prenatal and post natal growth of mandible

Prenatal and postnatal development of mandible

A.MAHESH KUMAR MDS 1ST yearDrs SIDSDept of PEDODONTICS2

Contents

1)References2)Introduction 3)Prenatal growth of mandible4) Meckel’s cartilage5) Anatomy6)Muscle attachment7)Ossification

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7)Remodelling8)Neonatal

mandible9)Postnatal

development 10)Theories of

growth11)Mechanism of

bone growth12)Age changes in

mandible 4

References

Craniofacial embryology -- SPERBERPrinciples and practice of orthodontics --GRABERContemporary orthodontics -- PROFFITOral Anatomy, Histology and Embryology –B . K. B

Berkovitz, Graham Rex Holland , B.J. Moxham.Clinical Pedodontics – Sidney B. FinnEnlow , D.H., and harris , D B; A study of postnatal

growth of the human mandible . Am. J. Orthodont., 50;25-50,1964

Moss , M.L.; Functional cranial analysis of the coronoid process in rat . Acta anat .,77;11-24

Sicher , H : The growth of the mandible. Am. J. Orthodont.,33:30-35, 1947.

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Growth definitionsAccording to “TODD” “Growth is an increase in

size.” &“Development is progress towards maturity .”

The self multiplication of living substance – JX Huxely

Quantitative aspect of biologic development per unit of time-Mayers.

Change in any morphological parameter, which is measurable-Moss.6

Growth and development of an individual can be divided into:-

1) PRENATAL & POSTNATAL periods. -The pre-natal period of development is a

dynamic phase in the development of a human being.

-During this period, the height increases by almost5000 times as compared to only a threefold increase during the post-natal period.

-The pre-natal life can be arbitrarily divided into three periods.

1. Period of the Ovum( from fertilization to 14th day )

2. Period of the Embryo (14th to 56th day )3. Period of the Fetus( 56th day to birth )

Embryonic phase

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Prenatal growth of mandibleThere is a marked acceleration of mandibular

growth between the eighth and twelfth weeks of fetal life .

As a result of mandibular length increases , the external auditory meatus appears to move posteriorly.

The mandible initially develops intramembranously , but its subsequent growth is related to the appearance of secondary cartilages

The developing mandible is preceded by the appearance of a rod of cartilage ( meckel’s cartilage )

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History • JOHN HUNTER (1771) compared a series of dried

mandibles and concluded that in order to attain space for permanent molar teeth the mandible must grow by posterior apposition of ramus accompanied by anterior ramus resorption.

• HUMPHRY (1866) studied growth of mandible by inserting metal wires in the mandible of young pigs.

• BJORK (1955): conducted implant studies on jaws to determine the growth pattern & rotation ,when subjected to serial cephalometric methods.

• DONALD ENLOW : proposed the V principle of growth and counterpart principle.

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The Pharyngeal Arches

The pharyngeal arches appear between 4th & 5th weeks of development

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Each arch containA central cartilage

that forms the skeleton of the arch

A muscular component

A vascular component

A neural component

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The 1st pharyngeal

arch is the mandibular arch which contains the Meckel’s Cartilage.

It appears at about 6th week of I.U. life.

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MECKEL’S CARTILAGEMakes little contribution towards the development of the

mandibleProvides a Template for subsequent development of the

mandible.During the 7th week of I.U. life, a centre of ossification

appearsMandibular ectomesenchyme must interact initially with the

epithelium of the mandibular arch before forming the primary ossification can occur ; the resulting intramembranous bone lies lateral to the meckel’s cartilage.

From this centre, bone formation spreads rapidly backwards, forwards & upwards around inferior alveolar nerve & its terminal branches.

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MECKEL’S CARTILAGEMeckel’s cartilage becomes

surrounded and invaded by bone.

Ossification stops dorsally at the site that will become the mandibular lingula, where meckel’s cartilage continues into the middle ear

The dorsal end of Meckel’s cartilage ossifies to form the basis of two of the auditory ossicles ( incus and malleus).

A small part of its ventral end forms accessory endochondral ossicles that are incorporated into the chin region of the mandible .14

The ossifying membrane is located lateral to the meckel’s cartilage and its accompanying neurovascular bundle.

From this primary centre, ossification spread below and around the inferior alveolar nerve and its incisive brand and upward to form a trough for a accommodating the developing tooth bud.15

MECKEL’S CARTILAGESpread of the intramembranous ossification dorsally and ventrally forms the body and ramus of the mandible.

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A major portion of the meckel’s cartilage disappears during growth and the remaining part develops into:

1. The mental ossicles.2. Incus and malleus.3. Spine of the spenoid bone.4. Anterior ligament of the malleus.5. Spheno-mandibular ligament.

MECKEL’S CARTILAGE

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SECONDARY CARTILAGESAppears between

10th & 14th week of I.U. life.

Forms the head of condyle, part of coronoid process & mental protuberances.

The secondary cartilage of the coronoid process develops within the temporalis muscle, as its predecessor.

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SECONDARY CARTILAGESIn the mental region, on either side of the

symphysis , one or two small cartilages appear and ossify in the 7th month of IUL to form variable number of mental ossicles in the fibrous tissue of the symphysis.

The condylar cartilage appears in the 10th week of IUL,which forms the future condyle .

The condylar cartilage serves as an important center of growth as primary or secondary .

By the middle of the fetal life cone shaped cartilage is replaced by the bone, but its upper persists into adulthood, acting as both growth and articular cartilage

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SECONDARY CARTILAGESChanges in the mandibular position and

form are related to the direction and amount of the condylar growth

The condylar growth rate increase at puberty, peaks between 12 1/2 and 14 years of age, and normally ceases at about 20 years of age .

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ANATOMY

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MUSCLE ATTACHMENTS

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Neonatal mandibleAscending

Ramus low and wide.

Large Coronoid process and projects well above the condyle.

Body – open shell containing tooth buds and partially formed deciduous teeth.

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Neonatal mandible

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Neonatal mandible Mandibular canal

that runs low in the body.

The initial separation of the right and left bodies of the mandible at the midline symphysis menti is gradually eliminated between the 4th and 12th month after birth.

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Postnatal growth of mandibleThe shape and size of the diminutive fetal

mandible undergoes considerable transformation during its growth and development.

Some indications of the directions of growth of the mandible can be obtained by superimposing traces of neonatal and adult mandibles

There is some evidence the region around the mental foramen is a fixed point for such an endeavor

Growth of the mandible occurs by the remodeling of bone

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Postnatal growth of mandibleAt birth the two rami of the mandible are quite short .

Condylar development is minimal and there is practically no articular eminence in the glenoid fossa.

A thin line of fibrocartilage and connective tissue exists at the midline of the symphysis to separate right and left mandibular bodies. Between 4 months of age and the end of first year, the symphysial cartilage is replaced by bone.

During the 1st year of life, appositional growth is especially active at the alveolar border, at the distal and superior surfaces of the ramus, at the condyle, along the lower border of the mandible and on its lateral surfaces.

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Postnatal growth of mandibleAlthough the mandible appears as a single

bone in the adult , it is developmentally and functionally divisible into several skeletal subunits

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Postnatal growth of mandibleThe growth pattern of each of these skeletal subunits

is influenced by a functional matrix that acts upon the bone

1) the teeth act as a functional matrix for the alveolar unit

2) the action of temporalis muscle influences the coronoid process

3) the masseter and medial pterygoid has some influence on the condylar process

Of all the facial bones , the mandible undergoes the most growth postnatally and evidences the greatest variation in morphology

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Postnatal growth of mandibleGrowth sites in mandible 1) Limited growth takes place at the

symphysis menti until fusion occurs.2) At the condylar cartilages 3) The posterior border of ramus 4) Alveolar ridges

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3

4

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Postnatal growth of mandibleThese areas of bone deposition largely

account for increase in the height , length and the width of the mandible.

Superimposed upon this basic incremental growth are numerous regional remodeling changes that are subjected to the local functional influences involving selective resorption and displacement of individual mandibular elements.

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Postnatal growth of mandibleThe condylar cartilage of the mandible

uniquely serves as both 1) An articular cartilage in the TMJ,

characterized by a fibrocartilage surface layer

2) A growth cartilage analogous to the epiphysial plate in a long bone, characterized by a deeper hypertrophying cartilage layer.

The growth cartilage may act as a functional matrix to stretch the periosteum, inducing the lengthened periosteum to form intramembranous bone beneath it

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Postnatal growth of mandibleThe formation of bone within the condylar

heads causes the mandibular rami to grow upward and backward , displacing the entire mandible in an opposite downward and forward direction.

Bone resorption subjacent to the condylar head accounts for the narrowed condylar neck.

Any damage to the condylar cartilage restricts the growth potential and normal downward and forward displacement of the mandible , unilaterally or bilaterally according to the sides damaged .36

Postnatal growth of mandible

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Postnatal growth of mandibleIn infants condyles of the mandible are

inclined almost horizontally, so that condylar growth leads to an increase in height.

After first year of life , mandibular growth becomes more selective. The condyle does show considerable activity as the mandible moves and grows downward and forward .

Heavy appositional growth occurs at the posterior border of the ramus and on the alveolar border. Significant growth still observed in at the tip of the coronoid process

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Resorption occurs along the anterior border of the ramus lengthening the alveolar border and maintaining the anteroposterior dimension of the ramus.

Major width contribution of the mandible is growth at the posterior border

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Literally the mandible is an “expanding V”. Additive growth at the ends of this “V” naturally increase the distance between the terminal points.

Continued growth of alveolar bone with the developing dentition increases the height of the mandibular body

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Scott divides the mandible into three basic types of bone – basal, muscular, alveolar (or) tooth supporting .

Basal portion is a tube like central foundation running from the condyle to the symphysis

Muscular portion is under the influence of masseter, internal pterygoid and temporal muscles

The third portion alveolar bone exists to hold the teeth.

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Moss speaks of the mandible as a group of microskeletal units .

Thus the coronoid process is one skeletal unit under the influence of the temporalis muscle.

The gonial angle is another skeletal unit under the influence of masseter and internal pterygoid muscles.

The alveolar bone under the influence of teeth.

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Postnatal growth of mandibleMoss delineates two basic types of

functional matrices.1) Periosteal matrices2)Capsular matricesMandibular growth demonstrates the

integrated activity of periosteal and capsular matrices in facial growth.

Since the condyles are not primary sites of mandibular growth but loci with secondary, compensatory growth potential , condylar removal does not inhibit the spatial translation of contiguous mandibular functional components

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Mandibular growth is seen now to be a combination of the morphologic effects of both capsular and periosteal matrices.

The capsular matrix growth causes an expansion of the capsule as a whole.

Under normal conditions then the periosteal matrices related to constituent mandibular microskeletal unit also respond to this volumetric expansion. Such alteration in spatial position inevitably causes them to grow.

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CHINIn infancy chin is under developed.As age advances the growth of chin

becomes significantMales are seen to have prominent chin

compared to females.The prominence is accentuated by bone

resorption in the alveolar region below it, creating a concavity

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Chin

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Mental Protuberance

Forms by osseous deposition during childhood

Prominence is accentuated by bone resorption above it

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Theories Of Mandibular Growth

Genetic Theory:-This theory states that all growth is

compelled by genetic influence i.e.: genetic encoding of mandible

determines its growth.

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Sutural TheoryThis theory states that genetic control is

expressed directly at the level of the bone & its locus is the periosteum.

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Cartilaginous TheoryThis theory states that the cartilage is the

primary determinant of skeletal growth while bone responds secondarily & passively.

According to this theory, the condyle by means of endochondral ossification deposits bone, which tends to the growth of the mandible.

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Functional Matrix TheoryAccording to this theory, the soft tissue

matrix in which the skeletal elements are embedded is the primary determinant of growth & both bone & cartilage are secondary followers.

Which means the muscles, connective tissues etc. carries the entire mandible away from the cranial base . The bone follows secondarily at the condyle to maintain constant contact with the glenoid fossa.

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Enlow’s Expanding ‘V’ Principle

This theory states that many facial bones or a part of the bone follows a ‘v’ pattern of enlargement.

Due to differential deposition & selective resorption Deposition is in the inner surface of wide ends of ‘v’ & along the ends of ‘v’. Resorption is seen along the outer surface of ‘v’.

CORONOID: Deposition –lingual surface, Resorption-buccal

CONDYLE: Deposition-ant. & post. Margins, Resorption-buccal & lingual surfaces.

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Counterpart PrincipleThis principle states that growth of any

given facial or cranial part relates specifically to other structural & geometric counterpart in the face & cranium

Eg;- The maxillary arch is the counter part of the mandibular arch.

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Mechanisms Of Bone GrowthGrowth Of The Mandible Primarily Involve 1. Bone remodeling Process of bone deposition and resorption 2. Cortical drift Combination of bone deposition and resorption resulting in growth movement towards deposition surface 3. Displacement Movement of whole bone as a unit I) Primary displacement II) Secondary displacement54

Mechanism Of Bone GrowthBone growth is based on certain basic principles .Bones do not grow symmetrically but grow by complex differentiation mechanism . All bone growth is a complicated mixture of the two basic principles deposition and resorption .

Deposition and resorption which are carried out by the growth fields comprised of the soft tissue investing the bone. As the fields grows and function differently on different parts of the bone ,the bone undergoes remodeling. When the amount of bone deposition is greater than the resorption , enlargement of the bone necessitates its displacement.

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Deposition and resorption•Bone grows by addition of new bone tissue on one side of the bony cortex.

•Bone formative changes occurs on the surface facing towards the direction of progressive growth resulting in new bone deposition.

•Deposition is observed on the tension side.

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Bone remodeling

Bone remodeling involves independent sites of resorption and formation that change the size and shape of a bone.

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E.g. The ramus moves posteriorly by the combination of deposition and resorption.

So the anterior part of the ramus gets remodeled

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Functions of Remodeling1.Progressively change the size of whole

bone2.Sequentially relocate each component

of the whole bone3.Progressively change the shape of the

bone to accommodate its various functions

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4. Progressive fine tune fitting of all the separate bones to each other and to their contiguous, growing, functioning soft tissues.

5. Carry out continuous structural adjustments to adapt to the intrinsic and extrinsic changes in conditions .

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Displacement

•It is the movement of the whole bone as a unit.

•It is a translatory movement of the whole bone caused by surrounding physical forces, and is the second characteristics mechanism of skull growth.

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•The entire bone is carried away from its articular interfaces( sutures , synchondroses, condyle) with adjacent bones.

•Displacement is of two types namely:

•Primary displacement- As a bone enlarges , it is simultaneously carried away from the other bones in direct contact with it.This creates space within which bony enlargement takes place.

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It is the physical movement of the whole bone ,as the bone grows & remodels by resorption and apposition.

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•Secondary displacement :It is the movement of a whole bone caused by the separate enlargement of other bones which may be nearby or quite distant.

•It is related to enlargement of other bone.

•For example: growth in the middle cranial fossa results in the movement of the maxillary complex anteriorly& inferiorly .

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Age Changes Of The Mandible

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AT BIRTH CHILDHOOD

ADULHOOD OLD AGE

AGE CHANGES


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Anomalies of mandible Some of the syndromes associated with

mandibular abnormalityi) Down’s syndromei) Marfan’s syndromeii) Turners syndromeiii) Kleinfelter’s syndromeiv) Pierre-robin syndromev) Treacher- collin syndrome

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1.Congenital• Agnathia• Micrognathia• Macrognathia• Facial

hemihypertrophy

• Facial hemiatropy

2. Developmental

• Infantile cortical hyperostosis

• Achondroplasia

• Torus mandibularis

• Stafne’s cyst

• Odontogenic cyst

• Odontogenic tumor71

Anomalies of development

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AGNATHIAIn this condition the mandible may be

absent or grossly deficient , reflecting a deficiency of neural crest tissue in the lower part of the face .


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Aplasia Aplasia of the mandible and hyoid bone

is a rare lethal condition with multiple defects of the orbit and maxilla.

Well developed ears and auditory ossicles in this syndrome suggest ischemic necrosis of the mandible and hyoid bone occurring after the formation of ear.


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Micrognathia The diminutive mandible of

micrognathia is characteristic of several syndromes including

1) Pierre robin syndrome 2) Mandibulofacial dysostosis3) Down syndrome 4) Oculomandibulodyscephaly5) Turners syndrome


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Hypoplastic mandible A central dysmorphogenic mechanism of

defective neural crest production, migration, or destruction may be responsible for the hypoplastic mandible.

Derivatives of the deficient ectomesenchyme are hypoplastic accounting for the typical faces common to these syndrome.


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Macrognathia Producing prognathism is usually an

inherited condition, but abnormal growth phenomena such as hyperpituitarism may produce mandibular overgrowth of increasing severity with age .


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Hemifacial hypertrophy Congenital hemifacial hypertrophy , evident

at birth , tends to intensify at puberty


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Unilateral condylar hyperplasia Unilateral enlargement of the mandible, the

mandibular fossa, and the teeth is of obscure etiology .

Silver-Russell syndrome : The mandible as well as the maxilla are

small and retrognathic. differences in mandibular

growth causing facial asymmetries

Treatment Of Abnormal Mandibular Growth During Its Growth Appropriate functional appliances in a

forward postural position increase the condyle cartilage growth rate and amount

Orthopedic appliancesIt is possible to use a chin cup to

deliberately rotate the mandible down and back, redirecting rather than directly restraining mandibular growth.

Surgical proceduresCORRECTION OF

ANTEROPOSTERIOR RELATIONSHIPMandibular advancement :-Bilateral

sagittal split osteotomy of mandibular ramus performed from an intra oral approach, is the preferred procedure.

Mandibular setback :- Bilateral sagittal split osteotomy and transoral vertical oblique ramus osteotomy can be done.

Surgical procedures

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CORRECTION OF VERTICAL RELATIONSHIPLong face patients have excessive eruption ofmandibular anterior teeth . This tooth chin problem canbe treated by orthodontic intrusion or by anteriorsegmental surgery to depress elongated incisorsegment. However the preferred treatment is inferiorborder osteotomy of mandible to reduce vertical heightof chin at the same time it is augmentedhorizontally. Many patients are treated by combinationof maxillary intrusion and repositioning chin.

prenatal and post natal growth of mandible

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