oral histology (second script )

8/2/2019 oral histology (second script )

1/37

If you remember last time we talked about thedevelopment of the oral region and we started talking

about branchial arches , we said these branchial archesare structures that appear in the lower part of the face andalso the neck , starting from the the end of week three andthey 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 archbelow 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 arecalled branchial pouches , so the groove is called pouch if

it is from inside , it is called cleft if its from outside , thearch itself is called branchial arch and we have six


2/37

arches , it is not necessary to see all the arches at thesame time but what you do actually you see , for examplearch number one and two and three maybe but when youstart see arch number four arch number one is disappear

because arch number one will have added to thedevelopment 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 ,

glossopharungeal for third and from four to six we havethe vagus nerve and also if you remember , each muscle

that is supplied by one of these nerves should alsooriginate within the arch , for example if we have the

muscle supply by trigeminal nerve like master muscle or temporalis muscle this means that these muscle developswithin the first branchial arch because this is the nerve for

the first branchial arch.


3/37

And we give an example about one of the muscle thatdevelops in two arches which is the digastric muscle , thedigastrics 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 isdeveloped in the second branchial arch , and also we

discussed the details of the muscular elements and thevascular elements and now we will come to the

pharyngeal pouches.


4/37

this is how the arches look like from inside , we make acut and we are looking at the arches from

inside not from outside . for this reason these grooveshere by this one and this one and this one are not called

branchial cleft because these are located inside andcalled branchial pouches so branchial pouches important

for the development of the tongue so the tongue isdevelop 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 themiddle , these three swelling they are related to whicharch ?? arch number one , so this makes the anterior

part part of the tounge , so these swelling , the twolateral swelling plus tuberculum impar which is the

medial swelling they later on fused together , they swelland fuse together making the anterior two third of the

tounge , now the swelling from the third arch , also wehave a big swelling It's called Copula/Hypobranchial

eminence this develops from arch # 3 as you see but itover grows the second arch it over laps the second

arch

arch 3


5/37

arch 2

And what does this lead to ?this lead to the developmentof the posterior part of the tounge or the posterior third of

the tounge


6/37

See here this is the tongue after development , we cansee the first part of the tongue or the anterior two third of

the tongue which is the body of the tongue , this developsfrom the first branchial arch and regarding the posterior part of the tongue it develops from third branchial arch.

The root of the tongue which is the very much posterior part of the tongue which is just next to the epiglottis thisdevelop 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 haveto 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 ?yesthe 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 tongue

from arch # 1 , the sensation or the sensory innervation isfrom trigeminal nerve and the posterior third of the tongueis innervated by glossopharngeal nerve which is the nerveof third arch , and the root of the tongue is from the vagus


7/37

nerve , and the taste buds of the tongue are from thefacial nerve because it develops from arch # 2.

Now what happens later on ?after fusion we still see somev-shape sulcus so when the anterior two third of the

tongue fuse with the posterior third of the tongue , fusionleads to sulcus

fusion 100 %

v-shape sulcus this is called sulcus terminalis , its the junction between the anterior part and posterior part of thetongue or if you like its the junction between the part of

the tongue that develops from the first branchial arch andthe part developing from the third branchial arch.

what is located anterior the sulcus terminalis should besupplied by trigeminal nerve which is the cranial nerve of

the first arch , and what is located posterior to it issupplied by glossopharngeal nerve.

the very median part of the median end of sulcusterminalis we have what we call foramen caecum which is

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

gland.


8/37

this actually happen by a duct that drops down from thisforamen cecum its called thyroglossal duct , why do wecall it thyroglossal ?? because its now within the tongue

so glossal , thyro from thyroid so thyroglossal, this dropsdown 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 betweenthe anterior two third and posterior third of the tongue , for this reason we may see thyroid tissue within the tongue ,

why ?? because this tissue is eminence Of the thyroidgland , we call it ectopic thyroid tissue , also this ectopic

thyroid tissue is functional.

we have group of papillae that are usually locatedanteriarly 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 circumvallatepapillae these are supplied by glossopharngeal nerve


9/37

although they are located anterior to sulcus terminalis ,,why ?? because during the development of the tongue

these papillae migrate from the posterior third to theanterior two third so they cross sulcus terminalis.

we have taste buds on vallate papillae , these taste budsare response for the sour taste . innervation for this

papillae is glossopharungeal nerve

papillae sulcusterminalis anterior two third of the tounge supplied by trigeminal supplied by

glossopharungeal posterior third sulcus terminalis

sulcus terminalis

For this reason they take the embryological inervation withthem . the tongue sensory the first nerve which is

trigeminal nerve provides sensory innervations for theanterior two third of the tongue , sure except the region of

the circumvallate papillae , the taste in the anterior twothird of the tongue is from the facial nerve , the taste at theposterior 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

vagus nerve which is the cranial nerve # 10 that isresponsible for the innervations of the 4 th , 5th , 6th arches ,so thats why the 4 th 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 byvagus nerve , the posterior third sensory and taste from


10/37

third branchial arch which is glossopharngeal nerve andregarding the motor supply , the muscles of the tonguethey get very special innervations from another nerve ,this nerve is called hypoglossal nerve which is cranialnerve # 12 hyogloosal nerve , the innervations of the

muscles of the tounge the intrinsic and extrinsic muscle.

Remember the myotoms , they are from the metoticsomites , remember last lecture we said we have the head

somites , we have the prootic somites will form themuscles of the eye and the myotom of metotic somites willform the muscles of the tongue , so thats why metotic

somites carry with them the hypoglossal nerve suppliedmuscle.

The development of the face:


11/37

The face grows by number of process .we have themaxillary 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 frontonasalprocess , this process here and here are the maxillaryprocess , and this long process here is the mandibular

process.

Face develop around stomodeum ,stomodeum is theprimitive mouth.


12/37

Can you see here this depression above the mandibular process ?this cavity is called stomodeum or the primitive

mouth of the embryo.

The primitive mouth of the embryo is separated from thebeginning of gastrointestinal tract by the buccopharngeal

membrane which came from prochordal plate , and wesaid before the age of 21 day this membrane is active so

this means that the stomodeum is separated from the

gastrointestinal tract . But at the age of 21 days thisbuccopharngeal 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(


13/37

Each branchial arch is covered outside by ectoderm andinside 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


14/37

**The frontonasal process is not from the brachial archonly the maxillary and mandible processes from firstbrachial arch.

The frontonasal process " the area in pink " develops pitsand its called nasal pits later it will become nostrils and at

the sides of these pits we find some swellings 2 onemedial 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 thereis swelling , lateral nasal swelling and medial nasal

swelling , the 2 medial nasal process of the 2 nostrils fusetogether forming the intermaxillary segment which form

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


15/37


16/37

Between the maxillary process and lateral nasal swelling

we have a groove this groove will deepen and create acanal called lacrimal canal or nasolacrimal duct ( joints thelacrimal 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 outand wet your skin . so what happens if something went

wrong the maxillary process fails to fuse with the philtrumof 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 regionof the palate that carries the central and lateral incisors iscalled the primary palate and the remain part is called thesecondry palate , primary and secondry palate are formed


17/37

separately and finally they fuse together forming the wholepalate.

Secondry 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 arethey vertically oriented not horizontal ? because we have

a structure that occupies the space between them , thisspace is occupied by the tongue , with time , with the

facial growth , the tongue becomes lower and drops in thespace between the two palatine processes , which allowsthe processes to go horizontally and fuse with the primarypalate , so now we have primary palate anteriorly and two

palatine processes posteriorly , the three part fusetogether and form the whole palate , thats why they start

to adjust themselves ( they start to go horizontal instead of vertical(

In anatomy the palate is formed by two bones the maxillaand the palatine bones , here we talk about separate

processes and not separate bones , that help in formingthe palate , so , the tongue is in between , horizontal

reorientation 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 nasalseptum so all of these fuse together .

The palate is completed by 60 days , the point of fusion isthe point where the two sides meet with primary palate ,

and then fusion goes in three directions.


18/37

If we have a problem in fusion , this problem actually willbe seen as failure of fusion , some people ( one case inevery 700 birth ) are born with the cleft palate . why thishappen ? It is because we have many reasons of fusion

failure . most of the cases are because of geneticproblems , so when the two palatine processes failed to

develop , they form what we call cleft palate , whathappens when the primary palate fails to fuse with one or

both of the secondry palates ? it gives cleft lip , theprimary palate which also called the premaxilla is formed

by the palatine processes of the maxilla so when theintermaxillary projections are failed to fuse to each other

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

Sometimes when the patient is unlucky we will have abilateral cleft . For example when the two palatine bones

fail to fuse to each other and also fail to fuse with theprimary palate ( premaxilla ) .These patients of cleft lipand palate require multiple surgical procedures whichneeded to be completed before the age of 12 , so the

management is going to be at early age.


19/37

Development of the maxilla:


20/37

Just to remember we have two type of bone formation:

1-Endochondral in which the preexisting cartilage

transform into bone2-Interamembranous no preexisting cartilage

The maxilla is formed by intramembranousossification in which membranous mesenchymal

tissue become bone.We have two ossification center in the maxillary

development which are:

1-Maxilla proper 2-Premaxilla ( primary palate(Ossification at the maxilla proper begin 40 days

after fertilization and become hollowed out later toform the maxillary sinus.


21/37

The ossification of the maxillary proper beginbelow the infraorbital foramen from here the

process of the maxilla arise which are:1-Frontal process which fuse with the

maxillary process of the frontal bone2-Palatine process3-Alveolar process which carry the teeth4-Zygomatic process

The most important thing mentioned above isthe medial and lateral alveolar plate which

forms the alveolar process which carries theteeth

Development of the mandible

We will divide its development into two parts thebody and the ramus

The body is formed by intramembranousossification , despite the fact we have cartilagein the region of the body of the mandible whichcalled meckels cartilage but this cartilage have


22/37

nothing to do with development itself it onlyguide the development so it act as scaffold

The ramus of the mandible is formed byendochondoralossification , we have two site of

cartilage : condylar cartilage : it appears at the11 week after fertilization and continues to

provide growth for the mandible until 21 yearsand it provide growth for the mandible in height

Coronoid cartilage : it only active prenatally because justbefore birth it gets replaced by bone

The other thing that we need to understand is that whenwe have muscle attachment there will be growth of bone

The angle of the mandible had two muscles of masticationattached to which contribute to its growth:

1-Medial pterygoid2-Masseter

The coronoid process has muscle attached to itwhich also contribute to its growth and called

temporalis muscleAlso in the mandible we have alveolar process which

carry the teeth.

Lecture 2:Development of the tooth and its supporting

structuresThe stomodeum (primitive mouth ) the primitive

mouth is lined by ectoderm and beneath theectoderm we have the mesoderm (and we said that


23/37

mesoderm in this region the head region is notactually the real mesoderm it is ectomesenchymaltissue which means that it rises from neural crest

cells ) the site where one tooth is going to developwe have condensation of ectomesenchymal tissue

just under the ectodermWe start to see the condensation of the

ectomesenchymal tissue and capillary networkbeneath oral epithelium at specific sites . Why atspecific sites ? Because we have more than one

tooth and each tooth should be developed at specificsite so at the site where the tooth should be

developed we have condensation of theectomesenchyme

Also we have capillary network at specific site then itleads to the formation of primary Epithelium band

(PEB) when the oral epithelium thickens andinvagenates into condensed ectomesenchyme . After

that the PEB divides into two parts : one part goesbuccully and also called vestibular lamina and the the

other part goes lingually and also called dentallamina

The dental lamina is the structure that will develop

the tooth and the vestibular lamina will become thesulcus (space ) it goes buccully and labially to formthe 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 _ anteriorly _ )


24/37

and the remaining part which goes lingually is calledthe dental lamina

So the vestibular lamina goes buccully to form theoral 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 acondensation . At the end of each one it will form ateeth 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

called Enamel organ which is the swelling thathappens in the first part of the tooth bud

.


25/37

This is a mandible this is the lower lip this is the areathat is covered by oral epithelial as u see this is the

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 eachone 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 of

primary tooth but also each primary tooth in additionto the dental lamina which forms primary tooth there


26/37

is another swelling responsible for forming thesuccessor of that tooth ( successor tooth that come

to replace the primary toothQ: what is the tooth successes the mandibular

deciduous central incisor ?Permanent mandible central incisor

That means if we lost the formed structure nopermanent tooth will be developed if the deciduous

tooth is missing also the permanent tooth ( thesuccessor ) will be missing why ?? because both the

deciduous pre successor and the permanentsuccessor they develop originally from the same

germ layer

But the opposite is not true if the primary is there butwithout swelling the permanent successor will not

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

What about non successor permanent teeth likepermanent 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 wherewe find swellings that will form the teeth

Tooth germ : is the early part of the tooth that formedit includes the enamel organ and the surrounding


27/37

ectomesenchymle tissue and we divide it into 3different stages:

1 _ bud stage2-cap stage3 bell stage

Here is the first stage of development we call it budstage it looks like a bud we see the oral epithelium

invaginating against condensed ectomasnchymelater on this epethiliuminvaginating will start to form a

concavity so it looks like a cap so we call it a capstage then this cavity will become a big cavity and

that will gives the bell shape then at the end of bellstage we start to see the formation of dentine in

Dentinogenesis and the after a short while we start


28/37

to see the formation of enamel which isAmelogenesis and finally the crown appear and

crown completion after this the root start to developand that will lead to the eruption of the tooth :D

Bud stageIt involves the formation of enamel organ which will

form the outer surface of the crown which is theenamel

Enamel organ : early structure of tooth that comefrom ectoderm.

So the enamel organ is the one which determine thethree dimensional shape of the crown

REMEMBER that teeth can not develop at the sametime .It s impossible to see the entire tooth

developing at the same timeIn the bud stage the enamel organ look spherical or

ovoidIn the bud stage we cant differentiate the shape of

the tooth it is poorly mrpho differentiated so thethree dimensional shape of the crown is not

recognized and poorly histo differentiated so we cantrecognize different type of cell.

Successive development of tooth germ involve

complex interaction between epithelial andmesenchymal componenetIn order to the development of the tooth there must

be kind of interaction between the epithelium andectomasynchyme or between ectoderm and

ectomesnchyme so if we make tissue culture for theenamel organ there will be no tooth development


29/37

because there no mesenchymal tissue which isneeded for process to continue and the opposite is

true and it is similar to the development of nails

The basement membrane which separate betweenthe epithelium and the underlying mesenchymal

tissue play an important role in order to facilitate thisinteraction

Remember the epithelium is the enamel organ andthe epithelium is ectodermal origin.

This is a tooth in the bud stage and here is the oralepithelium and underlying it we have the condensed

ectomesenchymal tissueCap stage

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

invaginate to form a cap shaped structure


30/37

Cell is still poorly differentiated : not similar to eachother but still we able to differentiate between two

populations of cell which are:1 _ Inner ( central )_ related to the concavity _cell

which have no specific function and it rounded inappearance

peripheral cell which further divided into _ 2)Internal enamel epithelium (IEE)External enamel epithelium ( EEE

Late cap stageHere 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 shapethe EEE become cuboidal

the ectomesenchymal tissue which surround theenamel 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 hasa concavity that looks like a cap so it is called cap

stage of enamel organ at this stage we can identifydifferent groups of cells the start of morpho


31/37

differentiation but it is still poorly histodifferentiatedwe can identify the border line or the peripheral cells

and the core_the central part _ like the outer cellsand the inside cells _

So there are : central portion and peripheral cells

The peripheral cells are divided into : ExternalEnamel Epithelium EEE outside and Internal Enamel

Epithelium IEE and the IEE are very importantbecause they will finally differentiate to become theameloblasts and secrete enamel ( those cells are in

the cconcavity(


32/37

Then we have the bell stage which is devided intoearly and late

What happens in early bell stage ?? The concavitydeepens starts to become deep until the tooth looks

like a bell thats why it called the bell stageSo what happens during the early bell stage???

*Defferential cell division a long IEE ( not at thesame way at different locations ) different rates of

cell division at different sites that what gives differentshapes of the tooth.

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

All our teeth will be spherical no incisors no canine

no premolars and no molars***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 tocontinue here because the tip of the tooth will swell

*Active cell division At fissure sites and margine*Dental lamina breaks down*losing connection with oral epithelium*Dental lamina between tooth germs is lost-Remnants of dental lamina may remain as epithelial

rests of series that may be involved in the aetiologyof cysts


33/37

*We can identify here in early bell stageHistodifferentiation:

We can identify different groups of cells each withdifferent function

EEE*

Cuboidal cells and they maintain the shape of theenamel organ and exchange substances between

enamel and dental follicle

**enamel organ is avascular in order to maintain theshape of the enamel

Cervical loop*Increased cell division*

At junction EEE and IEE*

Stellate reticulum :are found in the center of enamelorgan

stellate because it is a star shape with many branchyprocesses and reticulum because it is a net work

they have dendrites processes function in interacting

nutrients SR are those white cells


34/37

function : *it protects the underlying tissue againstphysical disturbance and that maintain the tooth

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

determine crown morphogenesisWhat happens if the hydrostatic pressure inside here

in dental papilla area increase over the hydro staticpressure of SR??

The tooth will look like spherical ( it will swell(

IEE : most important cells they are columner cells that become elonogated starting from the cusp

tips and incisal edgesDental papilla : less differentiated than enamel

organ


35/37

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

the last part of the crown that calcify is the mostcervical part

Appearance of alingual downgrowth of EEE*In adeciduous tooth germs

-Successor lamina-gives rise to tooth germs of permanent successor

teeth

*In permanent tooth germs :it is a transientstructure that disappears eventually

Behind the second deciduous molars we shouldhave first , second and third molars which are non

successors dental lamina grows backwards to budoff permanent molars successively.

:Reciprocal interaction very importantDentine and Enamel formation commences at-Cusp tips

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

differentiate into odontobasts and secret predentine


36/37

and dentine, then dentine induces ameloblasts tosecrete enamel.

Done by:Ala'a Al_ SelawiMais Maloul Al _Selawi

"It takes a little courage, and a little self-control, If you want to reach the goal. It takes


37/37

a great deal of striving, and a firm and stern-

set chin. No matter what the battle, if youreally want to win, there's no easy path toglory. 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 that will not quit".

GD LUCK TO U ALL

oral histology (second script )

Documents

Transcript of oral histology (second script )