During 4thweek ventral aspect of cranialThickening develop in lateral &most part of foregut called pharyngeal/branchial arches.
Later pharyngeal arches grow. First Branchial arch called MANDIBULAR ARCH . It grows ventro-medially cranial to main part of the arch which is called .
Primary cartilage of firstpharyngeal arch isMeckel’s cartilage helpsin formation of lowerjaw.Meckel’s cartilage firstappear at 6th week IUL.
Ossification starts atthe division of mentaland incisive branch ofinferior alveolar nervelateral to meckel’scartilage around 6th week IUL.
Centre of ossification From center of ossification bone formation spreads: Anteriorly - midline Posteriorly - where mandibular nerve divided into lingual and inferior alveolar branch. Bone formation spreads rapidly and surrounds the inferior alveolar nerve to form mandibular canal. Intramembranous ossification spreads in anterior and posterior direction forms the Body & Ramus of the mandible.
Ossification spread posteriorly to form ramus of mandible, turning away from meckel’s cartilage. Ossification stops at site where it whould be Lingula. Major cartilage disappears .
Between 10th and 14th week three secondary cartilage develops: I. Condylar cartilage – largest and appear beneath the fibrous articular layer of future condyle. II. Coronoid cartilage - seen associated with coronoid process.
Mandible develops largely by intramembranous ossification and by endochondral ossification in : 1. Condylar process 2. Coronoid process 3. Mental region
CONDYLAR PROCESS appear as separate Develops from condylar cartilage area of mesenchymal condensation along developing mandible around 8th week. This area develop in cone-shaped cartilage around 10th week. By the 14th week first evidence of endochondral bone formation appear in condylar region.
• Cartilage fuses with mandibular ramus around 4th month.
Cartilage replaced by bone but upper end persists in adulthood acting as Growth and Articular cartilage. Condylar growth rate increases at puberty . Peaks between 12 to 14 years of age.
Secondary cartilage appears in coronoid process around 10-14th week. Cartilage grow as a response of developing temporalis muscle. Coronoid cartilage become incorporated into expanding intramembranous bone of ramus and disappear before birth.
MENTAL REGION Throughout intrauterine life left and right mandible are not fused at midline. Joined by connective tissue at midline. On either side of symphysis, symphyseal cartilage appear between 10th & 14th week postconception.
MENTAL REGION Ossify in 7th month to form mental ossicles in fibrous tissue of symphysis. Mental ossicles fuses with mandibular body at the end of first year after birth.
• Mandible undergoes greatest amount of postnatal growth of all facial bones.
Major site of mandibular growth. Growth of condylar cartilage increases length & height of mandible. Interstitial & appositional growth within plate produce linear movement of condyle in upward & backward direction towardstemporal bone.
.• Cartilage plate moves by growth on one side & bone replacement on other side.• As condylar growth cartilage moves obliquely upward & posteriorly - entire head of condyle moves in same direction by forming new condyle behind moving cartilage.• This process is continuous & condyle moves by growth.
• Formation of bone within condyle causes mandible rami to grow Upward & Backward• Displacing entire mandible in Downward & Forward direction.
• As ramus elongates, former level occupied by head remodeled into upper neck• Buccal & lingual cortical plates moves inward towards each other results in reduced transverse dimension of neck.
SIGMOID NOTCH• The height of the ramus increased by : - addition of new bone along the entire superior surface of the sigmoid notch only at lingual surface.
SIGMOID NOTCH• Bone deposition –• post. Border of• coronoid process• Bone resorption -• ant. Face of neck.
• To produce backward movement of ramus : - Ant. Margin of ramus & coronoid process, must undergo progressive removal.-Forward facing ant. Border of coronoid process is resorptive around temporal crest on lingual side. -Greater portion of lingual surface is depositive -Entire buccal surface is resorptive. Light stippling – bone deposition Dark stippling – bone resorption
• Coronoid process follows “v” principle.• Movement of this v towards its wider ends.• Bone Deposition - inner surface• Bone Resorption - outer surface• Which bring about growth in upward & backward direction..
• BONE DEPOISITION - lingual surface (+ +)• BONE RESORPTION - buccal surface (- -)
• Ramus moves backward in relation to body of mandible• Post. displacement of ramus converts the formal ramal bone in post. Part of body of mandible.• Body of mandible lengthens & increase in mandibulararch to accommodate erupting permanent molars.
• Bone deposition (++) post. border of Ramus• Bone resorption (--) ant. border of Ramus• Leads to AP growth of mandibe
• Growth of chin occurs at puberty .• Chin become prominent at puberty especially in males, by selective remodelling.• Alveolar region growths posteriorly.• Mental protuberance growths forwardly.• Which brings increase projection of chin.
•Bone deposition - mental protuberance.•Bone resorption - alveolar region above theprominence, creating a concavity.
• Alveolar growth occurs around tooth buds.• As teeth develop & begin to erupt, alv. Process increases in size & height.• Continued growth of alveolar Bone increases height of mandibuar body.
• Alveolar Process growths upward & outward on expanding arch.