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.