DEVELOPMENTOF MANDIBLE

Presented by:GURINDER SINGHPg Ist yearDeptt. Of Orthodontics & Dentofacial Orthopedics

Contents

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 features

1. Mental spine

2. Mylohyoid line

3. Submandibular fossa

4. Sublingual fossa

5. Mylohyoid groove

6. Mandibular foramen

7. Lingula

PRENATAL

DEVELOPMENT OF

MANDIBLE

PRENATAL DEVELOPMENT OF MANDIBLE

Cartilage and bones of mandibular skeleton form from-

Embryonic neural crest cells in mid and hind brain region of neural folds.

4th week of IUL

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 cartilagePrimary 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 ossification

Ossification starts at the division of mental and incisive branch of inferior alveolar nerve lateral to meckel’s cartilage around 6th 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.

Fate of Meckel’s cartilage

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.

SECONDARY CARTILAGES IN MANDIBULAR DEVELOPMENT

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

CONDYLAR PROCESS 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.

CORONOID PROCESS

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

AT

BIRTH

MANDIBLE AT 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.

MANDIBLE AT BIRTH

Coronoid process – relatively large & projects well above condyle.

• Two ramii are quite short.

• Body is merely an open shell – containing buds of deciduous teeth.

MANDIBLE AT BIRTH

Mandibular canal runs low in the body

Angle of mandible is obtuse around 172* & more.

Mental foramen near to lower border.

POST NATAL DEVELOPMENT OF

MANDIBLE

POST NATAL DEVELOPMENT OF MANDIBLE

Right & left mandibular body fuses at midline symphysis one year after birth.

Mandible appears as single bone.

Growth of mandible in relation to various theory 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 for skeletal 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 in relation with functional matrix theory.

Teeth – Alveolar microskeletal unit.

Temporalis muscle - Coronoid microskeletal unit.

Masseter and Medial pterygoid - Angular microskeletal unit.

Lateral pterygoid - Condylar process

MANDIBULAR GROWTH

Mandibular condylar cartilage not primary site of mandibular growth.

Loci at 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

Click icon to add picture

• In general, the downward and forward mandibular growth follows the expanding “v” principle.

MANDIBULAR REMODELLING

Red arrows - bone resorption Blue arrows - bone deposition

GROWTH AT CONDYLE

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.

CONDYLAR NECK

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 bone follows “v” principle.

Bone deposition - inner surface.Bone resorption - outer surface of V shaped neck Results in growth movement of entire V 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 depositionDark 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.

CORONOID PROCESS

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 is resorptive around temporal crest on lingual side.

-Greater portion of lingual surface is depository

-Entire buccal surface is resorptive.

Light stippling – bone depositionDark 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 addition on lingual surface.

4 – bone removal on buccal surface

Growth sequence of coronoid process by “v” principle

Vertical section of coronoid process

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

GROWTH AT RAMUS

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

ANGLE OF MANDIBLE Selective bone remodelling causes flaring of

angle of mandible on age advancement.

Buccal surface

Bone deposition - posteroinferior surface

Bone resorption - anterosuperior surface

ANGLE OF MANDIBLE Lingual surface

Bone deposition - anterosuperior surface

Bone resorption - posteroinferior surface

Causes flaring of angle of mandible.

CHIN

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 the prominence, creating a concavity.

CHIN

Cortex is made of - typical endosteal bone.

Alveolar region grows posteriorly.

Mental protuberance grows forwardly.

Which brings increase projection of chin.

ALVEOLAR PROCESS

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 expanding arch.• This permits dental arch to accommodate larger permanent teeth.

Age changes in mandible INFANTS –

Mental foramen - near lower border Mandibular canal - lower border of body of

mandible Angle of mandible - obtuse around 140* or

more

• Mandibular canal - runs parallel with mylohyoid line.

• Angle of mandible - 110* - 120*

• Mental foramen - midway of upper & lower border.

ADULTS-

• OLD AGE Mandibular foramen - near alv. Bone Mandibular canal - near alv. Bone Angle of mandible - obtuse 140*

Timing of Growth in Width Length and 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.

MUSCLES ATTACHMENT ON LATERAL SURFACE

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.

TEMPORALISORIGIN: Temporal fossa

INSERTION: Coronoid process & ant. Border of ramus.

NERVE SUPPLY: Temporal branch from ant. Division of mandibular nerve.ACTIONS: -Elevates mandible.-Side to side grinding movement.-Post. Fibres Retract the protracted mandible.

BUCCINATOR

ORIGIN: From alv. Process of maxilla & mandible, TMJ.

INSERTION: in the fibres of orbicularis oris

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 : subcutaneous tissue of infraclavicular & supraclavicular.

INSERTION : Base of the mandible,skin of cheek & lower lip, angle of mouth.

NERVE SUPPLY : Cervical branch of facial nerve.

ACTIONS :- depresses mandible-Pulls angle of mouth downwords.

MENTALIS

ORIGIN: Incisive fossa of mandible

INSERTION: skin of chin.

ACTIONS: - elevates & wrinkles skin of chin.-protrude lower lip.

NERVE SUPPLY:Mandibular branch of facial nerve

MUSCLES ATTACHMENT ON MEDIAL SURFACE

LATERAL PTERYGOIDORIGIN:UPPER HEAD - crest of greater wing of sphenoidLOWER HEAD - lat. surface of lat. pterygoid plate

INSERTION: -Pterygoid fovea on ant. Surface of neck of mandible-Ant. Margin of articular disc & 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 of maxilla.

DEEP HEAD - Medial surface of lat. Pterygoid plate.

INSERTION:postero-inferiorly to medial surface of ramus.

MEDIAL PTERYGOID NERVE SUPPLY- - nerve to medial pterygoid.

ACTIONS –

- Elevates mandible.

- Protraction of the mandible.

- Side to side movement.

MYLOHYOID MUSCLE

ORIGIN: Mylohyoid line of mandible.

INSERTION: Post. Fibres – hyoid bone.

Middle & Ant. Fibres - median raphe between 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.

ANOMALIES

OF

DEVELOPMENT

AGNATHIA

- 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

Pierre Robin syndrome Prevelance 1: 8500

Mandible is underdeveloped

Small body

Obtuse antigonial angle

Posteriorly placed condyle

Cleft palate

Macrognathia

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

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