anatomy and development of mandible

ANATOMY & DEVELOPMENT OF

MANDIBLE

PRESENTED BY;Dr. NIKHIL REDDY

INTRODUCTION

ANATOMY OF MANDIBLE Parts Attachments and its relations Nerve supply Vascular supply Foramina and its relations

DEVELOPMENT OF MANDIBLE Prenatal growth Postnatal growth Age changes Anomalies of development

The word mandible derived from Latin word mandibula- "jawbone" or inferior maxillary bone.

It forms the lower jaw and holds the lower teeth in place.

It is the largest, strongest and lowest bone in the face.

Only movable bone in the skull It consists of an anterior Horseshoe-shaped body, and of

two rami that project upwards from the posterior part of the body.

It provides structure and protective support for the oral cavity. The mandible is articulated in ball and socket fashion at

the condylar process. Strength resides in its dense cortical plates.

contnd..

ANATOMYOF

MANDIBLE

ANATOMY OF MANDIBLE

Mandible

Body Two Rami

Surfaces SurfacesBorders Borders Processes

External/Outer

Internal/Inner

Superior/Alveolar

Inferior/Base

CoronoidCondyloidLateral/External

Medial/Internal

Anterior Posterior Superior Inferior

Horseshoe-shaped BODY Has two surfaces EXTERNAL and

INTERNAL surfaces , Two borders UPPER and LOWER borders.

BODY OF THE MANDIBLE

1. SYMPHYSIS MENTI : The line at which the right and left halves of the bone meet each other. It is marked by a faint ridge.

2. MENTAL PROTUBERANCE : median triangular projecting area in the lower part of the midline.

3. MENTAL FORAMEN : It lies below the interval between the premolar teeth

4. EXTERNAL OBLIQUE LINE : Continuation of the sharp anterior border of the ramus of mandible.

5. INCISIVE FOSSA : Depression that lies just below the incisor teeth

EXTERNAL SURFACE

1. MYLOHYOID LINE : Prominent ridge that runs obliquely downwards and forwards from below the third molar tooth to the median area below genial tubercle.

2. SUBMANDIBULAR FOSSA : It lies below the mylohyoid line, which lodges the submandibular gland

3. SUBLINGUAL FOSSA : It lies above the mylohyoid line, which lodges the sublingual gland

4. GENIAL TUBERCLES : Posterior surface of the symphysis menti is marked by four small elevations called the superior and inferior tubercle

INTERNAL SURFACE

5. MYLOHYOID GROOVE : Extends from ramus to the body below the posterior end of the mylohyoid line.

6.UPPER ALVEOLAR BORDER : It bears socket for the teeth.

7. LOWER BORDER /BASE :

8. DIGASTRIC FOSSA : Near the midline the base shows an oval depression.

SUPERIOR BORDER (ALVEOLAR BORDER)

It is hollowed into cavities for the reception of the teeth, these cavities are sixteen in number, and vary in depth and size according to the teeth which they contain.

TWO BORDERS.

is rounded, longer than the superior, and thicker in front than behind.

INFERIOR BORDER (base of mandible)

Is quadrilateral

2 surfaces1. Lateral2. Medial

4 borders1. Superior2. Inferior3. Anterior4. Posterior

2 processes1. Coronoid2. Condylar

RAMUS OF MANDIBLE

Lateral surface – flat with oblique ridges

Medial surface – Features-

1. MANDIBULAR FORAMEN : It lies little above the centre of ramus at the level of occlusal plane. It leads into mandibular canal.

2. LINGULA : Anterior margin of foramen marked by tongue shaped projection

SURFACES OF RAMUS

3. MYLOHYOID GROOVE : Begins just below mandibular foramen, runs forwards and downwards to be gradually lost over the submandibular fossa.

4. UPPER BORDER -Forms mandibular notch

5. LOWER BORDER- Forms angle( junction of the body and ramus ) 

The lower border of the ramus is thick, straight, and continuous with the inferior border of the body of the bone. At its junction with the posterior border is the angle of the mandible, and is marked by rough, oblique ridges on each side.

 The upper border is thin, and is surmounted by two processes, the coronoid in front and the condyloid behind, separated by a deep concavity, the mandibular notch.

BORDERS OF RAMUS:-

Borders

Superior

Anterior

Inferior

Posterior

Anterior border- thin & continuous

with coronoid process

Posterior border- thick & extends

from condyle to angle

AB

CORONOID PROCESS

Flat ,triangular Upward and forward projection

from anterolateral part of ramus Anterior border continuous with

anterior border of ramus Posterior border bounds the

mandibular notch

PROCESSES

CONDYLAR PROCESS

Upward projection from postero superior part of ramus

Apically enlarged as head of condyle. Articulates with temporal bone’s

mandibular fossa to form temperomandibular joint

Lateral aspect palpable in front of tragus

Pterygoid fovea anterior to neck

1. External oblique line- origin to buccinator, depressor inferioris, depressor anguli oris

2. Incisive fossa -origin of mentalis, mental slips of orbicularis oris

3. Mylohyoid line – origin to mylohyoid muscle , attachment to superior constrictor of pharynx, pterygomandibular raphae

4. superior genial tubercles -genioglossus

ATTACHMENTS AND RELATIONS

5. Lower genial tubercles –origin to geniohyoid

6. Diagastric fossa- anterior belly of diagastric

7. Lower border -deep cervical fascia and platysma

8. Lateral surface of ramus - insertion for masseter

9. Posterosuperior lateral surface of ramus-parotid gland

10. Lingula-sphenomandibular ligament

11. Medial surface of ramus-medial pterygoid muscle attachment

12. Apex of coronoid process - temporalis attachment

13. Pterygoid fovea - lateral pterygoid muscle

14. Lateral surface of neck - attachment to lateral ligament of temperomandibular joint , parotid gland

ARTERY SUPPLY OF MANDIBLE; Mainly by

Maxillary artery, Branch of external carotid artery By

its branches, mainly through inferior alveolar artery

Vascular supply of mandible

INFERIOR ALVEOLAR ARTERY

Lingual branch

Mental branch

Mylohyoid branch

Incisive artery

Artery supply of mandible

Venous supply of mandible

Drains into Internal jugular vein and external jugular vein through maxillary vein, facial vein and pterygoid plexus

Mainly through the trigeminal nerve - V cranial nerve

MANDIBULAR NERVE Main trunk Anterior trunk Posterior trunk

Nerve supply of mandible

Posterior division of the mandibular nerve

Mylohyoid nerve

Inferior alveolar nerve

Mental nerve

Incisive nerve

Auriculotemporal nerve

Lingual

Nerve supply of mandible

1. Mental foramina - mental nerve and vessels

2. Mandibular notch - massetric nerve and vessels

3. Medial side of neck - auriculo temporal nerve

4. Mylohyoid groove - mylohyoid nerve and vessels

5. Mylohyoid groove in front of ramus - lingual nerve

FORAMINA AND OTHER RELATIONS

Mandibular canal and foramina - inferior alveolar nerve and vessels

Articulation

Mandibular process of temporal bone and condylar part of mandible articulate to form temporomandibular joint.

DEVELOPMENT OF MANDIBLE

Development refers to all naturally occurring progressive, unidirectional, sequential changes in the life of an individual from it’s existence as a single cell to it’s elaboration as a multifunctional unit terminating in death” – Moyers

Prenatal growth Postnatal

growth

PRENATAL GROWTH OF THE MANDIBLE

Around the 4th week of intrauterine

life a shallow depression appears in

the embryo it corresponds to future

mouth called as – stomadeum.

Between the stomadeum and

pericardium, mesodermal

thickenings develops, these are

called as pharyngeal arches or

brancheal arches.

In humans, six pairs of pharyngeal

arches form on either side of the

pharyngeal foregut.

1st arch is known as mandibular arch,

2nd arch as hyoid arch.

Other arches don’t have any specific

names

The 5th arch disappears after its

formation

contnd..

Each arch has

1. Outer covering of ectoderm

2. An inner covering of endoderm

3. Core of mesoderm.

Arches are separated from each other by

1.Pharyngeal cleft or groove externally

2.Pharyngeal pouches internally

Contnd..

With in the arch,

1. A cartilaginous supporting

element

2. An aortic arch

3. An arch-associated cranial nerve

4. A muscular component –

branchiomere

Contnd..

The development of face begins

in the 4th to 8th week of intra-

uterine life.

The face is derived from

An unpaired frontonasal process

A pair of Maxillary process

A pair of Mandibular process

Mandibular arch gives of a bud

from dorsal end called maxillary

process

It grows ventro-medially, it is

called as mandibular process.

Mandibular processes of both

sides grow towards each other &

fuse in midline by fibrous tissue.

FORMATION OF BONE : Mainly by two mechanisms

• Intramembranous ossification

• Endochondral ossification

OSSIFICATION

INTRAMEMBRANEOUS OSSIFICATION

46

Mesenchymal condensation

Increased vascularity

A membrane is formed ( collage fibres)

47

Mesenchymal cells enlarge to become osteoblast

Secretion of gelatinous

matrix

Fibres swell up(osteoid)

Deposition of calcium salts

Layer of osteoid becomes lamellas of bone (trabeculae)

Anastomosing network of

trabeculae form spongy or cancellous bone

Continuing appositional growth & remodelling of bony trabeculae - convert cancellous bone into compact bone

Intramembranous ossification(cont..)

48

49

Endochondral ossification Mesenchymal condensation

– differentiation into chondroblasts – cartilage model with perichondrium

Capillaries grow into perichondrium – inner layer differentiates into osteoblasts – thin collar of bone matrix forms

Perichondrium is now called

periosteum Thin collar of bone –

subperiosteal bone

50

Endochondral ossification(cont..)

osteogenic cells & periosteal capillaries invade cartilage model - periosteal bud forms – initiate primary centre of ossification ( primary areolae)

Osteogenic cells give rise to osteoblasts- arranged along secondary areolae

Layer of ossein fibrils embedded in gelatinous intercellular substance

Osteoid is calcified and a lamellae of bone is formed

Mandible is the second bone to ossify in the body.

It is partly membranous & partly cartilaginous in

ossification.

• Incisive part below symphysis menti• Coronoid • Condyloid process• Upper half of ramus

Cartilage

• Whole of body except lower incisive part

• Lower half of ramus upto mandibular foramen

Membrane

Each half of mandible ossifies from only one centre of ossification at 6th week of intrauterine life, in the mesenchymal sheath of meckel’s cartilage near the future mental foramen.

The ventral end of meckel’s cartilage ossifies from parent centre during 10th week and forms the incisive part.

Secondary cartilages.

Condyloid cartilage

Coronoid cartilage

Symphyseal cartilage.

MECKEL’S CARTILAGE: Cartilage of first arch.

Meckel’s cartilage is derived from 1st

branchial arch around 41st – 45th day of IU

life.

It extends from the cartilagenous otic

capsule to the midline.

Provides a framework around which the

growth of the mandible occurs.

Meckel’s cartilage lacks the enzyme alkaline

phosphatase found in the ossifying cartilages, thus

precluding its early ossification.

A major portion of the Meckel’s cartilage disappears.

It persists until as long as the 24th week IU life

Remaining part develops:

1. Mental ossicles.

2. Incus & Malleus.

3. Spine of sphenoid bone.

4. Anterior ligament of malleus.

5. Spheno – mandibular

ligament.

The 1st structure to develop in the primordium of the lower

jaw is the mandibular division of the trigeminal nerve.

6th week of IU life → a single ossification centre for each

half of mandible in the region of the bifurcation of inferior

alveolar nerve.

Ossification spreads below & around the inferior alveolar nerve.

The Meckel’s cartilage is surrounded by bone and ossification

then stops at the lingula

The bony plate extends towards the midline where it comes to lie

in close relationship with the bone forming on the opposite side.

However, two plates of bone remain separated at the Mandibular

symphysis by fibrous tissue.

Bony union takes place at around 18 months after birth.

Endochondral bone formation seen in 3 areas.

They appear between the 10th and 14th week of IU life.

Condylar process

Coronoid process

Mental region

Condylar process:

5th week of IU life - mesenchymal condensation at the ventral aspect

mandible.

10th week - develops into a cone shaped cartilage.

14th week- begins ossifying.

4th month - fuses with the Ramus of the developing mandible.

It persists as Growth cartilage & Articular cartilage

Coronoid process:

10-14th week of IU life→ Secondary accessory cartilage appear in the

region of coronoid process.

It grows as a response to Temporalis muscle.

This accessory cartilage fuses with the ramus and disappears by birth.

Mental region:

On either side of the symphysis, one or two cartilages

appear which ossify to form the mental ossicles at 7th

month of IU life.

These get incorporated into the intramembranous bone

when the symphysis ossify completely ( 1st year of post

natal life.)

POSTNATAL GROWTH OF THE MANDIBLE

According to the data from the vital staining experiments, the posterior surface the ramus, the condyle and coronoid process are principal sites of growth.

Growth is quite general during the first year of life with all surfaces showing bone apposition.

Mandibular growth becomes more selective.

Postnatal Growth Of Mandible

The mandible can be divided into several sub-units like

Chin Alveolar process Body Lingual tuberosity Ramus Angular process Coronoid process Condylar process

Chin: 1-2 years→ chin prominence is seen The mental protuberance forms by bone deposition The change in the contour occurs by following two

mechanism. 1) The area just above the chin and the base of the alveolar process, is a resorptive area. 2) There is forward translation of chin as mandible grows forward.

Alveolar process: This develops in response to the developing tooth

buds.

Body: (corpus) The length of the body increases as the ramus moves

posteriorly

Lingual tuberosity:

It forms the boundary

between the ramus & body

A combination of the

resorption and deposition

accentuates its

prominence.

Ramus:

The ramus is seen to move posteriorly due to deposition at

its posterior border and resorption on its anterior border

Angle:

The combined deposition and resorption causes

flaring of the angle of the mandible.

Coronoid process :

Enlow’s enlarging “V” principle.

Birth: Coronoid process is at higher

level than condyloid process.

Childhood: Coronoid & condyloid

processes are at same level.

Adult: Condyloid process is at

higher level.

Condyle:

Condylar growth rate increases at

puberty and reaches its peak by 12-

14 years.

The growth ceases at around 20 years

Role of condyle:

o Primary displacement

AT BIRTH : The two halves of the mandible are united by

a fibrous symphysis menti. At this stage the body is a mere shell,

enclosing imperfectly separated sockets of deciduous teeth.

The mandibular canal is near the lower border The mental foramen opens below the first

deciduous molar and is directed forwards. The coronoid process projects above the

condyle The angle of the mandible is obtuse (above

140degrees or more) because the head is in line with the body.

AGE CHANGES IN MANDIBLE

IN ADULTS : The mental foramen opens midway

between the upper and lower borders as the alveolar and sub-alveolar regions are about equal in depth.

The mandibular canal nearly parallels the mylohyoid line

The angle between the lower border of the body and a plane touching the posterior surface of the condyle above and ramus below diminishes as ramal height increases with age (about 110 –120degrees)

In OLD AGE :

Bone is reduced in size as teeth are lost and alveolar region resorbed

The mandibular canal and the mental foramen are nearer the superior border

The ramus becomes oblique as angle becomes obtuse (140degrees) and the neck inclined backwards.

At Birth

Adult MandibleGeriatric Mandible

In Childhood

Agnathia : Agnathia is an extremely rare congenital defect characterized by absence of the maxilla or mandible. More commonly only a portion of one jaw is missing.

Micrognathia : It likely means a small jaw. Many cases of apparent micrognathia are due not to an abnormally small jaw in terms of absolute size, but rather to an abnormal positioning or an abnormal relation of one jaw to the other or to the skull which produces the illusion of micrognathia.

Developmental disturbances of the jaws

Macrognathia : It refers to the condition of abnormally large jaws. It may be associated with

Pagets disease Acromegaly Leontiasis ossea, a form of

fibrous dysplasia.

Facial hemi atrophy : It is a progressive atrophy

of some or all of the tissues on one side of the face, occasionally extending to other parts of the body. The etiology is unknown.

As the dental effects the hemiatrophy of the lips and the tongue is reported, the roots of the teeth may exhibit deficiency of root development and reduced growth of the jaws on the affected side. Eruption of teeth on the affected side may also be retarded. There is no specific treatment.

Cleft lip and cleft palate Cleft lip occurs due to

failure of fusion of maxillary process with the medial and lateral nasal process.

Cleft palate is due to failure of fusion between maxillary process and frontonasal process.

They can be treated by surgical management or by fabrication of passive obturator.

In order to construct a prosthesis a dentist requires an understanding of the foundation,it’s components,its properties and qualities must be analysed to assure proper support for the proposed prosthesis.

CONCLUSION:

Inderbersingh :text book of human osteology. B.D.Chaurasia: human osteology. Inderbersingh : human embryology. Warren .H.Lewis.-Gray’s anatomy of the human

body.2000:20th edition Langman’s medical embryology – T.W. Sadler, 5th

edition. Oral histology, development, structure and

function – a.R. Ten cate, 4th edition

REFERENCES: