Development of Maxilla

Prenatal:

It can be studied under following headings:

- Maxilla proper.

- Premaxilla.

- Palatine bones.

Maxilla proper: It develops from maxillary prominence out ending

cranioventrally from much large mandibular prominence derived

from first arch, maxillary process of mandibular arch. Like the

mandible it first appears as a membranous ossification but unlike

mandible, its further development and growth are little affected by

appearance of secondary cartilage.

First ossification center around of weeks IVL ossification in

maxilla commences little later than in mandible. The center of

ossification first appears in a bond of fibrocellular tissue which lies

on the outer side of cartilage of nasal capsule immediately lateral

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and slightly below infraorbital nerve where it gives of its anterior

superior alveolar nerve. It lies above the part of dental lamina from

which enamel organ of canine tooth gum areas.

Ossification spreads backwards towards the developing zygomatic

bone below the orbit and forward in front of anterior superior

alveolar nerve below the terminal part of infra orbital nerve,

towards developing premaxilla. At this stage bone takes the shape

of curved strip vertically with convex side medially.

From the anterior extraction, frontal process develops which with a

corresponding process of premaxilla forms frontal process of adult

bone. These processes of maxilla and premaxilla unite so rapidly

that no suture appears between them from the beginning.

The developing maxilla forms a bony trough for I.O. nerve. It

forms outer alveolar plate by the downward growth in relation to

canine-deciduous molar tooth germs.

Maxilla continues to grow mainly upward and downward, backward

and with the development palatal process also spreads in midline.

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A secondary cartilage appears in the zygomatic process and its

proliferation considerable adds to back of maxilla. During this

period palatine process with grow backward and a large mass of

bone of maxilla is formed. From this region lingual alveolar palate

develops some what later than buccal plate. The trough of bone

formed will be later divided by septa into alveoli small areas of

secondary cartilage may be formed in midline of developing hard

palate.

Secondary ossification centers are:

1. Zygomatic.

2. Orbitonasal.

3. Nasopalatine.

4. Intermaxillary.

The two intermaxillary ossification centers generate alveolar ridge

and primary palate region which is demarcated by a fissure between

LI and canine teeth.

Comparison between maxillary and mandibular development

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This bone disappear as a separate entity by fusion of the fissures

during first post nasal. Both commence as centers of ossification in

close life relations to a nerve at a place of bifurcation and close

relation to elements of cartilaginous facial skeleton. Both have

neural and alveolar elements. Both develop secondary cartilage in

their backward extraction. However, condylar cartilage remains

active for a long perio and zygomatic is limited to period of faetal

life.

Maxilla has no muscular process and mandible has no palatine

process.

Growth of maxilla is surface deposition and sutural.

Growth of mandible is surface deposition and replacement by

cartilage.

Development of Premaxilla:

By two ossification center (first 7 weeks and above incisive form,

2nd 10 weeks and ventral margin of nasal septum. Premaxilla is

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formed by frontonasal process and limited with the junction of

maxillary process.

At seven weeks of age a separate center of ossification appears for

premaxilla and it retains the identity for a very short period of time

and during 8 th week union takes place with maxillary ossification.

Thus a single mass of bone called maxillary corpus is formed at the

each side of face and later frontal process will arise which units

with frontal process of maxilla. A heavy trabecularized network of

bone appears on labial aspect of canine alveolar which spreads and

fuses with underlying frontal process. The alveolar processes arise

which surround the developing incisor tooth germ.

On the facial aspect, union between maxilla and premaxilla

disappears before birth but seen on palatal aspect after birth.

Development of Palatine bone:

It develops as a fibrocellular condensation on medial side of

cartilaginous nasal capsule. Ossification starts at 7-8 weeks IUL in

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the region of tuberosity in close relation to descending palatine

nerve. Ossification extrudes upwards and horizontally.

At first, the vertical plate of palatine bone is separated from

maxilla by lateral wall of nasal capsule.

Development of Maxilla

Prenatal:

By 8 th week of IUL, ossification centers which become maxillary

and mandibular skeleton become apparent in the lateral face.

Bilateral frontal bones cover the forebrain above the eyes. Small

nasal bones appear anterior to the nasal capsule. The premaxillary

ossification centers may appear as separate or united sites on

anterior surface of nasal capsule. The zygomatic bone and temporal

bone appear posterior to maxillary bone.

By 12 weeks, premaxillary and maxillary bones have increased in

size. During 10 th weeks, a ‘V’ shaped bone arises just below the

nasal septum of ethamoid and is called Vomer and its two diverging

parts grow up on either side of septum. The increase in height of

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the face occurs with addition to the size of ethamoid and the vomer

bone. The sphenoid is located just behind the ethmoid along the

base of skull.

During the faetal period, bone is deposted on the entire external

surface of maxilla and resorption occurs in each alveolus

surrounding the tooth buds and on the lingual surface of alveolar

ridges. Maxillary arch length increases by both anterior and

posterior growth. The orbit floor displaces throughout life

(prenatal) inferiorly bone resorbs on the nasal side of the palate and

forms on oral surface.

In the anterior palate, premaxilla has lingual and plates of bone

around incisor teeth. a suture septum the right and left sides. A

posterior suture septal, the premaxillary form from the maxillary

bones. At this stage the palate is relatively small compared with

cranial skeletal. Later, the palate becomes much larger.

By 8 th month of IUL, the bony configuration of palate is well

established and the sutures are still evident. Additional growth of

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the palate occurs around periphery which assures that growth of the

palate will keep pace with the growth of face.

Post natal

a) Sutures

Growth of the maxilla depends upon the influence of several

functional matrices that act upon different areas of bone. Thus

theoretically can be divided into:

The basal body develops beneath the infraorbital nerve, later

surrounding it to form infraorbital canal. The orbital unit responds

to growth of eye ball. Nasal unit responds to septal cartilage for its

growth and the teeth provide functional matrix for the alveolar unit.

The pneumatic unit reflects maxillary sinus expansion, which is

more a responder than a determiner of the skeletal unit.

The complexity of action of these function at forces on the facial

bones results in different effects on different sutures.

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Superozygomatic suture predominantly A-P direction. In order to

keep pace with growth of brain and spheno-occipital synchondrosal

cartilage.

Nasomaxillary suture A-P direction (predominantly) and creates

elevation of bridge of nose.

Frontomaxillary

Fronto zygomatic

Frontonasal Predominately vertically

Fronto ethmoidal

Ethmoido maxillary

Facial width is relatively less on preparation to neurocranium in

neonate than adult. The face of new born is twice as broad in

comparison with its height than in adult.

Growth at all these sutures is greatest until age of 4 years and

completes by the end of first decade and of more spurt during

puberty. Thereafter these sutures mainly act as sites of fibrous

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union allowing for adjustments brought about by surface deposition

and remodeling.

Surface remodeling

Remodelling takes place over all the surfaces of maxilla. Growth of

alveolar process will add to the vertical height of face and depth of

palate. Bone deposition on the posterior surface of maxillary

tuberosity induces corresponding anterior displacement of entire

maxilla. The growth pattern of dento-alveolar arch differs from

other surfaces. It is related to the sequence of tooth eruption.

Resorption along the anterior surface of body of maxilla creates

supra-alveolar concavity (point A).

The final form of maxillary complex is balanced by bone deposition

and resorption. It differs between individuals and same individual

at different periods.

Deposition is most active at the alveolar process, undersurface of

hard palate. Both resorption occurs in interior of the maxilla

(increasing size of sinuses), upper surface of hard palate. The

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overall effects is to increase the vertical component of facial

growth and reduce the forward component giving a characteristic

fracture of modern human face as compared with that of anthropoid

apes and early human races.

Surface deposition and resorption are more predominate during 2 nd

decade of life, predominately in vertical direction.

Development of Palate:

The palate develops from the elements:

- Primary palate portion of the frontonasal process.

- Two lateral maxillary processes.

and palate is formed from one medial and two lateral palatine

process.

The term palate refers to the tissues that interposes between oral

and nasal cavity. The median palatal process is also called as

primary palate which begins at 6 th week of IUL. It develops as a

wedge shaped mass between the maxillary process of the

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developing upper jaw. From this primary palate the developing four

maxillary teeth are supported.

At the end of 6 th week, the lateral palatine process which form

secondary palate develop from the medial edges of maxillary

processes. The lateral palatine process grow medially first, then

grow downward or vertically on either side of tongue.

Shelf elevation:

At about 8 ½ week of IUL, the lateral palatine shelves roll over the

body of tongue. The process of elevation occurs when the shelves

have developed sufficient strength to slide over tongue. It results

from combined action of shelf and tongue movement. Palates shelf

elevation begins in this posterior region and depresses the tongue

downward and forward, which releases the out part of shelves. Thus

the tongue utilizes lateral space occupied and broadens.

Palatal shelf closure:

After the shelves are in a horizontal position there is a final growth

spurt, and shelf contact occurs in midline.

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Closure fusion of LPP occurs first just posterior to median palatine

process. It is a process of contact with loss of intervening

epithelium and growth of connective tissue across the midline.

After this initial contact, there is fusion of LPP with MPP

anteriorly.

Posteriorly, closure takes place gradually over the next several

weeks and involves merging of the two LPP by cell proliferation at

the depth of midline grade behind the initial fusion. Fusion of LPP

also occurs with nasal septum except post where soft palate and

ovula remain unattached .

At about 12 week of IUL, palate is invaded anterior by bone from

premaxillary, maxillary and palatal centers to form hard palate and

post by muscle to form soft palate.

Premaxillary ossification center ( primary) 8 week of IUL

( Secondary)

Maxillary ossification center (single and appears at 6 week of IUL)

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Palato maxillary suture

Palatine ossification 8 th week ossification starts.

The fusion of three palatal components initially induced a flat,

unarched roof of mouth. The line of fusion of lateral, palatal

shelves is traced in adult the midpalatal suture. The mid palatal

suture strength is first widest at 10 ½ weeks. In adults it becomes

so interdigitated that mechanical interlocking and islets of bone are

formed (after 30 years). In adulthood palatine bone elements of the

palate remain separated from maxillary elements by transverse

palato-maxillary sutures.

The ossification does not occur in most posterior part of palate

giving rise to region of soft palate.

At birth, length and breadth of hard palate are almost equal. The

postural increase in palatal length is due to appositional growth at

tuberosity and to some extent at transverse maxillopalatine suture.

Growth at midpalatine suture ceases between 1 and 2 years of age.

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Lateral appositional growth continues till 7 years by which time

palate achieves its ultimate anterior width. Posterior appositional

growth continues after lateral growth has ceased so that palate

becomes longer than wider during late childhood.

The rougae which are most prominent in infant hold the nipple. The

anterior palatal furrow is more marked during 1 st year and life

(active suckling period). This normally flattens by 3-4 years once

the suckling is stopped. If complicated of thumb sucking, it may

remain in childhood.

Greater palatine foramen is situated between 2 nd and 3rd maxillary

molar about 1cm from the palatal gingival margin towards midline.

In child with only primary dentition erupted, the injection should

be made approximately 10mm posterior to the distal surface of the

second primary molar. It is not necessary to outer greater palatine

foramen. A few drops of solution can be injected slowly at the

point where the nerve is emerging from the foramen. The distal line

from the most posterior erupted teeth.

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- Deficiencies of maxillary prominence and brachial arch

ectomesenchyme may result in facial bones.

- Deficient maxillary development may also be associated with

clefts of upper lip and palate, downs syndrome.

- Entrapment of epithelial rest cells in the live of fusion of the

palatal shelves, may give rise to palatal rest cyst. The

common forms are Eptin pearls along the medial raphe of

hard palate and junction of hard and soft palate. Bohns

modules are mucosal found retention cysts occurring on

buccal and lingual aspect of alveolar ridges.

- Torus palatinus is a common genetic commonly of palate

with localized midpalatal over growth. It may enlarge in

adulthood and interfere with appliances.

- Delay in elevation of palatal shelves leads to clefting of the

palate.

- Inadequate use of the nasal cavity by mouth breathing has

been associated with the narrow pinched fall and high-

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vaulted palatal arch of adenoid facies. The erupt space of

nasal cavity may influence facial growth and form the cause

and effect relationship of this facial form with mouth

breathing has not been substantiated.

- Shapes of palate (u, v, high roofed).

- Cleft palate is a result associated with habits of non-fusion.

- R & L valves of embryonic palate. It may be of different

degrees. In the least severe type, the defect is confined to

soft palate and in severe cases it is continuous with cleft of

lip.

- Epigraphers is a teratome arising specifically from the palate.

- Absence of neural crest ectomesenchyme in frontonasal

prominence may result in cleft lips.

- Hemifacial microsomin produces asymmetric face on affected

side ear, zygomatic bone and mandible will be

underdeveloped.

- Supernumerary the pattern of bone remodeling.

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- It the palate thickness same all over?

- It narrows posteriorly.

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Development of Mandible

Introduction:

Human mandible does not have a single design for life. Rather it

adapts and remodels through different stages of life. It is rather a

exceptional bone in that it is largely derived from membrane bone,

yet main site of growth is at cartilage.

History:

Hunter (1961) proposed that mandible grows by apposition in on its

posterior border with resorption on anterior border. Humphry

(1966) supported the Hunter’s theory. He tied the wire around the

growing mandible of pig and found that wire was embedded in

posterior portion of mandible after portion of mandible after

growth.

Alizarin study by Weinman in 1944 suggested that condyle was

potential of growing in superior and posterior direction. Rickett’s

in 1950 supported this.

Prenatal:

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At about 6 week of IUL, as the nasal capsule becomes the

prominent cartilage in the upper face, Meekel’s cartilage bars

become apparent in mandibular arches (1 st pharyngeal arch).

The posterior part of each of these bars enlarge to become the

(dorsal) malleus, which articulates with a second small cartilage,

the incus. These two cartilages become enclosed in otic capsule.

They form a joint called primary TMJ articulation of these two

cartilages occurs until they undergo endochondral bone formation

during 18 week IUL. At this time secondary TMJ formed anterior to

middle ear and begins functioning. The shift of primary to

secondary occurs as Meekle’s cartilage is fused to mandible.

The mandible is formed in the lower or deeper part of 1 st arch. It is

preceded by Mekels cartilage. Mekels cartilage attains its full form

of 5mm by 6 weeks and then stretches downwards and forwards as

an unbroken rod of cartilage. In midline the ventral line turns

upward in contact with cartilage of opposite side. It is surrounded

in its whole length by a thick investment of fibrocellular tissue.

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Except for the dorsal part, the remaining part is associated with the

development of mandible.

The mandibular nerve: The main nerve issues from the skull medial

and ventral to dorsal end of cartilage and comes into direct relation

with it about the junction of its dorsal and midline 1/3rds. Here it

gives lingual and inferior alveolar nerve. The lingual nerve passes

medial to the cartilage and inferior A-N on lateral aspect. Running

forward terminates by dividing into ----- and incisive branches.

Body of the mandible:

Figure

The body of the mandible continues to develop as a rectangular

membrane bone. The ossification center appears at 7 week of IUL I

the angle by mental and incisive nerve. This is the area of future

mental foramen. From this center, the formation of bone spreads

rapidly backward below the mental nerve, which then lies in on

notch in bone and on the lateral side of inferior alveolar nerve. The

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bone in front of the region of the notch for mental nerve grows

medially below the incisive nerve and spreads upwards between

this nerve and Meckels cartilage, thus the incisive nerve contained

in a trough of bone. The notch containing the mental nerve is

converted into mental foramen. The bony trough grows rapidly

forward towards the midline where it comes in close relationship

with similar bone formation of opposite side but its separated from

connective tissue union takes place before the end of first year

postnatally. A similar spread of ossification (between 4-12months)

takes place in backward direction. Thus by these process, original

primary center of ossification produces the body proper of

mandible form mandibular foramen to symphises.

Fate of Meckels cartilage:

With the exception of at midline, the anterior part of mandible,

from in front of mental foramen included cartilage in its substance.

This part of cartilage first surrounded by on extension of bone from

the medial plate and then gradually resorbed and replaced by an

extension of ossification from membrane bone around it. The rest

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of Meckels cartilage disappears completely except for a part of its

fibrous covering which persists as sphenomandibular and spheno-

alveolar ligament.

The ramus:

The backward extension of mandible to form the ramus is produced

by a spread of ossification from the body, behind and above

mandibular foramen. As in body, here too the ramus and its

processes are first mapped out by extension of this condensation.

The formation of bone occurs rapidly so that the coronoid and

condylar processes are ossified to a greater extent. The further

growth of these processes is modified by secondary cartilages.

Alveolar bone:

As the enamel organ of deciduous tooth germs reach the early bell

stage, the bone of the mandible begins to come into close

relationship to them. This is brought about by the upward growth,

on each side, of the lateral and medial plates of mandibular bone

above the level where the roof of the canal for the incisive and

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inferior alveolar nerve is formed. By this growth, the developing

teeth come to lie in a trough of bone. This trough is later divided

into small alveoli for the teeth by the formation of septa between

two walls.

Secondary cartilage:

These occur at various sites in the region of membrane bone

formation, also called as accessory cartilage. They have no

connection with primary cartilage. The primary cartilage is hyaline.

These cartilages have less intercellular matrix than hyaline. These

cartilages increase in size by proliferation and transformation of the

cells of thick layer of fibrous cellular tissue covering them.

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Condylar cartilage:

There are three sites of secondary cartilage formation appears

between 10-14 th weeks of IUL. The largest and first one is condylar

cartilage. It appears on superior and lateral aspects of condylar

process. The cartilage forms a cone-shaped mass which not only

occupied the whole of condylar process but reaches forward and

downward into ramus upto level of mandibular foramen. Cartilage

in anterior part shows ossification and its continues till 5 month

IUL where only cartilage is left unresorbed beneath the

proliferating tissue of condylar articular surface. this persists until

the end of second decade of life. During this period, thickeness of

zone of cartilage disappears and the replacing bone forms whole of

condyle. This cartilage is responsible for whole of normal growth

period and increases length of mandible.

Coronoid cartilage:

Found along the anterior border and summit of coronoid process.

All the traces of cartilage disappears long before birth.

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Symphyseal cartilage:

This is the 3 rd cartilage occurring at the symphyseal end of each

half of bony mandible. These enable the mandible to grow in with

till they persist. Once the union of mandible occurs at birth, they do

not take any further part in growth.

At birth mandible has wide mandibular angle (135°), ramus is small

compared to body and chin is poorly developed.

Clinical importance:

The shape and size of the fetal mandible undergoes transformation

during its growth and development. The ascending ramus of

neonatal mandible is low and wide and coronoid process is

relatively large and projects well above the condyle. The

mandibular canal runs low in the body.

As the mandibular body is showing the direction of mental foramen

during infancy and childhood changes. The mental neuromuscular

bundle arises at right angles of slightly forward direction at birth.

In adulthood it is characteristically directed backward. This change

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may be due to forward growth in the body of mandible while

neurovascular bundle drags along. This changing direction of

foramen has clinical implication in administration of local

anesthetic i.e. in infancy and childhood syringe needle may be

applied at right angles where as in adult it has to be applied

obliquely from behind. The location of the mental foramen also

alters its vertical relationship within the body of mandible from

infancy to old age. When teeth are present it located midway

between upper and lower border of mandible and in edentulous

mandible appears to be near the upper margin.

The alveolar process develops as a protective trough in response to

tooth buds and becomes superimposed upon basal bone of

mandibular body. This bone fails to develop if teeth are absent and

resorbs in response to tooth extraction. The orthodontic movement

of teeth takes place in alveolar bone (bed) and does not involve

basal bone.

Torus mandibular is exostasis which usually develops bilaterally in

the canine-premolar region.

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During fetal life the relative sizes of the maxilla and mandible vary

wide. Initially at 6 week IUL, mandible is considerably larger than

maxilla. By about 8 week, greater development of maxilla.

Subsequently relatively larger growth of mandible results at 11

week and lower and upper grows are of equal size between 13-20

week, mandibular growth lags behind due to change over from

Meckels cartilage to condylar secondary cartilage. At birth

mandible tends to be retrognathic though two jaws are of equal

size. This is normally corrected by postnatal growth to develop

Angle Class I relationship (maxillo-mandibular). Inadequate growth

results in Class II and overgrowth into Class III relation.

The mandible may be grossly deficient or absent. This condition is

known as agnathia. Aplasia of mandible and hyoid bone is a rare

and lethal condition called as 1 st and 2nd arch syndrome. In this

syndrome ischaemic necrosis of the mandible and hyoid bone

occurs after formation of ear.

Micrognathia is characteristic of several syndromes.

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- Pierre robin syndrome.

- Cat-cry syndrome.

- Treacher Collin’s (mandibulofacial).

- Down’s syndrome (trisomy 21).

- Turners syndrome.

There may be double condyle or bifid condyle that results from

persistence of septa dividing fetal condylar cartilage. Unilateral

condylar hyperplastic is also common.

Prognathism is usually inherited condition hyperpituitarism may

produce mandibular over growth.

Angulation of angle of mandible is 135° at childhood and

senilehood and at adult hood decreases to 160°.

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