مهم 1

الله الله بســــــم بســــــمالرحيـــــم الرحيـــــم الرحمن الرحمن

ORTHODONTIC DENTISTRYORTHODONTIC DENTISTRYPRENATAL DEVELOPMENT PRENATAL DEVELOPMENT

OF MANDIBLEOF MANDIBLE . زيـــــــــــــنه: د . أشراف زيـــــــــــــنه: د أشراف

توفيــــقتوفيــــق : علي هنــــــــــد الطالبه : أعداد علي هنــــــــــد الطالبه أعداد

عبداللهعبداللهG.D.G.D.

Is the Is the largestlargest and and strongeststrongest bone of bone of the face, serves for the reception of the face, serves for the reception of the lower teeth. It consists of a the lower teeth. It consists of a curved, horizontal portion, the curved, horizontal portion, the bodybody,, and two perpendicular and two perpendicular portions, the portions, the ramirami,, which unite with which unite with the ends of the body nearly at right the ends of the body nearly at right angles. angles.

The Mandible

ANATOMY OF THE

MANDIBLE

Do u remember the development of the body of the mandible?

Prenatal development of Prenatal development of mandiblemandible

First thing to develop in primodrium of First thing to develop in primodrium of mandible of lower jaw is the mandible of lower jaw is the mandibular mandibular

division of trigiminal nerve.division of trigiminal nerve.

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Starting at the Starting at the 44thth week week of intrauterine of intrauterine life,the brain and pericardium form two life,the brain and pericardium form two prominent pulges on the ventral aspect prominent pulges on the ventral aspect

of the embryo which are seprated by of the embryo which are seprated by the the primitive oral cavity or stomodeum.primitive oral cavity or stomodeum.

The floor of stomodeum is formed by The floor of stomodeum is formed by buccopharyngeal membrane.buccopharyngeal membrane.

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Pharengeal arches are laid down on the Pharengeal arches are laid down on the lateral and ventral aspects of the cranial lateral and ventral aspects of the cranial most part of the foregut which are lies in most part of the foregut which are lies in

close with the close with the stomodeumstomodeum..

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Phryngeal arches:Phryngeal arches:

First we have 6 pharyngeal archesFirst we have 6 pharyngeal arches

The 5The 5thth arch after it is formation it will arch after it is formation it will disappear…so that the remaining only disappear…so that the remaining only

five.five.

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They are seprated by 4 branchial They are seprated by 4 branchial grooves.grooves.

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First ArchFirst Arch:mandibular arch:mandibular arch

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Second archSecond arch:hyoid Arch:hyoid Arch

Arches Contents:Arches Contents:

1.1.A central cartilage rod that forms the A central cartilage rod that forms the

2.2.skeleton of the arch.skeleton of the arch.

3.3.A muscular componenet called A muscular componenet called

4.4.branchiomerebranchiomere

5.5.A vascular componentA vascular component

6.6.A neural element.A neural element.

Meckels` Meckels` Cartilage Cartilage

It is come from the It is come from the 11stst branchial arch at branchial arch at 5_65_6week of intrauterine life.week of intrauterine life.

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it is extending from it is extending from cartilaginous otic cartilaginous otic capsule capsule to to the midline or symphesisthe midline or symphesis..

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It act as a guiding for growth of It act as a guiding for growth of mandible.mandible.

A major portion of this cartilage A major portion of this cartilage disappear during growth. disappear during growth.

The remaining part The remaining part develops into the develops into the

following:following:

1.1.The mental ossiclesThe mental ossicles

2.2. Incus and malleusIncus and malleus

3.3.Spine of sphenoid boneSpine of sphenoid bone

4.4.Ant. Ligament of malleusAnt. Ligament of malleus

5.5.Spheno mandibular ligamentSpheno mandibular ligament

At each half of mandible asingle At each half of mandible asingle ossification start at ossification start at the 6the 6thth week week of untra of untra

uterine life, in the region of the uterine life, in the region of the bifurcation of the inferior alveolar nerve bifurcation of the inferior alveolar nerve and artery into the mental and incisive and artery into the mental and incisive

branches.branches.

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The ossyfing membrane located laterl to The ossyfing membrane located laterl to the the meckles` cartilage meckles` cartilage and it and it

acompanying acompanying neuro_vascular bundleneuro_vascular bundle..

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there is marked acceleration of the there is marked acceleration of the mandibular growth between mandibular growth between 88thth and and 1212thth week. As aresult of mandibular length week. As aresult of mandibular length increaseincrease, the external auditory meatus , the external auditory meatus

appear to move posteriorely . bone begin appear to move posteriorely . bone begin to develop lateral to meckles` cartilage to develop lateral to meckles` cartilage during the during the 77thth week and continues until week and continues until

the posterior aspect is covered with the posterior aspect is covered with bone.bone.

Ossification stops at this point,which will Ossification stops at this point,which will later become the later become the “mandibular lingula” “mandibular lingula”

and the remaining part of meckels` and the remaining part of meckels` cartilage continues on it is own to form cartilage continues on it is own to form the sphenomandibular ligament the sphenomandibular ligament and the and the

spinous process of the spinous process of the sphenoidsphenoid(meckels`caritlage lacks (meckels`caritlage lacks

enzyme phosphate) found in ossifying enzyme phosphate) found in ossifying cartilage,thus precluding ossification. cartilage,thus precluding ossification.

Meckels` cartilage does,however persist Meckels` cartilage does,however persist until as long as the until as long as the 2424thth week IU before it week IU before it

disappear.disappear.

Secondary ”accessory Secondary ”accessory cartilage”cartilage”

appear between the appear between the 1010thth and and 1414thth weeks weeks Iu to form Iu to form the head of condyle the head of condyle , , part of part of the coronoid processthe coronoid process ,and ,and the mental the mental

protuberance.protuberance.‘‘

The mandibular processThe mandibular process

It come from It come from mandiblemandible and the and the temporal temporal bone(tympanic ring)bone(tympanic ring)

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Type of ossificationType of ossification:Intramembranous :Intramembranous

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TimingTiming: 6: 6thth week of intrauterine life week of intrauterine life

No. of ossification:No. of ossification:

2(on the right and left)2(on the right and left)