Growth and Development of Mandible

GROWTH AND
DEVELOPMENT OF
MANDIBLE
Farisha Mohammed

CONTENTS
• Introducation
• Pre Natal Growth and Development
• Post Natal Growth and Development
• Condyle and mandibular growth
• Theories of mandibular growth
• Logarithmic spiral
• Age changes
• Malformations related to mandible
• Conclusion

INTRODUCTION
• Mandible – Largest and Strongest bone of the
face
• Greek word ‘mandere’-to masticate/chew
• Latin word ‘mandibula’-lower jaw
• It forms the lower jaw and holds the lower teeth
in place

PRE NATAL GROWTH AND DEVELOPMENT
Period of Ovum
1-14th day
Period of embryo
14th – 56th day
Period of Fetus
56th – 270th day

PERIOD OF OVUM
Fertilization-Ampulla of uterine tube
zygote
mitosis
Cluster of cells ( Blastomere)
mitosis
Morula (16 cell structure)
Blastocyst

PERIOD OF EMBRYO
Blastocyst
Implantation in
the uterine wall
Trophoblast
Syncytiotrophoblast Cytotrophoblast
Embryoblast
Epiblast
All three germ
layers
Hypoblast
Prochordal plate

PRESOMITE PERIOD(8-20th day)
 Trophoblastic layer differentiate into synctiotrophoblast and
cytotrophoblast layers
SYNCTIOTROPHOBLAST- Outer cells that invades
endometrium and its vessels to establish maternal blood
circulation to developing embryo-UTEROPLACENTAL
CIRCULATION

INNER CELL MASS
Differentiates into hypoblast and epiblast
BLASTOCYSTIC CAVITY is now called as primitive yolk sac
AMNIOTIC CAVITY develops between epiblast andcytotrophoblast

Cells of primitive streak grow cranially to reach the
prochordal plate to form notochord which is a
solid cylinder of cells,axial skeleton of fetus forms
around notochord

NEURAL TUBE FORMATION
Ectoderm above notochord thickens
Neural plate
Midline of neural plate deepens
Neural groove
Neural folds grow towards each other
Fuse to form Neural tube- CNS
Edges of neural tube on either side-neural crests
Anterior end of neural tube-fore,mid,hind brain
Certain elevations called rhombomeres in area of hind brain-cells
that proliferate from neural crests

SOMITE PERIOD(21ST -31ST DAY OF
IUL)
 Rapid growth of cranial end of embryo, caudal end lags
behind- CEPHALOCAUDAL GRADIENT OF GROWTH
Head-1/2 of total embryonic disk length
BRANCHIAL /PHARYNGEAL ARCHES
 In specific areas,the migrating and rapidly proliferating ectomesenchyme cells
develops elevation between ectoderm and endoderm
 4th week of IUL Elevations seen in ventral foregut
5th arch perishes Formation of 6 pharyngeal arches
(bilaterally)
Finally 5 arches remain

BRANCHIAL ARCHES
Separated externally by small clefts
called branchial grooves
(Ectodermal clefts)-4 in number
On the inner aspect of pharyngeal wall
are corresponding small depressions
called pharyngeal pouches-5 in number

DEVELOPMENT OF MANDIBLE
•Develops from the mandibular process of 1st branchial
arch
•The cartilage of the 1st arch (Meckle’s cartilage) forms
lower jaw in the primitive vertebrates
•In human beings Meckel’s
cartilage has close positional
relationship to the developing
mandible but makes no
contribution to it
•Themandibular nerve has close relationship to the Meckel’s
cartilage, beginning 2/3 of the way along the length ofcartilage
•At this point mandibular nerve divides in to lingual and inferior alveolar branches

At around 36-38 days of IUL there is
ectomesenchymal condensation
Some mesenchymal cells enlarges,acquire a basophilic
cytoplasm and form osteoblasts
Osteoblast secrete a gelatinous matrix called osteoid and results in
ossification of osteogenic membrane
The resulting intramembranous bone lies lateral to meckels
cartilage of mandibular arch

In sixth wk ,a singleossification centre foreach half arises in the bifurcation of
inferioralveolar nerve into mental and incisive
7th wk-bone begin todevelop lateral to meckelscartilage and
continues until the postr aspect is covered with bone
Between 8th & 12th wk ,mandibular growth accelerate ,asa
result mandibular lengthincreases

Ossification stops at apoint,which later become lingula,the
remaining part of meckels cartilage continues to form sphenomandibular
ligament &spinous process of sphenoid
Secondary accessory cartilage appears between 10th &14th wk to
form head of condyle,part of coronoid process & mental protuberance

Fate of meckels cartilage
Posterior extremity forms
sphenomandibular ligament,
malleus, and incus
Most of the cartilage is absorbed
except for some portion in
midline which may cause
endochondral ossification

Endochondral bone formation seen only in 3areas
• Condylar process
• Coronoid process
• Mental region
FETAL PERIOD

CONDYLAR PROCESS
About 5th week of I.U.L. area of mesenchymal
condensation above
the ventral part of developing mandible
About 10th wk develops into cone shaped cartilage
By 14th week starts ossification
By 4 months migrates inferiorly and fuses with ramus
 4th month onwards replaced by bone but proximal end persists into adulthood acting as
Growth cartilage & Articular cartilage
 Condylar head separated from temporal bone by thin disc of connective tissue – future articular
disc

CORONOID PROCESS
 By 10th to 14th week of I.U.L. secondary cartilages seen in region of coronoid
 This cartilage becomes incorporated into expanding
intramembranous bone of ramus and disappears before birth
Mental region
 Secondary cartilages seen on both sides -- ossify by 7th wk I.U.L.
 They ossify to form mental ossicles in fibrous tissue of symphysis and later on gets
incorporated into it.

POST NATAL GROWTH AND DEVELOPMENT
OF MANDIBLE

MANDIBLE AT BIRTH
MANDIBULAR GROWTH-FIRST YEAR
GROWTH PROGRESSION AFTER FIRST
YEAR- MECHANISM & SITE

NEONATAL MANDIBLE
• Ascending ramus- low and wide
• Coronoid process- relatively large
• Body – merely an open shell containing buds
and partial crowns of decidous teeth
• Mandibular canal- runs low in the body

MANDIBULAR GROWTH DURING FIRST YEAR
• Appositional growth especially active at
 Alveolar border
 Distal and superior surface of ramus
 Condyle
 Lower border of mandible
 Lateral surface of mandible

By the end of first year mandible appears as a single bone.
It configures symmetrically as a U shaped structure as it accomodates
the mandibular dentition and completes the dental arch.

MANDIBULAR REMODELING
The mandible does not simply "grow“,
It "remodels“,

THE RAMUS
• The significance of the ramus - provides attachment base for the
masticatory muscles
What is the key role of ramus in placing the corpus and dental arch into ever
changing fit with growing maxilla and face’s limitless structural variations?
• This is provided by critical remodeling and adjustments in ramus
alignment, vertical length and anteroposterior breadth.

• The ramal remodeling is important
1. It positions the lower arch in occlusion with the upper
2. It is continuously adaptive to the multitude of changing cranio facial conditions
• The principal vectors of mandibular growth are posterior and superior
• The ramus is thereby remodelled in a generally posterosuperior manner while the
mandible as a whole becomes displaced antero-inferiorly.

MANDIBULAR FORAMEN
• Mandibular foramen relocates backward and upward by
deposition on the anterior and resorption from the posterior
part of the rim
• The foramen from childhood throughout the old age
maintains a constant position about midway between the
anterior and posterior borders of the ramus.

•The whole ramus- relocated by resorptive and depository remodelling
•The former anterior part of ramus- structurally altered – corpus, which therby
lengthened
•The remodeling of ramus has been pictured in a 2 dimensional process
•But it cannot be represented in a conventional 2 dimensional headfilms and
tracing
•Among this is the lingual tuberosity

LINGUAL TUBEROSITY
• This structure is not recognizable in the headfilm,
thus not included in basic vocabulory of
cephalometrics.
• It is not only a major growth and remodelling site
but also the effective boundary between ramus and
corpus

• The lingual tuberosity grows posteriorly by depostion on posterior facing
surface
• It protrudes noticebly in a lingual direction
• The prominence is augmented by the presence of a large resorptive field
just below it – which produces a depression, the lingual fossa
• The tuberosity remodels in an almost directly posterior direction with a a
slight lateral shift

• The posterior growth is accomplished by continued new deposits of bone on its
posterior facing exposure
• As this takes place, that part of ramus just behind tuberosity remodels medially
• This area becomes a part of the corpus, thereby lengthening it

RAMUS TO CORPUS
REMODELING CONVERSION
In general the arch length is increased and corpus has been lengthened by
1. Deposits on the posterior surface of lingual tuberosity and the contiguous lingual
side of ramus
2. A resultant lingual shift of anterior part of the ramus to become added to the
corpus

• The presence of resorption on the anterior border of the ramus is described as
“ making room for the last molar”
• It results in the entire relocation of ramus in a posterior direction
• This continues from the tiny mandible of foetus to the attainment of full adult
mandible size

• The bicondylar dimension is established much earlier in childhood- bilateral
growth separation between the right and left condyles is minimal beyond the
childhood years.

ANTEGONIAL NOTCH
 A single field of surface resorption is present on
the inferior edge of mandible at the ramus
corpus junction.
 This forms the antegonial notch by remodelling
from the ramus just behind it as the ramus
relocates posteriorly.
 The size of the notch can be increased whenever a
downward rotation of corpus relative to the ramus
takes place

• Deep antegonial notch-
indicative of a diminished
mandibular growth potential-
vertically directed mandibular
growth pattern

 Deep notched subjects have retrusive mandible with shorter corpus, less
ramus height and increase gonial angle.
 Mandibular growth directions in deep notched patients were more vertically
directed as measured by facial axis and the mandibular planeangle.
 Deep notched subjects had longer total facial height and longer lower facial
height, Smaller saddle angle
 Deep notch patients required a longer duration of orthodontic
treatment.

CORONOID PROCESS
• It has a propeller-like twist, so that its lingual surface face 3 directions at one;
Posteriorly, superiorly and medially

• Buccal side – resorptive type of periosteal surface
• The remainder of most of the superior part of ramus, including whole area just
below the mandibular notch and superior portion of condylar neck grows by
deposition on the lingual side and resorption on the buccal side

• The lower part of the ramus below the coronoid process also has a twisted contour.
• Its buccal side faces posteriorly towards the direction of the backsward growth and
thus, has a depository surface
• The opposite lingual side, facing away from the direction of growth is resorptive.

ROLE OF CONDYLAR CARTILAGE
• The condyle is of special interest because –major site of growth
• It is involved in one of the most complicated articulation of the body, and there
have been so many opinions about its role in growth of mandible
• The mandible is really a membrane remodeling over all surfaces, though one part
develops in response to a phylogenetically altered developmental situation and
becomes condylar region

• The condylar cartilage is a secondary cartilage which makes an
important contribution to the overall length of the mandible
• Regional adaptive growth in the condylar area is important because the
corpus of the mandible must be maintained in functioning
juxtaposition with the base of the skull where it articulates

• Many arguments about condylar growth focus on – Is the condylar cartilage the
principal force that produces the forward and downward displacement of mandible
• For many years, it was considered – Primary growth centre of bone
• Proponents of the functional matrix theory claims that some mandibles functions
adequately and seem to be positioned rather normally when condyles are absent.

• They concluded that soft tissue development
carries mandible forward and downward while
condylar growth fills the resultant space to
maintain the contact with the basicranium.

• The condyle doesnot determine the mandibular growth, rather it is the mandible
which determines the condylar growth
• Articular function determines condylar growth and articular function is dependent
on how the mandible grows.

• An endochondral growth mechanism is required because the condyle grows
in a direction of the articulation in the face of pressure, a situation which pure
intramembranous bone growth could not tolerate
• The condyle is a secondary cartilage and is presumed not to have such
potential. Thus assumption fits nearly with F.M theory

• The growth cartilage may act as a ‘functional matrix’ to stretch the
periosteum, inducing the lengthened periosteum to form intramembraneous
bone beneath it
• The formation of the bone within the condylar head causes the mandibular
rami to grow upwards and backwards, displacing the entire mandible in an
opposite downward and forward direction.

• In infants the condyles of the mandible are inclined horizontally, so that
condylar growth leads to an increase in the length of the mandible
• Due to the posterior divergence of the 2 halves of the body of the mandible,
growth in the condyar head of the more widely displaced rami results in overall
widening of the mandibular body.

ALTERATION OF THE DIRECTION
OF THE MENTAL FORAMEN

ALVEOLAR PROCESS
• It develops as a protective trough in response to the tooth buds and becomes
superimposed upon the basal bone of the mandibular body.
• It adds to the height and thickness of the body of the mandible
• It fails to develop if teeth are absent and resorbs in response to tooth extraction
• The orthodontic movement of teeth takes place in the labile alveolar bone of
both maxilla and mandible and fails to involve the underlying basal bone.

THE CHIN
• Man is one amongst two species having a chin
• It is formed by mental ossicles from accessory cartilages and the ventral end of
meckels cartilage, is very poorly developed in the infant.
• It develops almost as an independent subunit of mandible, influenced by sexual
as well as specific genetic factors
• Thus, the chin becomes significant only at adolescence from the development of
mental protruberence and tubercles

The remodelling process involves
a) Periosteal resorption on the labial
bony cortex
b) Deposition on the alveolar surface of
the labial cortex
c) Resorption on the alveolar surface of the lingual
cortex
d) Deposition on the lingual side of the lingual cortex

MENTAL PROTRUBERANCE
 At the same time, bone is progressively added
onto the external surface of the mandibular
basal bone area , including the mental
protuberance (chin).
 The reversal between these two growth fields
usually occurs at the point where the
concave surface contour becomes convex.
 The result of this two way growth process
is a progressively enlarging mental
protuberance

AMOUNT AND DIRECTIONS
1. HEIGHT
• The ramus height correlates well with corpus length and overall
mandibular length
• Alveolar process height increases are correlated with eruption
• Anterior mandibular height is related to dental development and overall
growth downwards and forwards

2. WIDTH
• Bigonial and bicondylar diameter increases.
• Most width increases occur simply because the mandible grow longer,
though some periosteal deposition occurs

4)ROTATION
• Mandibular growth rotations assume an important role because they are common
than maxillary rotations.
• Mandibular inclinations drastically affects facial morphology , and treatment
planning , treatment outcome

• Serial ceph studies, using cranial base registrations, imply that normally the
mandible is carried away from the posterior cranial base in a downward and
forward direction
• When the mandibular corpus is steeply related to the posterior cranial base
and anterior facial height increases and are greater than those of posteriorly,
the mandible sometime said to rotate POSTERIORLY

• When posterior facial height is greater than normal, the bite tends to be deeper
and mandible is said to display ANTERIOR rotation
• Bjork and others studies- this is called mandibular rotation- by use of metallic
implants and other methods
• The nature and amount of rotation are misinterpreted through the use of several
landmarks

• Bjork- 7 structural signs of extreme growth rotation in relation to condylar
growth direction
1. Inclination of the condylar head
2. Curvature of mandibular canal
3. Shape of the lower border of mandible
4. Inclination of symphysis
5. Interincisal angle
6. Interpremolar or intermolar angles
7. Anterior lower facial height

• He also made clear distinction between
1. Matrix rotation
Often goes in the form of a pendulum
movement with the rotation point in the
condyle

2. INTRA MATRIX ROTATION
Is the rotation of the mandibular
corpus, inner half of its matrix
within the mandibular corpus

5)TIMING
•Spurts in mandibular dimensions are common but are not
universal and are more frequently seen in boys than girls,
occuring app one and half years earlier in girls
•The most important spurt in mandular growth is that related
to puberty

THEORIES OF MANDIBULAR GROWTH
• GENETIC THEORY:-
• This theory states that all growth is compelled by genetic influence ie: genetic
encoding of mandible determines its growth.
• CARTILAGENOUS THEORY
• This theory states that the cartilage is the primary determinant of skeletal
growth while bone responds secondarily & passively.
• According to this theory, the condyle by means of endochondral ossification
deposits bone, which tends to grow the mandible.

ENLOW’S EXPANDING ‘V’ PRINCIPLE
 This theory states that many facial bones ora part of the bone follows a ‘v’
pattern ofenlargement.
 Deposition is in the inner surface of of ‘V’ . Resorption is seen along theouter
surface of ‘V’.
• CORONOID PROCESS: Deposition –lingualsurface, Resorption-buccal
• CONDYLE PROCESS: Deposition-ant. & post. Margins,
• Resorption-buccal & lingual surfaces

ENLOW’S COUNTERPART PRINCIPLE
• This principle states that growth
of any given facial or cranial
part relates specifically to
other structural & geometric
counterpart in the face &
cranium

SERVO SYSTEM THEORY
• Alexander Petrovic
• Control of primary cartilages takes a
cybernetic form of ‘command’
whereas control of secondary
cartilage like condyle is comprised of
both direct effect of cell multiplication
and also indirect effects

• Upper dental arch- Constantly changing reference input
• Lower arch- Controlled variable
• When there is disturbance between respective positions of upper and lower
jaws(peripheral comparator)- sends actuating signals through the stimulation of
retrodiscal pad and lateral pterygoid muscles
• Output signal- Final sagittal position of mandible- which depends on modification of
condylar growth

UNLOADED NERVE CONCEPT
 The skeletal units & growth fields fulfill the demand of protection of
mandibular nerve by formation of bone around
 The basal tubular portion of mandible serves as a protection for the
mandibular canal & follows a logarithmic spiral in its downward & forward
movement from beneath the cranium

 The most constant part of mandible is the arc from
foramen ovale to the mandibular foramen
and mental foramen.
 The U.N.C. also accounts for stress trajectory
alignment & trabecular structure from condyle to
symphysis .

GNOMONIC GROWTH & LOGARITHMIC SPIRAL
A mathematical model was proposed by Moss that describes mandibular
growth along a logarithmicspiral
• This was based on D’ArcyThompsons study on sea-shells ( Nautilus)
• The characteristics of its growthare
 Original shape remains constant, with increase in
size.
 Gnomonic growth can be described by a curve called
as equiangular or logarithmic spiral

LOGARITHMIC GROWTH OF MANDIBLE
 Moss found it reasonable to speculate that the pathway
of the inferior alveolar nerve follows a logarithmic spiral
 These foramina (foramen ovale,mandibular foramen,
mental foramen) are aligned on a curve that fits them all.
 The corpus stays in essentially a horizontal position. At
the same time, the mandible moves down the
logarithmic spiral course of the inferior alveolarnerve.

 The logarithmic spiral formulated by moss, which
coincide with three foramina of inferior alveolar nerve
and describes path of mandibular growth.
 Mandible moves to a position where there is less
curvature of spiral becauseas the bone lengthens with
growth,the distance between the foramina increases
 As mandible increase in size, it does not actually grow
up and out ,the whole spiral rotates clockwise and
corpus remains horizontal

FUNCTIONAL MATRIX THEORY
• Moss speaks mandible as a group of microskeletal units and a basal core part
• Coronoid process- microskeletal unit- under the influence- temporalis muscle
• Gonial angle- microskeletal unit- under the influence-masseter and pterygoid muscles
• Alveolar base- microskeletal unit- teeth
• Basal tubular portion- protection for mand canal- follows logarithmic spiral-Unloaded
Nerve Concept

• Important concepts in mandibular growth
1. Constancy of the relative position of mental foramen in the mandibular
corpus
2. Absolute migration of the dentition through the alveolar bone
3. Change in direction of mental foramen

NEUROTROPHISM
• Moss- FMT- soft tissues regulate the skeletal growth through functional stimuli
• The process- functional stimulus transmitted to skeletal unit interface involves-
Neurotrophism
• Neurotrophism is a non impulsive transmittive neurofunction involving axoplasmic
transport, providing for the long-term interactions between neurons and innervated
tissues which homeostatically regulate the morphological, compositional and
functional integrity of those tissues

3 types-
1. Neuroepithelial trophism
• Growth after intimate neuroepithelail contact. Eg- facial hypoplasia and cleft palate exhibit
sensory deficits
2. Neurovisceral trophism
• Salivary glands are regulated
• Hyperplasia and hypertrophy-gland seems to be under neurotrophic control partially
3. Neuromuscular trophism
• Moss- nerve influences gene expression
• Periosteal muscuular matrices-regulate size and shape-microskeletal units

PROBLEMS OF MANDIBULAR GROWTH AND
THEIR ORTHODONTIC SIGNIFICANCE
• Agnathia - mandible may be grossly deficient or absent which reflects deficiency of neural
crest cell tissue in lower part of the face.
• First arch and second arch syndrome – Aplasia of mandible and hyoid bone
• Micrognathia - a diminutive mandible, occurs in
• Pierre Robin’s syndrome Cat cry syndrome
Mandibulofacial dysostosis Progeria
• Down’s syndrome
• Oculo-auriculo vertebral syndrome
• Turner’s syndrome

PRS is a sequence, i.e. a chain of certain developmental
malformations, one entailing the next.
The three main features are cleft palate, Retrognathia and
glossoptosis (airway obstruction caused by backwards
displacement of the tongue)
Hemifacial microsomia
(Goldenhar’s syndrome)
 Rare congenital defect characterized by incomplete
development of the ear, nose, soft palate, lip, and
mandible.
It is associated with anomalous development
of the first and second branchial arch
Pierre Robin’s syndrome

 Common in males and in conditions like acromegaly
 Anterior and posterior crossbite will be present
 Increased mandibular corpus length
 Dental and skeletal class III malocclusion
TMJ ANKYLOSIS
 Limited mouth opening
 Unilateral/bilateral OR Osseous /fibrous
 Crossbite on affected side
 Deviation of jaw to affected site while opening
 Flatness or fullness of affected side
PROGNATHISM

CONDYLAR HYPERTROPHY
 Mostly due to genetic or hormonal causes
 Common in males
 Usually expressed in late teen age when the growth of
mandible continues at condyle
 More likely to be a high angle case
 Unilateral-chin divergent on side opposite to hypertrophy
facial assymetry
buccal crossbite on unaffected side

 Due to genetic reasons
 Common in prognathic patients
 Brachiofacial appearance
 Bilateral crossbite
 Anterior divergent face
 In severe cases there can be total lingual non occlusion-Crocodile bite
POOR TRANSVERSE GROWTH
 Common in hypognathic patients
 Usually class II cases
 Posterior divergent patients
 In severe cases there is complete buccal non occlusion-Brodie’s Bite
EXCESSIVE TRANSVERSE GROWTH

PROBLEMS OF RAMAL GROWTH
 Excessive vertical ramal growth
• Brachiofacial patients, low angle cases, anterior deepbite
 Poor vertical ramal growth
•Dolichofacial patients , high angle cases , anterior open bite
 Excessive horizontal ramal growth
• More broad oropharynx
 Poor horizontal ramal growth
• Narrow oropharynx, Chances of airway constriction

PROBLEMS OF CHIN GROWTH
• PROMINENT CHIN
• Common in males
• Excessive mental bone resorption
• Can be treated with genioplasty in adults
• DEFECTS DUE TO FAILURE OF FUSION OF PROCESSES
MANDIBULAR CLEFT; Rare condition
due to persistence of furrow between
2 mandibular processes
MICROSTOMIA/MACROSTOMIA;Determined by fusion of maxillary and
mandibular process at their lateral extent

SIGNIFICANCE
 Timely identification of growth disturbances helps in interception of
developing malocclusions and other orthodontic and esthetic facial
problems
 Knowing the timing of developmentof different facial structures gives
you idea about the long term facial apppearence of the patient
 Timely diagnosis of growth problems gives you a chance to treat the problem
with functional appliances

CONCLUSION
Bone growth in mandible is a remodelling process represented by apposition
and resorption.
Knowledge of general facial growth provides a background to the
understanding of the etiology and development of of malocclusion, such an
understanding is in turn an important part of diagnosis and treatment
planning.

REFERENCES
1. THE HUMAN FACE-DONALD H ENLOW
2. CONTEMPORARY ORTHODONTICS,FIFTH EDITION-WILLIAM R
PROFITT
3. CRANIOFACIAL DEVELOPMENT-GEOFFREY H SPERBER
4. CRANIOFACIAL GROWTH- SRIDHAR PREMKUMAR
5. ORTHODONTICS-SRIDHAR PREMKUMAR

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, porcelain like
problem that we struggle to repair in the
adversity of old age
–D.E POSWILLO

Growth and Development of Mandible

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