PRE NATAL AND POST NATAL

DEVELOPMENT OF MANDIBLE

CONTENTS

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• Introduction

• Pharyngeal arches• Contents and derivatives of arch

• Meckel’s cartilage

• Prenatal growth• Fate of meckel’s cartilage

• Ossification

• Secondary cartilage

• Postnatal growth• Growth of mandible

• Anomalies of growth

• Conclusion

• Reference

INTRODUCTION

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• Growth and development of an individual can be divided into pre-natal and post-natal period.

• Prenatal period is a dynamic phase where, gowth occurs at a higher rate when compared to post natal growth.

• Among facial bones, mandible undergoes largestamount of growth post natally and exhibits largevariability in morphology

PERIODS OF GROWTH

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• Period of ovumo Fertilization – 2 weeks

oAttachment of ovum to intra uterine wall

• Period of embryoo14 -56th day of IU life

oMajor deelopment of facial and cranial region

• Period of fetuso56th day- birth

oAccelerated growth of craniofacial structures.

PRE-NATAL GROWTH

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PRE NATAL GROWTH

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• Embryonic neural crest cells

• Cells migrate ventrally to form mandibular prominence.

• Form mandibular division of trigeminal nerve.

• Ectomesenchymal condensation forming first pharyngial arch

PHARYNGEAL ARCHES

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• After 4th week of post conception, lateral plate of ventral foregut region becomes segmented.

• Pharyngeal arch separated by pharyngeal groove externally

• five outpouchings internally – pharyngeal pouches

CONTENTS OF EACH ARCH

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• Central cartilage rod – from neural crest cells

• Muscular component – somitomeric origin

• Vascular component – mesoderm & neural cresttissue angioblast

• Nervous element - ectoderm

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FIRST PHARYNGEAL ARCH

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• Precursor of both maxilla & mandible.

• It forms the lateral wall of stomatodeum.

• Maxilla derived from cranio ventral extension of mandibular arch at 28th day – 4th week.

mandibular• Arch grows ventro-medially process

• Grows towards each other &fuses in midline lower margin of stomatodeum.

• Gives rise to lower lip & lower jaw.

• Maxillary & mandibular partly fuses to form cheek.

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NERVE SUPPLY

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• Post-trematic• Runs along the cranial

border of arch

• It is mandibular nerve

• Pre-trematic• Runs along caudal

border of arch.

• It is chorda tympani.

MECKEL’S CARTILAGE

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• Present at 41st – 45th day of post conception.

• Most cartilage substance disappears in mandible.

• Extent cartilaginous otic capsule-symphysis

• Persisiting portion of meckel’s cartilage are :

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• Malleus & Incus

• Two ligaments - 1. Ant.ligament of malleus

2. Sphenomandibular ligament

(sheath or perichondrium)

• Muscles – muscles of mastication

Mylohoid ,

Ant. Belly of digastric

Tensor tympani, Tensor veli palatini

• Nerves - Mandibular division of trigeminal nerve.

• Arteries - maxillary artery & part of external carotid artery.

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FATE OF MECKEL’S CARTILAGE

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• Meckels cartilage meets its fellow opposite side ventrally.

• diverge dorsally and ends in tympanic cavity-malleus and incus

• Remnants of ventral end are seen in fibrous tissue of symphysis- CHONDRIOLA SYMPHYSEA .

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• Rest of meckels cartilage disappears by 24th week.

• Except its most proximal dorsal part, which give rise to

• Sphenomandilar ligament• Ant.ligament of malleus

• Dorsal to mental foramen undergoes resorption, lateral surface replaced by intramembranous bony trabeculae.

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OSSIFICATION OF MANDIBLE

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• 2 types of ossification.• Intramembranous ossification

• Endochondral ossification.

• Mandible is derived from ossification of an osteogenic membrane at 36-38 days

Ectomesenchyme

Epithelium of mandibular arch

Intramembranous bone .

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(Lateral to meckel’s cartilage)

PROCESS OF OSSIFICATION OF

MANDIBLE

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• Intra membranous ossification• Body of mandible except anterior

part

• Ramus of mandible till mandibular foramen

• Endochondral ossification• Symphysis of mandible

• Ramus above mandibular foramen

• Coronoid process

• Condylar process

• Single ossification centre for each half of mandibleat 6th week.

• Occurs in the region of bifurcation of Inferioralvolar nerve & artery into mental & incisivebranches.

• Ossification stops dorsally forming – Lingula

• Prior presence of nerovascular bundles gives--Mandibular foramen& canal

-Mental foramen

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• Ossification dorsally and ventrally gives rise to-body and ramus of mandible

• Primary ossification centre spreads upwards to form a strong base for teeth.

• Meckels catilage will be invaded by bone.

• Mandible & clavicle. First bone to begin osssify.

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• Initial woven bone is replaced by lamellar bone. Harvesian system seen at 5th month.

• Lacks the enzyme phosphatase found in ossifying cartilages – precludes ossification.

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SECONDARY CARTILAGES

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• Appears between 10th – 14th week

• Forms head of condyle, part of coronoid process, mental protuberance

• Coronoid process cartilage develops within temporalis muscle.

• Later it is incorporated into the expanding intramembranous bone of ramus and disappear before birth.

CONDYLAR CARTILAGE

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• Appears at 10th week .

• Seen as a cone shaped structure in ramal region.

• Primordium for future condyle.

• Condylar head increases by interstitial and appositional growth.

• Important centre of growth for ramus and body.

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• Most of cartilage is replaced by bone, except its upper end which persist in adulthood.

• Act as both growth and articular cartilage.

• Growth peaks between 12.5 – 14 yrs of age, and ceases at 20yrs of age.

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CORONOID PROCESS

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•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

ALVEOLAR PROCESS

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Lingual swellings

Linguo-gingival sulcus

Labio-gingival sulcus

Sulci deepensAlveolar process

MENTAL REGION

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Cartilage ossify at 7th

month

Mental ossicles

Fused to intramembranous bone & ossifies at 1 yr.

POST NATAL GROWTH

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NEONATAL MANDIBLE

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• Ascending rami is low and wide.

• Coronoid process large and projects above condyle.

• Body is an open shell containing buds & partial crowns

• Mandibular canal runs low in body

• Separation of mandible at symphysis menti closed by 4th-12th month after birth

GROWTH OF MANDIBLE

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• In adults developmentally and functionally divided into many units – body, condyle, coronoid, chin.

• Each of this influenced by ‘functional matrix’.

•alveolar boneTeeth

•coronoid processTemporalis muscle

•angle & ramusMasseter &

medial pterygoid

MAJOR SITES FOR GROWTH

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1. Condylaar cartilage

2. Posterior borders of rami

3. Alveolar ridge

4. Symphysis -limited

CONDYLE

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• Both articular cartilage in TMJ & growth cartilage.

In medullary core

appositional proliferation of

cartilage in condyle head

Provides basisfor the growth

• On outer surface – cortex of intramembranous bone is laid.

Formation of bone in condylar head

Rami grows upward and backward

Displacing mandible downward and forward direction

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• In infants codyles are inclined horizontally.

Condylar growth –increase in length of mandible

posteror divergance of two halves of body of mandible

Results in widening of mandible

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SYMPHYSIS MENTI

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• No interstitial widening after it is fused at 1 year.

• Widening only happens by surface apposition

RAMUS OF MANDIBLE

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• Deposition at posterior borders & resorption at anterior borders

• cause ramus to move backward I.r.t body of mandible.

• Repositions the mandibular foramen posteriorly.

• Accomadate place for the eruption of molars

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BODY OF MANDIBLE

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• Post. Displacement of ramus converts - former ramal bone into post.part of body of mandible.

• Changes in the direction of mental foramen. Infancy – neurovascular bundles emerge at right angles

Adulthood – directed backwards

• Clinical implication – administrating L.A in mental nerve.

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ALVEOLAR PROCESS

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• If teeth are absent – alveolar process fails to develop & resorbtion will occur

• Orthodontic movement takes place in labile alveolar bone. Does not involve the basal bone.

LINGUAL TUBEROSITY

• Important structure as it is direct anatomic equivalent of the

maxillary tuberosity

• site of growth for mandible.

• Grows posteriorly by deposits on the posterio facing surface.

• The prominence of tuberosity is increased by presence of large

resorptive fields just below it - the lingual fossa.

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LINGUAL TUBEROSITY

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• Remodels in posterior direction with slight lateral shift

• Increases the length of body of mandible

CHIN

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• Accesory cartilage End of meckels cartilage.

• Unique human trait, lacks in other primates.

• Mental protuberance formed byOsseous depostion at mental region

Bone resorption at alveolar bone – supramental concavity

AGE CHANGES INMANDIBLE

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ANOMALIES OF DEVELOMENT

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• Severe 1st arch anomalyAgnathia

Synotia

Microstomia

• Lesser severeTreacher collins syndrome

Pierre robin syndrome

External ear deficiencies- anotia, microtia

Persistent pharyngeal clefts – auricular sinuses.

CONGENITAL

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• Agnathia -The mandible may be grossly deficient or absent in condition of agnathia, which is probably due to a neural crest deficiency in the lower face.

• Micrognathia-small jaw• Macrognathia –large jaw

• Facial hemihypertrophy – one side of face is larger than other side

• Facial hemiatropy- degeneration of oneside of face

ANOMALIES OFMANDIBLE

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SOME OF THE SYNDROMES ASSOCIATED WITH MANDIBULAR ABNORMALITY

• MARFAN SYNDROME- genetic disorder of connective tissue. There isspeech disorder due to small jaws

• PIERRE-ROBIN SYNDROME – micrognathia, cleft palate, glossoptosis

• TREACHER- COLLINS SYNDROME (mandibulo facial dysostosis) - craniofacial deformity having micrognathia , hypoplasia of mandible, bird like face

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Mandibular Cleft:

Midline defects also occur in mandible although they are rare. They result from a lack of development of the midline of the first branchial arch resulting in both skeletal and soft tissue deficiency at that site.

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CONCLUSION

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• Variations in mandible morphology and size more significant than maxillary variability as related to malocclusions

e.g.; Class II, Class III

• Many dental abnormalities have underlying skeletal problems . In order to correct the underlying skeletal discrepancy knowledge of growth and development of the mandible is imperative

• Mandible is clinically controllable to a certain extent. Orthopedic appliances during growth period are used by orthodontists, with which mandibular position can be controlled redirected or altered

REFERENCE

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• Proffit, William R., Henry W. Fields Jr, and David M.Sarver. Contemporary orthodontics. Elsevier HealthSciences, 2014.

• Sperber, Geoffrey H., Geoffrey D. Guttmann, and StevenM. Sperber.Craniofacial Development.

• Fundamentals of Craniofacial Growth. Andrew D. Dixon, David A.N. Hoyte, Olli Ronning

• Singh, Inderbir. Human embryology. JP Medical Ltd, 2014.

Thank you..

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