Postnatal growth of mandible

detailed discussion of post natal growth of mandible.

1. Good Morning

2. Postnatal Growth
of
Mandible
Presented by
Dr SankhaNilayDas
PG 1
st
Year

3. Contents
Introduction
Anatomy
Functional Components
Principles of Growth
MandibularRemodeling
Anomalies of Development
Summary
Reference

4. The shape and size of the diminutive fetal
mandible undergo considerable transformation
during its growth and development. The
ascending ramusof the neonatal mandible is
low and wide, the coronoidprocess is relatively
large and projects well above the condyle, the
body is merely an open shell containing the
buds and partial crowns of the deciduous
teeth, and the mandibularcanal runs low in the
body
INTRODUCTION

5. Atbirththeramusisquiteshortbothinabsolutetermsandin
propostiontothemandibularcorpus.
Duringpostnataldevelopment,theramusbecomesmuch
moreprominent,particularlyinheightbutalsoinwidthasthe
musclesofmasticationbecomemoredeveloped.

6. Anatomy

12. FUNCTIONAL COMPONENTS
of
THE MANDIBLE

13. Eachoftheseanatomicalunitscanalsobe
consideredlogicallyintermsofaseriesofatleast
fiveoverlappingfunctionalunits.

14. mandibularcondyleis obviously most related to the
function of the TMJ. Variation in the function of the TMJ,
such as might occur in association with differences in
mastication, jaw movements and jaw position, for example,
is most likely to affect its growth and form.

15. Thegonialregionofthemandible,atthe
inferioraspectoftheramus,isrelatedtothe
masseterandmedialpterygoidcomplexofmuscles.

16. Thecoronoidprocess,attheanterosuperior
aspectoftheramus,isprimarilyrelatedtothe
temporalismuscle.Variationinthegrowthandformof
eachoftheseregionsisdueinlargeparttovariationin
thefunctionofthemusclesofmastication.

17. Thealveolarprocessofthemandiblefunctions
toprovideanchorageandsupportforthedentition.In
fact,thepresenceofalveolarboneinspecificlocalities
withinthemandible,asinthemaxilla,isdependent
completelyonthepresenceofanassociatedtooth.

18. Finally,thebodyofthemandible,extendingfromtheneck
ofthecondyletothechin,providesastructuralconnection
betweenthevariousfunctionalcomponentsofthemandible
Mandibleremodelsandissimultaneously"displaced“as
"forwardanddownward"movementproceedsfromthe
temporomandibularinterface.

19. Principles
Of
Growth

20. Drift
Displacement
V Principle
Counterpart Principle-Enlow
Remodeling
Rotation

21. Drift
All bones have one common growth principle, that is drift,
which was termed by Enlow(1963).
Drift is growth movement (relocation or shifting) of an
enlarging portion of a bone by the remodeling action of its
osteogenictissues

22. Displacement
Displacement is movement of the whole bone as a unit.
Primary Secondary
Bone moves from one position to
another not only because of
deposition and resorptionbut also
because of space created by
enlarging bones
Bone moves from one position to
another not because of deposition
and resorptionbut because of
surrounding physical forces

23. V Principle
A most useful and basic concept in facial growth is the V principle
Bone deposition occurs on the inner side of the V; resorption
takes place on the outside surface. The direction of movement
is toward the wide end of the V. Thus, a simultaneous growth
movement and enlargement proceeds by additions of bone on
the inside with removal from the outside.

24. Counterpart Principle-Enlow
According to Enlow, the growth activity in
one region is invariably accompanied by
complementary growth in other regions.
This complementary activity is essential for
maintaining functional and esthetic balance.
Enlowpointed out, both the dimensions and
alignment of the craniofacial components
are important in determining the overall
facial balance.

25. Segments a, b, and c are short with respect to their
segment counterparts in the other legs. Overall symmetry
is balanced, because of all these regional imbalances
offset one another, and the total length of each leg is,
therefore, the same.

26. (A) Mandible grows
downward and forward
if cranial base is taken
as reference
(B) Vital studies have
shown that the concept
B is correct and the
mandible grows
backwards and upwards

27. For example, if maxilla were rotated
down posteriorly, a long ramusand
acute gonialangle would compensate
and allow normal facial proportions,
but even a slightly short ramuswould
produce downward-backward
mandibularrotation and a long
face-open bite tendency.

28. Remodeling
Facialbonesundergoresizingandreshapingsimultaneousto
bonedepositionandresorption.Thereshapingofbone
occursnotduetogeneralizeddepositionandresorption.
Boneshapingrequiresdifferentialgrowthactivity,knownas
remodeling.Remodelingisapartofgrowthprocess,provides
regionalchangesinshape,dimensionsandproportions.

29. Types of Remodeling
There are four kinds of remodeling in bone tissues
Biochemical remodeling: this involves continuous
deposition and removal of ions to maintain mineral
homeostasis;
Growth remodeling: the constant replacement of bone
during childhood;
Haversianremodeling: the secondary process of cortical
reconstruction of bone as primarily vascular bone is
replaced
Pathological remodeling: regeneration and reconstruction
of bone during pathology or trauma.

30. GROWTHROTATIONS
Thereare2basiccategoriesofrotations
1)Remodelingrotations
2)Displacementrotations
Itisprimarilyremodelingoftheramusandnotthe
corpus,thatisresponsibleanditisacombination
ofremodelingfieldsthatcarriesoutthe
remodelingrotationoftheramus.

31. OCCLUSALCHANGESWITHMANDIBULAR GROWTHROTATIONS
Wherethereisananteriorgrowthrotation,andinthe
absenceofcompensatingtoothmovementsthelowerincisors
wouldbecomemoreretroclinedwithintheface.
However,dentoalveolaradaptationundertheinfluenceof
tongueandlipsresultsinalabialtippingoftheincisorssothat
theirinclinationtoreferencelineswithintheupperfacial
skeletonismoreorlessmaintained.
Fulladaptationtotherotationmaynotoccurbecauseof
contactwiththeupperincisorsandbecauseatthesametime
themandiblemaybegrowingforwardrelativetothemaxilla.

32. Mandibular
Remodeling

33. Mandibledoesnotgrowsimplybygeneralized
uniformdepositionofnewboneonalloutside
surfaceswithcorrespondingresorptionfromall
insidesurfaces.
Becauseofthetopographicallycomplexnatureof
eachbone'sshape,thebonemusthaveadifferential
modeofenlargement,inwhichsomeofitspartsand
areasgrowmuchfasterandtoamuchgreater
extentthanothers.

34. Themandibleappearsasasingleboneintheadult,itis
developmentallyandfunctionallydivisibleintoseveral
skeletalsubunits.Thebasalboneofthebodyformsone
unit,towhichareattachedthealveolar,coronoid,angular,
condylarprocessesandthechin.

35. The Ramus
The Lingual Tuberosity
The Ramus-to-Corpus Remodeling Conversion
The MandibularCondyle
The Adaptive Role of the Condyle
The Ramusand Middle Cranial FossaRelationship
RamusUprighting
The Human Chin
The Ramus-Corpus Combine

36. THERAMUS
Thekeyroleoftheramusinplacing
thecorpusanddentalarchinto
everchangingfitwiththegrowing
maxillaandtheface'slimitlessstructural
variations.
Thisisprovidedbycriticalremodeling
andadjustmentsinramusalignment,
verticallength,andanteroposterior
breadth.

37. Theprincipalvectorsofmandibular"growth"are
posteriorandsuperior.Theramusistherebyremodeled
inagenerallyposterosuperiormannerwhilethe
mandibleasawholebecomesdisplacedanteriorlyand
inferiorly,

38. THE LINGUAL TUBEROSITY
Thisisanimportant
structurebecauseitis
thedirectanatomic
equivalentofthe
maxillarytuberosity.

39. Yet, this structure is not even
included in the basic
vocabulary of cephalometrics.
The reason simply, is that it is
not recognizable in the
headfilm.

40. thispresentsaseverehandicapbecausethe
lingualtuberosityisnotonlyamajor
growthandremodelingsitebutitalsothe
effectiveboundarybetweenthetwobasic
partsofthemandible:theramusandthe
corpus.
The inaccessibility of the lingual tuberosity
for routine cephalometric study is a great
loss.

41. Thelingualtuberosityprotrudesnoticeablyinalingual
(medial)direction,andthatitlieswelltowardthemidline
fromtheramus.Theprominenceofthetuberosityis
augmentedbythepresenceofalargeresorptivefieldjust
belowit.Thisresorptivefieldproducesasizabledepression,
thelingualfossa.

42. Thecombinationofperiostealresorptioninthefossa
anddepositiononthemedial-facingsurfaceofthe
tuberosityitselfgreatlyaccentuatesthecontoursof
bothregions

43. The human basicraniumis notably
wide and thus also the bicondylar
dimension, and this calls for a key
remodeling movement to
accommodate
the more narrow arch

44. Theposteriorgrowthofthetuberosityisaccomplished
bycontinuednewdepositsofboneonitsposterior-
facingexposure.Asthistakesplace,thatpartofthe
ramusjustbehindthetuberosityremodelsmedially.

45. THE RAMUS-TO-CORPUS
REMODELING CONVERSION
The whole ramus is also becoming
relocated in a posterior direction at the
same time.
What has happened ?

46. Insummary,isthatbonyarchlengthhasbeen
increasedandthecorpushasbeenlengthened
by
(1)Depositsontheposteriorsurfaceofthelingual
tuberosityandthecontiguouslingualsideofthe
ramus
(2)Aresultantlingualshiftoftheanteriorpartof
theramustobecomeaddedtothecorpus.
The presence of resorption on the anterior
border of the ramus is often described as
"making room for the last molar."

47. The traditional description
of posterior ramus
movement implies a straight
line backward growth
process in a
two-dimensional plane

48. Thisisnotthecaseatall.Suchapictureoframus
growthshowssimply,resorptionontheanterior
edgeanddepositionontheposterioredge.
Developmentactuallytakesplaceasindicatedby
thisfigure.

49. Thegrowthdirectionfollowsthexarrows,ratherthan
thestraightlineaxisshownbythearrows.Aspointed
outabove,becausethebicondylardimensionis
establishedmuchearlierinchildhood,bilateralgrowth
separationbetweentherightandleftcondylesis
minimalbeyondtheearlychildhoodyears.

50. Thecoronoidprocesshasapropeller-liketwist,sothat
itslingualsidefacesthreegeneraldirectionsallatonce:
posteriorly,superiorly,andmedially.

51. Deposits of bone on the lingual side also
function to carry the base of the coronoid
process and the anterior part of the ramusin a
medial direction in order to add this part to the
lengthening corpus, which lies well medial to
the coronoidprocess.
This is an example of the V principle because a
wider part undergoes relocation into a more
narrow part as the whole V moves toward its
wide end.

52. Thus,theareaoccupiedbytheanteriorpartoftheearly
childhoodramusin1isrelocatedanditsformerlocation
becomesremodeledintotheposteriorpartofthecorpus
in2.

53. Thelowerpartoftheramusbelowthecoronoidprocess
alsohasatwistedcontour.
Itsbuccalsidefacesposteriorlytowardthedirectionof
backwardgrowthandthus,hasadepositorytypeof
surface.Theoppositelingualside,facingawayfromthe
directionofgrowth,isresorptive.

54. Asinglefieldofsurfaceresorptionispresentonthe
inferioredgeofthemandibleattheramus-corpus
junction.
Thisformstheantegonialnotchbyremodelingfrom
theramusjustbehinditastheramusrelocates
posteriorly.

55. Ramusdevelopmentofteninvolvesaremodelingrotationof
thewholeramus,andaresorptivefieldthenoccursonthe
posteriormarginbelowthecondyle.

56. The Mandibular Condyle it
is a major site of growth,
having considerable clinical
significance.
Historically,thecondylehas
beenregardedasakindof
cornucopiafromwhichthe
wholemandibleitselfpours
forth.
The MandibularCondyle

57. Duringmandibulardevelopment,thecondyle
functionsasaregionalfieldofgrowththat
providesanadaptationforitsownlocalized
growthcircumstances.
Cartilageisaspecialnon-vasculartissueandis
involvedbecausevariablelevelsofcompression
occuratitsarticularcontactwiththetemporal
boneofthebasicranium.Theintercellularmatrix
ofcartilageismarkedlyhydrophilicand
therefore,isturgidandunyieldingtosurface
pressure.

58. Anendochondralgrowthmechanismisrequiredfor
thispartofthemandiblebecausethecondyle
growsinadirectiontowarditsarticulationintothe
faceofdirectpressure.

59. Auniquecapsularlayerofpoorlyvascularizedconnective
tissuecoversthearticularsurfaceofthecondyle.This
membraneishighlycellularearlyindevelopment,but
becomesdenselyfibrouswithageandfunction.

60. The lingual and buccalsides of the neck
characteristically have resorptivesurfaces.
This is because the condyleis quite broad and the
neck is narrow. The neck is progressively relocated
into areas previously held by the much wider
condyle, and it is sequentially derived from the
condyleas the condylemoves in a superoposterior
course. What used to be condylein turn becomes
the neck as one is remodeled from the other
This is done by periostealresorptioncombined
with endostealdeposition.

62. THE CONDYLAR QUESTION
Agreatpuzzlewascreatedwhenitwaspointedoutthat
functionalmandiblestotallylackingcondylesexistinnature.
Thesebilaterallycondyle-lackingmandiblesoccupyan
essentiallynormalanatomicposition;thebonyarchis
properlyplacedforocclusion,andthemandiblefunctionsin
masticatorymovementseventhoughitlacksanarticulation.
Theserevealingobservationssuggestedtwoconclusions.
First,thecondylesmaynotplaythekingpinroleofa"master
center"pace-settingthegrowthprocessesintheotherparts
ofthemandible.Second,thewholemandiblecanbecome
displacedanteriorlyandinferiorlyintoitsfunctionalposition
withouta"push"againstthebasicranium.

63. The whole mandible is displaced
"away" from its articulation in
each glenoidfossaby the growth
enlargement of the composite
of soft tissues in the developing
face. As this occurs, the condyle
and ramusgrow upward and
backward (relocate) into the
"space" created by the
displacement process.

64. Theseobservationsledtoaconsiderationofthe
fabled"functionalmatrix".
Theideaisessentiallythatthemandibleiscarried
forwardanddownward,justasthemaxillais
presumablycarriedanteroinferiorlyinconjunction
withthegrowthexpansionofthesofttissuematrix
associatedwithit.
Itisapassivetypeofcarryinginwhichcondylar
remodelingactswithdisplacementasco-
participantsbutnotasthedrivingforce.They
proceedtogetherinmutualresponsetocommon
activatingsignals.

65. THEADAPTIVEROLEOFTHECONDYLE
Therandomarrangementofthecondylarprechondroblasts,
isincontrasttothelinearcolumnsofdaughtercells
associatedwiththeessentiallyunidirectionalgrowthoflong
bones.Thisisahistogeneticadaptationofthecondylar
cartilagethatprovidesopportunityforselected,
multidirectionalgrowthpotential.
Itistheadaptiveresponsivenatureofthecondylargrowth
processthatallowsforalatitudeofmorphologicand
morphogenicadjustmentsandaworkingfunctional
relationshipamongallofthem(Thevirtuallylimitlessrange
ofanatomicvariationsthatoccurinthestructuralpatterns
ofthenasomaxillarycomplexandbasicranium).

66. THE NEW IMAGE OF THE CONDYLE AND
"CONDYLAR GROWTH"
Itisdirectlyinvolvedasaunique,regionalgrowthsite;it
providesanindispensablelatitudeforadaptivegrowth;it
providesmovablearticulation;itispressuretolerantand
providesameansforbonegrowth(endochondral)ina
situationinwhichordinaryperiosteal(intramembranous)
growthwouldnotbepossible.
Withregardtothegrowthandadaptiverequirementsforthe
mandible,itisnotjustthecondyle,however,thatparticipates
asthekeycomponent.
Thewholeramusisdirectlyinvolved.

67. THE RAMUS AND MIDDLE CRANIAL FOSSA RELATIONSHIP
As the horizontal enlargement of the middle
cranial fossa and brain growth advance the
nasomaxillary complex by forward displacement,
the horizontal span of the pharynxcorrespondingly
increases.
The skeletal dimension of the pharynx is
established by the size of the middle cranial fossa
because the floor of this basicranial fossa is the
roof of the pharyngeal compartment.

68. Acorrespondinglygreateramountofmatchingresorptionon
theanteriorbordertakesplaceinferiorlythansuperiorly.A
"remodeling"rotationoframusalignmentthusoccurs.
Condylargrowthbecomesdirectedinamoreverticalcourse
alongwiththerestoftheramus.
RAMUSUPRIGHTING

69. In this schematic diagram, the
pharynx (and middle cranial fossa)
enlarges horizontally from a to a'.
The ramusenlarges,
correspondingly, from b to b' to
match it. It also lengthens
vertically, however. Angle c is
thereby reduced to c‘ in order to
accommodate the vertical
nasomaxillarygrowth also taking
place at the same time. The "gonial
angle" thus must undergo change
(close) in order to prevent change
in the occlusalrelationship
between the maxillary and
mandibulararches.

70. If mandible a is superimposedover b in the
anatomically functional position, it can be seen
that all the complex remodeling changes
outlined above serve simply to alter the ramus
angle without increasing its breadth.

71. Duringthedescentofthemaxillaryarchandtheverticaldrift
ofthemandibularteeth,theanteriormandibularteeth
simultaneouslydriftlinguallyandsuperiorly.
Thisproducesagreaterorlesseramountofanterioroverjet
andoverbite.Theremodelingprocessthatbringsthisabout
involvesperiostealresorptiononthelabialbonycortex(a),
depositiononthealveolarsurfaceofthelabialcortex(b),
resorptiononthealveolarsurfaceofthelingualcortex(c),and
depositiononthelingualsideofthelingualcortex(d).

72. THEHUMANCHIN
Thereisconsiderablevariationintheplacementofthe
reversallinebetweentheresorptivealveolarandthe
depositorypartsofthechin:itmaybefairlyhighorlow.
Variationsalsooccurintherelativeamountsofresorption
anddeposition.
Thereare,correspondingly,markedvariationsintheshape
andthesizeofthechinamongdifferentindividuals.Itisone
ofthemostvariable(butslow-growing)areasintheentire
mandibleasseenamongthedifferentbasicfacialtypesand
patterns.

73. THERAMUS-CORPUSCOMBINE
Mostoftheoutersurfacesofthemandibularcorpus
receiveprogressivedepositsofboneonbothits
buccalandlingualsides,withresorptionoccurring
fromtheendostealsurfaces.
Theabovechangesenlargethebreadthofthe
corpus;thebuccalsideremodels,toaslightly
greaterextentthanthelingualsidebecausebony
archwidthincreasesslightlyduringpostnatal
mandibulardevelopment,butnotasmuchasthe
bonymaxillaryarchincreasesinwidth.

74. Theadaptivetrajectoryofcondylargrowthisusuallyafactor,
asshownbya,b,andc.Variablegrowthdirectionsare
producedbyselectiveproliferationofprechondroblastsinsome
partsaroundtheperipheryofthecondyle,withretardationof
celldivisionsinotherparts.Thus,"condylargrowth"isan
activerespondentindevelopmentalfunctionthatcanadaptto
thewidelyvariableconditionsimposedonit.

75. A mandible characteristically has a less promjnentantegonial
notch if the angle between the ramusand corpus becomes closed,
and a much more prominent antegonialnotch (a) if it becomes
opened. The antegonialnotch itself is surface resorptivebecause it
is relocated posteriorly, as the corpus lengthens, into the former
gonialregion of the ramus.

76. Anomalies
of
Development

77. CLINICALIMPLICATIONS
IDEVELOPMENTAL ANAMOLIES
a)Agnathia:mandiblemaybegrosslydeficientor
absentwhichreflectsdeficiencyofneuralcrestcell
tissueinlowerpartoftheface.

78. b)Macrognathia, producing prognathism, is usually an
inherited condition, but abnormal-growth phenomena
such as hyperpituitarismmay produce mandibular
overgrowth of increasing severity with age

79. c)Micrognathia-adiminutivemandible,occursin
i)PierreRobin'ssyndromeii)Catcrysyndromeiii)
Mandibulofacialdysostosisiv)Progeriav)Down's
syndromevi)Occulomandibulodycephalyvii)
Turner'ssyndrome

80. PierreRobin'ssyndrome-theunderdevelopedmandible
demonstratescatchupgrowthinthechild.
Firstarchandsecondarchsyndrome-aplasiaofmandible
andhyoidbone.

81. Mandibulofacialdysostosis-itisaconditioninwhichboth
maxillaandmandibleareunderdevelopedasaresultof
generalizedlackofmesenchymaltissueandalsodueto
diminishedneuralcrestcellmigration.
Hemifacialmicrosomia(Goldehar'ssyndrome)-thisisa
conditionwhichisunilateralandischaracterizedbylackof
tissueontheaffectedside.
Inthisconditiontypically,theexternalearisdeformedand
ramusofmandibleandassociatedsofttissuearedeficientor
missing.Thisarisesfromearlylossofneuralcrestcells.

82. IIDEFECTSDUETOFAILUREOFFUSIONOF
THEVARIOUSPROCESSES:
Mandibularcleft-Rareconditionduetopersistenceoffurrow
betweenmandibularprocess.
Microstomia/Macrostomia-determinedbyfusionofmaxillary
andmandibularprocessattheirlateralextent

83. III.Muscledysfunction
Facialmusclescanaffectthejawgrowthintwoways:
i)Formationofboneatthepointofmuscleattachmentsdepends
onthemuscleactivity.
ii)Themusculatureisanimportantpartoftotalsofttissuematrix
whosegrowthnormallycarriesthejawsdownwardandforward.
Lossofpartofthemusculatureasaresultofmotornerve
damage-resultsinunderdevelopmentofthatpartofface.

84. MandibularHypertrophy
1)Acromegaly-ananteriorpituitarytumorthatsecrets
excessiveamountsofgrowthhormone,excessivegrow,hof
mandiblemayoccurcreatingskeletalclassIIImalocclusionin
adultlife.

85. 2)Hemimandibularhypertrophy-unilateralexcessivegrowth
ofmandibleoccursandpreviouslyitwasascondylar
hyperplasiaascondylarproliferationisaprominentaspect.
Theexcessivegrowthmaystopspontaneouslybutinsevere
casesmayrequireremovalofaffectedcondyle.Condylar
hyperplasiacausesmandibularandfacialasymmetry.

86. ASYMMETRIC MANDIBULAR DEFICIENCY
Itislikelytoresultifmandibularcondylesareaffectedby
eitheracongenitalconditionorbirthinjury.
Inhemifacialmicrosomiathereisabsenceoftissueinthe
regionofmandibularcondyleandinmoreseverecases
entiredistalportionofmandiblemaybemissingalongwith
associatedsofttissues.
Inhemifacialmicrosomiatheproblemislackoftissue,so
normalgrowthpotentialisnotpresentwhereasinpostinjury
problemsthereispotentialfornormalgrowth.

87. Summary
Asignificantpointisthatclinicalmanipulationof
theramusiseffectiveonlysolongasitisactively
engagedinmandibulargrowth.Thereafter,howto
unlockitsresponsiveremodelingcapacityis
poorlyunderstood,sinceadevelopmental
''balance''haslongsincebeenachievedwiththe
vertical,anteroposteriorand bilateral
relationshipswiththebasicranium,airway,
nasomaxillarycomplex,dentition,tongue,andthe
masticatoryandhyoidmusculature.

88. References
1.Essential of facial growth –DONALD H. ENLOW
2.Craniofacial Growth –Sridhar Premkumar
3.Craniofacial development –SPERBER
4.Growth of the craniofacial skeleton –MOYERS
5.Contemporary orthodontics –WILLIAM R. PROFFIT

89. Thank You