Growth and development of mandible

GROWTH AND
DEVELOPMENT OF
MANDIBLE
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CONTENTS
 INTRODUCTION
 ANATOMY
 PRENATAL GROWTH &
DEVELOPMENT
 POSTNATAL GROWTH &
DEVELOPMENT
 THEORIES OF MANDIBULAR
GROWTH


 GROWTH ROTATIONS
 TRAJECTORIES OF FORCE
 AGE CHANGES IN MANDIBLE
 ANOMALIES OF DEVELOPMENT
 CONCLUSION

ANATOMY

MUSCLE ATTACHMENTS

EMBRYONIC PERIODEMBRYONIC PERIOD
During 3rd
& 8th
week of development, a period
known as the embryonic period, each of the 3
germ layers (endoderm, ectoderm &
mesoderm) give rise to a number of specific
tissues & organs.

THE PHARYNGEAL ARCHES
The pharyngeal
arches appear
between 4th
& 5th
weeks of
development

Each arch contain
 A central cartilage
that forms the
skeleton of the arch
 A muscular
component
 A vascular
component
 A neural component

 The 1st
pharyngeal
arch is the
mandibular arch
which contains the
Meckel’s Cartilage.
 It appears at about
6th
week of I.U. life.

MECKEL’S CARTILAGE
 Makes little
contribution towards
the development of
the mandible
 Provides a Template
for subsequent
development of the
mandible.

 During the 7th
week of I.U. life, a centre
of ossification appears lateral to the
meckel’s cartilage.
 From this centre, bone formation
spreads rapidly backwards, forwards &
upwards around inferior alveolar nerve
& its terminal branches.

SECONDARY CARTILAGES
 Appears between
10th
& 14th
week of
I.U. life.
 Forms the head of
condyle, part of
coronoid process &
mental
protruberances

POSTNATAL GROWTH
OF MANDIBLE
Of all the facial bones mandible
undergoes the largest amount of growth
postnatally.

THE SYMPHYSIS
 BY THE 1ST
YEAR
THE SYMPHYSEAL
CARTILAGE IS
REPLACED BY
BONE.

THE RAMUS
 THE PRINCIPLE
GROWTH
VECTORS ARE IN
POSTERIOR &
SUPERIOR
DIRECTION

FUNCTIONS OF
REMODELING
OF RAMUS
 To accommodate & provide an attachment
base for the increasing mass of masticatory
muscles.
 To accommodate the enlarged breadth of the
pharyngeal space.
 To accommodate the vertical lengthening of
the nasomaxillary part of the growing face.
 To facilitate the lengthening of the corpus
which in turn accommodate the erupting
molars.

RAMUS MIDDLE CRANIAL
FOSSA RELATIONSHIP
 THE RAMUS IS
STRUCTURAL
COUNTERPART
OF THE MIDDLE
CRANIAL FOSSA.

RAMUS UPRIGHTING
 Greater amounts of
bone deposition takes
inferiorly than superiorly
on the posterior border
of ramus.
 Correspondingly
greater amounts of
resorption on ant.
Border takes places
inferiorly than superiorly
resulting in a
REMODELLING
ROTATION

 IN ORDER TO MATCH THE
CONTINUED GROWTH OF
THE MIDFACE THE
DIRECTION OF
DEPOSITION &
RESORPTION REVERSES
& MORE UPRIGHTING
TAKES PLACES.-
DEVELOPMENTAL
COMPENSATION

ANGLE OF MANDIBLE
 FLARING OF
ANGLE OF
MANDIBLE

CORPUS OF MANDIBLE

 REMODELLING
AT DIFFERENT
SECTIONS

ANTEGONIAL NOTCH

MANDIBULAR FORAMEN
 Maintains
constant position
midway between
the anterior &
posterior borders
of the ramus

CORONOID PROCESS

MANDIBULAR CONDYLE

CHIN
 In infancy chin is under
developed.
 As age advances the growth
of chin becomes significant
 Males are seen to have
prominent chin compared to
females.
 The prominence is
accentuated by bone
resorption in the alveolar
region below it, creating a
concavity

THE ALVEOLAR PROCESS
 IT DEVELOPS IN RESPONSE TO THE PRESENCE
OF TOOTH BUDS .
 ITS FORMATION IS CONTROLLED BY DENTAL
ERUPTION & IT RESORBS WHERE TEETH ARE
EXFOLIATED / EXTRACTED.
 WHEN CORPUS GROWTH IS OVER, VERTICAL
ALVEOLAR GROWTH PERSISTS AS THE
OCCLUSAL SURFACES WEAR & THE OCCLUSAL
HEIGHT IS MAINTAINED
 ADAPTIVE REMODELLING OF ALVEOLAR
PROCESS MAKES ORTHODONTC TOOTH
MOVEMENT POSSIBLE.www.indiandentalacademy.com

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.

SUTURAL THEORY
 THIS THEORY STATES THAT
GENETIC CONTROL IS EXPRESSED
DIRECTY AT THE LEVEL OF THE
BONE & ITS LOCUS IS THE
PERIOSTEUM.

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 the
growth of the mandible.

FUNCTIONAL MATRIX THOERY
 According to this theory, the soft tissue
matrix in which the skeletal elements are
embedded is the primary determinant of
growth & both bone & carilage are secondary
followers.
 Which means the muscles, connective tisses
etc. carries the entire mandible away from
the cranial base . The bone follows
secondarily at the condyle to maintain
constant contact with the glenoid fossa.

ENLOW’S EXPANDING ‘V’ PRINCIPLE
 This theory states that many facial bones or a part of
the bone follows a ‘v’ pattern of enlargement.
> Due to differential deposition & selective
resorption
> Deposition is in the inner surface of wide ends
of ‘v’ & along the ends of ‘v’. Resorptionis seen along
the outer surface of ‘v’.
CORONOID: Deposition –lingualsurface, Resorption-
buccal
CONDYLE: Deposition-ant. & post. Margins,
Resorption-buccal & lingual surfaces.

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
Eg;- The maxillary arch is the counter part of
the mandibular arch.

UNLOADED NERVE CONCEPT
 SCOTT divides mandi. Into
3 types: BASAL,
MUSCULAR & ALVEOLAR
 The basal tubular portion of
mandi. 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 mandi. is the arc from
foramen ovale –mandi. forma. –mental formen.
 The U.N.C. also accounts for stress trajectory
alignment & trabacular structure from condyle to
symphysis . The mandi. canal & nerve are protected
by this concentration of trabaculae

SERVO SYSTEM THEORY
 PETROVIC attributes the control of growth &
development to cybernetics
 Growth of the condyle is mainly attributed to the
quantitative response to the growth of the maxilla ie:
the maxilla is the constantly changing reference input
& mandible is the controlled variable
 This means the mandible grows in response to
feedback mechanism that occurs as a result of
maxillary growth.

STUDIES ON
MANDIBULAR
GROWTH
 JOHN HUNTER(1771):Gave classic description on growth &
development of mandible. He proposed that mandi. grows by
addition of bone on its post. surface & resorption on ant. surface
 HUMPHRY(1866): He conducted experiments on jaws of
pigs to study mandi. growth pattern. Wires were twisted at post.
margin of ramus & ant. Border, post. wire became tight & ant.
wire became loose.
 BRODIE(1941): Stated that glenoid fossa cause vertical
displacement of mandible.

 BJORK(1955): Conducted implant studies on jaws
to determine the growth pattern & rotation.
 DONALD ENLOW: Proposed the ‘v’ principle of
growth & couterpart principle.

MANDIBULAR ROTATIONS
 IN 1960 BJORK & COWORKERS
CARRIED OUT LONGITUDINAL
STUDIES USING IMPLANTS TO
STUDY JAW ROTATIONS
DURING GROWTH

 INTERNAL
ROTATION-
CORE
 EXTERNAL
ROTATION-
SURFACE
CHANGES

 MATRIX
ROTATION-
Around the condyle
 INTRA MATRIX
ROTATION-within the
body of mandible

BJORK SOLOW PROFFIT
ROTATIONOFMANDIBULARCORE
RELATIVETOCRANIALBASE TOTALROTATION TRUEROTATION INTERNAL
ROTATION
ROTATIONOFMANDIBULARPLANE
RELATIVETOCRANIALBASE
MATRIXROTATION APPARENT
ROTATION
TOTALROTATION
ROTATIONOFMANDIBULARPLANE
RELATIVETOCOREOFMANDIBLE
INTRAMATRIX
ROTATION
ANGULAR
REMODELLING
OFLOWER
BORDER
EXTERNAL
ROTATION

SHORT FACE TYPE
 Low mandibular
plane angle
 ^ sed internal
rotation &
reduced external
rotation
 Deep bite with
crowed incisors

LONG FACE TYPE
 Lack of forward
internal rotation
 ^sed mandibular
plane angle
 Open bite &
mandibular
deficiency

TRAJECTORIES OF
FORCE
 According to koch in 1817 the
lines of orientations of the bony
trabaculae corresponds to the
pathway of maximal pressure &
tension & bone
Trabaculae are thicker in this region
where the stress is greater

 In 1867 an anatomist named Meyer with the help of
mathematician Culman propounded the
TRAJECTORIAL THEORY OF BONE FORMATIONTRAJECTORIAL THEORY OF BONE FORMATION
 He pointed out that the alignment of bony trabaculae
followed a definite engineering principles eg:
trajectories seen in a crane.
 Many of these trasjectories are crossed at right
angles– an exellent arrangement to resist the
manifold stresses on the condyle of femur

 BENNINGHOFF studied the natural lines of stress in
the skull by piercing small holes into fresh skull .
When skull were dried he observed that the holes
assumed a linear form in the direction of bony
trabaculae
 THESE LINES OF STRESS ARE CALLED
BENNINGHOFF LINES indicates the direction of
functional stresses

TRAJECTORIES OF THE MANDIBLE
 A line of stress extends from
one condyle to the other
passing along the symphysis
 A no: of trajectories radiate
down below the roots of teeth
 Lower border & mylohyoid
ridges are
other butresses of mandible.
 TMJ plays an important role
in transmission of functional
forces
To the base of the cranium

AGE CHANGES IN
MANDIBLE
 SYMPHYSIS MENTI
 ALV. PROCESS NOT YET
FORMED
 RAMUS IS QUITE SHORT
 MIN. CONDYLAR
DEVELOPMENT
 MAND. CANAL LOWER
BORDER
 MENTAL FORAMEN
 CORONOID PROCESS
PROJECTS ABOVE THE
CONDYLE
AT BIRTH

AT INFANCY
 SYMPHYSISJOIN AT 1ST
YEAR
 BODY ELONGATES–
ACCOMMODATE ERUPTING
MOLAR
 PERIOSTEAL DRAG
 DEVELOPMENT OF CHIN
 ^SED GROWTH OFCONDYLAR
CARTILAGE
 ALVEOLAR GROWTH TAKES
PLACE
 RAMUS IS RELOCATED IN
POST. DIRECTION
 ANGLE B/W LOWER & POST.
BORDER OF RAMUS IS
OBTUSE 140 OR MOREwww.indiandentalacademy.com

IN ADULT HOOD
 Mental foramen lies
midway b/w upper &
lower boders
 The mandi. canal lies in
line with mylohyoid line
 Angle b/w the lower &
post. Bordersof ramus
decreases

IN OLD AGE
 Resorption of alv. Region
due to loss of teeth
 Mandi. Canal & mental
foramen
Lies closer to superior border
 Ramus becomes oblique
140
 Neck of condyle is inclined
backwards.
 Alv. bone loss with loss of
teeth

ANOMALIES OF DEVELOPMENT
 AGNATHIA: Grossly deficient or absent mandible
which refects of neural crest tissue in lower part of
face
 MICROGNATHIA: small jaw
 BIFID OR DOUBLE CONDYLE: Results from the
persistence of septa dividing the foetal condylar
cartilage.
 MACROGNATHIA: Large mandible or mandibular
prognathism.

 HEMIFACIAL HYPERTROPHY: Unilateral
enlargement of mandible, the mandibular fossae &
the teeth of unknown aetiology.
 MANDIBULAR CLEFTS: Occasionally both lip &
jaw may be involved

Growth and development of mandible

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