Embryology of the Head

Embryology of the Head,

Face and Oral Cavity

Prenatal Development

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Differentiation of the Morula into Blastocyst

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Formation of Two-Layered Embryo (2nd week of gestation)
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.
Called bilaminar germ disk
Ectoderm
Endoderm

Pre/prochordal plate

Firm union between ectodermal and
endodermal cells occur at prechordal
plate

Formation of Three-Layered Embryo: Gastrulation (3rd week)

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Triploblastic embryo






Formation of Three-Layered Embryo: Gastrulation (3rd week)
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

First 3 weeks: Leads to formation of triploblastic embryo

Next 3-4 weeks: differentiation of major tissues and organs

includes head and face and tissues responsible

for teeth development

differentiation of nervous tissue from ectoderm

differentiation of neural crest cells (ectoderm)

differentiation of mesoderm

folding of the embryo (2 planes-rostrocaudal and lateral)





Neural tube undergoes massive expansion to form the forebrain,
midbrain and hindbrain
Formation of neural tube and neural groove
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

Neural groove

Components of the mesoderm

Along the trunk paraxial mesoderm breaks up into segmented
blocks called somites

Each somite has: sclerotome- 2 adjacent vertebrae and disks

myotome-muscle
dermatome-connective tissue of the skin over the somite

In the head region the paraxial mesoderm only partially fragments to form a series

of numbered somatomeres which contribute to head and neck musculature


Intermediate mesoderm: urogenital system

Lateral plate mesoderm: connective tissue of muscle annd viscera; serous

membranes of the pleura; pericardium and peritoneum; blood and lymphatic cells;
cardiovascular and lympahtic systems, spleen and adrenal cortex.
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

In the head, the neural tube undergoes massive expansion to form

the forebrain, midbrain and hindbrain

The hindbrain segments into series of eight bulges called

rhombomeres which play an important role in development of the head

Folding of the Embryo

Head fold forms a primitive

stomatodeum or oral cavity; leading
to ectoderm lining the stomatodeum
and the stomatodeum separated from
the gut by buccopharyngeal membrane
Onset of folding is at 24 days and
continues till the end of week 4
Embryo just before folding (21 days)
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Neural Crest Cells

Group of cells separate from the neuroectoderm, migrate and

differentiate extensively leading to formation of cranial sensory
ganglia and most of the connective tissue of the head

Embryonic connective tissue elsewhere is derived form mesoderm

and is known as mesenchyme

But in the head it is known as ectomesenchyme because of its

origin from neuroectoderm
Look up Fig 2-12 in text book for derivative of the germ layers
and neural crest





Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Avian neural crest cells

Head Formation

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Rhombomeres

(one of the first are the
occipital somites)

Neural Crest Cell Migration

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition





Pharyngeal arches expand by proliferation of
neural crest cells
Couly et al., 2002
Forebrain
(prosencephalon)
Midbrain
(mesencephalon)
Hindbrain
(rhombencephalon)
r3
r5

Migration of cranial neural crest cells

Anterior midbrain
Posterior midbrain
Anterior hindbrain
Imai et al., 1996







E
E
E
FNM

TG
TG
TG

Md
Md

Clinical Correlation

Treacher Collins Syndrome is characterized by defects of
structures that are derived form the 1st and 2nd branchial arches and
is due to failure of neural crest cells to migrate properly to the
facial region

Sagittal section through a 25-day embryo

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition
Buccopharyngeal membrane ruptures at 24 to 26 days

Internal View of the Oral Pit at 3.5 weeks

26-day embryo

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition


The Developing Human by Moore & Persaud

groove/cleft

pouch
arch
membrane

esophagus

The pharyngeal apparatus


1
2
3
4
Branchial arches form in the pharyngeal wall (which has lateral plate mesoderm sandwiched
between ectoderm and endoderm) as a result of lateral plate mesoderm proliferation and
subsequent migration by neural crest cells

3 weeks

Sagittal view of the branchial arches with corresponding grooves between each arch.

Pharyngeal pouches are seen in the wall of the pharynx. The aortic arch vasculature
leads from the heart dorsally through the arches to the face

Fate of the Pharyngeal Grooves and Pouches

First groove and pouch: external auditory meatus
tympanic membrane
tympanic antrum
mastoid antrum
pharyngotympanic or eustachian tube

2nd, 3rd and 4th grooves are obliterated by overgrowth of the second

arch forming a cervical sinus – if persists forms the branchial fistula
that opens into the side of the neck extending form the tonsillar sinus


2nd pouch is obliterated by development of palatine tonsil

3rd pouch: dorsally forms inferior parathyroid gland

ventrally forms the thymus gland by fusing with the
counterpart from opposite side

4th pouch: dorsal gives rise to the superior parathyroid gland

ventral gives rise to the ultimobranchial body (which
gives rise to the parafollicular cells of the thyroid gland)

5th pouch in humans is incorporated with the 4th pouch

(A) Tissue from arch II and V growing towards each other (arrows) to make branchial

arches and grooves disappear
(B) Resulting appearance following overgrowth
(C) Contribution of each pharyngeal pouch

Anatomy of the Branchial Arches

• Posttrematic branch: covers the anterior

• Prettrematic: covers the posterior half
of the arch epithelium
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

Meckel’s cartilage: Has a close relationship with the

developing mandible BUT DOES NOT CONTRIBUTE TO IT
Indicates the position of the future mandible.The mandible develops by intramembranous ossification.The malleus and the incus develop by endochondral ossification of
the dorsal aspect of this cartilage. Innervation: V cranial nerve

Reichert’s: Dorsal end: stapes and styloid process

Ventral end: lesser horns of hyoid bone and superior
part of the body of the hyoid bone
Innervation: VII cranial nerve

Cartilage of the 3rd arch: inferior part of the body and greater

horns of the hyoid bone


Cartilage of 4th and 6th arches: fuse to form the laryngeal cartilage

Aortic Vasculature Development

• At 4 weeks the anterior vessels have passed through each branchial arch tissue
• At 5 weeks the 3rd branchial arch vessel becomes the common carotid, which
supplies the face by means of the internal carotid and stapedial arteries.

Face, Neck and Brain are supplied by the common carotid through internal carotid.

But by 7 weeks the circulation of face and neck shifts from the internal carotid to
external carotid. The internal carotid continues to supply the brain.

Shift in the vascular supply to the face

• Face and brain are supplied first by the internal carotid artery
• Facial vessels detach from the internal carotid and attach to the
external carotid

Muscle cells in the first arch become apparent

during the 5th week and begin to spread within
the mandibular arch into each muscle site’s
origin in the 6th and 7th week. These form the
muscles of mastication – masseter, medial
pterygoid, lateral pterygoid and temporalis
muscle. They all relate to the developing mandible

By 7 weeks the muscles of 2nd arch grow

upward to form the muscles of face.
As these muscles grow and expand they
forms sheet over the face and forms the
muscles of facial expression

Facial muscles grow from

the 2nd branchial arch to cover
the face, scalp and posterior
to the ear



Masticatory muscles of the mandibular arch

Cranial Nerves growing into Branchial Arches

Cartilages derived from the

branchial arches

Arch 1: Meckels cartilage and incus

Arch 2: Stapes, stylohyoid and lesser
hyoid
Arch 3: Greater hyoid
Arch 4 and 6 thyroid and
laryngeal cartilage

Congenital auricular sinuses and cysts

Branchial cysts

Branchial sinuses

Branchial fistula

Branchial vestiges

(cartilaginous or bony remnants)

Branchial cysts

Anomalies of the head and neck

Dermatlas

Dermatlas

Apparent fusion of facial processes by

elimination of furrows
True fusion of facial processes by
breakdown of surface epithelium
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Development of the Face

The face develops between the 24th and 38th days of gestation

On 24th day, the 1st branchial arch divides into maxillary and mandibular arches
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

Frontonasal process

Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

Middle portion of the upper lip: Formed by the fusion of the medial
nasal process of both sides along with the frontonasal process


Lateral portion of the upper lip: Fusion of the maxillary processes
of each side and medial nasal process

Lower lip: Formed by the fusion of the two mandibular processes

Formation of the Lips
Unusual fusion between maxillary process and lateral nasal process
leading to canalization and formation of the nasolacrimal duct

Human embryo at 7 weeks

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Cleft Lip

are variations of a type of clefting congenital deformity caused by abnormal facial development during gestation
Genetic factors contributing to cleft lip and cleft palate formation have been identified for some syndromic cases, but knowledge about genetic factors that contribute to the more common isolated cases of cleft lip/palate is still patchy.


Pituitary Gland Development
• An upgrowth from the ectodermal roof of the stomatodeum
• A downgrowth from the neuroectoderm of the diencephalon
called the neurohypophysial diverticulum – neurohypophysis

During the 4th week of development, a hypophysial diverticulum

(Rathke’s pouch) projects from the roof of the stomatodeum and lies
adjacent to the floor (ventral wall) of the diencephalon. By the 5th
week, this pouch has elongated and has become constricted
at its attachment to the oral epithelium and is in contact with the
infundibulum (derived from the neurohypophysis)

Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

Derivation and Terminology of the Pituitary Gland
Oral Ectoderm Adenohypophysis Pars distalis (distal part)
(hypophysial diverticulum (glandular portion) Pars tuberalis (tubular part)
from roof of stomodeum) Pars intermedia
(intermediate part)

Neuroectoderm Neurohypophysis Pars nervosa

(neurohypophysial (nervous portion) (posterior pituitory)
diverticulum from
floor of diencephalon)

Formation of the palate (weeks 7 to 9)

Palate develops from the primary palate and the secondary palate


The primary palate develops at about 28 days of gestation

Primary palate develops from the frontonasal and medial nasal

processes and eventually forms the premaxillary portion of the maxilla

The secondary palate develops between 7th and 8th week of gestation

and completes in the 3rd month

The critical period of palate development is from the end of 6th week

till the beginning of 9th week

Formation of the secondary palate

(starts between 7 to 8 weeks and completed around 3 months)
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition




Formation of the Tongue
The tongue begins to develop at about 4 weeks. The oral part (anterior two-thirds) develops from two distal tongue buds (lateral lingual swellings) and a median tongue bud (tuberculum impar) [1st branchial arch].Innervation: V nerve The pharyngeal part develops from the copula and the hypobranchial eminence (hill) [2nd, 3rd and 4th branchial arches]. Innervation: IX cranial nerveThe line of fusion of the oral and pharyngeal parts of the tongue is roughly indicated in the adult by a V-shaped line called the terminal sulcus.At the apex of the terminal sulcus is the foramen cecum.

Muscles of the tongue develop form the occipital somites and innervated by hypoglossal nerve

Lingual swelling

Tuberculum impar
Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.






The lingual papillae appear by the end of 8th week

Vallate and foliate papillae appear first, fungiform and

filiform (10-11 weeks) papillae appear later

Taste buds develop during the 11 to 13 weeks by inductive

interaction between epithelial cells of the tongue and invading
gustatory nerve cells from chorda tympani, glossopharyngeal
and vagus nerves

Thyroid gland development (4 to 7 weeks)

Figures obtained from “Before We Were Born; Moore and Persaud, 6th edition, 2003”.

Thyroglossal duct cystis a neck mass or lump that develops from cells and tissues remaining after the formation of the thyroid gland during embryonic development
Lingual thyroid results from lack of normal caudal migration of the thyroid gland.

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Development of Jaw Bones

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Development of Mandible

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Fate of Meckel’s Cartilage
Posterior – malleus of the inner ear

Sphenomandibular ligament

Anteriorly, may contribute to mandible
by endochondral ossification (some evidence)

Rest are resorbed completely

• Condylar cartilage (most important)
• Coronoid cartilage
• Symphysial cartilage
Secondary Cartilages





Appears during 12th week and occupies most
of the ramus and is quickly ossified by
endochondral ossification, with a very thin
layer of cartilage present in the condylar head.
This remnant persists until 2nd decade of life
and is important for growth of mandible
Appears at 4 months and
disappears immediately
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Development of Maxilla

Develops from one center of ossification in maxillary process of
the 1st branchial arch

Center of ossification is angle between the divisions where the

anterosuperior dental nerve is given off from inferior orbital nerve
from where it spreads posteriorly, anteriorly and superiorly

No arch cartilage is present, so maxilla develops in close

association with the nasal cartilage


One secondary cartilage also contributes to maxilla
development: zygomatic cartilage

GROWTH OF THE MANDIBLE

Condyle

Lingula

MORE DETAILS

NOTE THE DIVERGANCE OF THE RAMI STARTING FROM THE SITE OF THE LINGULAE

SUMMARY OF GROWTH

I – CONDYLAR GROWTH
A – Increase Ramus’s Height
B – Increase Mandibule’s Length.
C – Increase Inter-condylar Distance.
II - BONE APPOSITION AND BONE RESORPTION:
A – Increase The Body Length.
B – Increase The Body Height.
C – Increase The Body Strength.
D – Increase The Distance Between The Mandibular Canal And The Teeth
Roots.
E – Adjust The Ramus’s Width..
F - Widening Of The Mandible And Increase Its Transverse Dimension.














Thyroglossal cyst and Fistula: Cysts and fistulae found along the midline of the neck usually develop from remnants of thyroglossal duct.
Generally, thyroglossal cysts maybe found at any point along the course of the thyroglossal duct but it is usually found at the level of the hyoid bone and the thyroid cartilage.
Mandibulofacial Dysostosis or Treacher Collins Syndrome: This results from failure or incomplete migration of the neural crest cells to the facial region.
The zygomatic bone is severely hypoplastic . The face appears to be drooping, and the ears are usually malformed. The lower border of the mandible appears concave, and cleft palate is occasionally seen.

Abnormal Development

• Fissural cysts: Cystic cavities which arise along the fusion of various bones or embryonic processes and lined by epithelium.
• Median Rhomboid Glossitis: It results from persistence of the tuberculum impar and characterised by a red smooth region anterior to the foramen caecum.
• Ankyloglossia: This occurs as a result of incomplete degeneration of cells while the body of the tongue is freed, so that the tip of the tongue remains tied to the floor of the mouth.
• Macroglossia: or abnormally large tongue is not common, but is seen sometimes at birth when tongue slightly protrudes from mouth. This corrects itself when the jaws grow at a rapid rate. True macroglossia is seen in mongolism.
• Bifid tongue: This is a malformation common in south American infants and is the result of failure of the lateral lingual swellings.


Developmental Anomalies
• Hare lip
• Oblique facial cleft
• Cleft palate
• Macrostomia
• Microstomia
• Hypertelorism
• Congenital lip pits or fistulae
• Double lip
• Congenital tumours in relation to the face
• Bifid nose