Growth & development of mandible /fixed orthodontic courses

GROWTH AND
DEVELOPMENT OF
MANDIBLE
www.indiandentalacademy.com

INDIAN DENTAL ACADEMY
Leader in continuing dental education


INTRODUCTION
The human mandible has no one design for
life. Rather it adapts & remodels through the
seven stages of life, from the slim arbiter of
things to come in infant, through a powerful
dentate machine & 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.”
“


prenatal growth of mandible


PRENATAL GROWTH OF
MANDIBLE


°Nerve→osteogenesis(Neurotrophic
factors)
Ectomesenchyme
interacts(36-38days iul)
Epi of 1st Arch

Osteogenic Memberane

Trough for acc dev Tooth buds

1 centre of ossification(6th week)
below

around

Inferior Alv Nerve
Incisive branch

• spread of IM ossification
dorsally and ventrally
→body and ramus of the
mandible

presence of neuromuscular
bundle→Mandibular
foramen and canal and
mental foramen


Fate of Meckel`s cartilage


PRENATAL GROWTH OF
MANDIBLE
SECONDARY ACC CARTILAGES
(10TH -14TH WEEK I U L)
-condylar cartilage
-coronoid cartilage
-Mental ossicle cartilage


PRENATAL GROWTH OF MANDIBLE
• Secondary cartilage of coronoid process
• Develop within temporalis muscle
• Incorporated into IMB of ramus
• Disappear before birth

PRENATAL GROWTH OF
MANDIBLE
• 1/2 Cartilages
Ossify (7th month of IUL)

Mental ossicles
syndesmosi
s

Intramembranous bone

→


synostosis

PRENATAL GROWTH OF
MANDIBLE
• CONDYLAR CARTILAGE(10TH WEEK IUL)
• Grow interstitially and oppositionally


CONDYLAR CARTILAGE
• 1ST Evidence of endochondral bone (14th week iul)
• Much of cartilage replaced with Bone by middle of fetal life
• Upper end →Growth cartilage and Articular cartilage
• Changes Mand position and form
• Growth ↑ at puberty peak b/n 12 ½ -14yrs
• Ceases →2o yrs of life

NEONATAL MANDIBLE
Ramus→Low & wide
coronoid→large & above
the condyle
Body→open shell
containing tooth buds
Mand canal→low in the
body

DIFFERENTIAL GROWTH
During fetal life
8weeks - MANDIBLE> MAXILLA
11weeks -MANDIBLE= MAXILLA
13-20weeksMAXILLA>MANDIBLE
AT BIRTH
Mandible tends to be retrognathic
Early postnatal life -orthognathic

POST NATAL GROWTH &
DEVELOPMENT OF
MANDIBLE


MECHANISMS OF GROWTH
Growth Of The Mandible Primarily Involve
Bone remodeling
Process Of Bone Deposition And Resorption
Cortical drift
Combination of bone deposition and resorption resulting
in growth movement towards deposition surface
Displacement
Movement of whole bone as a unit
I) Primary displacement
II) Secondary displacement

THEORIES OF GROWTH
• GENETIC THEORY

Bone ̶ primary determinent
Cartilage̶ primary determinent
The soft tissue matrix

SUTURAL THEORY
• Craniofacial growth→sutures
• Suture transplanted
• Sutures pulled apart
• Sutures compressed
• Sutures are sites that react ̶ not primary
dereminants

CARTILAGINOUS THEORY
• Growth of maxilla ̶ Nasalseptum cartilage
• Transplantation
Epiphyseal plate
Nasalseptal cartilage
Condylar cartilage
Removal of condyle


FUNCTIONAL MATRIX THEORY OF
GROWTH
• Skeletal growth occur as a response to
functional needs & mediated by the soft
tissue in which it is embedded


ENLOW’S EXPANDING ‘V’
PRINCIPLE
The growth movement &
enlargement of these Bones
occur towards the wide ends
of the ‘V’ as a result of
differential deposition &
selective resorption


ENLOW’S COUNTERPART
PRINCIPLE
• The growth of any given facial /cranial part
relates specifically to other structural &
geometric ‘counterparts’ in the face &
cranium
Diff parts & counter parts
Maxillary & Mandibular arches
Middle cranial fossa breadth of Ramus

Parts of Mandible derived From
1. INTRAMEMBRANOUS OSSIFICATION
* Whole body of mandible except the anterior part
* Ramus of mandible as far as mandibular foramen
2 . ENDOCHONDRAL OSSIFICATION
* Anterior portion of the mandible (symphysis)
* Part of ramus above the mandibular foramen
* Coronoid process
* Condylar process


Timing of growth
• Growth in width is completed 1st then
growth in length finally growth in height


Growth in width
• Intercanine width does not ↑ much after 12yrs
• Both molar & bicondylar width show small ↑
until the end of growth in length
• Ant width stabilize earlier


Growth in length
• Continues through the period of puberty
Girls – 14 -15 yrs
Boys – 18 yrs


POST NATAL GROWTH OF
MANDIBLE
• Mandible – Developmentally & Functionally
divisible into skeletal subunits


• Mandible undergoes largest amt of growth
postnatally and exhibits largest variability in
morphology
• The main sites of postnatal growth
‫٭‬At condylar cartilages
‫ ٭‬Posterior border of rami
‫٭‬Alveolar ridges

THE RAMUS
• Key role of ramus in placing the corpus &
dental arch into ever changing fit with
growing maxilla & the faces limitless strl
variations
• By Remodeling adjustments in Ramus
length & Ant post width.

THE RAMUS
Relocates postly
Resorption

Deposition posteriorly
anteriorly


LINGUAL TUBEROSITY
• Direct Anatomic equivalent of Max tuberosity
• Inaccessible to cephalometric studies
• Major Growth & Remodeling site
• Effective boundary b/n Ramus & corps


LINGUAL TUBEROSITY
• Deposition
• Resorption

Postly & Medially
Below (Lingual fossa )


Lingual Tuberosity
Remodels in post direction with
slight lateral shift

Lingual shift of Ant part of Ramus

↑ Length of corpus

Ramus to carpus Remodeling
• Making room last
Molar


Ramus to carpus Remodeling

Growth direction fallows‘V’PRINCIPLE
‘X’ arrows
Remodeling activity does not occur only
on ant & post barder

Coronoid process
• Propellar like twist
• Lingual side faces
posteriorly
superiorly
medially


Coronoid process
Fallows ‘V’ PRINCIPLE

‘V’ oriented vertically


Coronoid process
‘v’ PRINCIPLE
‘V’Oriented horizontally


Coronoid process
Coronoid process → medially
to become post part of carpus

Buccal side → Resorptive


Ramus
• Superior part of
ramus the area below
sigmoid
notch


Ramus


Antigonial notch
Size of the notch ↑ed –
downward rotation
Of carpus relative to the
Ramus


The size of the notch depends upon Ramus – Carpus junction


Post edge Ramus is a major
growth site
Condyle grows obliquely upward &
backward
The angle of growth is variable
The gonial region is Anatomically
variable


Mand Foramen – midway b/n
Ant & post borders of Ramus


The Mandibular condyle
• Secondary cartilage
•

not a primary center of growth, but rather
* Secondary in Evolution
* Secondary in Embryonic origin
* Secondary in adaptive responses


condyle
• Cartilage is special nonvascular tissue
• firm matrix – unyielding to the pressure
• Endochondral growth mechanism


• Provides pressure tolerant articular
contact
• Multidimensional growth capacity in
response to ever changing developmental
conditions & variations


• Capsular layer of poorly
vascularised connective
tissue –highly cellular
• Chondroblasts –cellular
proliferation
• Chondroblasts –
hypertrophy
• Zone of resorptive &
Bone deposition

• Proliferative process
produces upward &
backward growth
movement
• Multidirectional
proliferative capacitythe arrangement of
daughter cells does
not reflect direction of
growth

• The cortical layer of IMB
continues on to the
condylar neck
Ant margin of condylar
neck – depository
grows supe’ly
post margin - depository
grows on to post barder

• Lingual & Buccal
sides - Resorptive


• V-shaped cone of condylar neck growing
towards its wider end


• The condyle can’t play king pin role of
“Master center” in pace-setting the growth
Bilaterally condyle-lacking mand occupy
normal Anatomic position
Condylar remodeling acts with displacement
as co-participants but not as driving force

Current concept
• Condylar cartilage does have some intrinsic
genetic programming
• But extracondylar factors are needed to sustain
this activity
1)Intrinsic & extrinsic biomechanical forces
2)physiologic inductors
ENLOW;
↑amt of pressure – inhibit the growth
↓ amt of pressure – stimulate the growth

• Mandible is less responsive to orthopedic
forces than maxilla
• Mand orthopedics must modify growth
signals targeted at both ramus & condyle
to
be maximally effective

MENTAL FORAMEN


ALVEOLAR PROCESS
Adds ht & thickness to the
body of the Mand
Teeth absent fails to develop
Resorbs after tooth extraction


Alveolar process
• Maintain occlusal relationship during differential
mandibular & midfacial growth– buffer zones
• Maintains vertical height
• Adaptive remodeling makes orthodontic tooth
movement possible


Lingual movement of anteriors


Mental protuberance
Formed by mental ossicles from accessory
cartilage and ventral end of Meckel’s cartilage
Poorly developed in infants


Mental protuberance
Forms by osseous deposition
during childhood
Prominence is accentuated by
bone resorption above it
Reversal between 2 growth
fields
Concave  convex
Reversal line could be High or
low

Chin
• Protrusive chin is unique human trait
• More prominent in male
• Less prominent in female


Factors Affecting Growth
Systemic Factors
Genetic
Hormonal imbalance
Nutrition
Systemic illness or chronic illness
Localized alteration/ diseases of uterus
Systemic illness in mother
Drugs


B) Local factors
1. Vascular abnormality
2. Lymphatic disturbance
3. Neurologic disease
4. Local infection
5. Ear infection or mastoiditis
6. Ankylosis
7. Trauma or fracture
8. Birth injury
9. Habits

Anomalies of mandible
Some of the syndromes associated with
mandibular abnormality
1)Down’s syndrome
2)Marfan’s syndrome
3)Turners syndrome
4)Kleinfelter’s syndrome
5) Pierre-robin syndrome
6) Treacher- collin syndrome

Congenital
• Agnathia
• Micrognathia
• Macrognathia
• Facial hemihypertrophy
• Facial hemiatropy


Developmental
• Infantile cortical hyperostosis
• Achondroplasia
• Torus mandibularis
• Stafne’s cyst
• Odontogenic cyst
• Odontogenic tumor

Age changes of Mandible
At birth

Adult

Old age

1 Mental
foramen

Near the lower
border

Midway b/n upper
& lower border

Near the upper border

2 Angle of the
mandible
3 coronoid &
condyloid
processes

Obtuse (180)

Right angle

Obtuse (140)

Coronoid is
larger & above
condyle

Condyle is above
the coronoid

4 Mandibular
canal

Runs little
above the
mylohyoid line
Present;two
halves united
fibrous tissue

Runs parallel to
the mylohyoid line

Condyle is above the
coronoid but in
extreme old age –bent
backwards
Runs close to the
upper border

5 Symphysis
menti

Reprasented by
faint ridge only in
the upper part


Not recognisable or
absent

References
* Craniofacial embryology – SPERBER
* Facial growth – ENLOW
* Contemporary orthodontics – PROFFIT
* Handbook of orthodontics – MOYERS
* Principles and practice of orthodontics –GRABER


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Leader in continuing dental education


Growth & development of mandible /fixed orthodontic courses

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