Facial and Palatal Development

FacialFacial andand palatalpalatal developmentdevelopment

L.MossL.Moss--SalentijnSalentijn TimelineTimeline forfor developmentdevelopment

Secondary palate Completion of soft palate

Primary palate

External face Pharyngeal arches

4 wks 6 wks 8 wks 12 wks

Decrease of severity of potential congenital malformations ContributionsContributions toto thethe externalexternal faceface

„ PeriprosencephalonPeriprosencephalon:: ectodermectoderm andand mostlymostly ncnc-- derivedderived mesenchymemesenchyme surroundingsurrounding thethe forebrain.forebrain. FrontonasalFrontonasal process.process. „ FirstFirst pharyngealpharyngeal ((mandibularmandibular)) arch.arch. MandibularMandibular andand maxillarymaxillary processes.processes. ContributionsContributions toto externalexternal faceface OropharyngealOropharyngeal membranemembrane ((buccopharyngealbuccopharyngeal,, oral)oral)

MembraneMembrane isis composedcomposed ofof ectodermectoderm andand endodermendoderm DisintegrationDisintegration ofof oropharyngealoropharyngeal membranemembrane

CommunicationCommunication betweenbetween foregutforegut andand amnioticamniotic cavitycavity atat approximatelyapproximately 44 weeksweeks ofof developmentdevelopment StomodeumStomodeum atat 44 weeksweeks FacialFacial processesprocesses (prominences)(prominences)

Bilaterally:Bilaterally: LateralLateral nasalnasal MedialMedial nasalnasal MaxillaryMaxillary MandibularMandibular DevelopmentDevelopment externalexternal faceface (4(4--55 wks)wks) DevelopmentDevelopment externalexternal faceface (6(6--88 wks)wks) Gasser R (2006) FaceFace developmentdevelopment animationanimation 11 DimensionalDimensional changeschanges (4(4--66 wks)wks) 1010--foldfold linearlinear increaseincrease inin sizesize !! FaceFace developmentdevelopment –– animationanimation 22 MergingMerging

DifferentialDifferential mesenchymalmesenchymal proliferation.proliferation. EliminationElimination ofof groove.groove. MergingMerging withwith epithelialepithelial inclusioninclusion

MayMay resultresult inin facialfacial cleft.cleft.

MayMay bebe normalnormal betweenbetween LNPLNP andand maxillarymaxillary processprocess wherewhere enclosedenclosed epitheliumepithelium givesgives riserise toto partpart ofof nasolacrimalnasolacrimal ductduct epithelium.epithelium. Nasolacrimal duct between maxillary and lateral nasal processes SitesSites ofof potentialpotential facialfacial cleftsclefts FusionFusion

ContactContact andand fusionfusion ofof epitheliumepithelium-- coveredcovered surfaces.surfaces. RemovalRemoval ofof epitheliumepithelium FusionFusion inin primaryprimary andand secondarysecondary palatepalate developmentdevelopment FateFate ofof fusedfused epitheliumepithelium

„„ NonNon--proliferatingproliferating epitheliumepithelium inin rapidlyrapidly growinggrowing environment:environment: passivepassive stretchstretch andand incorporationincorporation inin nearbynearby surfacesurface epitheliaepithelia „„ ApoptosisApoptosis andand phagocytosisphagocytosis „„ EpithelialEpithelial--mesenchymalmesenchymal transformationtransformation DevelopmentDevelopment ofof nosenose InitialInitial fusionfusion ofof medialmedial andand laterallateral nasalnasal processes,processes, andand subsequentlysubsequently betweenbetween medialmedial nasalnasal andand maxillarymaxillary processes.processes. AllAll epitheliumepithelium inin fusionfusion lineline isis removedremoved exceptexcept oronasaloronasal membranemembrane (ectoderm(ectoderm--ectoderm)ectoderm)

OronasalOronasal membranemembrane

BreaksBreaks downdown atat aboutabout 66 wkswks ofof development.development. PrimaryPrimary (primitive)(primitive) palatepalate

Primary palate composed of: intermaxillary segment of merged MNP’s and the rostral tips of the maxillary processes. P: primary (primitive) choana permitting oro-nasal communication DevelopmentDevelopment ofof primaryprimary andand secondarysecondary palatepalate

SecondarySecondary palatepalate developmentdevelopment IntrinsicIntrinsic factorsfactors inin thethe successfulsuccessful developmentdevelopment ofof thethe secondarysecondary palate:palate: increaseincrease inin sizesize ofof palatalpalatal processesprocesses

„ MesenchymalMesenchymal cellcell proliferationproliferation –– ceasesceases hourshours beforebefore palatalpalatal processesprocesses becomebecome horizontalhorizontal „ ECMECM productionproduction increasingincreasing volumevolume ofof palatalpalatal processesprocesses „ HydrationHydration ofof ECMECM –– majormajor increaseincrease inin volumevolume andand turgorturgor justjust priorprior toto horizontalizationhorizontalization SecondarySecondary palatepalate developmentdevelopment

Palatal processes develop on the oral surfaces of the maxillary processes: initially vertically oriented, they assume horizontal orientation during eighth week of development. HorizontalizationHorizontalization ofof palatalpalatal processesprocesses FactorsFactors contributingcontributing toto thethe horizontalizationhorizontalization ofof thethe palatalpalatal processesprocesses „ TurgorTurgor inin thethe palatalpalatal processesprocesses „ MovementsMovements ofof thethe tonguetongue –– primitiveprimitive swallowingswallowing-- allowingallowing tonguetongue toto movemove outout ofof thethe wayway „ DownwardDownward andand forwardforward growthgrowth ofof lowerlower jawjaw complexcomplex –– providingproviding spacespace forfor thethe secondarysecondary palatepalate „ StraighteningStraightening ofof thethe cranialcranial basebase –– providingproviding mechanicalmechanical conditionsconditions forfor horizontalizationhorizontalization

FactorsFactors contributingcontributing toto thethe successfulsuccessful fusionfusion ofof thethe secondarysecondary palate:palate: thethe medialmedial edgeedge epitheliumepithelium (MEE)(MEE)

„ ApoptosisApoptosis ofof MEEMEE surfacesurface cellscells immediatelyimmediately priorprior toto fusionfusion „ DevelopmentDevelopment ofof temporarytemporary glycoproteinglycoprotein membranemembrane coating,coating, enablingenabling adhesionadhesion betweenbetween MEEMEE cellscells ofof opposingopposing palatalpalatal processesprocesses „ SuccessfulSuccessful removalremoval ofof MEEMEE fromfrom fusionfusion lineline Fate of MEE cells: apoptosis (TUNEL reaction above) and phagocytosis CompletionCompletion ofof palatepalate formationformation SitesSites ofof potentialpotential palatalpalatal cleftsclefts