DEFINATIONDEFINATION

““Growth was concieved by an Growth was concieved by an anatomist, born to a biologist, delivered by a anatomist, born to a biologist, delivered by a physician, left on a chemist doorstep, and physician, left on a chemist doorstep, and adopted by a physiologist.At an early ageadopted by a physiologist.At an early age-- she she eloped with a statistician, divorced him for a eloped with a statistician, divorced him for a psycologist, and is now wooed, alternatively psycologist, and is now wooed, alternatively and concurrently, by an endrocrinologist, a and concurrently, by an endrocrinologist, a biochemist,a physicist, a mathematician, an biochemist,a physicist, a mathematician, an orthodontist, a eugenicist and the children’s orthodontist, a eugenicist and the children’s bureau”.bureau”.

Growth and development of an indiviual Growth and development of an indiviual

is divided into two periodsis divided into two periods--

Prenatal period Prenatal period

Post natal periodPost natal period

THE PRENATAL LIFE IS DIVIDED THE PRENATAL LIFE IS DIVIDED

INTO THREE PERIODS INTO THREE PERIODS ––

1.PERIOD OF THE OVUM1.PERIOD OF THE OVUM

2.PERIOD OF THE EMBRYO2.PERIOD OF THE EMBRYO

3.PERIOD OF THE FETUS3.PERIOD OF THE FETUS

PRE NATAL GROWTH PHASE PRE NATAL GROWTH PHASE

About the About the fourth fourth

week of intrauterine lifeweek of intrauterine life, ,

the the pharyngeal pharyngeal

archesarches are laid downare laid down

The first arch is The first arch is

called the called the mandibular mandibular

archarch and the and the

second arch the second arch the hyoid hyoid

arch.arch.

Each of these five arches contain Each of these five arches contain --

1.1. A central cartilageA central cartilage rod that form the skeleton rod that form the skeleton

of the arch.of the arch.

2.2. A muscular componentA muscular component termed as termed as

bronchomerebronchomere

3.3. A vascular componentA vascular component..

4.4. A neural element.A neural element.

INTRAMEMBRANOUS BONE INTRAMEMBRANOUS BONE

FORMATIONFORMATION

The first structure to The first structure to

develop in the develop in the

primodium of the lower primodium of the lower

jaw is the jaw is the mandibular mandibular

division ofdivision of trigeminal trigeminal

nervenerve that precedes the that precedes the

mesenchymal mesenchymal

condensation forming condensation forming

the first [mandibular] the first [mandibular]

arch.arch.

At around 36 At around 36 --38 days38 days of intrauterine life there of intrauterine life there is is ectomesenchymal condensationectomesenchymal condensation

Some Some mesenchymal cellsmesenchymal cells enlarges , acquire a enlarges , acquire a basophilic cytoplasm and form basophilic cytoplasm and form osteoblastsosteoblasts

These osteoblasts secrete a gelatinous matrix These osteoblasts secrete a gelatinous matrix calledcalled osteoidosteoid and result in and result in ossification of an ossification of an osteogenic membrane.osteogenic membrane.

The resulting The resulting intramembranous boneintramembranous bone lies lateral to meckel’s lies lateral to meckel’s cartilage of first [mandibular ] arch.cartilage of first [mandibular ] arch.

In the In the sixth week of the intrauterine lifesixth week of the intrauterine life a single ossification centre a single ossification centre for each half of the mandible arises in the for each half of the mandible arises in the bifurcation of inferior bifurcation of inferior alveolar nerve into mental and incisive branchesalveolar nerve into mental and incisive branches

During During seventh week of intrauterine lifeseventh week of intrauterine life bone bone

begin to develop lateral to begin to develop lateral to meckel’s cartilagemeckel’s cartilage

& continues until the posterior aspect is & continues until the posterior aspect is

covered with bonecovered with bone

Between Between eigth & tewelth week of intrauterine eigth & tewelth week of intrauterine

lifelife mandibular growth accelerate , as a result mandibular growth accelerate , as a result

mandibular length increses.mandibular length increses.

Ossification stops at a piont , which later become Ossification stops at a piont , which later become mandibular mandibular lingulalingula, the remaining part of meckels cartilage continues to , the remaining part of meckels cartilage continues to form form sphenomandibular ligament & spinous process of sphenomandibular ligament & spinous process of sphenoidsphenoid..

Secondary accseeory cartilageSecondary accseeory cartilage appear between tenth & appear between tenth & fourteenth week of intrauterine life to form fourteenth week of intrauterine life to form head of condyle , head of condyle , part of coronoid process & mental protuberancepart of coronoid process & mental protuberance

ENDROCHONDRAL BONE ENDROCHONDRAL BONE

FORMATIONFORMATION

Endrocondral bone formation is seen in 3 Endrocondral bone formation is seen in 3

areas of mandibleareas of mandible--

1)1) The condylar processThe condylar process

2)2) The coronoid processThe coronoid process

3)3) The mental processThe mental process

THE CONDYLAR PROCESSTHE CONDYLAR PROCESS--

At fifth week of At fifth week of

intruterine lifeintruterine life , an area of mesenchymal , an area of mesenchymal

condensation is seen above the condensation is seen above the ventral part of ventral part of

developing mandible.developing mandible.

At about At about tenth weektenth week it develops in it develops in cone shaped cone shaped

cartilage.cartilage.

It migrate inferior & fuses with It migrate inferior & fuses with mandibular ramusmandibular ramus at at

about about 4 month.4 month.

This cone shaped cartilageThis cone shaped cartilage is replaced by bone but its is replaced by bone but its

upper end persists acting as upper end persists acting as growth cartilage & articular growth cartilage & articular

cartilage.cartilage.

THE CORONOID PROCESSTHE CORONOID PROCESS--

Secondary Secondary

accessory cartilageaccessory cartilage appear in region of appear in region of

coronoid process at about coronoid process at about 1010-- 14 week of 14 week of

intrauterine life.intrauterine life.

This cartilage become incorporated into This cartilage become incorporated into

expanding expanding intramembranous bone of ramusintramembranous bone of ramus & &

dissapear before birth.dissapear before birth.

THE MENTAL REGIONTHE MENTAL REGION--

In mental region , on In mental region , on

either side of symphysis , one or two small either side of symphysis , one or two small

cartilage appear and ossify in cartilage appear and ossify in seventh week of seventh week of

intrauterine lifeintrauterine life to become to become mental ossicles.mental ossicles.

These ossicles become incorporated into These ossicles become incorporated into

intramembranous boneintramembranous bone when symphysis ossify when symphysis ossify

completely. completely.

POST NATAL GROWTH PHASEPOST NATAL GROWTH PHASE

At birthAt birth the two rami of the mandible are short , the two rami of the mandible are short , condylar development is minimum and there is no condylar development is minimum and there is no articular eminence in glenoid fossa. A thin layer of articular eminence in glenoid fossa. A thin layer of fibrocartilage & connective tissue exists fibrocartilage & connective tissue exists at the midline at the midline of symphysis to separate right & left mandibular of symphysis to separate right & left mandibular bodies.bodies.

At fourth month of age and end of first yearAt fourth month of age and end of first yearsymphysial cartilage is replaced by bonesymphysial cartilage is replaced by bone

During first year of lifeDuring first year of life

appositional growth is appositional growth is

active at alveolar active at alveolar

border, border, at distal & at distal &

superior surfaces of the superior surfaces of the

ramus, at the condyle, ramus, at the condyle,

along the lower border along the lower border

of mandible and on its of mandible and on its

lateral surface.lateral surface.

After first year of life these changes occurs After first year of life these changes occurs --

Mandibular growth become more selective , condyle Mandibular growth become more selective , condyle

shows considerable activities, shows considerable activities, mandible moves and mandible moves and

grows downward & forward.grows downward & forward.

Appositional growth occurs on Appositional growth occurs on posterior border of the posterior border of the

ramus and on the alveolar process.ramus and on the alveolar process.

Resorption occurs along the Resorption occurs along the anterior border of ramusanterior border of ramus

lenthening the alveolar border & maintaining the lenthening the alveolar border & maintaining the

anterioranterior-- posterior dimension of ramus.posterior dimension of ramus.

Gonial angleGonial angle changes after little muscle activity.changes after little muscle activity.

Transverse dimension is mainly due to growth at Transverse dimension is mainly due to growth at

posterior border in an posterior border in an expanding V patternexpanding V pattern..

The two rami also The two rami also diverge outwarddiverge outward from below to from below to

above so that additive growth at above so that additive growth at coronoid notch , coronoid notch ,

coronoid process &condylecoronoid process &condyle also increses the superior also increses the superior

interinter--ramus dimension.ramus dimension.

Alveolar process of mandibleAlveolar process of mandible grows grows upward & upward &

outwardoutward on an expanding arc. This permit dental arc to on an expanding arc. This permit dental arc to

accommodate the larger permanent teeth.accommodate the larger permanent teeth.

Scott Scott divides the mandible into three basic divides the mandible into three basic

types of bone types of bone ––

1)1) BasalBasal

2)2) MuscularMuscular

3)3) AlveolarAlveolar

Basal portionBasal portion is tube like central foundation running is tube like central foundation running

from condyle to the symphysis.from condyle to the symphysis.

Muscular portionMuscular portion [gonial angle &coronoid process] [gonial angle &coronoid process]

is under influence of is under influence of masseter, internal pterygoid & masseter, internal pterygoid &

temporal muscle.temporal muscle. They determine the ultimate form They determine the ultimate form

of the mandible in these areas.of the mandible in these areas.

Alveolar portionAlveolar portion exists to hold the teeth & exists to hold the teeth &

gradually resorbed in the event of tooth loss.gradually resorbed in the event of tooth loss.

Reduced muscular activity Reduced muscular activity

would account for would account for flattening of gonial angle flattening of gonial angle

and reduction of the coronoid process.and reduction of the coronoid process.

MOSS say that the mandible as a group of microskeleton unit MOSS say that the mandible as a group of microskeleton unit ––

Coronoid processCoronoid process as one skeleton unit under influence of temporalis.as one skeleton unit under influence of temporalis.

Gonial angleGonial angle is another skeleton unit under influence of massetor & is another skeleton unit under influence of massetor & internal pterygoid muscles.internal pterygoid muscles.

Alveolar processAlveolar process is under the influence of the dentition.is under the influence of the dentition.

Basal tubular portion of mandibleBasal tubular portion of mandible serves as protection for the serves as protection for the mandibular canal and follows a mandibular canal and follows a logarithim spirallogarithim spiral in its downward & in its downward & forward movement from beneath the cranium.forward movement from beneath the cranium.

THE CHINTHE CHIN ––

Enlow & harrisEnlow & harris feel that chin is feel that chin is

““associated with a generalised cortical associated with a generalised cortical

recession in the flattened regions positioned recession in the flattened regions positioned

between the canine teeth. The process involves between the canine teeth. The process involves

a mechanism of endosteal cortical growtha mechanism of endosteal cortical growth.”.”

On lingual surface, behind the chin heavy On lingual surface, behind the chin heavy

periosteal growthperiosteal growth occurs , with the dense occurs , with the dense

lamellar bone merginglamellar bone merging and overlaping on the and overlaping on the

labial side of the chin. labial side of the chin.

In male ,In male , the the apposition of the boneapposition of the bone at at

symphysissymphysis seems to be about the last change in seems to be about the last change in

shape during the growing period. This change shape during the growing period. This change

is much less apparent in is much less apparent in the females.the females.