Mandible growth / /certified fixed orthodontic courses by Indian dental academy

GROWTH OF
MANDIBLE
www.indiandentalacademy.com

INDIAN DENTAL ACADEMY
Leader in continuing dental education


The human mandible has no one design
for life. Rather, it adapts and remodels
through the seven stages of life, from the
slim arbiter of things to come in the
infant, through a powerful dentate
machine and even weapon in the full flesh
of maturity, to the pencil-thin, porcelainlike problem that we struggle to repair in
the adversity of old age.
D.E. Poswillo.

CONTENTS

GROWTH
ANATOMY OF MANDIBLE
AGE CHANGES IN MANDIBLE
EVOLUTION OF MANDIBLE
PRE NATAL GROWTH
POST NATAL GROWTH


GROWTH

What is growth ?
The very term growth and development is difficult to
understand.Development means an increase degree of organizations
with increase in complexity and carries an overtone of increasing
specialization. There is no universally accepted definition of growth.
Various clinicians have defined growth in different ways.
Moss: change in morphological parameters which is measurable.
Moyers: Quantitative aspect of biological development per unit of
time.
Todd: An increase in size.
Krogman: increase in size change in proportions and progressive
complexity
J.S. Huxley: The self multiplications of living substance
MERIDITH:entire series of sequential anatomic and
Physiologic changes taking place from beginning of pre natal life to
serenity


ANATOMY OF THE MANDIBLE

Mandible is largest, strongest and lowest bone in the face.
Body – Horse shoe shaped
2 Parts – Body
Pair of Rami
Body – Outer aspect
Inner aspect
Upper border
Lower border
Outer surface presents the following factors
Symphysis menti
mental protruberance
Mental foramen
Oblique line
Incisive fossa
Inner surface
Mylohyoid line
Submandibular fossa – lodges submandibular gland.
Sublingual fossa – sub lingual gland
Genial tubercle
Mylohyoid groove

Upper border
Socket of teeth
Lower border
Midline of base is digastric fossa
Ramus – quadilateral in shape
Coronoid process
Condylar process
Mandibular foramen
Lingula
Mylohyoid groove
.

Attachments and relations of mandible
Oblique line – buccinator muscle
Oblique line below mental foramen – depressor labii inferious,
depressor anguli oris
Incisive fossa – mentalis muscle
Mylohyoid line – mylohyoid muscle
Posterior end of mylohyoid line – superior constructor muscle
Genial tubucle – geniohyoid, genioglossus muscle
Digastric fossa – anterior belly of digastric muscle
Lateral side of ramus – masseter muscle
Lower border – Platysma muscle
Postero superior part of lateral surface – Parotid gland muscle
Lingula – sphenomandibular ligament muscle
Medial aspect of ramus – medial pterygoid muscle
Mid surface of coronoid - temporalis muscle
Pterygoid fossa - lateral pterygoid muscle
Lateral surface of neck – attachment to lateral ligament of TMJ


Age Changes in Mandible
Infants
2 halves of mandible fuse during 1st year of age.
At birth mental foramen open below sockets for 2 deci molar teeth
near lower border (therefore an alveolar part of bone is present).
Angle is obtuse (140°) because head is in lie with the body.
Coronoid process is large and projects upward above the level of
condyle.
In Adults
Mental for opens midway between upper and lower border.
Therefore alveolar and sub alveolar parts are equally developed.
Angle reduce to 110° to 120° because ramus becomes vertical.
Old Age
Teeth fall out and alveolar border is resorbed. Height of body is
reduced.
Mental foramen and mandible canal are close to alveolar border.
Angle becomes obtuse.


EVOLUTION
OF MANDIBLE

The agnatha, the earliest type of vertebrate, had
its mouth opening on the ventral side anteriorly
along the vertebral axis. This opening led through
an oropharyngeal channel to the gut proper.
synarthrosis, which was considered to be the
earliest form of a jaw joint. This structure
remains as an epiceratobranchial joint in the
present-day shark.
In the gnathostomes, more highly evolved than
the Agnatha, the first and second arches
disappeared into the skull, and the third and
fourth arches began to function in prey capture:
the apparatus of the jaw.
As evolution proceeded, a more highly developed
moveable jaw joint appeared in the osteichthyes.
Formed by gill arches, the cartilaginous jaw was
covered by bony dermal plates that formed the
second jaws. The teeth developed in the bony
plates around the mouth. In the amphibians and
reptiles the oral organ was used only for
prehension. The amphibia had a dentary bone in
the anterior end of the original cartilaginous jaw.
At its posterior extremity it articulated with the
quadrate bone, a structure of the maxilla. The
auditory apparatus also developed in the
amphibia. The tympanic membrane moved
toward the hyomandibular bone, which was
involved in sound transmission by conduction
vibrations to the inner ear.

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In mammals, the dentary-squamosal joint
was formed after the completion of the
contact between the dentary bone and the
skull. This entirely new joint took overjaw
function and the original joint decreased in
size. The original jaw articulation formed
the malleolar-incus joint, making a
connection with the hyomandibular bone
that was found in the amphibia to form a
sound transmitting apparatus.
In mammal-like reptiles, the dentary bone
increased in size and the quadratoarticulate joint continued to evolve as the
sound transmitter. As the function and size
of the dentary bone increased, the
coronoid process temporal fossa were
formed.
As mentioned, mammals differ from other
vertebrates in the structure of the jaw and
ear, and the intimate association between
the jaw joint and the ear can be
recognized.

PRE NATAL
GROWTH

prenatal growth
{day1 to 266 day}


It is divided into 3 periods
1) period of ovum (ferti. to 14th
day)
2)period of embryo (14th day to
56thday)
3)period of fetous(56th day to
birth)

f

Endometrium (progestational stage)
., ,.< ---I. ,I


Period of embryo
(14th day major development of
to 56th day
It is the period where

It is the period where major development of
organ specifically craniofacial structure occur.
on 17th day process of gastrulation occurs to
form different germ layers. Ectoderm above
notochord thickens to form neural plate
which forms nervous system . On 21st day
embryo is of 3mm now primordial of brain
eye are seen in prosenceophalon. On 3rd week
otic &optic plocodes are seen. In the same
period most inferior part of prosencephalon
starts growing to from front nasal process
which overhangs future oral cavity which is
wide & shallow.

P
rimitive pit and
neurenteric canal

Amnion
Wallo!
yolk sac

Cloacal plate
(membrane)

A

Notochordal plate

c

E
ndoderm

Intraembry onic mesoderm

Extraembry onic
mesoderm

E

Notochord
- ,u :1 I "e+r ~t;n a for ,

,f/,'~
M.
W,'.
:~:i:
:> "-'.~
,

I ~.


on 3-4week oral groove starts deepening.
Same time bud for max and man process
show their presence lat to oral groove. Deepened
oral cavity is now called stomodium and is
separated by hind gut with a membranes formed
by endoderm and ectoderm called buccopharyngeal
membranes . on 4th week the embryo is 5mm . Now
frontal elevation shows some ectodermal
proliferation which form future nasal placode and
olfactory epithelium optic placodes which are
formed are placed very widely apart


Otic placode

Lens
placode

Limb
ridge

B

28 days


Front nasal process show more growth
mesially than laterally which forms medial
nasal process. As medial nasal process
grows faster, in future it unites with
maxillary process to form part of upper lip
specifically along line of philtrum . lateral
nasal process mainly contribute formation
of columella .on 5th week caudal to
frontonasal and maxillary process brachial
arches show their development they are
totally six with 5th one turning to be
rudimentary. 2nd brachial arch develop
faster than other and covers other brachial
arches

;
Pharyngeal pouch
Endoderma! epithelium

Nerve

1 st pharyngeal
arch

Cartilage

cleft

Ectodermal
epithelium.

2nd arch with ner ve,

artery, and
c<1rtllage

Mesenchymal tissue in
4th arch

A

J

Auditory tube

Primitive
tympanic
cavity
External
auditory
meatus
Palatine tonsil

Ventral side of
phary nx

- Foramen cecum
f

,
f

I
f
!
I
f

,
I

Superior parathy roid gland

,
'¥

(f rom 4th pouch)
Thy roid gland
Inf erior parathy roid gland
(f rom 3rd pouch)

Ultimobranchial body

Foregut

same time between and around primordial of
brian and eye Mesenchymal condensation
appears which gives a shape of skull.
Mesenchyma of brachial arch also appears by 5th
week. 1st brachial grows faster to become
distant .In 6th week mandibular arch show
accentuated growth to divide in maxillary
and mandibular process both process
grows medially . medial nasal process
from above also grows downwards and
towards midline as a result by the 7th
week fusion between maxillary and
frontonasal process occurs and this time
embryo is 14.5mm in length

Now eye starts migrating towards midline
Mesenchymal of cranial and brachial arch
differentiates into cartilage
(CHONDRIFICATION)

cartilage in the base of skull thins to
join with nasal and optic capsules. same
time centers for endochondral ossification
appears in the cartilage of base of skull,
also Mesenchymal condensation in
intramembranous bone is seen. At 8th week
nasal septum further narrows to become a
prominent structure ,also external ear
starts its development. nasal pit breaks
down to form nostrils. Demarcation seen
between lateral nasal and maxillary to
form nasolacrimal groove which in future
closes to form nasolacrimal duct

primary palate starts its
development at 8th week .so till this
time their occurs a direct
communication between oral and
nasal cavity . lidless eyes increase
their movement towards midline
.both lateral halves of mandibular
process fuse by 8th week. at this time
embryo is 18mm in length .
Rough head and face shape is almost
completed by 8th week . By end of 8th
week embryo increases in length
almost by 4 times to that of 7th week

 main structures formed in the embryonic
period are
 neural plate -2
 buccopharyngeal membrane -2
 mandibular arch –3
 hypoglossal muscle—5
 median and lateral nasal process-5
 lens of eye-5, retina—5
 external carotid artery-6
 middle ear-6
 larynx -6
 maxillary process -6
 external ear -7
 nasal septum-8
 palatal shelves-8
*IN WEEKS OF
IUL

FETAL PERIOD
(56days--9 months )
Eye lid formation occurs .eyes get
close . nostrils are formed.
This period shows accelerated rate
of craniofacial growth resulting in
an increase size and proportion In
8th to 12 weeks fetus increases in
length by 22—60mm .
mandible increases in size and
anteroposterior relationship of
both jaws develop as it is seen at
birth

meckels cartilage

it derived from first brachial arch on 41st
to 45th day of IUL .extends from
cartilaginous otic capsule to sysmphysis .it
acts as template and guide for growth of
mandible . a major portion of this
disappears and remaining part develops in
to
mental ossicle
incus, malleus
spine of sphenoid
ant. Ligament of malleus
sphenomandibular ligament
1st structure that develops in promordia of
man. Is mandibular division of 5th nerve
this is followed by osteogenesis
(neurotropic theory )

on 6th week of IUL single ossification
center for each man. Arise in the
region of bifurcation of inferior
alveolar nerve in to mental and
incisive. ossifying membrane is
located lateral to meckels cartilage
.IM ossification spreads dorsally and
ventrally to form body and ramus of
man. Ossification continues till
region of future linguala. meckels
cartilage continues into middle ear
and develops in to auditory ossicle
that is malleus and incus and SML

Endochondral bone formation in man.
Seen in3 areas
condylar process
mental region
coronoid process
condylar process; at 5th week of IUL
mesanchymal condensation seen above
ventral part of man. By 10th week it
develops into cone shaped cartilage. by
14th week it starts ossifying. it then
migrates inferiorly and fuse with man.
Ramus by4th months . by 6-7 th month of
IUL much of cartilage ossifies except
upper end which ossifies at adult hood

mental region
on either of symphysis 2 small
cartilage appears in 7th month of
IUL .it then incorporates into body .
symphysis ossifies after 1yr after
birth

coronoid process
it is formed by secondary cartilage.
appears at 10-14th week of IUL. it
grows as response to temporalis
muscle. it then join with ramus

POST NATAL
GROWTH OF
MANDIBLE

It is defined as the first 20 years of growth after birth . Of three
periods infancy , childhood and adolesecence .It is divided into 1-6
years midddle phase 6-10years and late phase10 - 15 years
.Puberty occurs in late childhoood at about 13 to 14 years and 12
-13 years in female . Adolescence is from 14 to 20 years in males
and 13 -20 years in female
Timing of growth in width length and height
Growth occurs in definite sequence. growth of the mandible occurs
three dimensionally . Growth in width is completed first then
growth in length and finally growth in height.Growth in width of
both jaws including the width of the dental arches tends to be
completed before the adolescent growth changes.intercanine
width is more likely to decrease than increase after age 12.there is
a partial exception to this rule however .As the jaws in length
posteriorly they also grow wider.
In the case of mandible both the molar and bicondylar width
shows small increase until the end of growth in length.Anterior
width dimensions of the mandible stabilize earlier.


Growth in length and height of both the jaws continue
through the period of puberty.Growth in vertical height
of the face continue longer than growth in length with
the later vertical growth primarily in the
mandible.growth of the mandible continue at 9
.relatively steady rate before puberty.Ramus increase 1
to 2mm per year and body length increases 2 to 3mm
per year.
Of the facial bones the mandible undergoes the largest
amount of growth post natally and also inhibit the
largest variability in morphology.
One of the most important element of the facial growth
process two separate but closely inter related system of
movements remodelling and displacement. A bone such
as the mandible does not grow simply by
generalised,uniform deposition .Of new bone(+)on all
the outside surfaces with corresponding resorption on
the inside.

At birth the two rami of the mandible are quite
short. Condylar development is minimal and
there is practically no articular eminence in the
glenoid fossa. A thin line of fibrocartilage and
connective tissue exists at the midline of the
symphysis to separate right and left mandibular
bodies. Between the four months of age and at
the end of the first year the symphyseal
cartilage is replaced by bone. Although growth
is quite general during the first year of life, with
all surfaces showing bone apposition, there is
apparently no significant growth between the
two halves before they unite. During the first
year of life, appositional growth is especially
active at the alveolar border, at the distal and
superior surface of the ramus, at the condyle,
along the lower border of the mandible and on
its lateral surfaces.

After the first year of extra uterine life, mandibular
growth becomes more selective. The condyle shows
considerable activity as the mandible moves and grows
downward and forward. Heavy appositional growth
occurs also on the posterior border of the ramus and on
the alveolar border. Significant increments of growth
are still observed at the tip of the coronoid process.
Resorption is said to occur at anterior border of the
ramus thus lengthening the alveolar border and
maintaining the antero-posterior dimension of ramus.
Cephalometric studies indicate that the body of the
mandible maintains a relatively constant angular
relationship to the ramus throughout life. The gonial
angle changes little after muscle function has become
well defined with approaching senescence and a
marked reduction of muscle activity there is evidence
that the gonial angle tends to become more acute.

Width of the mandible generally shows a subtle change.
Actually after the first year of life, during which there is
appositional growth on all surfaces, the major width
contribution of the mandible is growth at the posterior
border.
Literally the mandible is an “expanding V” additive
growth at the ends of “V” naturally increases the
distance between the terminal points. The two ramus
also diverge outward from below to above so that
additive growth at the coronoid notch and process and
condyle also increases the superior inter-ramus
dimension continued growth of the alveolar bone with
the developing dentition increases the height of the
mandibular body. But we are again dealing with a 3dimensional object. The alveolar process of the
mandible grows upward and outward on an expanding
arc. This permits the dental arch to accommodate the
larger permanent teeth. Relatively little increase in
mandibular body width is noted after cessation of
lateral surfaces appositional growth. Modelling
deposition at the canine eminence and along the lateral
inferior border is seen.

Scott divides the mandible into 3 basic types
of bone basal, muscular and alveolar.
The basal portion is a tube-like central
foundation running from the condyle to the
symphysis.
The musculature (the gonial angle and
coronoid process) is under the influence of the
massetter, internal pterygoid and temporal
muscles. Muscles function determines the
ultimate form of the mandible in these areas.
The third portion, alveolar bone, exists to
hold the teeth. When the teeth are lost there
is gradual resorption of the alveolar bone.
Reduced muscle activity accounts for the
flattening of the gonial angle and reduced
coronoid process.

Regional Details of Post-Natal
Growth of Mandible
The Ramus
It plays a key role in placing the corpus
and dental arch into ever-changing fit
with the growing maxilla and the faces
limitless structural variations. This is
provided by critical remodeling and
adjustments in ramus alignment,
vertical length and antero posterior
breadth.
The posterior border of mandibular bony
arch has to proceed into a region
already occupied by the ramus. This
requires a remodeling conversion from
ramus to mandibular corpus i.e. the
ramus becomes relocated posteriorly.
Some of the key anatomic parts
participate in the relocation and
remodeling process of the ramus and
the corpus. One of them is the lingual
tuberosity.

Lingual Tuberosity
The lingual tuberosity is a major site of
growth for the mandible.
It grows posteriorly by deposits on its
posterior facing surface.
The lingual tuberosity protrudes in a lingual
direction i.e. towards the midline. The
prominence of the tuberosity is increased by
the presence of larger resorptive field just
below it i.e. the lingual fossa. (the
combination of the periosteal resorption in
the fossa and deposition on the medial
facing surface of the tuberosity itself greatly
accentuates the contours of both regions.
As the posterior growth of the tuberosity
occurs that part of the ramus first behind
tuberosity grows medially. This brings the
ramus into alignment with the axis of the
arch (i.e. corpus) thus eventually becomes a
part of the corpus thus lengthening it.

Ramus to corpus remodeling
conversion
The bony arch length and corpus length has been
increased by
Deposits on the lingual tuberosity and the contiguous
lingual side of the ramus
Resultant lingual shift of the anterior part of the ramus
to become added to the corpus.
The presence of resorption on the anterior border of the
ramus not only makes room for the last molar but it
progressively relocates the entire ramus in posterior
direction from tiny mandible of fetus to attainment of
adulthood.
The posterior movement of the ramus does not occur in
a straight line. This is because the remodeling activity
does not occur only on the anterior and posterior
border but also on the surfaces between them

Coronoid Process
It has a propeller like twist so that
its lingual sides faces 3 directions
posteriorly superiorly and medially.
The growth occurs superiorly thus
increasing the vertical dimension. It
also brings about posterior direction
of growth movement. This is also
an example of expanding Vprinciple in horizontal direction. This
also contributes to the width of the
mandible. Lingual deposits also
carry the base of the coronoid in a
medial direction to add this part to
the lengthening corpus which lies
medial to the coronoid process.
Buccal side of the coronoid process
has a resorptive type of periosteal
surface.
On the inferior edge of the
mandible at the ramus corpus
junction, a field of surface
resorption is present. This forms
the antegonial notch

Mandibular foramenAs the whole ramus
grows posteriorly and
superiorly the
mandibular foramen
also drifts backward
and upward to
maintain a constant
position i.e. midway
between the anterior
and posterior border
of ramus.

Mandibular Condyle
This is an anatomic part of special interest
because it is a major site of growth, having
considerable clinical significance. Historically the
condyle has been regarded as a kind of
cornucopia from which the mandible pours
forth. It has believed that condyle was a growth
center and which determined the rate of growth
amount of growth, growth direction, overall
mandibular size and shape.
Condylar cartilage: condylar cartilage is a
secondary type of cartilage which develops
because of the functional and developmental
conditions imposed upon the part of the
mandible.
It is now believed that the condyle is a growth
site and its role is to provide regional adaptive
growth i.e. it maintains the condylar region in
proper anatomic relationship with the temporal
bone as the whole mandible is simultaneously
been carried forward and downward.

Neck of the condyle
As the growth is taking place in the
condyle the endosteum and
periosteam are actively producing
the cortical bone that encloses the
medullary core of endochondral
bone tissue. This occurs upto the
neck of the condyle on which both
the anterior margin and posterior
margin are both depository unless
if mandibular relations occurs
where the posterior edge can be
resorptive.
The lingual and the buccal sides of
the neck have resorptive surface.
This is because as the condyle
moves superoposteriorly hence,
what used to be the condyle
becomes the neck. This again
following the V-principle www.indiandentalacademy.com

Mandibular Corpus
Since the mandibular arch relates specially to
the bony maxillary arch, the mandibular corpus
lengthens to match the growth of the maxilla
and it does this by remodeling conversion from
the ramus.

Chin: Bone is added on the external surface of
the basal bone area including the mental
protuberance, a reversal occurs at a point
where the concave surface contour becomes
convex. This results in enlargement of the chin.
The process involves a mechanisms of
endosteal cortical growth on the lingual surface
behind the chin, heavy periosteal growth
occurs, with the dense lamellar bone merging
and overlapping on the labial side of the chin.
The point of periosteal to endosteal contact is
variable but usually occurs at a level just
superior to the projecting apex of the clip.

Symphyseal region

There is periosteal resorption on the labial side
of the labial bony cortex and deposition on the
alveolar surface of the labial cortex and
resorption on the labial side of the lingual
cortex and deposition on the lingual side of the
lingual cortex. This occurs when the teeth drift
lingually and superiorly to bring the upper and
lower teeth into occlusion.
In the mandibular corpus, except for a
resorptive zone on the lingual side there is
deposition. This enlarges the breadth on each
side of the corpus. But there is only slight
increase in width during post-natal growth.
The gonial angle is determined largely by the
growth direction of the ramus and condyle, but
a small extent of downward corpus alignment
can be produced by new bone deposition on its
antero inferior surface.

REFERENCES
CONTEMPORARY ORTHODONTICS –
PROFFIT
A SYNOPSIS OF CRANIOFACIAL
GROWTH-RANTLEY
ORTHODONTICS PRINCIPLES AND
PRACTICE-T M GRABER


ESSENTIALS OF FACIAL GROWTHDONALD H ENLOW
TEXT BOOK OF ORTHODONTICS-SAMIR E
BISHARA
HUMAN EMBRYOLOGY-INDERBIR SINGH
HUMAN ANATOMY-B D CHAURASIA
http://www.nature.com/news/nature
events
http//therapsd.htm


Thank you
Leader in continuing dental education


Mandible growth / /certified fixed orthodontic courses by Indian dental academy

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