Introduction Anatomy of Mandible Prenatal Development of Mandible Mandible at birth
Postnatal Development of Mandible Age changes in mandible Muscle attachment Developmental anomalies Development of mandible in relation to various theory of growth.
INTRODUCTION• Mandible is -largest & lowest bone of face.• Horseshoe shaped body which is curved horizontally.• Two ramii vertically with two processes one condylar & other is coronoid process.
• Two broad rami ascending posteriorly.• Two surfaces: - Internal - External• Separated by upper and lower border. - Upper border - bears sockets for teeth - Lower border - base of mandible
LATERAL SURFACE PRESENTS THE FOLLOWING FEATURES 1. Symphisis menti 2. Mental foramen 3. Mental protuberance 4. Mental tubercle 5. The oblique line 6. Condylar process 7. Coronoid process 8. Mandibular notch 9. Alveolar process
The Medial surface presents the following features1. Mental spine2. Mylohyoid line3. Submandibular fossa4. Sublingual fossa5. Mylohyoid groove6. Mandibular foramen7. Lingula
Cartilage and bones of mandibular skeleton form from- Embryonic neural crest cells in mid and hind brain region of neural folds.
During 4th week Thickening develop in lateral & ventral aspect of cranialmost part of foregut called pharyngeal/branchial arches.
• Later pharyngeal arches grow.• First Branchial arch called MANDIBULAR ARCH .
• Mandibular arch gives off a bud from its dorsal end called maxillary process.• It grows ventro-medially cranial to main part of the arch which is called mandibular process.
• Mandibular process of each side grow towards each other.• fuse in midline give rise to mandible.• First structure develop in lower jaw : - Mandibular division of Trigeminal nerve. - Neurotrophic factor produced by nerve induce osteogenesis.
Meckel’s cartilage Primary cartilage of first pharyngeal arch is Meckel’s cartilage helps in formation of lower jaw.
.• Meckel’s cartilage first appear at 6th week IUL.• Solid hyaline cartilagenous rod surrounded by fibrocellular capsule.• Extending from otic capsule to midsymphysis.• Symphyseal Cartilage of each side of mandible don’t meet at midline - Separates by thin band of mesenchyme.
Centre of ossificationOssification startsat the division ofmental and incisivebranch of inferioralveolar nervelateral to meckel’scartilage around6th week IUL.
.• 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.
• Anteriorly bone extends towards midline and comes in approximation with similar bone forming on opposite side.• These two bones remain separated by fibrous tissue mental symphysis untill shortly after birth.• Continued bone formation increases size of mandible with development of alveolar process to surround the developing tooth germ.
. Ossification spread posteriorly to form ramus of mandible, turning away from meckel’s cartilage. This point of divergence is marked by lingula in adult mandible.
Lacks enzyme phosphatase found in ossifying cartilage thus precluding its ossification. Greater part of meckel’s cartilage degenerate without contributing formation of mandible by 24th week. Most posterior extremity forms ‘incus’ and ‘malleus’ of inner ear.
• Fibrocellular capsule persists as sphenomandibular ligament• Small part of its ventral end forms accesory endochondral ossicles.• Incorporated in the chin region of the mandible.
Further growth until birth influenced by appearance of secondary cartilage . 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.
• Symphyseal cartilage – in the mandibular symphysis region.• Mandible develops largely by intramembranous ossification and by endochondral ossification in 1. Condylar process 2. Coronoid process 3. Mental region
Develops from condylar cartilage appear as separate 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.• Normally ceases about 20 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.
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.
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.
Two half of mandible not fused. Joined by connective tissue at midline of the symphysis. Condylar development minimal & no articular eminence in glenoid fossa.
Coronoid process – relatively large & projects well above condyle. • Two ramii are quite short. • Body is merely an open shell – containing buds of deciduous teeth.
Mandibular canal runs low in the body Angle of mandible is obtuse around 172* & more. Mental foramen near to lower border.
Right & left mandibular body fuses at midline symphysis one year after birth. Mandible appears as single bone.
Growth of mandible in relation to varioustheory of growth Genetic theory - BRODIE (1941) Cartilagenous theory - JAMES SCOTT Expanding V principle – ENLOW Enlow counterpart theory
Van limborgh’s theory – (1970) Servosystem theory - PETROVIC & STUTZMAN (1980) Functional matrix theory – MELVIN MOSS
Functional matrix forskeletal units All growth changes in size, shape & spatial position of skeletal units are secondary to temporal primary changes in their specific functional matrix. Growth of skeletal units -influenced by functional matrix
FUNCTIONAL MATRIX - carries out functions. ex : muscle, nerve , gland , vessels- There is periosteal capsule and capsular matrices. SKELETAL UNITS - supports & protects the relative functional matrices- divided in to macroskeletal & microskeletal units.
• Developmentally & functionally mandible divisible into several subunits :
MANDIBULAR GROWTH Mandibular condylar cartilage not primary site of mandibular growth. Lociat which secondary compensatory periosteal growth occurs.
Bil. Removal of condylar cartilage in growing man - doesn’t inhibit spatial translation of now acondylar complex of mand. Functional cranial component
- also doesn’t inhibit change in microskeletal unit. Mandibular growth is combination of morphologic effect of both capsular & periosteal matrices. Capsular matrices growth causes expansion of orofacial capsule. Enclose macroskeletal unit (mandible) passively & secondarily translated in new position.
Periosteal matrices related to mandibular microskeletal units responds to this volumetric expansion. Such alterations in their spatial position causes them to grow. Both translation & change in form comprises totality of mandibular growth.
• Two points are implicit : - periosteal matrices not capable of functioning normally –spatial related skeletal unit alter their spatial position without changes in their size & shape. - such changes in size & shape of themselves are insufficient biological cause of translation.
Difference in mand. Position & form due to both periosteal & capsular matrices. Growth of mandible is accomplished by both spatial translation & change in form.
• Mandible undergoes greatest amount of postnatal growth of all facial bones.• Limited growth at symphysis menti untill fusion.• The main site of postnatal mandibular growth: - Condylar cartilage - Ant. & Post. Border of rami - Alveolar ridge
•In general, the downward and forwardmandibular growth follows the expanding“v” principle.
MANDIBULAR REMODELLING Red arrows - bone resorption Blue arrows - bone deposition
Major site of mandibular growth. Growth of condylar cartilage increases length & height of mandible. Condylar cartilage serves as both : Articular cartilage : characterised by fibrocartilage surface.
• Growth cartilage : analogous to epiphyseal plate in long bone.• Interstitial & appositional growth within plate produce linear movement of condyle in upward & backward direction towards temporal bone.
• As it grows, deeper portion of proliferating cartilage replaced by endochondral bone.• Which adds to medullary bone in condyle & its neck.• Endochondral bone formation results - medullary core of fine cancellous bone.• Cortex formed by activity of the periosteum & endosteum.
.• 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.
Former condyle simultaneously converted into elongated neck by sequential series of remodelling. As ramus elongates, former level occupied by head remodeled into upper neck. Former upper part of neck remodeled into new lower part. Entire process is continuous & repetitive .
.• All changes takes place simultaneously.• Condylar head is broad & neck derived from head by remodeling with marked reduction in width.• Reduction brought about by surface resorption on outer(periosteum) surface & deposition on inner(endosteum) surface.
• Buccal & lingual cortical plates moves inward towards each other results in reduced transverse dimension of neck. Inward growth of buccal & lingual cortices
Growth remodeling process in condylar bonefollows “v” principle. Bone deposition -inner surface.Bone resorption -outer surface ofV shaped neck Results in growthmovement of entireV in post. & sup.direction.
SIGMOID NOTCH• Bone deposition - post. Border of coronoid process• Bone resorption - ant. Face of neck.
• Periosteal bone added - lingual surface of ramus just below sigmoid notch continue down from condylar head around lingual side of sigmoid notch , then extends up to apex of coronoid process. Light stippling – bone deposition Dark stippling – bone resorption
• Periosteal bone deposition - lingual surface• Periosteal bone resorption - buccal surface of sigmoid notch.• Results in shift of ant. Base of neck in lingual direction.
• The height of the ramus increased by - addition of new bone along the entire superior surface of the sigmoid notch only at lingual surface.• Continued bone deposition results in growth in lingual & cephalic direction.
To produce backward movement of ramus : - Ant. Margin of ramus & coronoid process, must undergo progressive removal. This growth change first recognized by JOHN HUNTER & later verified by HUMPHRY (1864).
-Forward facing ant. Border of coronoid process isresorptive around temporal crest on lingual side.-Greater portion of lingual surface is depository-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..
4’ – bone additionon lingual surface.4 – bone removalon buccal surface Growth sequence of coronoid process by “v” principle
BONE DEPOISITION - lingual surface (+ +) BONE RESORPTION - buccal surface (- -)
GROWTH AT RAMUS• Bone deposition (++) post. border of Ramus• Bone resorption (--) ant. border of Ramus• Leads to AP growth of mandibe
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 mandibular arch to accommodate erupting permanent molars.
BUCCAL SIDE OF RAMUS• Upper part of mand. Ramus possesses a resorptive surface.• Resorptive surface continuous down from neck on to upper part of ramus.• Below this area deposition occur. Dark stippling - resorption Light stippling - deposition
LINGUAL SIDE OF RAMUS• Bone deposition - part of ramus located ant. & sup. to oblique ridge extending down from neck on to ramus.• Producing growth in sup. as well as in post. direction. Dark stippling - resorption Light stippling - deposition
Selective bone remodelling causes flaring of angle of mandible on age advancement. Buccal surface Bone deposition - posteroinferior surface Bone resorption - anterosuperior surface
Lingual surface Bone deposition - anterosuperior surface Bone resorption - posteroinferior surface Causes flaring of angle of mandible.
Growth of chin occurs at puberty as age advances. Chin become prominent at puberty especially in males, by selective remodelling. Bone deposition - mental protuberance. Cortex is : thick, dense composed of slow growing type of lamellar bone.
•Bone resorption - alveolar region above theprominence, creating a concavity.
Cortex is made of - typical endosteal bone. Alveolar region grows posteriorly. Mental protuberance grows forwardly. Which brings increase projection of chin.
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 grows upward & outward on expandingarch.• This permits dental arch to accommodate largerpermanent teeth.
INFANTS –Mental foramen - near lower borderMandibular canal - lower border of body of mandibleAngle of mandible - obtuse around 140* or more
ADULTS-• Mental foramen -midway of upper & lowerborder.• Mandibular canal - runsparallel with mylohyoid line.• Angle of mandible - 110* -120*
• OLD AGEMandibular foramen - near alv. BoneMandibular canal - near alv. BoneAngle of mandible - obtuse 140*
Timing of Growth in Width Lengthand Height: Growth in width is completed 1st then growth in length and finally growth in height (W>L>H). Mandibular intercanine width is more likely to decrease than increase after age 12. Intercanine width is essentially completed by the end of ninth year in girls and the tenth year in boys. Both molar and bicondylar widths show small increases until the end of growth in length .
Growth of mandible continues at a relatively steady rate before puberty. On the average, ramus height increases 1-2 mm/year. body length increases 2-3 mm/year. In girls growth in length of the jaw has caused by age 14-15 years. In boys, it does not decline to the basal adult level until 18 years.
MASSETER ORIGIN: Ant. 2/3rd of lower border of zygomatic arch & zygomatic process of maxilla. INSERTION: Ramus & coronoid process of mandible. NERVE SUPPLY: Masseteric branch from ant. Division of mandibular nerve. ACTIONS:- Elevates mandible to close mouth. - Superficial fibres Protract the mandible.
BUCCINATORORIGIN:From alv. Process ofmaxilla & mandible, TMJ.INSERTION:in the fibres of orbicularisoris
BUCCINATOR• NERVE SUPPLY: buccal branch of facial nerve.• ACTIONS: - Flattens cheek against gums &teeth. - Prevents accumulatiom of food in the vestibule. - aids whistling & smiling. - neonates helps in suckle.
PLATYSMAORIGIN : subcutaneoustissue of infraclavicular& supraclavicular.INSERTION : Base ofthe mandible,skin ofcheek & lower lip, angleof mouth.NERVE SUPPLY :Cervical branch of facialnerve.ACTIONS :- depressesmandible-Pulls angle of mouthdownwords.
LATERAL PTERYGOIDORIGIN:UPPER HEAD - crest ofgreater wing ofsphenoidLOWER HEAD - lat.surface of lat. pterygoidplateINSERTION:-Pterygoid fovea on ant.Surface of neck ofmandible-Ant. Margin of articulardisc & capsule of TMJ
LATERAL PTERYGOID• NERVE SUPPLY: - Branch of ant. division of mabdibular nerve.• ACTIONS: - Depresses the mandible to open mouth. - Protract the mandible. - Helps in grinding movement.
MEDIAL PTERYGOIDORIGIN:SUPERFICIAL HEAD– Tuberosity ofmaxilla.DEEP HEAD - Medialsurface of lat.Pterygoid plate.INSERTION:postero-inferiorly tomedial surface oframus.
MEDIAL PTERYGOID NERVE SUPPLY-- nerve to medial pterygoid. ACTIONS – - Elevates mandible. - Protraction of the mandible. - Side to side movement.
MYLOHYOID MUSCLEORIGIN: Mylohyoidline of mandible.INSERTION:Post. Fibres – hyoidbone.Middle & Ant. Fibres -median raphebetween mandible &hyoid bone
MYLOHYOID MUSCLE• NERVE SUPPLY : - Mylohyoid nerve , from inf. Alveolar branch of mandibular nerve.• ACTIONS : - Elevate floor of mouth at first stage of deglutition. - depression of mandible. - Elevation of hyoid bone.
- Mandible grossly deficient or absent.- deficiency of neural crest tissue in lower part of face.
Hemifacial Microsomia Also called goldenhar syndrome Due to lack of mesenchymal tissue or neural crest cells Underdeveloped mandible Unilateral and asymmetrical
Mandibular Dysostosis also called Treacher-collins syndrome Due to disturbance in origins, migration & interaction of neural crest cells. Prevelance 1:25000 Hypoplasia of mandible
Prevelance 1: 8500 Mandible is underdeveloped Small body Obtuse antigonial angle Posteriorly placed condyle Cleft palate
Produce prognathism usually inherited Abnormal growth phenomenon – hyperpituitarism.
BIBLIOGRAPHY Gray’s anatomy Craniofacial development - Steven M Sperber Human embryology - Inderbir Singh Contemporary orthodontics - William R Proffit The human face - Donald H Enlow Shafer’s textbook of oral pathology