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 age- she adopted by a physiologist.At an early age- 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 periods-is 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 down are laid down

The first arch is The first arch is called the called the mandibular mandibular archarch and the second and the second arch the arch the hyoid arch.hyoid 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 -38 daysAt around 36 -38 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 osteoid osteoid 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 a single ossification centre for each half of the mandible arises in the centre for each half of the mandible arises in the bifurcation of bifurcation of inferior alveolar nerve into mental and incisive branchesinferior alveolar 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 mandible-areas 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 PROCESS-THE 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 PROCESS-THE CORONOID PROCESS-

Secondary Secondary accessory cartilageaccessory cartilage appear in region of appear in region of coronoid process at about coronoid process at about 10- 14 week of 10- 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 REGION-THE 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 year symphysial 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 anterior- posterior dimension of ramus.anterior- 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 inter-ramus dimension.inter-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 MOSS say that the mandible as a group of microskeleton unit – 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.

Development of MaxillaDevelopment of Maxilla

Deevelops from mesenchyme of maxillary Deevelops from mesenchyme of maxillary process of 1process of 1stst branchial arch. branchial arch.

At 7At 7thth week week of intrauterine life there is of intrauterine life there is primary intra primary intra membranous ossification membranous ossification centre appears for each centre appears for each maxilla ….infraorbital nerve just above the future maxilla ….infraorbital nerve just above the future canine area.canine area.

From this center ossification proceeds in all From this center ossification proceeds in all directions directions

. …posteriorly below the orbit to zygoma.. …posteriorly below the orbit to zygoma. Anteriorly toward the future incisor region.Anteriorly toward the future incisor region. Superiorly to frontal process.Superiorly to frontal process. To palate to form hard palate To palate to form hard palate

At junction of body of maxilla nd palatal At junction of body of maxilla nd palatal process together with lateral alveolar plate process together with lateral alveolar plate forms a trough around the developing tooth.forms a trough around the developing tooth.

Bony septas ..divide these troughs into Bony septas ..divide these troughs into separate bony compartments acoomodating the separate bony compartments acoomodating the developing tooth germs. developing tooth germs.