PREPARED BYPREPARED BY::ANJUCHANDRANANJUCHANDRANFINAL YEAR FINAL YEAR

PART1PART1

INTRODUCTIONINTRODUCTION

Mandible is the largest of the Mandible is the largest of the facial bones and is the only facial bones and is the only movablemovable bone in the bone in the craniofacial regioncraniofacial region

It undergoes theIt undergoes the largest largest amount of growth amount of growth postnatally and also exhibits postnatally and also exhibits the largest the largest variabilityvariability in in morphologymorphology

Mandible consists of the Mandible consists of the following microskeletal unitsfollowing microskeletal units

►BodyBody►RamusRamus►CondyleCondyle►Coronoid processCoronoid process►Angular processAngular process►Lingual Lingual

tuberositytuberosity►Alveolar processAlveolar process►ChinChin

GROWTH OF MANDIBLEGROWTH OF MANDIBLE

PRENATAL GOWTHPRENATAL GOWTH

POSTNATAL GROWTHPOSTNATAL GROWTH

PRENATAL GROWTHPRENATAL GROWTH 11stst structure to develop in the structure to develop in the

primordium of lower jaw :primordium of lower jaw :MandibularMandibular division of division of trigeminal nerve.trigeminal nerve.

Prior presence of nerve induce Prior presence of nerve induce osteogenesisosteogenesis by production of by production of neurotrophic neurotrophic factors factors

► The ossification of an osteogenic membrane The ossification of an osteogenic membrane formed at around 36-38 days of IU life.formed at around 36-38 days of IU life.

► A single ossification centre for each half of A single ossification centre for each half of mandible arises in the 6mandible arises in the 6thth week of IU life. week of IU life.

► Marked acceleration of growth b/w 8Marked acceleration of growth b/w 8thth &12 &12thth week of foetal life.week of foetal life.

► The resulting intramembraneous bone lies The resulting intramembraneous bone lies lateral to Meckel’s Cartilage of 1lateral to Meckel’s Cartilage of 1stst arch. arch.

►Growth continues around the Growth continues around the meckel’s cartilage until its posterior meckel’s cartilage until its posterior aspect is covered by bone.aspect is covered by bone.

►Ossification stops at this point which Ossification stops at this point which later becomes mandibular lingula.later becomes mandibular lingula.

Mandible at 36Mandible at 36thth week week of IU lifeof IU life

POSTNATAL POSTNATAL GROWTHGROWTH

► Completes by Completes by 2020 yrs of age. yrs of age.

► 3 PERIODS OF GROWTH;3 PERIODS OF GROWTH;Infancy[1Infancy[1stst year of life] year of life]

Childhood[1-13 yrs]Childhood[1-13 yrs]

Adolescence[13-20yrs]Adolescence[13-20yrs]

##Postnatal growth is is the first 20 yearsPostnatal growth is is the first 20 years of of growth after birth. It has three growth after birth. It has three periods : Infancy(1periods : Infancy(1stst year of life) year of life)

childhood (1-13 years) and adolescence childhood (1-13 years) and adolescence (13-20 years) (13-20 years)

#Postnatal growth results in the #Postnatal growth results in the

metamorphosis of the rudimentary metamorphosis of the rudimentary structure structure

seen at birth to the full-fledged and seen at birth to the full-fledged and multifunctional adult formmultifunctional adult form

#At birth, mandible is composed of two #At birth, mandible is composed of two small U shaped bars, separated by a thin small U shaped bars, separated by a thin

line of fibrocartilage and connective line of fibrocartilage and connective tissue at the midline of symphysis,rami tissue at the midline of symphysis,rami are quite short,condylar development is are quite short,condylar development is

minimal and there is practically no minimal and there is practically no articular eminencearticular eminence

Pattern of Pattern of growthgrowth►SCAMMON’S GROWTH CURVESCAMMON’S GROWTH CURVE

Birth 10 Years 20 Years

100%

200% Lymphoid

Neural

Maxillary

Mandibular

General

Genital

Cephalo caudal Cephalo caudal gradient of growthgradient of growth

►Axis of increased growth from head Axis of increased growth from head towards mandible.towards mandible.

►Explains why mandible grows more Explains why mandible grows more than maxilla.than maxilla.

Concept of mandibular Concept of mandibular growthgrowth

►11stst concept- cranium reference point & concept- cranium reference point & chin moves downwards & forwards.chin moves downwards & forwards.

►Vital staining experiments-posterior Vital staining experiments-posterior ramus ,cornoid & condyle as growth ramus ,cornoid & condyle as growth sites.sites.

►Correct concept- mandible is translated Correct concept- mandible is translated downward n forward&in response to this downward n forward&in response to this it grows upward & backward to maintain it grows upward & backward to maintain contact with skullcontact with skull

How postnatal growth How postnatal growth occurs?occurs?

► Explained by;Explained by;

1.1. Theories of growth Theories of growth

2.2. Growth rotationsGrowth rotations

Genetic theory Genetic theory

► Intrinsic genetic Intrinsic genetic stimulus in bone stimulus in bone cause mandibular cause mandibular growth.growth.

► Inheritance of jaw Inheritance of jaw shape from parents.shape from parents.

► HAPSBURG JAW the HAPSBURG JAW the prognathic mandible prognathic mandible of german royal familyof german royal family

Cartilagenous theoryCartilagenous theory►By SICHER & WIENMANNBy SICHER & WIENMANN

►Visualize mandible as diaphysis of long Visualize mandible as diaphysis of long

bone bent into horse shoe shapebone bent into horse shoe shape with with epiphysis removed with condyles epiphysis removed with condyles representing epiphseal plates.representing epiphseal plates.

► Condylar cartilage as Condylar cartilage as Growth Centre.Growth Centre.

►Transplantation experiments proved Transplantation experiments proved condyles condyles

dosent have innate growth potential.dosent have innate growth potential.

►Thus condylar growth is regional Thus condylar growth is regional adaptive growth.adaptive growth.

►Hence CONDYLE as Hence CONDYLE as growth site not growth site not centre.centre.

►SECONDARY OR FILL IN RESPONSESECONDARY OR FILL IN RESPONSE

FUNCTIONAL MATRIX THEORYFUNCTIONAL MATRIX THEORY

► Niether bone nor cartilage as growth Niether bone nor cartilage as growth determinents.determinents.

► Mandible grows in response to functional Mandible grows in response to functional needs & is mediated by soft tissue needs & is mediated by soft tissue surrounding.surrounding.

► Endochondral growth at condyles and Endochondral growth at condyles and appositional at other surfaces is in response appositional at other surfaces is in response to growth of adjacent muscles & expansion to growth of adjacent muscles & expansion of orofacial capsule causing mandible to of orofacial capsule causing mandible to translate in space. translate in space.

E XPANDING‘V’ PRINCIPLEE XPANDING‘V’ PRINCIPLE

RAMUSRAMUS► It moves more posteriorly by It moves more posteriorly by

combination of deposition and combination of deposition and resorption:resorption:

► resorption at anterior border resorption at anterior border ► deposition at posterior border deposition at posterior border

On growing the two rami also diverges On growing the two rami also diverges outward from below to above thus outward from below to above thus increasing the superior inter-ramus increasing the superior inter-ramus distance;creating a ‘V’ SHAPE. Hence distance;creating a ‘V’ SHAPE. Hence mandibular growth can also be mandibular growth can also be explained with ENLOW’S EXPANDING explained with ENLOW’S EXPANDING “V” PRINCIPLE.“V” PRINCIPLE.

EXPANDING ‘V’EXPANDING ‘V’

CORPUS / BODY OF THE MANDIBLECORPUS / BODY OF THE MANDIBLE

►Body lengthens by conversion of the Body lengthens by conversion of the former ramal bone into its posterior former ramal bone into its posterior partpart

►Deposition at the posterior surface of Deposition at the posterior surface of lingual tuberosity and contiguous lingual tuberosity and contiguous lingual side of the ramus also lingual side of the ramus also account for a small increase in the account for a small increase in the length of the bodylength of the body

►Deposition occurs also at the outer Deposition occurs also at the outer surface of the body and also around surface of the body and also around the mandibular canalthe mandibular canal

THE CORONOID PROCESSTHE CORONOID PROCESS►Growth at coronoid is best explained using Growth at coronoid is best explained using

the expanding V principlethe expanding V principle

► Condyle has a “propeller - like – twist “,o its Condyle has a “propeller - like – twist “,o its

lingual side faces 3 general directions all at lingual side faces 3 general directions all at once : posteriorly , superiorly and mediallyonce : posteriorly , superiorly and medially

►Deposition at lingual surface results in a Deposition at lingual surface results in a superior growth movement because the superior growth movement because the surface faces superiorly. Deposition also surface faces superiorly. Deposition also carries the base of coronoid and anterior carries the base of coronoid and anterior part of ramus mediallypart of ramus medially

►Since the lingual surface also faces Since the lingual surface also faces

posteriorly, deposition t this surface posteriorly, deposition t this surface brings about a posteriorly directed brings about a posteriorly directed growth movementgrowth movement

►Buccal side has a resorptive surface an Buccal side has a resorptive surface an faces away from the medial , superior faces away from the medial , superior and posterior directions of growthand posterior directions of growth

►Sigmoid notch grows superiorly by Sigmoid notch grows superiorly by deposition on the lingual side and deposition on the lingual side and resorption from the buccal sideresorption from the buccal side

ANGLE OF THE MANDIBLEANGLE OF THE MANDIBLE

►Lingual side :Lingual side :

deposition - anterosuperiordeposition - anterosuperior

resorption - posteroinferior resorption - posteroinferior

►Buccal side : Buccal side :

deposition - posteroinferior deposition - posteroinferior

resorption - anterosuperior resorption - anterosuperior

►As a result , angle flares out as age As a result , angle flares out as age advances advances

LINGUAL TUBEROSITYLINGUAL TUBEROSITY

A major growth site of mandibleA major growth site of mandible

Deposition at the posterior facing surface Deposition at the posterior facing surface with a resultant posterior growth with a resultant posterior growth movement .This also helps in lengthening movement .This also helps in lengthening of the bodyof the body

► It grows more prominent by It grows more prominent by deposition at the medial surfacedeposition at the medial surface

►The prominence is accentuated by a The prominence is accentuated by a large resorptive field just below itlarge resorptive field just below it

►The resorptive field produces a The resorptive field produces a depression called lingual fossadepression called lingual fossa

THE ALVEOLAR PROCESSTHE ALVEOLAR PROCESS

►Alveolar process develops in response Alveolar process develops in response to the presence of tooth budsto the presence of tooth buds

► As teeth erupt , the process grows in As teeth erupt , the process grows in height by deposition at the marginsheight by deposition at the margins

► It grows in an upward and outward It grows in an upward and outward

direction to accommodate the larger direction to accommodate the larger permanent teethpermanent teeth

THE CHINTHE CHIN

►Chin is a specific human characteristic and is Chin is a specific human characteristic and is the most recent phylogenic acquisitionthe most recent phylogenic acquisition

► Influenced by sexual and specific genetic Influenced by sexual and specific genetic factorsfactors

► Is more prominent in malesIs more prominent in males

►Mental protuberance forms by bony Mental protuberance forms by bony deposition during childhood The prominence deposition during childhood The prominence is accentuated by resorption in the alveolar is accentuated by resorption in the alveolar region above itregion above it

GROWTH ROTATIONSGROWTH ROTATIONS► Two types of growth rotations:Two types of growth rotations: Internal rotationInternal rotation External rotationExternal rotationInternal rotation: rotation taking place at the core of Internal rotation: rotation taking place at the core of It is of two types:It is of two types: Matrix rotation : rotation of the core around theMatrix rotation : rotation of the core around the condyle. It accounts for 25% of total condyle. It accounts for 25% of total internal rotationinternal rotationIntramatrix rotation: rotation centered within the Intramatrix rotation: rotation centered within the body of mandible. It accounts for body of mandible. It accounts for 75% of total internal rotation75% of total internal rotation

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►External rotation : It is the rotation External rotation : It is the rotation brought about by surface changes and brought about by surface changes and alterations in the rate of tooth eruptionalterations in the rate of tooth eruption

►External rotation is opposite to internal External rotation is opposite to internal rotation androtation and

tends to mask it. tends to mask it.

► Internal rotation tends to decrease the Internal rotation tends to decrease the

mandibular plane angle i.e. , up mandibular plane angle i.e. , up anteriorly and down posteriorly and is anteriorly and down posteriorly and is given a negative signgiven a negative sign

► Total internTotal intern00al rotation will be between al rotation will be between ► -10-1000to -15to -1500

►External rotation is designated by a External rotation is designated by a positive sign positive sign

► Total external rotation will be between Total external rotation will be between ► +10+1000 to + 12 to + 1200

► Net rotation : -2Net rotation : -20 0 to -4 to -400

CLINICAL RELEVANCECLINICAL RELEVANCE

►ACROMEGALY CHINCAPACROMEGALY CHINCAP

ANCHORAGE ANCHORAGE DISTRACTION OSTEOGENESISDISTRACTION OSTEOGENESIS

CONCLUSIONCONCLUSION

A knowledge of the normal growth pattern A knowledge of the normal growth pattern helps in identifying normal variations in helps in identifying normal variations in growth , any variation from norm and growth , any variation from norm and

also in growth prediction .It also helps in also in growth prediction .It also helps in the planning and evaluation of the planning and evaluation of

orthodontic treatment orthodontic treatment

REFERENCES REFERENCES 1.1. Orthodontics – Principles and Practice Orthodontics – Principles and Practice

Graber TM Graber TM

2.2. contemporary orthodontics contemporary orthodontics Proffit Proffit

3.3. essentials of facial growth essentials of facial growth Enlow & Hans Enlow & Hans

4.4. Orthodontics –The Art and Science Orthodontics –The Art and Science BhalajhiBhalajhi

5.5. Textbook of orthodontics – Gurukeerat Textbook of orthodontics – Gurukeerat SinghSingh