embryology of the head neck and face slides(2)

7/27/2019 Embryology of the Head Neck and Face Slides(2)

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EmbryologyEmbryology

Alex Forrest

Associate Professor of Forensic OdontologyForensic Science Research & Innovation Centre, Griffith University

Consultant Forensic Odontologist,

Queensland Health Forensic and Scientific Services,

39 Kessels Rd, Coopers Plains, Queensland, Australia 4108

Oral Biology


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(The Act; a copy of the Act is available at SCALEPlus, the legal

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The material in this communication may be subject to copyright under the

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Information or excerpts from this material may be used for the purposes of

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Do not remove this notice


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Learning ObjectivesLearning Objectives

1. You should be able to understand and explain the basicembryological formation of the face, including the times

at which crucial events occur.

2. You should understand and be able to identify themajor possible causes of interruption to the formation

of the face, and to explain the clinical consequences

that result.

3. You should be able to describe and explain the fates of

the derivatives of branchial arches I,II,III,IV and VI in

man.


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Learning ObjectivesLearning Objectives

4. You should be able to relate your embryological

knowledge to recognition of patterns in the head andneck, such as the innervation of the palate, and the

innervation of major muscle groups in the head.


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Early DevelopmentEarly Development


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As you will remember, the embryodevelops from the original fertilized

cell, and as cell numbers increase,

they become specialized in different

regions to form tissues and organs.

Developing neural and blood

systems provide communicationsbetween the different cells and

groups of cells.

From:

http://www.luc.edu/depts/biol

ogy/devf.htm


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Recall that the embryodevelops into a three-

layered plate shape that

folds into a tube to create

the primitive gut, and

curves at the head and tail

to end up with a C-shaped

form that curves aroundthe developing heart.

Ten Cate, AR, Oral Histology, Development, Structure &

Function, St. Louis, CV Mosby, 1980, p. 14



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Initially, however, the

embryo forms a two-

layered (or bilaminar)

embryonic disk.

Mesoderm develops in the

third week.



What about the Germ Layers?What about the Germ Layers?


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Ectodermal cells migrate towards this primitive streak, and

then invaginate beneath it and spread between the ectoderm

and endoderm to form the third layer.

Modified from https://reader008.{domain}/reader008/html5/0417/5ad58335731fe/5ad5833bbe5d6.jpg

Formation of MesodermFormation of Mesoderm


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Clearly, however, in the head of a developed organism we still

have mesoderm. But to understand where it comes from, we

need to examine the formation of the nervous system.

Modified from https://reader008.{domain}/reader008/html5/0417/5ad58335731fe/5ad5833d39097.jpg

Formation of MesodermFormation of Mesoderm


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The nervous systembegins its development

towards the head end of

the embryo.

It begins as a thickening in

the ectoderm in this area

called the neural plate.

Modified from

https://reader008.{domain}/reader008/html5/0417/5ad58335731fe/5ad5833de

Development of Nervous SystemDevelopment of Nervous System


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The neural folds continue to develop until they meet on top of

the neural fold to produce a neural tube. This will become the

ventricles and central canal of the nervous system.

Modified from http://publish.uwo.ca/~jkiernan/nrltub.gif



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Notice however the group of cells that develop alongside the

growing neural folds called the neural crest, and shown in the

diagram above.




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As you can see, the neural crest cells separate from the

remainder of the neural tube to form a group of cells in their

own right.




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There is ongoing debate in the literature as to whether the

neural crest cells really are a derivative of the developing

nervous cell population or are a distinct group themselves.

e.g: Weston JA, Yoshida H, Robinson V, Nishikawa S and Fraser ST (2004). Neural crest and the origin of

ectomesenchyme: neural fold heterogeneity suggests an alternative hypothesis. Dev Dyn. 229: 118-30.


Development of EctomesenchymeDevelopment of Ectomesenchyme


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Either way, these cells are most important to the continued

development of the embryo.

They migrate extensively and give rise to components of the

peripheral nervous system including sensory ganglia,

sympathetic neurons, Schwann cells, meninges and pigment

cells.



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They also give rise to the embryonic connective tissue of the

facial region and to the cartilages of the branchial arches.

This embryonic connective tissue is known as

ectomesenchyme, to differentiate it from the mesenchyme

produced at the primitive streak.



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It has been regarded as a fourth germ layer by some authors,and there are cogent reasons for thinking of it in this way.



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It has properties slightly different to those of mesenchyme

elsewhere in the body.

For instance, the bones of the face and cranium (but not of the

base of the skull, which derive from conventional mesoderm)

form by intramembranous ossification rather than theendochondral method common in other bones.



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You should look up Treacher Collins Syndrome, which results

from interference in the migration of neural crest cells in the

facial area.

Treacher Collins SyndromeTreacher Collins Syndrome

http://www.dental.mu.edu/oralpath/lesions/treachercollins/treachercollins.htm


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Note that the skeletal muscles of the head and neck do not

derive from the ectomesenchyme. They develop from somites

or somitomeres which migrate into the branchial arches or the

frontonasal process.

(Somitomeres are similar to somites but derived from paraxial

mesoderm. They arise as 7 pairs and give rise to facial

muscles, muscles of mastication, extraocular muscles andsome muscles of the pharynx.)

Origin of MusclesOrigin of Muscles


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Facial DevelopmentFacial Development


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Facial DevelopmentFacial Development

The face develops from five embryonic tissue

masses, also known as processes. They all arise byrapid multiplication of neural crest cells which

originate from ectoderm:

Frontonasal Process

Mandibular Processes (paired)

Maxillary Processes (paired)

Modified from Ten Cate, AR, Oral Histology, Development, Structure &



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MouthMouth

The developing

mouth is given aspecial name: the

stomodeum or

stomatodeum.

From http://www.llk.ie/cleftpalate/embryology.shtml


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MouthMouth

It appears as a

depression in the

embryonic surfaceat about the fourth

week of

development, so it

is an early feature.

From http://www.llk.ie/cleftpalate/embryology.shtml


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Eventually, the stomatodeum will give rise to the oral

cavity.

At first, it is lined with oral ectoderm, which will give rise

to the teeth and finally become the oral epithelium.

MouthMouth


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The floor of this depression

pushes against the

developing gut, and the wall

that separates them is

termed the buccopharyngealmembrane.

It represents the meeting of

ectoderm and endoderm.

MouthMouth

Modified from http://www.bartleby.com/107/241.html


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This soon breaks down so that the stomatodeum can open

directly into the primitive pharynx of the foregut.

MouthMouth

Ten Cate, AR, Oral Histology, Development, Structure & Function, St. Louis, CV Mosby, 1980, p. 29


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At the sides, the

stomatodeum

becomes limited by

the formation of thefirst pair of branchial

arches, which give

rise to the lower part

of the face.

MouthMouth

Modified from Berkovitz, BKB et al. Color Atlas of Oral Anatomy, Histology &Embryology, London, Mosby-Wolfe, 2nd Ed 1992, p. 231


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NeckNeck

Development of the neck begins at the same time as

development of the face, in the fourth week of embryonic

life.

It is completed before birth. It arises from the branchial

arches and the primitive pharynx, which is part of the

digestive tube.


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The caudal part of theprimitive pharynx

forms the

oesophagus, and a

ventral outgrowth

leads to formation of

the larynx, and

trachea, which end atthe developing lungs.

NeckNeck

Arey, Developmental Anatomy, Philadelphia, WB Saunders, 4th

Ed 1941, p 218


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Branchial ArchesBranchial Arches

The branchial archesare bulges on the

embryo visible

immediately beneath

the developing brain

mass.

The first one will form

the lower part of theface.

Modified from: Arey, Developmental Anatomy, Philadelphia, WBSaunders, 4th Ed 1941, p. 145


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Of the six branchial

arches, only fivesurvive in man.

From:https://reader008.{domain}/reader008/html5/0417/5ad58335731fe/5ad5834



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Each branchial arch

contains a portion of

primitive striated muscle

tissue, some nervous

tissue from the neural

crest, some vascular

tissue, and a bar ofcartilage in its

mesodermal core.

Each arch therefore

contains an artery and a

nerve.

Ten Cate, AR, Oral Histology, Development, Structure & Function, St.Louis, CV Mosby, 1980, p. 20


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The branchial arches are

covered on the external

surface by ectoderm, and

on the internal surface by

endoderm, and support

the lateral wall of the

primitive pharynx.

Modified from:https://reader008.{domain}/reader008/html5/0417/5ad58335731fe/5ad



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The first two archesare mainly involved

in the formation of

the face, and the

remaining arches

are more involved

in the formation of

structures withinthe neck.

Modified from Arey, Developmental Anatomy, Philadelphia, WBSaunders, 4th Ed 1941, p 146



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Called the mandibular arch.

Cartilage is termed Meckel's

cartilage, after the anatomist

who first described it.

It forms the mandible and the

maxillae, the muscles of

mastication and the mandibulardivision of the trigeminal nerve.

Modified from: Grays Anatomy, London, Longman,35th Ed, 1973, p.117

1st Branchial Arch1st Branchial Arch


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The cartilage of the mandibular arch gives rise to the

incus and malleus bones, the anterior ligament of the

malleus and the sphenomandibular ligament, but the

bones of the mandible and maxilla do not form from it.

Instead they form by intramembranous ossification

following degeneration of the cartilage.



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The nerve becomes mandibular division of the trigeminal

nerve, and migrates with the muscles.

Modified from: Grays Anatomy, London, Longman, 35th Ed, 1973, p.132



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The muscle tissue becomes the muscles of mastication,

tensor tympani and tensor veli palatini as well as the

mylohyoid muscle and the anterior belly of the digastric.

All of these muscles take their motor nerve supplies from

branches of the mandibular division of the trigeminal

nerve.

The artery of the first arch does not survive.



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The second arch is

called the hyoid arch.

Its cartilage is termedReichert's cartilage,

again after the anatomist

who first described it.

Modified from: Grays Anatomy, London, Longman,

35th Ed, 1973, p.117

2nd Branchial Arch2nd Branchial Arch


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Its muscle tissue forms the muscles of facial expression,

and its nerve is the facial nerve (VII).



dd


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The Muscles of Facial Expression therefore all share a

common motor nerve supply the facial nerve.

Its muscle tissue also forms the stapedius muscle, the

stylohyoid and the posterior belly of digastric.


2 d2 d


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Its cartilage contributes to the stapes, styloid process of

the temporal bone, and some of the hyoid bone including

the upper part of its body and the lesser cornu (to whichthe stylohyoid ligament attaches), as well as the

stylohyoid ligament.

The artery of the second arch also degenerates and

cannot be recognized in the adult.


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3rd B hi l A h3rd B hi l A h


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The cartilage of the third arch contributes to the hyoid bone. Its muscle

becomes the stylopharyngeus muscle, and its nerve becomes the

glossopharyngeal nerve (IX).


3rd Branchial Arch3rd Branchial Arch

3rd B hi l A h3rd B hi l A h


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3rd Branchial Arch3rd Branchial Arch

Its artery becomes the common carotid artery and it also

contributes to the proximal part of the internal carotid

artery.

4th 6th Branchial Arch4th 6th Branchial Arch


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The fourth and sixth arches fuse.

Their cartilages contribute to most of the laryngealcartilages (thyroid, cricoid, arytenoid, corniculate and

cuneiform cartilages).

4th - 6th Branchial Arch4th - 6th Branchial Arch


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4th 6th Branchial Arch4th 6th Branchial Arch


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The artery of the fourth arch becomes the arch of the

aorta on the left side, and contributes to the right

subclavian and brachiocephalic arteries.

The artery of the sixth arch contributes to the pulmonary

arteries.

4th - 6th Branchial Arch4th - 6th Branchial Arch

5th Branchial Arch5th Branchial Arch


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5th Branchial Arch5th Branchial Arch

The fifth arch degenerates and becomesunrecognizable in man.

Branchial Pouches & CleftsBranchial Pouches & Clefts


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A branchial pouch is the fold seen on the inside aspect

of the branchial complex between adjacent arches.

Branchial cleft is the name given to the fold seen on the

outside.



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The first pharyngeal pouch becomes the auditory tube

and middle ear.

The first pharyngeal cleft becomes the external auditory

meatus, and the tympanic membrane remains as the

structure resulting from their meeting.



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The second pharyngeal pouch becomes the tonsillar

fossa between the palataglossal and palatopharyngeal

folds.

As development of the embryo continues, this develops a

mass of lymphoid tissue called the palatine tonsil.

Formation of the FaceFormation of the Face


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The face develops

between the 24th and

38th day of gestation.

In the early stages, the

development of the face

is dominated by the

changes that create theprimitive nasal cavities.





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At about 24 days, the first

branchial arch starts to bud

off a process called the

maxillary process.

The stomatodeum is now

limited by the developing

brain rostrally, by the first

branchial arch caudally,

Modified from Ten Cate, AR, Oral Histology, Development,

Structure & Function, St. Louis, CV Mosby, 1980, p. 24

and by the newly formed maxillary process laterally.

The first arch also contains the mandibular process, and

contains Meckel's cartilage.



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o at o o t e aceo at o o t e ace

The frontonasal process

develops two nasal pits,

and tissue builds up

around them in a horse-shoe shape to form the

lateral and medial nasal

processes.





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The maxillary process

grows medially and

approaches the lateral

and medial nasalprocesses.

At this stage, it remains

separated from them bya groove.

Modified from Berkovitz, BKB et al. Color Atlas of

Oral Anatomy, Histology & Embryology, London,

Mosby-Wolfe, 2nd Ed 1992, p. 232



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The continued central growth of the maxillary process

pushes the medial nasal process towards the midline.

From Ten Cate, AR, Oral Histology, Development, Structure & Function, St. Louis, CV Mosby, 1980, p. 27



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Here they fuse to create the middle part of the nose, the

middle part of the upper lip, the anterior part of the maxilla

and the primary palate.

Modified from: Arey, Developmental Anatomy, Philadelphia, WB Saunders, 4th Ed 1941, p. 199



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This is known as the premaxilla, and it carries the

odontogenic epithelium for the maxillary incisors.


Formation of the PalateFormation of the Palate


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It is, however, only after the formation of the secondary

palate that the distinction between the oral and nasal

cavities can be made clearly.




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The formation of the

secondary palate takes

place between the 7th

and 8th weeks ofdevelopment. It results

from the fusion of

shelves which arise from

the maxillary processes.

Modified from: Berkovitz, BKB et al. Color Atlas of


Mosby-Wolfe, 2nd Edition 1992, p. 234



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The nerve of theprimary palate is

the incisive branch

of the long

nasopalatine

branch of the

maxillary division

of the trigeminalnerve (V).

From Jamieson, EB, Illustrations of Regional Anatomy, Section II Head andNeck, Edinburgh, Livingstone Ltd, 8th Edition, p 35.



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The nerve of the

secondary palate

is the greater

palatine branch ofthe maxillary

division of V.

From Jamieson, EB, Illustrations of Regional Anatomy, Section II Head and Neck,Edinburgh, Livingstone Ltd, 8th Edition, p 35.



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This photograph shows the portions of the adult palate

derived from the primary and secondary palates. Correlate

this with the palatal nerve supply.

Formation of the TongueFormation of the Tongue


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A mesenchymal swelling

arises in the midline in the

mandibular process of the firstbranchial arch. It is called the

tuberculum impar.

Two other swellings appear,

one on either side of the

tuberculum impar, and these

enlarge rapidly and merge

with each other and with thetuberculum to form a large

mass.Modified from: Berkovitz, BKB et al. Color Atlas of





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The mucous membrane of

the anterior two-thirds of

the tongue is formed fromthis mass.

This is why the anterior

two-thirds of the tonguehave the mandibular

division of the trigeminal

nerve (via the lingual

nerve) as their sensorynerve supply.






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The nerve of the second arch contributes taste fibres to

the anterior two-thirds of the tongue, via the chordatympani.



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The posterior part of the

tongue arises from the

hypobranchial

eminence, a largemidline swelling from the

third branchial arch, the

nerve of which becomes

the glossopharyngeal.

Therefore, the posterior

third of the tongue

comes to be supplied by

IX.




Formation of the MandibleFormation of the Mandible


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The mandible develops in the mandibular process, which we

have already mentioned. The cartilage of the first arch is

called Meckel's cartilage.

From Ten Cate, AR, Oral Histology, Development, Structure & Function, St. Louis, CV Mosby, 1980, p. 36



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It is important to

realize that, while this

cartilage is in close

proximity to the

developing mandible,

it does not make a

large contribution toit.





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The two mandibular

processes fuse in themidline to form a

mandibular arch.

Now, the bone of themandible begins to form in

the mesenchymal tissue

that condenses laterally to

the cartilage, and thecartilage begins to

disappear.From Ten Cate, AR, Oral Histology, Development,




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The bone forms a trough which contains the

inferior dental nerve.

From: Grays Anatomy, London, Longman, 35th Ed, 1973, p.283



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The bone above this forms a series of compartments

for the individual teeth, and finally closes over the tooth

germs to form a roof over the trough.

From http://www.usc.edu/hsc/dental/ohisto/Cards/odev/17_bb.html



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By 10 weeks of age, the rudimentary mandible is formed

almost entirely from intramembranous ossification withlittle direct involvement by Meckel's cartilage.



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The cartilage does, however, contribute to the development

of the malleus of the middle ear and its ligament, and to the

sphenomandibular ligament.

From: Grays Anatomy, London, Longman, 35th Ed, 1973, p.283


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Formation of the Maxil laFormation of the Maxil la


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The maxilla also develops from a condensation of

mesenchyme from the first branchial arch.

There is no branchial arch cartilage in the maxillaryprocess, so the bone formation is entirely by

intramembranous ossification.

The maxillary sinus forms in the 16th week.


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Origin

Unknown

Congenital DefectsCongenital Defects


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You will by now be aware that the development of aperson is a very complicated and finely-balanced

process.

Malfunctions of this process at different points canproduce congenital defects.

Some of these will be genetic in origin, but environmental

factors including drugs can also be responsible.



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The types of environmental factors that can affect theembryo can be classified into five groups:

1. Infectious agents

2. Ionizing radiation

3. Drugs

4. Hormones

5. Nutritional deficiencies



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Among the most common of the defects that occur are

the orofacial clefts.

These constitute approximately 13% of the reported

anomalies and are the second most common reported

malformation.


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Modified from Ten Cate, AR, Oral Histology,

Development, Structure & Function, St. Louis, CV

Mosby, 1980, p. 43



Mosby, 1980, p. 45


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Origin

Unknown


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Mosby, 1980, p. 43



Mosby, 1980, p. 45


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Origin

Unknown


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Origin

Unknown


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The End

embryology of the head neck and face slides(2)

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