Growth and development of stomatognathic system/ dental crown & bridge courses

GROWTH
AND
DEVELOPMENT
OF
STOMATOGNATHIC
SYSTEM
INDIAN DENTAL ACADEMY
Leader in continuing Dental Educationwww.indiandentalacademy.com

Contents of this seminar
1. Introduction
2. Definitions
3. Phases of Development
4. Early orofacial development
5. Formation of face
6. Development of maxilla
7. Branchial arches
8. Bone development and growth
9. Growth factors
10. Differential growth
11. The mandible
12. Temporomandibular
joint
13. Tongue
14. Palate
15. Anomalies of
development
www.indiandentalacademy.com

Over the structure of the cell rises the structure
of plants and animals, which exhibit the yet more
complicated, elaborate combinations of millions and
billions of cells coordinated and differentiated in the
most extremely different ways.
- Hertwig

Introduction:
Human development is a continuous process
that begins when an oocyte(ovum) from a female is
fertilized by a sperm(spermatozoon) from a male.
Development involves many changes that transform a
single cell, the zygote(fertilized ovum), into a
multicellular human being. Most development
changes occur before birth, but important changes
also occur during the later periods of development;
infancy childhood, adolescence, and adulthood.

The mating of male and female gametes in the
maternal uterine tube initiates the development of a
zygote-the first identification of an individual. The
union of the haploid number of chromosomes (23) of
each gamete confers the hereditary material of each
parent upon the newly established diploid number of
chromosomes (46) of the zygote. All the inherited
characteristics of an individual and its sex are thereby
established at the time of union of the gametes. The
single totipotential cell of approximately 140 µ m
diameter resulting from the union very soon
commences mitotic division to produce a rapidly
increasing number of smaller cells, so that the 16-cell
stage, known as the morula, is not much larger than
the initial zygote. www.indiandentalacademy.com

These cells of the early zygote reveal no
significant outward differences of form.
However, the chromosomes of these cells must
necessarily contain the potential for
differentiation of subsequent cell generations
into the variety of cell forms that later
constitute the different tissues of the body. The
differentiation of the these early pluripotential
cells into specialized forms is dependent upon
genetic, cytoplasmic and environmental factors
that act at critical times during their
proliferation and growthwww.indiandentalacademy.com

A compendium of manifold biochemical
reactions leads to cytodifferentiation and
histodifferentiation, resulting in the formation of
epithelial and mesenchymal tissues that acquire
specialized structure and function. Epithelial
mesenchymal interaction that provide for reciprocal
cell differentiation are essential to organogenesis, i.e.
the production of organs and systems.
Growth is a fundamental attribute of
developing organisms. The dramatic increase in size
that characterizes the living embryo is a consequence
of :

1) Increased number of cells resulting from mitotic
divisions (hyperplasia)
2) Increased size of individual cells (hypertrophy)
3) Increased amount of non-cellular material
(accretion). Hyperplasia tends to predominate in the
early embryo, whereas hypertrophy largely prevails
later. Once differentiation of the tissue has been
established, further development is predominantly
that of growth .The rate of growth of the tissue is
inherently determined, but is, of course is also
dependent upon environmental conditions. The
health, diet, race and sex of an individual influence
the rate and extent of growth.

Growth may be interstitial, where increase in bulk
occurs within a tissue or organ, or appositional, where
surface deposition of tissue enlarges its size. Interstitial
growth characterizes soft tissues, whereas hard tissues
(bone, dental tissues) necessarily increase by apposition.
The growth and development sequence is
genetically determined and operates through the
mechanism of inductors, metabolic modulators,
neurotrophic and hormonal substances and interacting
systems of contact stimulation and inhibition of
contiguous tissues. Should these differential, but
integrated, rates of development fail to maintain their
normal determined ‘pace’, aberrations of overall
development will manifest themselves as malformations
that may require clinical interception for correction.

Maturation is a counterpart of growth;
it indicates not only the attainment of adult
size and proportions but also the full adult
constituents of tissues (e.g. mineralization)
and the complete capability for performance
of each organ’s destined functions.

Definitions:
The British Medical Dictionary defines growth “As the
progressive development of a living being or part of an
organism from its earliest stage to maturity including
the resultant increase in size”.
o J.S. Huxley – Growth is defined as the self-
multiplication of a living substance.
o Krogman – Increase in size, proportion and
progressive complexities.
o Mevedith – Entire series of sequential anatomic and
physiologic changes taking place from the beginning of
parental life to senility.
o Todd - Growth is an increase in size.

o Moyers – Quantitative aspect of biologic
development per unit of time.
o Moss – change in any morphologic parameter that
is measurable.
Growth can result in an:
Increase in size, Decrease in size, change in form,
change in proportion, change in complexity, change
in texture.
Decrease in size, e.g. Thymus Gland.

Development:
- The term connotes an increasing degree of organization.
- It is series of changes by which the individual embryo
becomes a mature organization.
- Development is a progress towards maturity – Todd
- It is the sequences of changes from cell fertilization to
maturity. It relates to cell division, growth, differentiation
and maturation – J.H. Salsamann.
- Development refers to all the changes that are natural and
unidirectional in life of an individual from its existence as a
single cell to its elaboration as a multifunctional unity
terminating in death. – Moyers.

Growth and development though closely related are not
synonymous.
According to W.R.Proffit, Growth is largely an anatomic
phenomenon, whereas development is physiologic and
behavioral.
Development = Growth and differentiation &
Translocation

Phases of Growth and Development –Pre Natal Life:
Period of the ovum – The period from fertilization to the
end of the 14th
day.
Embryonal period – From the 14th
day to about 56th
day.
The fertilized ovum differentiates rapidly into an organism
that has most of the gross anatomic features of human.
1st
week : Active cell division
2nd
week : Tissue differentiation into ectoderm
and endoderm
3rd
Week : The 3rd
layer Mesoderm is added
4th
to 8th
week : Active & Rapid differentiation.

Fetal Period – the second trimester of
pregnancy ending by about the 28th
week is
characterized by rapid fetal growth especially
primarily.
The 3rd
trimester shows further increase
in size of the new viable fetus involving
primarily subcutaneous tissue and muscle
mass.

STAGE TIME RELATED
SYNDROMES
Formation of
organ systems-
primary palate
Days 28-38 Cleft lip &
palate, facial
clefts
Secondary palate Days 42-55 Cleft of palate
Final
differentiation of
tissues
Days 50- birth Achondroplasia,
Crouzon’s disease
Apert’s syndrome

Post Natal Life:
1. Infancy: Refers to first year after birth and
the first four weeks are designated as the new born
or neonatal period.
2. Childhood: this is a period from 15 months to
12-13 years. During early childhood, there is active
ossification, but this rate goes down, as the child
grows older.
3. Puberty: This is the period between the ages
of 12-15 years in girls and 13-16 years in boys, now
is the time when secondary sexual characteristics
develop and are expressed.

4 Adolescence: Period of 3 to 4 years after
puberty extending from the earliest signs of
sexual maturity until, the attainment of
physical, mental and emotional maturity.
5 Adulthood: Ossification and growth are
virtually completed during early adulthood,
18-25 years thereafter development changes
occur slowly.

Phases of development:
Embryogenesis is divided into three distinct
phases during the 280 days of gestation (ten 28-day
menstrual cycles). The phases are the
preimplantation period (the first 7 days), the
embryonic period (the next 7 weeks), and the fetal
period (the next 7 calendar months)

The preimplantation period(1-7 days)
During the first 2-3 days post conception the zygote
progresses from a single cell to a 16 cell cluster, the morula,
no larger than the original ovum . The early totipotential
blastomeres can develop into any tissue, but later
differentiation creates an approximately 100-cell fluid-filled
blastocyst. The outer sphere of cells forms the trophoblast,
and the inner cell mass will form the embryo. During this
period, the conceptus passes along the uterine tube to enter
the uterus, where it implants into the uterine endometrium on
the 7th
postconception day. The trophoblast converts into the
chorion by sprouting villi. Chorionic implantation
establishes the placenta, the organ of fetomaternal exchange
of nutrition and waste disposal.www.indiandentalacademy.com

The embryonic period(2-8 weeks)
This phase, from the end of the 1st
week until the 8th
week, can be subdivided into three periods: presomite (8-
21 days postconception), somite (21-31 days) and
postsomite (32-56 days postconception). During the
presomite period, the primary germ layers of the embryo
and the embryonic adnexa (fetal membranes) are formed in
the inner cell mass. In the somite period, characterized by
the appearance of prominent dorsal metameric segments,
the basic patterns of the main body systems and organs are
established. The postsomite period is characterized by
formation of body’s external features.

The fetal period
The beginning of this long phase, from the 8th
week until
term, is identified by the first appearance of ossification centers
and the earliest movements by the fetus. There is little new tissue
differentiation or organogenesis, but there is rapid growth and
expansion of the basic structures already formed.
Embryonic adnexa form membranes surrounding cavities
in which the embryo (and subsequently the fetus) develops. These
fluid filled cavities, membranes, and organs protect the fetus
physically and save its nutritional and waste disposal
requirements, casting off at birth. The main cavities and their
membranes are the chorion and amnion, surrounding the fetus.
Lesser cavities and their membranes are the yolk sac and a
transient diverticulum, the allantois, that become incorporated
into the umbilical cord, connected to the placenta, the chief organ
of fetal sustenance. www.indiandentalacademy.com

The chorion arises from the trophoblast as
an all encompassing membrane that, with the
maternal endometrium, forms the placenta. The
amnion and yolk sac, which form and fluid filled
sacs in the inner cell mass within the chorion, are
separated by a bilaminar plate; this plate forms
the embryonic disk that later gives rise to the
definitive embryo. The attachment of the inner
cell mass to the chorion constitutes the
connecting (body) stalk that contains the yolk sac
and allantois. The stalk converts into the
umbilical cord.

The presomite period
(8-21 days)
The primordial
embryonic germ disk is
composed of two
primary germ layers; the
ectoderm, which forms
the floor or the amniotic
cavity, and the
endoderm, which forms
the roof of the yolk sac.
Early embryogenesis: Embryonic period
(8-56 days)

There is early
demarcation, at the 14th
day, of the anterior pole
of the initially oval disk;
an endodermal
thickening, the
prechordal plate appears
in the future
midcephalic region. The
prechordal plate preface
the development of the
orofacial region, giving
rise later to the
endodermal layer of the
orpharyngeal membrane.www.indiandentalacademy.com

The third primary germ layer, the mesoderm, makes its
appearance at the beginning of the 3rd
week as a result of ectodermal
cell proliferation and differentiation in the caudal region of the
embryonic disk. The resultant bulge in the disk is grooved
cranicaudally, by which characteristic it is termed primitive streak.
From the primitive streak the rapidly proliferating tissue known as
mesenchyme forms the intraembryonic mesoderm which migrates in
all direction between the ectoderm and endoderm except the sites of
the oropharyngeal membrane anteriorly and the cloacal membrane
posteriorly.

The appearance of the mesoderm coverts the bilaminar
disk into a trilaminar structure. The midline axis becomes
defined by the formation of the notochord from the
proliferation and differentiation of the cranial end of the
primitive streak. The notochord terminates anteriorly at the
prechordal plate at the future site of the pituitary gland. The
notochord serves as an axial skeleton of the embryo, and
induces formation of the neural plate in the overlying ectoderm
(neural ectoderm), and the lateral mesoderm induces
epidermal development (cutaneous ectoderm).

The three primary germ layers serve as a basis for
differentiating the tissues and organs that are largely
derived from each of the layers. The cutaneous and neural
systems develop from the ectoderm. The cutaneous
structures include the skin and its appendages, the oral
mucous membrane, and the enamel of teeth. The neural
structures include the central and peripheral nervous
systems. The mesoderm gives rise to the cardiovascular
system (heart and blood vessels), the locomotor system
(bones and muscles), connective tissues and dental pulp.
The endoderm develops into the lining epithelium of the
respiratory system and of the alimentary canal between the
pharynx and the anus as well as the secretory cells of the
liver and pancreas. www.indiandentalacademy.com

Development of
the ectoderm into its
cutaneous and neural
portions occurs at 20
days, by infolding of the
neural plate ectoderm
along the midline
forming the neural
folds; this creates a
neural groove. Neural
folds and neural groove
give rise to neural crest
cells, which are
pleuripotential and give
rise to following
structures. www.indiandentalacademy.com

Derivatives of neural crest cells
Connective tissues:Ectomesenchyme of facial prominences and
branchial arches
Bones and cartilages of facial and visceral skeleton (basicranial
and brachial arch cartilages)
- Dermis of face and ventral aspects of neck
- Stroma of salivary, thymus, thyroid, parathyroid and pituitary
glands
- Corneal mesenchyme
- Sclera and choroids optic coats
-Blood vessel walls (excepting endothelium); aortic arch arteries
- Dental papilla (dentine); portion of periodontal ligament;
cementum www.indiandentalacademy.com

Muscle tissues:
- Ciliary muscles
- Covering connective tissue of branchial arch
muscles (masticatory, facial, laryngeal) combined
with mesodermal components

Nervous tissues
 Supporting tissues:Leptomeninges of prosencephalon and
part of mesencephalon, Glia
 Schwann sheath cells
 Sensory ganglia:
 Autonomic ganglia
 Spinal dorsal root ganglia
 Sensory ganglia (in part) of trigeminal, facial
(geniculate), glosspharyngeal (otic and superior) and vagal
(jugular) nerves
 Autonomic nervous system:
 Sympathetic ganglia and plexuse
 Parasympathetic ganglia (cilliary, ethmoid,
sphenopalatine, submandibular ganglions)

Endocrine tissues
- Adrenomedullary cells and adrengergic paragangilia
- Calcitonin ‘C’ cells –thyroid gland (ultimobranchial
body)
- Carotid body
Pigment cells
- Melanocytes in all tissues; melanophores of iris.
- Neural crest cells migrating ventrally and caudally
encounter the pharyngeal endoderm that induces formation
of branchial arches. Many brachial derivatives, including
facial bone are of neural crest origin.www.indiandentalacademy.com

The somite period (21 days- 31 days)
During this period i.e. for next 10 days, development is
characterized by foldings and structuring, as well as by
differentiation of the basic tissues that convert the flat
embryonic disk into a tubular body.
 The folding of neural plate gives rise to brain and
spinal cord.
 The mesoderm develops into three aggregations.
(a) Lateral plate mesoderm
(b) Intermediate mesoderm
(c) Paraxial mesoderm

• Lateral plate mesoderm
 Pleural cavity
 Pericardial cavity
 Peritoneal cavity
 Peripharyngeal connective tissue
• Intermediate mesoderm
 Gonads
 Kidneys
 Adrenal cortex
• Paraxial mesoderm
 Somatomeres, which gives, rise to somites.

The postsomite period (36-56 days)
The predominance of the segmental somites as an
external feature of the early embryo fades during the 6th
week i.u. (Intrauterine). The head dominates much of the
development of this period. Facial features become
recognizable, when the ears, eyes and nose assume a
‘human’ form, and the neck becomes defined by it
elongation and the sheathing of the branchial arches. The
paddle shaped limb buds of the early part of the period
expand and differentiate into their divisions to the first
demarcation of their digits; the earliest muscular movements
are first manifest at this time.

The thoracic region
swells enormously, as the
heart, which becomes
very prominent in the
somite period, is joined
by the rapidly growing
liver, whose size
dominates the early
abdominal organs. The
long tail of the beginning
of the embryonic period
regresses as the growing buttocks aid in its
concealment. The embryo at the end of this period
is now termed a fetus.www.indiandentalacademy.com

The fetal period
The main organs and systems having developed
during the embryonic, period, the last 7 months of fetal
life are devoted to very rapid growth and reproportioning
of body components, with little further organogenesis or
tissue differentiation. The precocious growth and
development of the head in the embryonic period is not
maintained in the fetal period, with the result that the body
develops relatively more rapidly. The proportions of the
head are thereby reduced from about half the overall body
length at the beginning of the fetal period to about one-
third at the 5th
month and about one fourth at birth.

At 4 months i.u. the face assumes a human
appearance as the laterally directed eyes move to the
front of the face and the ears rise from their original
mandibulocervical site to eye level.
Ossification centers make their appearance in most
of the bones during this a period. The sex of the fetus
can be observed externally by the 3rd
month, and the
wrinkled skin acquires a covering of downy hairs
(lanugo) by the 5th
month. During this month, fetal
movements are first felt by the mother.

The 42-44 paired somites appear sequentially
craniocaudally and are identified as:
4 - occipital
8 - cervical
12 – Thoracic
5 – lumbar
6 – sacral
8-10 – coccygeal somites
Each somite has got 1) Sclerotome – vertebral column
2) Dermatome – Skin
3)Myotome – muscles

4 6 7 8
121420
24 30 32

Birth

Early orofacial development:
Development of Head depends upon the inductive
activities of the
1. Prosencephalic organizing center gives rise to
a) Visual and inner ear apparatus
b) Upper third of face
2. Rhombencephalic organizing center gives rise
to – Middle & lower thirds of face

Oral development in the embryo is demarcated
extremely early in life by the appearance of the
prechordal plate in the bilaminar germ disk on the
14th
day of development, even before the
mesodermal germ layer appears. The endodermal
thickening of the prechordal plate designates the
cranial pole of the oval embryonic disk, and later
contributes to the oropharyngeal membrane. This
temporary bilaminar membrane is the site of junction
of the ectoderm that forms the mucosa of the mouth
and the endoderm that forms the mucosa of the
pharynx, which is the most cranial part of the
foregut.

. The oropharyngeal membrane is one of two
sites of contiguity between ectoderm and
endoderm, where mesoderm fails to intervene
between the two primary germ layers; the other
site is the cloacal membrane at the terminal end
of the hindgut. The oropharyngeal membrane
also demarcates the site of a shallow depression,
the stomodeum, the primitive mouth that forms
the topographical center of the developing face.

Formation of face
The face derives from five prominences that surround
a central depression, the stomodium, which constitutes the
future mouth
The prominences are:
 Frontonasal prominence
 Paired maxillary prominences
 Paired mandibular prominences
The maxillary and mandibular prominences are
derivatives of the first pair of six branchial arches. All these
prominences and arches arise from neural crest
ectomesenchyme, which migrates into facial and neck
regions.

Now we see that the floor of the stomatodoeum is
formed by the buccopharyngeal membrane, which
separates it from the foregut. Soon the mesoderm
covering the developing forebrain proliferates and forms a
down ward projection that overlaps the upper part of the
stomatodoeum. This downward projection is called
frontonasal process.
At this stage, each
mandibular arch forms the lateral
wall of the stomatodeoum. This
arch gives off a bud from its
dorsal end. This bud is called
maxillary process. It grows
cranial to the main part of the
arch, which is now called the
mandibular process. www.indiandentalacademy.com

These placodes soon sink below the surface to
form nasal pits. The pits are continuous below with
stomatodaeum. The edges of the pit are raised above
the surface and are called
1. Medial nasal process
2. Lateral nasal process
The ectoderm overlying
the frontonasal process soon
shows bilateral localized
thickening that are situated a
little above the stomatodaeum.
These are called nasal placodes.

We are now in a position to study the formation
of the various parts of the face.
Lower lip and lower jaw: the mandibular process
of the two sides grove toward each other and fuse in
the midline. They now form the lower margin of the
stomatodaeum. This fused mandibular process give
rise to lower jaw and lower lip.

The lateral merging of the maxillary and
mandibular prominences creates the commeasures of
the mouth.
There is marked acceleration of mandibular
growth between the 8th
and 12th
week of fetal life. The
development of Meckel’s cartilage during the second
month serves as a precursor of mandibular mesenchyme
which forms around and responsible for mandibular
growth activity.
Bone begins to develop lateral to meckel’s
cartilage during the seventh week and continues until
the posterior aspect is covered with bone.

Ossification stops at the point that will later become
the mandibular lingula and the remaining part of the
cartilage continues on its own to form sphenomandibular
ligament and the spinous part of the sphenoid. The part of
the meckel’s cartilage that has been encapsulated with
bone appears to have served its purpose as a splint for
intramembranous ossification and it largely deteriorates.
The early development and ossification of the bones
of stomatognathic system are quite evident at 14 weeks.
I.U ossification in the downwardly proliferating condylar
cartilage does not appear until 4th
or 5th
month of life. This
center shows signs of activity almost till the 20th
year of
life.

Development of Maxilla:
All the facial processes or prominences in the developing
embryo unite by either of the two developmental events at a
different location.
- By merging the frontonasal, maxillary and mandibular
process or
- By fusion of the central maxillonasal components.
Merging occurs when the incompletely separated
prominences migrate into the intervening grooves or by
proliferation of the underlying mesenchyme into the grooves.
Fusion occurs when the contacting surface epithelia of
the process disintegrate allowing intermingling of the
underlying mesenchymal cells. The medial nasal process joins
with the maxillary and lateral nasal process by fusion.www.indiandentalacademy.com

Each maxillary
process grows medially,
fuses first with the
lateral nasal process,
and then with the
medial nasal process.
The medial and lateral
nasal processes also
fuse with each other. In
this way the nasal pits
(now called anterior
nares) are cut off from
the stomatodaeum.

The maxillary process undergo
considerable growth. At the same time the
frontonasal process becomes much narrower
from side to side, so that the two anterior nares
come closer.

The stomatodaeum is now bounded above by the
upper lip, which is derived as follows.
a) The mesodermal basis of the lateral part of the lip
is formed from the maxillary process. The overlying
skin is derived from ectoderm covering this process
b) The mesodermal basis of the median part of the lip
(called philtrum) is formed from the frontonasal process.
The ectoderm of the maxillary process however
overgrows this mesoderm to meet that of the opposite
maxillary process in the midline. As a result, the skin of
the entire upper lip is innervated by the maxillary nerve.
The muscles of the face (including the lips are
derived from mesoderm of the second brachial arch and
are therefore supplied by the facial nerve.www.indiandentalacademy.com

During the late
somite period (4th
week
IU) the mesoderm
lateral plate of the
ventral foregut region
becomes segmented to
form a series of five
distinct bilateral
mesenchyme swellings,
the BRANCHIAL (Pharyngeal) ARCHES. These
brachial arches are separated by branchial groves on the
external aspect of the embryo, which correspond internally
with five out pouching of the elongated pharynx of the
foregut known as the five pharyngeal pouches or
endodermal pouches.
The Branchial arches:

Each of the five pairs of arches contains a
basic set of structures.
1. A central cartilage rod which forms
skeleton of the arch
2. A muscular component
3. A vascular component, an aortic arch
artery
4. A nervous element

Branchial
arch
Endoder
mal
pouch
Branchia
l arch
arteries
Muscles Nerves Skeleton
(viscerocran
ium)
1st
arch
mandibular
Auditory
tube and
middle
ear
cavity
External
carotid
and
maxillary
arteries
Muscles of
mastication
(temporal,
masseter, and
pterygoids)
mylohyoid, ant
diagastric, tensor
velipalatini, tensor
tympani
(Originate from
somitomere 4)
Trigemina
l nerve,
three
divisions;
sensory
mandibula
r division
motor
Facial bones,
incus,
malleus,
anterior
ligament of
malleus,
sphenomandi
bular
ligament and
core of
mandible
from
Meckel’s
cartilage.

Branchial
arch
Endodermal
pouch
Branchial
arch
arteries
(viscerocra
nium)
2nd
arch
hyoid
Palatine
tonsillar
fossa
Stapedial
artery (in
part),
possibly
small
contributi
on to
facial
artery
Muscles of
facial
expression,
posterior
digastric,
stylohyoid
stapedius
(originate
from
somitomere
6)
VII
facial
nerve
motor to
facial
muscles;
sensory
to ant.
2/3
tongue
Stapes,
styloid
process,
stylohyoid
ligament,
lesser
horn and
upper part
of hyoid
body
(Reichert”
s
cartilage)

Branchial
arch
Endodermal
pouch
Branchial
arch arteries
(viscerocr
anium)
3rd
arch Inferior
Parathyroid
III Thymus
Proximal 1/3
of internal
carotid,
possibly small
contribution
to common
carotid
Stylopharyn
geus? Upper
pharyngeal
muscle
IX
Glossoph
aryngeal
nerve
(pharynge
al plexus)
motor to
pharynx.
Muscles
sensory;
to post.
1/3
tongue
Greater
horn and
lower part
of hyoid
body.

Branchial
arch
Endodermal
pouch
Branchial
arch arteries
(viscerocra
nium)
4th
arch Superior
parathyroid
IV lateral
thyroid
vestigial
thymus
Arch of
aorta (left)
Proximal
part of right
subclavian
Pharyngeal
constrictor’s
cricothyroid
and laryngeal
muscles
palatoglossus
palatopharyn
geus Levator
veli palatini
X Vegas
nerve
superior
laryngeal
nerve
(pharyngeal
nerve
plexus)
Thyroid
and
laryngeal
cartilages.

Branchial
arch
Endoderm
al pouch
Branchial
arch
arteries
(viscerocra
nium)
5th
arch Ultimobran
chial body
or cyst
calcitonin
‘C’ cells
Nothing
rarely seen
Same as 4th
branchial
arch
Lower part
of thyroid
cartilage
and
laryngeal
cartilages
6th
arch None Proximal
part of both
pulmonary
arteries and
of ductus
arteriosus
(left)
Laryngeal
muscles
except
cricothyroi
d, striated
muscles of
esophagus
X vagus
nerve
Inferior
laryngeal
nerve
Cricoid
cartilage

Bone development and growth
Bone is formed by two methods of differentiation of
mesenchymal tissue that may be of either
mesodermal or ectomesenchymal (neural crest)
origin. The two varieties of ossification are
described as intramembranous and endochondral. In
both, however, the fundamental laying down of
osteoid matrix by osteoblasts and its calcification by
amorphous and crystalline appetite deposition is
similar.

Intramembranous ossification occurs in sheet like
osteogenic membranes, whereas endochondral ossification
occurs in hyaline cartilage prototype models of the future
bone. The adult structure of osseous tissue formed by the
two methods is indistinguishable; furthermore, both
methods can participate in forming what may eventually
become a single bone, with the distinctions of its different
origins effaced. In the main, the long bones of the limbs
and the bones of the thoracic cage and cranial base are of
endochondral origin, whereas those of the vault of the skull,
the mandible and clavicle are predominantly of
intramembranous origin. Membrane bones appear to be off
neural crest origin, and arise after the ectomesenchyme
interacts with an epithelium.

Endochondral bone formation:
- Growth of soft tissues occurs by combination of
hypertrophy and hyperplasia
- Secretion of extra cellular material accompanies with
hyperplasia primarily and hypertrophy secondarily in
certain condition.
- Interstitial growth is characteristic of certain soft tissues
and uncalcified surface.
- This way a cartilaginous model and scaffold is formed.
The height of cartilaginous development occurs during the
third month of intrauterine life. But the cartilaginous
model is a vascular and nutrients are supplied to internal
cells by diffusion through the outer layers – so of course
the cartilage must be thin.www.indiandentalacademy.com

- During the fourth month in utero there is an in
growth of blood vascular elements into various parts
of chondro cranium
- These areas are the centers of ossification at
which cartilage is transformed into bone and islands of
bone appear in the sea of surrounding cartilage.

To summarize
a.Mesenchymal cells become condensed
b.Some cells differentiate into chodroblasts and lays hyaline
c.Cartilage is surrounded by a membrane perichondrium, which
is highly vascular
d.The inter cellular substance surrounding the cartilage cells
become calcified due to influence of enzyme alkaline
phosphatase secreted by the cartilage cells.
e.Therefore, the nutrient supply to the cells is cut off leading to
their death, which results in empty cells “Primary Areola”.
f.The blood vessels and osteogenic cells from the perichondrium
invade the calcified cartilaginous matrix, which is now reduced
to bars or walls due to eating away of calcified matrix. This
forms large spaces called secondary areolae.www.indiandentalacademy.com

Intra Membranous Bone Growth:
Bone is formed by direct secretion of bone matrix and
it is calcified.
a. Mesenchymal cells becomes aggregated at the site
b. Some cells lay down bundles of collagen.
c. Some cells enlarge to form basophilic osteoblasts
d. Osteoblast secretes oseoid – a gelatinous matrix around
the collagen fibres.
e. Mineralization of osteoid takes place.
f. Some of osteoblasts get entrapped to form osteocytes.

 Direct addition of new bone to the
surface of existing bone does occurs through
the activity of cells in the periosteum, the
extra cellular materials secreted is
mineralized and becomes new bone -surface
apposition of bone.

Theories of Growth and Development:
1. Genetic Theory- By Raye Stewart- the theory
states that all growth is controlled by genetic influence
and is preplanned.
2. Sutural Dominance Theory – By Weinmann
and Sicher in 1955: the theory supports the fact that
genetic control is expressed directly at the level of
bone. Particularly the sutures between the
membranous bones especially of cranium and jaws
were considered as growth centers, along with the
sites of Endochondral ossification in the cranial base
and mandibular condyle.

But certain factors had strongly let down the theory:
1. When an area of the suture between the facial bones is
transplanted to another location the tissue fails to continue
to develop.
2. Growth takes place in cleft palate patients.
3. Growth at sutures responds to outside influences under a
number of circumstances.
4. Microcephaly and hydrocephaly raised doubts about the
intrinsic genetic stimulus at sutures.

3.     Cartilage Dominance Theory – By James scott,
1953, 1954, 1967 – according to the theory the genetic
control is expressed at cartilage. Scott said that the
cartilaginous sites through out the skull are primary
growth centers.
-        The nasal septal cartilage is the pacemaker for
growth of the entire nasomaxillary complex.
-         The mandible is considered as a long bone bent
into a horseshoe shape with the epiphysis removed, so
that the cartilage constitutes epiphyseal palate at the
ends, which are represented by condyles.

4. Functional Matrix Theory – By Melvin Moss,
1960,62,97 –
-          Moss’s idea of growth control is that the growth
control lies in adjacent soft tissues and cartilage – bones are
just sites.
-        The growth of the face occurs as a response to
functional needs and is mediated by the soft tissues
conceptually – the soft tissues grow and bone and cartilage
reacts to it.
-          A number of relatively independent functions are
carried out in the craniofacial regions or the human body
like, respiration, olfaction, vision hearing, balance,
chewing digestion, swallowing speech and neural
integration. www.indiandentalacademy.com

Functional cranial components:
Skeletal Unit - Micro skeletal, Macro skeletal Unit
Functional Matrices - Capsular Matrices, Periosteal
Matrices
Skeletal Unit:
All skeletal tissues associated with a single function
are called “the skeletal unit”. It is compromised of bone,
cartilage and tendinous tissues.
The functional matrix:
The functional matrix consists of muscles, glands,
nerves, vessels, fat, teeth and the functional spaces.www.indiandentalacademy.com

Periosteal Matrix:
Their action is directly and actively upon
the related skeletal units. Alternations in their
functional demands produce a secondary
compensatory transformation of the size or
shape of their skeletal units. Such process are
brought about by the inter related process of
bone deposition and resorption E.g. Muscles,
blood vessels, nerves glands etc.

Capsular Matrix:
They act indirectly and passively on their
related skeletal units producing secondary
compensatory translation in space. These alterations
in spatial position of skeletal units are bought by
expansion of the orofacial capsule within which the
facial bones arise, grow and are maintained. The
facial skeletal units are passively and secondarily
moved in space as their enveloping capsule is
expanded. Deposition and resorption do not bring
about this kind of translative growth.

The Neuro-crainial capsule and the oro-facial
capsule are examples of capsular matrices. Each of the
capsules is an envelope, which contains a series of
functional cranial components (skeletal units), which as a
whole are sandwiched in between two covering layers. In
Neuro-cranial capsule, the cover is skin and duramater
and in oro-facial capsule, the skin and mucosa forms the
covering.
The neurocranial capsule surrounds and protects the
neurocranial capsular functional matrix, which is the
brain,leptomeninges and CSF. The neuro cranial capsule
is made up of skin, connective tissue aponeurotic layer,
loose connective tissue layer, periosteum, base of skull
and layers of dura mater.www.indiandentalacademy.com

The orofacial capsule surrounds and protects the
oro-naso-pharyngeal spaces, which constitute the matrix.
The growth of the facial skull is influenced by the
volume and potency of the spaces.
5.  Van Limborgh’s Theory, 1970
Limborgh explains the process of growth and
development in the view that combines all the major
theories.
- He supports the Moss’s functional Matrix     Theory
- Acknowledges certain concepts of Sicher’s Theory
- Never did he rule out the genetic theory.

6. Unloaded Nerve Theory – by Melvin Moss
The skeletal units and growth field fulfills the
demands for protection of the mandibular nerve by
formation of bone around.
7. Servo System Theory – By Petrovic and Stutzmann
1980 The theory states that the influence of
somatotropic complex is STH – Somatomedin
hormones, sexual hormones and thyroniel harmones on
the primary cartilages (epiphyseal cartilages of long
bones, cartilages of the nasal septum and spheno
occipital synchondrosis, lateral cartilaginous masses of
the ethmoid, cartilage between the body of greater
wings of sphenoid etc.) has the “Cybernetic” form of
command www.indiandentalacademy.com

Growth Spurts
Growth does not take place uniformly at all times.
There seems to be periods when a sudden acceleration of
growth occurs. This sudden increase in growth is termed
“growth spurt”.
The physiological alteration in hormonal secretion is
believed to be the cause for such accentuated growth. The
timing of the growth spurts differs in boys and girls.

The following are timing of growth spurts.
a. Just before birth
b. One year after birth
c. Pre pubertal Growth spurt
Boys: 8-11 years
Girls: 7-9 years
d. Pubertal growth spurt
Boys: 14-16 years
Girls : 11-13years

Differential Growth:
The human body does not grow at the same rate
throughout life.  Different organs grow at different rates
to a different amount and at different times. This is
termed differential growth.
Here it would be best to mention two important
aspects of growth, both of which help us understand the
concepts of differential growth more clearly.  These are:
1. Scammon’s curve of growth
2. Cephalo caudal gradient of growth.

Scammon’s curve of growth
The body tissues can be broadly classified into four
types. They are lymphoid tissue, neural tissue, general
tissue and genital tissue.  Each of these tissues grows at
different times and rate lymphoid tissue proliferates
rapidly in late childhood and reaches almost 200% of
adult size.  This is an adaptation to protect children from
infection, as they are more prone to them.  By about 18
years of age, lymphoid tissue undergoes involution to
reach adult size.

Neural tissue grows very rapidly and almost
reaches adult size by 6-7 years of age. Very little growth
of neural tissue occurs after 6-7 years. This facilitates
intake of further knowledge. General tissue or visceral
tissue consists of the muscles, bones and other organs.
These tissues exhibit an “S” shaped curve with rapid
growth upto 2-3 years of age followed by a slow phase of
growth between 3-10years. After the tenth year, a rapid
phase of growth occurs terminating by the 18-20th
year.
Genital tissue consists
of the reproductive organs.
They show negligible growth
until puberty. However, they
grow rapidly at puberty
reaching adult size after
which growth ceases.www.indiandentalacademy.com

Cephalocaudal Gradient of Growth
Cephalocaudal gradient of growth simply means that
there is an axis of increased growth extending from head
towards the feet. A comparison of the body proportion
between prenatal and postnatal life reveals that post natal
growth of regions of the body that are away from the
hypophysis is more.
This growth concept can be illustrated as follows:
a. The head takes up about 50% of the total body length
around the third month of intra uterine life. At the time of
birth, the trunk and the limbs have grown more than the
head, thereby reducing the head to about 30% of body
length. The overall pattern of growth continues with a
progressive reduction in the relative size of the head to
about 12% in the adult.

b) The lower limbs are rudimentary around the
2nd
month of intrauterine life. They later grow and
represent almost 50% of the body length at adulthood.

Growth factors
The mitogenic factors include polypeptide growth
factors, cytokines, and many other substances named based
on their cellular origin, target cells and effects (Cantley et
al 1991; Nathan and Sporn 1991; Sporn and Robert 1990)
Following gene expression, cell differentiation and
organ development continue to be controlled by locally
secreted molecules that provide a specific instructional
signal to target cells. Among these signals, growth factors,
cell surface, glycoprotiens and components of extra cellular
matrix appear to be prime candidates for governing
developmental processes.

Growth factors are soluble polypeptides secreted
by cells that will act within the local environment. They
include platelet derived growth factors (PDGF),
Epidermal growth factor (EGF), Fibroblast growth
factors (FGF), Insulin like growth factors I and II (IGF-I
and IGF –II), transforming growth factors α and β and
(TGF - α and β), Nerve growth factors (NGF), Bone
morphogenic proteins (BMP) insulin and other hormones.
Target for these molecules are mescnchymal,
epithelia and endothelial cells.
- The growth factors act on the target cells by means
of specific receptors present on the cell surface
- The action of some of the important mitogenic
factors i.e., growth factors, cytokines and lymphokines an
given below. www.indiandentalacademy.com

GROWTH FACTORS
Molecule Target cell Major effect on Cell
PDGF Mesenchymal cell Growth promotion
FGF 1-9 Mesenchymal cells Growth
promotion
Angiogenesis
EGF Epithelial cells Proliferation
Epidermal cells Differentiation
TGF α Epidermal cells Proliferation
Epidermal cells Differentiation

Molecule Target cell Major effects on cells
TGF β Epithelial cells Growth inhibition
Mesenchymal cells Matrix synthesis
Angiogenesis
BMP 2-8 Osteoblasts Bone formation

CYTOKINES AND LYMPHOKINES
Molecules Target Cell Major effects on cells
IL –1 Many cells Growth promotion
Matrix degradation
TNF -α Many cells Growth promotion
Matrix degradation
IL – 8 PMN Chemotaxis
IFN –8 Fibroblasts Growth inhibition
Monocytes Matrix inhibition

The Mandible
The cartilages and bones of the mandibular skeleton
form from embryonic neural crest cells that originated in
mid and hindbrain regions of the neural folds. These cells
migrate ventrally to form the mandibular (and maxillary)
facial prominences, where they differentiate into bones and
connective tissues.
The first structure to develop in the region of the
lower jaw is the mandibular division of the trigeminal
nerve that precedes the ectomesenchymal condensation
forming the first (mandibular) branchial arch. The prior
presence of the nerve has been postulated as requisite for
inducing osteogenesis by the production of neurotrophic
factors. www.indiandentalacademy.com

The mandible is derived from ossification of an
osteogenic membrane formed from ectomesenchymal
condensation at 36-38 days of development. This
mandibular ectomesenchyme must interact initially with
the epithelium of the mandibular arch, before primary
ossification can occur; the resulting intramembranous bone
lies lateral to Meckel’s cartilage of the first (mandibular)
branchial arch.

A single ossification center for each half of the mandible
arises in the 6th
week, in the region of the bifurcation of the
inferior alveolar nerve and artery into mental and incisive
branches. The ossifying membrane is lateral to Meckel’s
cartilage and its accompanying neurovascular bundle.
Ossification spreads from the primary center below and
around the inferior alveolar nerve and its incisive branch, and
upwards to form a trough for the developing teeth. Spread of
the intramembranous ossification dorsally and ventrally forms
the body and ramus of the mandible. Meckel’s cartilage
becomes surrounded and invaded by bone. Ossification stops
dorsally at the site that will become the mandibular lingula,
from where Meckel’s cartilage continues into the middle ear.
The prior presence of the neurovascular bundle ensures
formation of the mandibular foramen and canal and mental
foramen. www.indiandentalacademy.com

Secondary accessory cartilages appear between the
10th
and 14th
weeks i.u. to form the head of the condyle, part
of the coronoid process, and the mental protuberance.
The coronoid accessory cartilage becomes
incorporated into the expanding intramembranous bone of
the ramus and disappears before birth. In the mental region,
on either side of the symphysis, one or two small cartilages
appear and ossify in the 7th
month i.u. to form a variable
number of mental ossicles in the fibrous tissue of the
symphysis. The ossicles become incorporated into the
intramembranous bone when the symphysis menti is
converted from a syndesmosis into a synostosis during the
first postnatal year.

The condylar secondary cartilage appears
during the 10the week i.u. as a cone-shaped structure
in the ramal region. This condylar cartilage is the
primordium of the future condyle. Cartilage cells
differentiate from its center, and the cartilage of
condylar head increases by intestinal and oppositional
growth. By the 14th
week, the first evidence of
endochondral bone appears in the condylar region.
The condylar cartilage serves as an important center
of growth for ramus and body of the mandible.

The ascending ramus of the neonatal mandible is
low and wide, the coronoid process is relatively large
and projects well above the condyle, the body is merely
an open shell containing the buds and partial crowns of
the deciduous teeth, the mandibular canal runs low in
the body. The initial separation of the right and left
bodies of the mandible at the midline symphysis menti
is gradually eliminated between the 4th
and 12 months
postnatally, when ossification converts the syndesmosis
into synostosis uniting the two halves.

Although the mandible appears in the adult as a
single bone, it is developmentally and functionally
divisible into several skeletal subunits. The ‘basal bone’
of the body forms one unit, to which are attached the
alveolar, coronoid, angular and condylar processes and
the chin.

Each of these skeletal subunits is influenced in its growth
pattern by a functional matrix that acts upon the bone: the teeth
act as a functional matrix for the alveolar unit; the action of the
temporalis muscle influences the coronoid process; the masseter
and medial pterygoid muscles act upon the angle and ramus of
the mandible; and the lateral pterygoid has some influence on the
condylar process.
The main sites of postnatal
mandibular growth are at the
condylar cartilages, the posterior
borders of the rami and the
alveolar ridges. These areas of
bone deposition account grossly for
increases in the height, length and
width of the mandible.

It was long considered that the condylar cartilage
was the primary growth center of the mandible. Lately
however proponents of the functional matrix theory
contradicts this saying that the mandibles where the
condyles are absent also shows adequate growth and are
positioned near normally. Thus, they say that the
condyle does not play the role of the master growth
center or cause mandibular displacement. According to
them it is the soft tissue growth that displaces the
mandible downward and forward and that the condylar
growth fills the resultant space to maintain the contact
with the basicranium.

Cartilage is present because variable degrees of
pressure are present at the articular contacts. An
endochondral mechanism of growth is necessary for
this because the condyle grows in the direction of
articulation in the face of pressure, which the pure
intramembranous growth mechanism could not
tolerate. The condylar cartilage is quite different from
primary cartilage in that the primary cartilage is
capable of intrinsic growth. Whereas the condylar
cartilage is said to be having no such growth potential.
(Petrovic states that there is a role of hormones in
condylar cartilage growth). Koski states that periosteal
tension in the condylar neck provides a built in control
for growth of the ramus by way of the cartilage and
other local factors, such as the lateral pterygoid may
induce outside control.www.indiandentalacademy.com

He indicates that periosteal integrity is important for
normal proliferative activity of the connective tissue cells of the
condyle apart from the role of lateral pterygoid muscle.
The growth of cartilage may act as a ‘functional matrix’
to stretch the periosteum, inducing the lengthened periosteum
to form intramembranous bone beneath it. The formation of
bone within the condylar heads causes the mandibular rami to
grow upward and backward, displacing the entire mandible in
an opposite downward, forward direction.
Any damage to the condylar cartilages restricts the
growth potential and normal downward and forward
displacement of the mandible, unilaterally or bilaterally,
according to the sides(s) damaged. Lateral deviations of the
mandible, and varying degrees of micrognathia and
accompanying malocclusion result.

In the infant, the condyles
of the mandible are inclined
almost horizontally, so that
condylar growth leads to an
increase in the length of the
mandible, rather than increase
in height. Due to the posterior
divergence of the two halves of
the body of the mandible (in a V
shape), growth at the condylar
heads of the increasingly more
widely displaced rami results in
overall widening of the
mandibular body, which with
remodeling keeps pace with the
widening cranial base.www.indiandentalacademy.com

The forward shift of the growing mandibular body
changes the direction of the mental foramen during infancy
and childhood. The mental neurovascular bundle emanates
from the mandible at right angles or even a slightly forward
direction at birth. In adulthood, the mental foramen (and
its neurovascular content) is characteristically directed
backward. This change may be ascribed to forward growth
in the body of the mandible, while the neurovascular bundle
drags along. The changing direction of the foramen has
clinical implications in the administration of local anesthetic
to the mental nerve: in infancy and childhood, the syringe
needle may be applied at right angles to the body of the
mandible to enter the mental foramen, whereas in the adult
the needle has to be applied obliquely from behind to
achieve entry.

Growth of Nasomaxillary Complex:
A primary intramembranous ossification center
appears for each maxilla in the 7th
week, at the
termination of the infraorbital nerve just above the
canine tooth dental lamina. Secondary zygomatic,
orbitonasal, nasopalatine and intermaxillary
ossification centers appear and fuse rapidly with the
primary centers.

The two intermaxillary ossification centers generate
the alveolar ridge and primary palate region that is
homologous with the premaxilla in other mammals. In
humans, this area encloses the four maxillary incisor teeth.
The nasal cavity, and in particular the nasal septum,
have considerable influence in determining facial form.  In
the fetus, a septomaxillary ligament arising from the sides
and anteroinferior border of the nasal septum, and inserting
into the anterior nasal spine, transmits septal growth pull
upon the maxilla.  Facial growth is directed downwards and
forwards by the septal cartilage which, between the 10th

and 40th
  weeks i.u., expands its vertical length sevenfold.

The ‘thrust’ and ‘pull’ created by nasal septal
growth separate to varying degrees the frontomaxillary
frontonasal, frontozygomatic and zygomaticomaxillary
sutures.
Growth of the maxilla depends upon the influence
of several functional matrices that act upon different areas
of the bone, thus theoretically allowing its subdivision
into ‘skeletal units’. The basal body’ develops beneath
the infraorbital nerve, later surrounding it to form the
infraorbital canal. The ‘orbital unit’ responds to the
growth of the eyeball; the ‘nasal unit’ depends upon the
septal cartilage for its growth; and the teeth provide the
functional matrix for the ‘alveolar unit’. The ‘pneumatic
unit’ reflects maxillary sinus expansion. www.indiandentalacademy.com

Postnatal development of the maxilla:
The growth of the maxilla should adapt to the
basicranium to which it is attached and also to the
mandible with which it functions (in mastication,
speech, facial expression, respiration etc).
The mechanism for growth of the maxilla is the
sutures, nasal septum, the periosteal, endosteal
surfaces, and the alveolar process. Mills pointed out
that the maxilla increases in size by subperiosteal
activity during postnatal growth even though the
periosteum has different names at different sites.

Over the majority of areas it is called simply,
periosteum and over some areas, it is called mucoperiosteum.
Where the periosteum of one bone meets that of another
bone, it is called a suture. Periosteum is also called
periodontal membrane where the alveolar bone meets the
modified bone of tooth’s root (cementum). Periosteum
though called differently at different sites carry out the role
of remodeling. The maxilla is attached to the cranial vault
and the cranial base by the following sutures.
a) Zygomatico-maxillary suture
b) Fronto-maxillary suture
c) Zygomatico-temporal suture
d) Pterygo platine suture.www.indiandentalacademy.com

This suture system is the most complicated found in the
human body.Endochondral mechanism for bone growth is not
very prevalent in the mid face. Only growth by endochondral
mechanism is the midfacial extensions of the ethmoid.
The growth of the cartilaginous part of the nasal septum
has long been regarded as a source of the force that displaces
the maxilla downward and forward (antero-inferiorly). This
theory does not hold good in its entirety at present. Most of the
bone formation occurs at the mid face by intra membranous
process. All the endosteal and periosteal surfaces are
blanketed by localized growth fields, which operate essentially
independently but in harmony with each other. Thus, surface
growth remodeling is very active providing much regional
increase and remodeling which accompany and adapt to the
additions taking place in sutures, synchondroses, condyles and
so forth. www.indiandentalacademy.com

Maxilla is joined to the cranial base and the
position of the maxilla is dependent on the growth at the
sphenooccipital and spheno-ethmoidal synchondrosis.
Maxillary postnatal growth can be divided into –
1. Shift in position of maxillary complex- secondary
displacement or translocation or passive displacement.
2. Enlargement of the complex itself – Primary
displacement or transposition or active displacement

Most of the bone of the cranial base is formed by
the cartilaginous process. Later the cartilage is replaced
by bone but certain bands of cartilage remain at junction
of various bone. These areas are called synchondrosis.
These are important growth sites. These are the
synchondrosis between the sphenoid and occipital bones,
or spheno-occipital synchondrosis, the intersphenoid
synchondrosis, between two parts of the sphenoid bone
and the spheno-ethmoidal synchondrosis between the
sphenoid and ethmoid bones.

Bone gets deposited on the posterior facing
cortical plate surface of maxillary tuberosity. The
endosteal surface within the tuberosity is having a
resorptive field. The amount of anterior maxillary shift
is equal to the amount of bone deposited on the posterior
surface of the tuberosity.
The bone resorption on nasal (superior) side of the
palate and bone deposition on the inferior oral side
produces a downward growth of the whole palate. In
maxilla, the palate grows downward by periosteal
resorption on the nasal side and periosteal deposition on
the oral side.

The maxillary height increases because of
sutural growth towards the frontal and zygomatic bone
and oppositional growth in the alveolar process.
Apposition also occurs on the floor of the orbits with
resorptive remodeling of the lower surfaces. The nasal
floor is lowered by resorption while apposition occurs
on the hard palate. The growth at the median suture
produces more millimeters of width increase than
appositional remodeling but surface remodeling must
everywhere accompany sutural additions.

Alveolar remodeling contributing to
significant early vertical growth is also important in
the attainment of width because of divergence of
alveolar processes. As they grow vertically, their
divergence increases the width. Upto the time that
the mandibular condyles have deceased their most
active growth, maxillary alveolar process increase
constitutes nearly 40% of the total maxillary height
increases.

The Temporomandibular Joint
The temporomandibular joint is a secondary
development, both in its evolutionally (phylogenetic) and
embryological (ontogenetic) history. The joint between
malleus and incus that develops at the dorsal end of
Meckel’s cartilage is phylogenetically the primary jaw joint,
and is homologous with the jaw point of reptiles. With the
development, both in evolution and embryologically, of the
middle-ear chamber, this primary Meckel’s joint loses its
association with the mandible, reflecting adaptation of the
bones of the primitive jaw joint to sound conduction. The
mammalian temporomandibular joint develops an entirely
new and separate jaw joint mechanism.

In the human fetus, the primitive joint within
Meckel’s cartilage, before the malleus and incus form,
functions briefly as a jaw joint, mouth opening movements
having started at 8 weeks i.u – well before development of
the definitive temporomandibular joint. When the
temporomandibular joint forms at 10 weeks i.u. both the
malleo-incudal and definitive jaw joints move in
synchrony for about 8 weeks in fetal life. They are both
moved by muscles supplied by the same mandibular
division of the trigeminal nerve i.e. the tensor tympani to
the malleus, and the masticatory muscles to the mandible

The temporomandibular joint develops from
initially widely separated temporal and condylar
blastemata that grow towards each other. The temporal
blastema arises from the otic capsule, a component of
the basicranium that forms the petrous temporal bone.
The condylar blastema arises from the secondary
condylar cartilage of mandible. In contrast to other
Synovial joints, fibrous cartilage, rather than hyaline
cartilage, forms on the articular facets of the temporal
mandibular fossa and mandibular condyle. In the latter
site, the underlying secondary cartilage acts as a growth
center.

Membranous
bone forming lateral
to Meckel’s cartilage,
first appearing at 6
weeks i.u., forms the
initial mandibular
body and ramus.
Concomitantly
condylar area and
initiates movement of
Meckel’s cartilage by
its contractions at 8
weeks i.u., functioning
through the primary
meckelian joint.

Between the 10th
and 12th
weeks i.u., the
accessory mandibular condylar cartilage develops as
the first blastema, growing towards the later
developing temporal blastema. The temporal articular
fossa is initial convex, but progressively assumes its
definitive concave shape. The initially wide
intervening mesenchyme is narrowed by condylar
growth and differentiates into layers of fibrous tissue.
During the 10the week i.u., two clefts develop in the
interposed vascular fibrous connective tissue, forming
the two joint cavities and thereby defining the
intervening articular disk.

The inferior compartment forms first (at 10 weeks),
separating the future disk from the developing condyle,
and the upper compartment starts to appear at about 11/ ½
weeks. Cavitation occurs by degradation rather than by
enzymic liquefaction or cell death. Synovial membrane
invasion may be necessary for cavitation. Synovial fluid
production by this method lubricates movements in the
joint.
Muscle movement is requisite to joint cavitation:
the connective tissues separating the initially discrete,
small spaces, have to be ruptured for the spaces to
coalesce into functional cavities.

The joint capsule composed of fibrous tissue,
recognizable by the 11th
week i.u., forms lateral ligaments.
The temporomandibular joint of the newborn child
is a comparatively lax structure with stability solely
dependent upon the capsule surrounding the joint; it is
more mobile than at any time later. At birth, the
mandibular fossa is almost flat and bears no articular
tubercle: only after eruption of the permanent dentition, at
7 years, does the articular tubercle begin to become
prominent; its development accelerates until the 12th
year
of life.
The joint structures grow laterally, concomitant
with widening of the neurocranium.www.indiandentalacademy.com

The temporal element, rather than the condyles,
is critical in establishing this lateral growth. The
articular surface of the fossa and tubercle becomes
more fibrous and less vascular with age. In postnatal
life, as the articular tubercle grows the disk changes
shape and becomes more compact, less cellular and
more collagenous. The mature disk is avascular and
aneural in its central portion, but is filled with vessels,
nerves and elastic fibres posteriorly, attaching it to the
squamotympanic suture.

Tongue
The tongue develops in relation to the
pharyngeal arches in the floor of the developing
mouth. We have seen that each pharyngeal arch
arises as a mesodermal thickening in the lateral
wall of the foregut and that it grows ventrally to
become continuous with the corresponding arch of
the opposite side. The medial most parts of the
mandibular arches proliferate to form two lingual
swellings.

The lingual swellings are partially separated
from each other by another swelling that appears in
the midline. This median swelling is called the
tuberculum impar. Immediately behind the
tuberculum impar, the epithelium proliferates to form
a down growth from which the thyroid gland
develops. The site of this down growth is
subsequently marked by a depression called the
foramen caecum.

Another midline swelling is seen in relation to the
medial ends of the second, third and fourth arches. This
swelling is called the hypobranchial eminence. The
eminence soon shows a subdivision into a cranial part
related to the second and third arches and a caudal part
related to the 4th
arches. The caudal part forms the
epiglottis.
The anterior two third of the tongue is formed by fusion
of
(a) The tuberculum impar, and
(b) The two lingual swellings

It is thus derived from the mandibular arch;
according to some, the tuberculum impar does not make
any significant contribution to the tongue.
The posterior one third of the tongue is formed
from the cranial part of the hypobranchial eminence. In
this situation, the second arch mesoderm becomes buried
below the surface. The third arch mesoderm grows over
it to fuse with the mesoderm of the first arch. The
posterior one third of the tongue is thus formed by third
arch mesoderm. The posterior most part of the tongue is
derived from the fourth arch.

In keeping with its embryological origin, the
anterior two third of the tongue is supplied by the
lingual branch of the mandibular nerve, which is the
post trematic nerve of the first arch, and by chorda
tympani which is the pretrematic nerve of this arch.
The posterior one third of the tongue is supplied by
the glossopharyngeal nerve, which is the nerve of the
third arch. The posterior most part of the tongue is
supplied by the superior laryngeal nerve, which is
the nerve of the fourth arch.

The musculature of the tongue is derived from
the occipital mytomes. This explains its nerve supply
by the hypoglossal nerve, which is the nerve of these
mytomes.
The epithelium of the tongue is at first made
up of a single layer of cells. Later it becomes
stratified and papillae become evident. Taste buds
are formed in relation to the terminal braches of the
innervating nerve fibres.

Palate

Muscles of stomatomasticatory system:
Craniofacial voluntary muscles develop from
paraxial mesoderm that condenses rostrally as
incompletely segmented somitomeres and segmented
somites of the occipital and rostral cervical regions. The
myomeres of the somitomeres and the myotomes of the
somites form primitive muscle cells, termed myoblasts;
these divide and fuse to form multinucleated myotubes,
that cease further mitosis and thus become myocytes
(muscle fibres). Most muscle fibres develop before birth,
but increase in number and size in early infancy. Motor
nerves establish contact with the myocytes, stimulating
their activity and further growth by hypertrophy; failure of
nerve contact or activity result in muscle atrophy.www.indiandentalacademy.com

The fourth somitomere myomere invades the first
branchial arch to provide the four muscles of mastication
(masseter, temporalis, medial and lateral pterygoids)
innervated by the trigeminal (Vth cranial) nerve.
Somitomeres (1-7) and somites (1-7) give rise to all
other muscles of craniomandibular system.

The masticatory muscles differentiate as individual
entities from first arch mesenchyme, migrate, and gain
attachment to their respective sites of origin on the
cranium and of insertion on the mandible. The masseter
and medial pterygoid have little distance to migrate, but
their growth and attachments are closely associated with
the mandibular ramus, which undergoes remodeling
throughout the early active growth period.
The insertion of the lateral pterygoid into the head
and neck of the rapidly remodeling mandibular condyle
requires its constant reattachment, together with
elongation concomitant with sphenooccipital
synchondrosal growth. The temporalis muscle’s
attachment to the temporal fossa stretches a considerable
distance from its site of mandibular coronoid insertion as
the muscle becomes employed in mastication.www.indiandentalacademy.com

The insertion of the lateral pterygoid into the head
and neck of the rapidly remodeling mandibular condyle
requires its constant reattachment, together with
elongation concomitant with sphenooccipital
synchondrosal growth. The temporalis muscle’s
attachment to the temporal fossa stretches a considerable
distance from its site of mandibular coronoid insertion as
the muscle becomes employed in mastication.

Anomalies of development
Defects of facial development are the result of
multiple etiological factors, some genetic, most
unknown. The study these anomalies constitute
teratology.
The range of facial anomalies is enormous, but
all produce some degree of disfigurement and result in
impairment of function or even incompatibility with
life. The mechanisms of facial maldevelopment are ill
understood, but inductive phenomena arising from the
cerebral prosencephalic and rhombencephalic
organizing centers are essential to normal facial
development. Defective brain development almost
inevitably causes cranial or facial dysmorphism.www.indiandentalacademy.com

Acephaly, absence of the head is the most extreme
defect. Post cranial structures can continue developing in
utero however; the condition is lethal upon birth
Absence of the brain anencephaly results in acrania
(absent skull) acalvaria (roofless skull), or cranioschisis
(fissured cranium), with variable effects upon the face.
These fetuses have minimal survival.
Defects of the rhombencephalic-organizing center,
which is responsible for induction of the viscerofacial
skeleton, account for dysmorphology of the middle and
lower thirds of the face (otomandibular syndromes).

Defective mandibular development may range
from agnathia (absent mandible) associated with
ventrally placed cervically located ears synotia to
varying degrees of micrognathia and
mandibulofacial dysostosis. The rare failure of
merging of the mandibular prominence results in
mandibular midline cleft.

Mild development defects of the face are comparatively
common. Failure of the facial prominence to merge or fuse
result in abnormal developmental clefts. These clefts are due
to disruption of the many intergrated processes of induction,
cell migration, local growth and mesenchymal merging.
Unilateral clefting of the upper lip (cheiloschisis) is the result
of the medial nasal prominence’s failure to merge with the
maxillary prominence on either side of the midline. Unilateral
cleft lip, more usual on the left side, is a relatively common
congenital defect ( 1 in 800 births) that has a strong familial
tendency, suggesting a genetic background. The rare bilateral
cleft lip results in a wide midline defect of the upper lip and
may produce a protuberant proboscis. The exceedingly rare
median cleft lip ( ‘hare-lip’) is due to incomplete merging of
the two medial nasal prominences and, therefore in most cases
with deep midline grooving of the nose leading to various
forms of bifid nose www.indiandentalacademy.com

Merging of the maxillary and mandibular
prominences beyond or short of the site for normal
mouth size results in mouth that is too small
(microstomia) or too wide (macrostomia). Rarely, the
maxillary and mandibular prominences fuse producing
closed mouth (ostomia)
An oblique facial cleft results from persistence of
the groove between the maxillary prominence and the
lateral nasal prominence running from the medial
canthus of the eye to the ala of the nose. Persistence of
the furrow between the two mandibular prominences
produces the rare midline mandibular cleft.

Retardation of mandibular development gives
rise to micrognathia of varying degrees with
accompanying dental malocclusion. Total failure of
development of the mandible, agnathia, is associated
with abnormal ventral placement of the external ears
(synotia)

Defective development of the joint results in
ankylosis, resulting in impaired mandibular
formation. Absence of all elements of the joint is
exceedingly rare. Failure of cavitation of one or both
joint compartments results in ankylosis that may be
uni or bilateral. The functionless joint results in
mandibular maldevelopment together with
masticatory distress of varying severity. Whereas
absence of the articular disk is exceedingly rare, its
perforation resulting in intercompartmental
communication is fairly common, and not debilitating

Retention of an abnormally short lingual
frenum results in ankyloglossia (tongue tie), a
common developmental abnormally. Persistence
of the thyroglossal duct may give rise to islands of
aberrant thyroid tissue, cysts, fistulae or sinuses in
the midline. A lingual thyroid gland at the site of
the foramen caecum, at the junction of the body
and root of the tongue, is not uncommon. Because
the tongue influences the paths of eruption of the
teeth, the state of its development is of
considerable interest to the orthodontist.

The tongue may fail to achieve normal
growth rate, resulting in an abnormally small
tongue (microglossia) or conversely, over
development (macroglossia). Rarely, the tongue
fails to develop (aglossia) or, because of failure
of fusion of its components, it becomes forked,
bifid or trifid.

References
1. Craniofacial embryology - IVth Edition – G.H Sperber
2. Human embryology – William J. Larse
3. Before we are born – Essentials of embrology and birth
defects – Vth Edition – Moore and Persaud
4. Human embryology – Vth Edition – Inderbir Singh
5. Facial growth – IIIrd Edition – Enlow
6. Handbook of Orthodontics – IVth Edition – Robert E.
Moyers

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