should also originate

within the arch , for example if we have the muscle supply

by trigeminal nerve like master muscle or temporalismuscle this means that these muscle develops within the

first branchial arch because this is the nerve for the first

branchial arch .


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And we give an example about one of the muscle that

develops in two arches which is the digastric muscle , the

digastrics muscle located in the floor of the mouth , it has

two bellies , the first belly is supplied by trigeminal , by thisreason it develops in the first arch , the posterior belly is

supplied by facial nerve , for this reason this belly is

developed in the second branchial arch , and also we

discussed the details of the muscular elements and the

vascular elements and now we will come to the

pharyngeal pouches .


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this is how the arches look like from inside , we make a cut

and we are looking at the arches from insidenot from outside . for this reason these grooves here by

this one and this one and this one are not called branchialcleft because these are located inside and called branchial

pouches so branchial pouches important for the

development of the tongue so the tongue is develop from

the branchial pouches .

The first part of the tongue starts to appear at age of

thirty two days and it develops from different swelling

, notice first that here we have the natural swellings

and also we have what we called tuberculum impar

in the middle , these three swelling they are related

to which arch ?? arch number one , so this makes

the anterior part of the tongue , so these swelling ,

the two lateral swelling plus tuberculum impar which

is the medial swelling they later on fused together ,

they swell and fuse together making the anterior two

third of the tongue , now the swelling from the third

arch , also we have a big swelling It's called

Copula/Hypobranchial eminence this develops from

arch # 3 as you see but it over grows the second

arch it over laps the second arch

arch 3

arch 2


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And what does this lead to ?this lead to the development

of the posterior part of the tongue or the posterior third of

the tongue

See here this is the tongue after development , we can

see the first part of the tongue or the anterior two third of

the tongue which is the body of the tongue , this develops

from the first branchial arch and regarding the posterior

part of the tongue it develops from third branchial arch .


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The root of the tongue which is the very much posterior

part of the tongue which is just next to the epiglottis this

develop from arch number 4 , so we have also swelling

from the fourth arch which is particularly . these twoswelling or this part as we see these are the extreme

posterior of the tongue ( root of the tongue )

So on the exam if I said tongue develops from ?? we have

to say arch one , arch three and arch four , these three

gives the body of the tongue . arch one give the anterior

two third of the tongue and arch 3 give the posterior third

of the tongue and arch 4 give the root of the tongue .

Do we have any contribution from the second arch ?yes

the second arch only contribute to the taste buds so the

taste buds of on the tongue they are derived from the

second arch.

For this reason because the anterior part of the tonguefrom arch # 1 , the sensation or the sensory innervation is

from trigeminal nerve and the posterior third of the tongue

is innervated by glossopharngeal nerve which is the nerve

of third arch , and the root of the tongue is from the vagus

nerve , and the taste buds of the tongue are from the

facial nerve because it develops from arch # 2 .

Now what happens later on ?after fusion we still see some

v-shape sulcus so when the anterior two third of the

tongue fuse with the posterior third of the tongue , fusion

leads to sulcus

Fusion 011 %

v-shape sulcus this is called sulcus terminalis , its the

junction between the anterior part and posterior part of the


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tongue or if you like its the junction between the part of

the tongue that develops from the first branchial arch and

the part developing from the third branchial arch.

what is located anterior the sulcus terminalis should be

supplied by trigeminal nerve which is the cranial nerve of

the first arch , and what is located posterior to it is

supplied by glossopharngeal nerve .

the very median part of the median end of sulcus

terminalis we have what we call foramen cecum which is

small depression , this foramen cecum is importantbecause this is the origin for the development of thyroid

gland .

this actually happen by a duct that drops down from this

foramen cecum its called thyroglossal duct , why do we

call it thyroglossal ?? because it's now within the tongue

so glossal , thyro from thyroid so thyroglossal, this drops

down from foramen cecum and descend until it reach the

neck region where it swell and develop the thyroid gland.

this means thyroid gland develops from the area between

the anterior two third and posterior third of the tongue , forthis reason we may see thyroid tissue within the tongue ,


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why ?? because this tissue is eminence Of the thyroid

gland , we call it ectopic thyroid tissue , also this ectopic

thyroid tissue is functional.

we have group of papillae that are usually located

anteriarly To sulcus terminalis , so these are located within

the anterior two third of the tongue , but the origin of these

papillae is from the posterior third , for this reason these

taste buds that are present on the circumvallate papillae

these are supplied by glossopharngeal nerve although

they are located anterior to sulcus terminalis ,, why ??

because during the development of the tongue these

papillae migrate from the posterior third to the anterior two

third so they cross sulcus terminalis.

we have taste buds on vallate papillae , these taste buds

are response for the sour taste . innervation for this

papillae is glossopharngeal nerve

sulcus papillae terminalis anterior two third of the tongue

supplied by trigeminal supplied by

glossopharngeal

posterior third sulcus terminalis sulcus terminalis

For this reason they take the embryological innervationwith them . the tongue sensory the first nerve which is

trigeminal nerve provides sensory innervations for the

anterior two third of the tongue , sure except the region of

the circumvallate papillae , the taste in the anterior two

third of the tongue is from the facial nerve , the taste at the

posterior part of the tongue is from glossopharngeal nerve

this is also include the taste buds located at the vallatepapillae , the extreme posterior of the tongue is from


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vagus nerve which is the cranial nerve # 10 that is

responsible for the innervations of the 4th , 5th , 6th arches ,

so thats why the 4th arch nerve through the branch called

superior laryngeal nerve , its supply both sensory andtaste to the root of the tongue , if we have taste buds at

the extreme posterior part of the tongue this is supplied by

vagus nerve , the posterior third sensory and taste from

third branchial arch which is glossopharngeal nerve and

regarding the motor supply , the muscles of the tongue

they get very special innervations from another nerve , this

nerve is called hypoglossal nerve which is cranial nerve #12 hyogloosal nerve , the innervations of the muscles of

the tongue the intrinsic and extrinsic muscle.

Remember the myotoms , they are from the metotic

somites , remember last lecture we said we have the head

somites , we have the prootic somites will form the

muscles of the eye and the myotom of metotic somites will

form the muscles of the tongue , so thats why metotic

somites carry with them the hypoglossal nerve supplied

muscle .


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The development of the face :

The face grows by number of process .we have the

maxillary process , mandibular process and frontonasal

process , together these proceses they make the face .

Maxillary and mandibular process are paired process ,

one process on the right and the another on the left .

Let us see this big process , FNP this is the frontonasal

process , this process here and here are the maxillary

process , and this long process here is the mandibular

process .

Face develop around stomodeum ,stomodeum is the

primitive mouth .

Can you see here this depression above the mandibular

process ?this cavity is called stomodeum or the primitive

mouth of the embryo .


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The primitive mouth of the embryo is separated from the

beginning of gastrointestinal tract by the buccopharngeal

membrane which came from prochordal plate , and we

said before the age of 21 day this membrane is active sothis means that the stomodeum is separated from the

gastrointestinal tract . But at the age of 21 days this

buccopharngeal or oropharungeal membrane is rupture

Q: the mouth is communicated with GIT tract at the age of

1 _ 10 days ( F )

2_ one month ( T )

Each branchial arch is covered outside by ectoderm and

inside by endoderm . for example arch 2 the outside

covering is ectoderm and the covering inside is endoderm.

the tongue in the first brachial arch from inside and

outside is covered with ectoderm. *** question in the exam


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**The frontonasal process is not from the brachial arch

only the maxillary and mandible processes from firstbrachial arch.

The frontonasal process " the area in pink " develops pits

and it's called nasal pits later it will become nostrils and at

the sides of these pits we find some swellings 2 one

medial called the medial nasal prominence and the lateral

nasal prominence . notice how big the distance isbetween the pits at the beginning after that they start to

migrate towards each other , around each nasal pit there

is swelling , lateral nasal swelling and medial nasal

swelling , the 2 medial nasal process of the 2 nostrils fuse

together forming the intermaxillary segment which form

the tip of the nose , the collamela of the nose (area

between the nostrils )and the median part of the upper lip.and we call it like that because it descends down and take


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place between the 2 maxillary processes , the lateral nasal

process remain within the frontonasal process this gives

the mid portion of the nose and the philtrum of upper lip

inside it there is the area of bone that carries the maxillarypalate ( contain the maxillary incisors central and lateral

incisors ) .

**The upper margin of the upper lip is like M but the lower

lip is one piece and why is that ? because the median part

of the upper lip from the frontonassal process

Regarding to the lateral nasal swelling it becomes the alaeof the nose ( lateral to the nostril ) , the maxillary

processes become the maxilla and the mandibular

processes fuse together forming the mandible .

Nasolacrimal duct :

Its a canal that take the tears down to the nose and its

form in the groove between the maxillary process and thelateral nasal swelling.


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Between the maxillary process and lateral nasal swelling

we have a groove this groove will deepen and create a

canal called lacrimal canal or nasolacrimal duct ( joints the

lacrimal bone with the nose ) when u start crying when ustart releasing tears the first thing to feel is running nose

now the extra tears that the duct can't coop with will go out

and wet your skin . so what happens if something went

wrong the maxillary process fails to fuse with the philtrum

of the upper lip we will have a condition called cleft lip .

We have to define two types of two part of the palate ,

primary palate and secondary palate , the anterior region

of the palate that carries the central and lateral incisors is

called the primary palate and the remain part is called the

secondary palate , primary and secondary palate are

formed separately and finally they fuse together forming

the whole palate .

Secondary palate has two parts one on the left side andone on the other side , these are called the palatine

processes , at first these processes are vertical , why are

they vertically oriented not horizontal ? because we have

a structure that occupies the space between them , this

space is occupied by the tongue , with time , with the

facial growth , the tongue becomes lower and drops in the

space between the two palatine processes , which allowsthe processes to go horizontally and fuse with the primary

palate , so now we have primary palate anteriarly and two

palatine processes posteriorly , the three part fuse

together and form the whole palate , thats why they start

to adjust themselves ( they start to go horizontal instead of

vertical )


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In anatomy the palate is formed by two bones the maxilla

and the palatine bones , here we talk about separate

processes and not separate bones , that help in forming

the palate , so , the tongue is in between , horizontalreorientation and then they start to reorient themselves ,

the tongue goes down , first they fuse with the nasal

septum , because in the nasal cavity we have the nasal

septum so all of these fuse together.

The palate is completed by 60 days , the point of fusion is

the point where the two sides meet with primary palate ,

and then fusion goes in three directions .

If we have a problem in fusion , this problem actually will

be seen as failure of fusion , some people ( one case in

every 700 birth ) are born with the cleft palate . why this

happen ? It is because we have many reasons of fusion

failure . most of the cases are because of genetic

problems , so when the two palatine processes failed todevelop , they form what we call cleft palate , what

happens when the primary palate fails to fuse with one or

both of the secondary palates ? it gives cleft lip , the

primary palate which also called the premaxilla is formed

by the palatine processes of the maxilla so when the

intermaxillary projections are failed to fuse to each other

the resultant will be cleft lip and failure of the primary andsecondary palate to each other .


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Sometimes when the patient is unlucky we will have a

bilateral cleft . For example when the two palatine bones

fail to fuse to each other and also fail to fuse with the

primary palate ( premaxilla ) .These patients of cleft lip andpalate require multiple surgical procedures which needed

to be completed before the age of 12 , so the

management is going to be at early age .


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Development of the maxilla :

Just to remember we have two type of bone formation :

0-Endochondral in which the preexisting cartilagetransform into bone

2-Interamembranous no preexisting cartilageThe maxilla is formed by intramembranous

ossification in which membranous mesenchymal

tissue become bone.

We have two ossification center in the maxillary

development which are :

0-Maxilla proper2-Premaxilla ( primary palate )

Ossification at the maxilla proper begin 40 days

after fertilization and become hollowed out later to

form the maxillary sinus.

The ossification of the maxillary proper begin

below the infraorbital foramen from here the

process of the maxilla arise which are :


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0-Frontal process which fuse with themaxillary process of the frontal bone

2-Palatine process

3-Alveolar process which carry the teeth 4-Zygomatic processThe most important thing mentioned above is

the medial and lateral alveolar plate which forms

the alveolar process which carries the teeth

Development of the mandible

We will divide its development into two parts the

body and the ramus

The body is formed by intramembranous

ossification , despite the fact we have cartilage

in the region of the body of the mandible which

called meckels cartilage but this cartilage have

nothing to do with development itself it only

guide the development so it act as scaffold

The ramus of the mandible is formed by

endochondoralossification , we have two site of

cartilage : condylar cartilage : it appears at the

11 week after fertilization and continues to


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provide growth for the mandible until 21 years

and it provide growth for the mandible in height

Coronoid cartilage : it only active prenatally because just

before birth it gets replaced by bone

The other thing that we need to understand is that when

we have muscle attachment there will be growth of bone

The angle of the mandible had two muscles of mastication

attached to which contribute to its growth :

0-Medial pterygoid2-MasseterThe coronoid process has muscle attached to it

which also contribute to its growth and called

temporalis muscle

Also in the mandible we have alveolar process which

carry the teeth .

Lecture 2 :Development of the tooth and its supporting

structures

The stomodeum (primitive mouth ) the primitive

mouth is lined by ectoderm and beneath the

ectoderm we have the mesoderm (and we said that

mesoderm in this region the head region is notactually the real mesoderm it is ectomesenchymal

tissue which means that it rises from neural crest

cells ) the site where one tooth is going to develop

we have condensation of ectomesenchymal tissue

just under the ectoderm

We start to see the condensation of the

ectomesenchymal tissue and capillary networkbeneath oral epithelium at specific sites . Why at


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specific sites ? Because we have more than one

tooth and each tooth should be developed at specific

site so at the site where the tooth should be

developed we have condensation of theectomesenchyme

Also we have capillary network at specific site then it

leads to the formation of primary Epithelium band

(PEB) when the oral epithelium thickens and

invagenates into condensed ectomesenchyme . After

that the PEB divides into two parts : one part goes

buccully and also called vestibular lamina and theother part goes lingually and also called dental

lamina

The dental lamina is the structure that will develop

the tooth and the vestibular lamina will become the

sulcus (space ) it goes buccully and labially to form

the oral vestibule ( vestibular lamina with time the

cells inside it become lost and well get a space thisis the space between the teeth and the cheeks _

posteriorly _ or the teeth and the lips _ anteriarly _ )

and the remaining part which goes lingually is called

the dental lamina

So the vestibular lamina goes buccully to form the

oral vestibule ( the space between the teeth and the

cheeks or the teeth and the lips)The dental lamina goes lingually to form the teeth .Thats why its called arch shaped because we r

talking about all teeth together _arch shaped banded

tissue going lingually and it is surrounded by a

condensation . At the end of each one it will form a

teeth but not at the same time .A series of swelling

happens at the deep surface , the terminal end of thedental lamina .These swelling at the terminal end is


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called Enamel organ which is the swelling that

happens in the first part of the tooth bud

.

This is a mandible this is the lower lip this is the area

that is covered by oral epithelial as u see this is the


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primary epithelial band (PEB) starts here and divided

to vestibular lamina and lingual lamina.

Lingual is a band as u see at the edge of this

mandible we have swelling each swelling isresponsible of one of the teeth.

Q: do u think that the band appear as one?? no each

one will form a tooth but not at the same time as we

said in dental anatomy for example mandible central

incisor erupt before the maxillary central incisor

We cant see all the tooth forming together

crown formation

*The dental lamina is responsible for formation ofprimary tooth but also each primary tooth in addition

to the dental lamina which forms primary tooth there

is another swelling responsible for forming the

successor of that tooth ( successor tooth that come

to replace the primary tooth )Q: what is the tooth successes the mandibular

deciduous central incisor ?

Permanent mandible central incisor

That means if we lost the formed structure no

permanent tooth will be developed if the deciduous

tooth is missing also the permanent tooth ( the

successor ) will be missing why ?? because both thedeciduous pre successor and the permanent

successor they develop originally from the same

germ layer

But the opposite is not true if the primary is there but

without swelling the permanent successor will not

***if the primary is missed no permanent will develop


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What about non successor permanent teeth like

permanent first, second and third molar???

They will develop from this extension of the generallamina

And here is the PEB (primary epithelium band )

divide the vestibular lamina from dental lamina where

we find swellings that will form the teeth

Tooth germ : is the early part of the tooth that formed

it includes the enamel organ and the surroundingectomesenchymle tissue and we divide it into 3

different stages:0_bud stage

2-cap stage3bell stage


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Here is the first stage of development we call it bud

stage it looks like a bud we see the oral epithelium

invaginating against condensed ectomasnchyme

later on this epethilium invaginating will start to forma concavity so it looks like a cap so we call it a cap

stage then this cavity will become a big cavity and

that will gives the bell shape then at the end of bell

stage we start to see the formation of dentine in

Dentinogenesis and the after a short while we start

to see the formation of enamel which is

Amelogenesis and finally the crown appear andcrown completion after this the root start to develop

and that will lead to the eruption of the tooth :D

Bud stage

It involves the formation of enamel organ which will

form the outer surface of the crown which is the

enamel

Enamel organ : early structure of tooth that comefrom ectoderm.

So the enamel organ is the one which determine the

three dimensional shape of the crown

REMEMBER that teeth can't develop at the same

time .It s impossible to see the entire tooth

developing at the same time

In the bud stage the enamel organ look spherical orovoid

In the bud stage we cant differentiate the shape of

the tooth it is poorly morpho differentiated so the

three dimensional shape of the crown is not

recognized and poorly histo differentiated so we cant

recognize different type of cell .


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Successive development of tooth germ involve

complex interaction between epithelial and

mesenchymal component

In order to the development of the tooth there mustbe kind of interaction between the epithelium and

ectomasynchyme or between ectoderm and

ectomesnchyme so if we make tissue culture for the

enamel organ there will be no tooth development

because there no mesenchymal tissue which is

needed for process to continue and the opposite is

true and it is similar to the development of nails

The basement membrane which separate between

the epithelium and the underlying mesenchymal

tissue play an important role in order to facilitate this

interaction

Remember the epithelium is the enamel organ and

the epithelium is ectodermal origin .

This is a tooth in the bud stage and here is the oral

epithelium and underlying it we have the condensed

ectomesenchymal tissue


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Cap stage

We divide it into early cap stage and late cap stageEarly cap stageThe down surface of enamel organ

invaginate to form a cap shaped structureCell is still poorly differentiated : not similar to each

other but still we able to differentiate between two

populations of cell which are :

1_ Inner ( central )_ related to the concavity _cellwhich have no specific function and it rounded in

appearance

peripheral cell which further divided into_2 (Internal enamel epithelium (IEE(External enamel epithelium ( EEE

Late cap stage

Here we have the development of cells called stellate

reticulum which in the early cap stage were roundcell with no specific function but here in this stage the

cell start to develop intercellular spaces.

the IEE cell become columnar in shape

the EEE become cuboidal

the ectomesenchymal tissue which surround the

enamel organ is recognized here in 2 different region

1-Dental papilla which is the future pulp and dentine(related to the cells in the central of the concavity)

2-Dental follicle is very important in the formation of

the supporting structure of the tooth like cementum ,

alveolar bone and periodontal ligament

So the whole structure is called enamel organ it has

a concavity that looks like a cap so it is called capstage of enamel organ at this stage we can identify


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Then we have the bell stage which is divided into

early and late

What happens in early bell stage ?? The concavity

deepens starts to become deep until the tooth lookslike a bell thats why it called the bell stage

So what happens during the early bell stage???*Deferential cell division a long IEE ( not at the

same way at different locations ) different rates of

cell division at different sites that what gives different

shapes of the tooth.

What will happen if the rate of cell division rate is thesame in all sites?

***important***

Mapping out the occlusal pattern of the crown*(Cessation of cell division ( stopping*

For example if I have a cell division at a cusp or anincisal edge after awhile I dont want cell division to

continue here because the tip of the tooth will swell

*Active cell division At fissure sites and margin

*Dental lamina breaks down

*losing connection with oral epithelium

*Dental lamina between tooth germs is lost

-Remnants of dental lamina may remain as epithelialrests of series that may be involved in the aetiologyof cysts

*We can identify here in early bell stage

Histodifferentiation :

We can identify different groups of cells each with

different function


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EEE*

Cuboidal cells and they maintain the shape of the

enamel organ and exchange substances betweenenamel and dental follicle

**enamel organ is avascular in order to maintain the

shape of the enamel

Cervical loop*Increased cell division*

At junction EEE and IEE*Stellate reticulum :are found in the center of enamel

organ

stellate because it is a star shape with many branchy

processes and reticulum because it is a net work

they have dendrites processes function in interacting

nutrientsSR are those white cells


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function : *it protects the underlying tissue against

physical disturbance and that maintain the tooth

shape

its hydrostatic pressure is in equilibrium with that ofthe dental papilla allowing the proliferation of IEE to

determine crown morphogenesis

What happens if the hydrostatic pressure inside here

in dental papilla area increase over the hydro static

pressure of SR??The tooth will look like spherical ( it will swell )

IEE : most important cells they are columnar

cells that become elongated starting from the cusp

tips and incisal edges

Dental papilla : less differentiated than enamelorgan

And now what happens In the late stage (

appositional stage)Hard tissue formation ** dentine formation precedesenamel formation**

The first part of the tooth that start to calcify is

the tip of the tooth ( incisal edge or cusp tip)

the last part of the crown that calcify is the most

cervical partAppearance of a lingual down growth of EEE*

In a deciduous tooth germs-Successor lamina

-gives rise to tooth germs of permanent successorteeth


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*In permanent tooth germs :it is a transient

structure that disappears eventually

Behind the second deciduous molars we should

have first , second and third molars which are nonsuccessors dental lamina grows backwards to bud

off permanent molars successively .

:Reciprocal interactionvery important

Dentine and Enamel formation commences at-Cusp tips

-preameloblasts (mature IEE cells ) induce adjacentmesenchymal cells to become columnar and

differentiate into odontobasts and secret predentine

and dentine, then dentine induces ameloblasts to

secrete enamel.


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Done by :Ala'a Al_ Selawi Mais Maloul Al _Selawi

o"It takes a little courage, and a little self-control, Ifyou want to reach the goal. It takes a great deal ofstriving, and a firm and stern-set chin. No matterwhat the battle, if you really want to win, there's noeasy path to glory. There is no road to fame. Life,however we may view it, Is no simple game; But itsprizes call for fighting For a rugged disposition thatwill not quit."

GD LUCK TO U ALL

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