PRENATAL GROWTH OF CRANIOFACIAL STRUCTURES

Development of face and tongue

presented by roshni mauryadept. of pedodontics &preventive dentistry

INTRODUCTIONHuman embryology is the science that is concerned with prenatal development of man.

The new reproductive technologic revolution has sparked enormous advances in understanding cascade of reactions.

Embryology has been transformed as predictive science rather than descriptive earlier.

DEFINITION OF GROWTHQuantitative aspect of biologic development per unit of time-By Moyers

Change in any morphological parameter which is measurable-By Moss

Increase in size,change in proportion and progressive complexity-By Krogman

DEVELOPMENTRefers to all the naturally occuring unidirectional changes in the life of an individual from its existance as a single cell to its elaboration as a multifunctional unit terminating in death By Moyers

INITIAL EVENTS IN DEVELOPMENTAL PROCESS Zygote

Morula (16 celled)

Blastula(inner cell mass)

Implantation(attaches to endometrix)

Amniotic cavity(between embryoblast and trophoblast)

Bilaminar embryonic disc

Yolk sac

Chorionic sac

Germ layers

Primitive streak

The third weekPrimitive streak.Gastrulation.The notochordal process.Notochord.Neuralation.The neural crest cells.

Gastrulation It is process by which the bilaminar embryonic disc is converted into a trilaminar embryonic disc resulting in the formation of the three germ layers and the primitive streak.

Primitive streakIt is a thickened linear band of epiblast which appears caudally in the median plane and on the dorsal aspect of the embryonic disc.

Primitive node

Primitive pit

Primitive node

Germ layersMesoblast/Mesenchyme--mesodermPrimitive streak cell displace hypoblast -- endodermEpiblast -- ectoderm

Developing germ layers

Notochordal processSome mesenchymal cells migrate cranially from the primitive node to form a median cellular cord known as notochordal process

notochordal canal

The notochordal processprochordal plate

Notochordal canal

cloacal membrane

Formation of the notochordIt is a cellular rod that develops by transformation of notochordal process - defines the primitive axis of embryo - gives rigidity - future site of vertebral column

Formation of the notochord1. As notochordal process elongates ,notochordal canal extends cranially from primitive node to prochordal plate .

2. Floor of the notochordal process fuses with the underlying embryonic endoderm.

3. Fused region gradually undergo degeneration creating an opening.

Developing notochord

Formation of the notochord3 . The opening rapidly becomes confluent and notochordal canal disappears .4. Beginning at cranial end ,notochordal plate infolds to form notochord.5. The notochord finally detached from the embryonic endoderm.

NeuralationIt is process involved in the formation of the neural plate and neural folds and the closure of these folds to form the neural tube.

Neurla

Neural plate As the notochord develops ,embryonic ectoderm over it thickens to form the neural plate-neuroectoderm. Around the 18th day

Neural tube

The neural crestSome neuroectodermal cells lying along the crest of each neural fold lose their epithelial affinities and are called neural crest cells.These form an irregular flattened mass called neural crest

Characteristics of the neural crest cells Migration

Active Passive

Without the With the ectoderm ectoderm

Factors affecting migration Extra cellular molecules- such as fibronectin are encountered along the way of migration are used by Ncc to govern their path(Rovasio et.al.1983).Vitamin A slows the migration - acts as a teratogen

Factors affecting migrationDrugs-isotretenion(13-cis-retinoic acid)cause sever malformations by affecting the neural crest cell migration

Characteristics of the neural crest cellsRegulation- reffers to the ability of an embryo to compensate for the loss of cells .

Migration of the Ncc across the midline.By increase proliferation of the remaining Ncc.

Characteristics of the neural crest cellsCessation-refers to the property of the Ncc to cease the process of migration once they reach the site of future craniofacial structure.

Structure derived by the neural crest cellsConnective tissue- Ectomesenchyme of facial prominences and brachial arches. Bones and cartilages of facial and visceral skeleton. Dermis of face and neck. Stroma of salivary ,thymus ,thyroid, parathyroid and pituitary gland.

PRENATAL GROWTH & DEVELOPMENT OF NASOMAXILLARY COMPLEX

Pre-natal growth At fourth week of of IUL- 1.migration of neural crest cells 2.formation of branchial arches MAXILLARY FRONTONASAL STOMODEUM MANDIBULAR

MAXILLARYMANDIBULAR

Medial nasal processLateral nasal processMaxillary processMandibular process

Maxillary and Mandibular processes- { first brachial arch}

Frontonasal processes- { downward proliferation of mesenchyme of developing brain

AT SEVENTH WEEK IUL- 1.Formation of upper lip 2.Intramembranous Bone ossification Takes Place 3.Formation of Nasal Septum 4.Nasolacrimal Duct 5.Formation of Primary Palate

AT SEVENTH WEEK IULPrimary ossification center -for each maxilla at termination of infraorbital nerve above canine tooth dental lamina.

ZYGOMATIC ORBITONASALSecondary centre NASOPALATINE INTERMAXILLARY

AT EIGHT WEEK IULIntramembranous ossification centers appear for;-Nasal and lacrimal bones.-Medial pterygoid plate of sphenoid.-Vomer.-Zygomatic bone

BY TWELFTH WEEKAnteroposterior maxillo- mandibular relationship approaches that of newborn infant

Maxilla increases in height

FRIEBAND-[THE GROWTH OF PALATE IN HUMAN FETUS1st trimester-narrow2st trimester-moderate width3st trimester- wideBreadth>lengthHeight changes less dramatic

Pre-natal Growth and development of palateFormation of primary and secondary palate

Elevation of palatal shelves

Fusion of palatal shelves

Early palate formation28th day of IUL-disintegration of buccopharangeal membrane ORAL CAVITY -stomadeal chamber NASAL CAVITYHorizontol extensions 2 PALATAL SHELVES SINGLE PRIMARY PALAT

Structure of

Primary Palate Secondary Palate

PALATOGENESIS

5 week IUL 6 9 12 week IUL

Primary palate

Secondary palateMaxillary prominence 2HORIZONTAL MESENCHYMAL PROJECTION

LATERAL PALATINE PROCESS WITH EACH OTHER FUSE PRIMARY PALATE NASAL SEPTUM

SECONDARY PALATE

Secondary palate

PALATAL SHELVES

Elevation of palatal shelvesAt 6 weeks1. Tongue {undifferentiated tissue} pushes dorsallypalatal shelves become verticalElevation occurs from vertical to horizontal position

Elevation of palate

Nasal septumPalatal shelvestongue

Fusion of palatal shelves

Fusion of palate

Incisive foramenMid palatine raphe

Musculature of palateTensor veli palatini 40 days 1st archPalatopharangeous 45 days Levator veli palatini 8th week 2nd archPalatoglossus 9th week Uvular muscle 11th week 2nd arch

Growth in dimensions

Height Width

Length - 7-8 weeks IUL Width - 4th month onwardsArched palate

Factors affecting growth of palateelevation of head and lower jawOxygen and nutritional deficiencyExcess endocrine substancesDrugs Irradiationvascularity

ELEVATION OF HEAD AND LOWER JAW

ANOMALIES OF PALATE

Epithelial pearls

ANOMALIES OF PALATE

High arched palateMARFANS SYNDROMECROUZON SYNDROMECLEIDOCRANIAL DYSOSTOSIS

Cleft palateFailure of fusion of the lateral palatine process with each other or with the median palatine process

Genesis of cleft palateDelay in shelf elevationDisturbance in mechanism of shelf elevationFailure of shelves to contact due to lack of growthFailure to displace the tongue during closure [Pierre Robin syndrome]Failure to fuse after contact as epithelium does not break down

Rupture after fusion

defective merging

Types of cleft palate

Bifid uvulaUnilateral cleft palateBilateral cleft palate

Clinical features of cleft palateFeeding problems particularly in infants in whom suckling process demands intact palate

Nasal regurgitation/nasal twang in voice

Collapsed arch

Difficulty in speech and swallowing

DEVELOPMENT OF FACE Development of the head depends upon inductive activities of 2 organizing centers-- Prosencephalic-- Rhombencephalic

ORGANIZING CENTERS

Prosencephalic organizing center :-- Derived from prechordal mesoderm that migrates from the primitive streak.

-- Situated at the rostral end of the notochord below the fore brain.

Induces the formation of :

Visual apparatus Inner ear apparatus Upper third of face

Rhombencephalic organizing center : -- Caudal in relation to the Prosencephalic centre. Induces the formation of: -- Middle and lower third of the face. -- Middle and external ears.

Oral development in embryo is demarcated extremely early in life by the appearance of the prechordal plate (14th day) + Endodermal Thickening

Oropharyngeal Membrane

Oropharyngeal membrane is a temporary bilaminar membrane which functions as: 1. Site of junction of ectoderm and endoderm. 2. Demarcates the stomodeum from the rest. i.e. initial demarcation of the future mouth.

This differential rates of growth results in the formation of pear-shaped embryonic disc. -- Cranial/Head region forming the expanded portion of the pear. Further, the 3 germ layers show specific development by the middle of the 3rd week in the cranial portion as compared to 4-5 wks in the caudal portion.

The face derives from five prominences that surround a central depression, --The Stomodeum ( Future mouth)

Prominences: -- Single median Frontonasal -- Paired Maxillary + Mandibular

These placodes induced by the underlying olfactory nerves

Invaginate Demarcate the medial and lateral nasal prominences. Nasal pits Precursors to Anterior nares

Next, is the union of the facial prominences by either of the 2 below developmental events. 1. Merging of the frontonasal, maxillary and mandibular prominences. OR 2. Fusion of the central maxillonasal components.

Merging is completed as a result of proliferation of the underlying mesenchyme into the intervening grooves.

The above is guided by the disintegration of the contacting surface epithelium b/w the processes termed as Nasal fin

Midline merging of median nasal prominences forms : Philtrum of upper lipMedian tubercle.Tip of the nose.Primary palate.

Post. Merging of Medial nasal processes

Median primary palate

Premaxilla Future site of 4 upper incisors

Midline merging of the paired mandibular prominences

Lower jaw + Lower lip -- First to get definitely established

Lateral merging of maxillary and mandibular prominences.

Commisures of mouth

Specific structures : -- Nose -- Cheeks -- Lips -- Tongue

Nose : Complex structure with contributions from : -- Frontal prominence - Bridge -- Merged MNP - Median ridge + Tip -- Lateral nasal Prominence - Alae -- Cartilage nasal capsule - Septum + Nasal conchae

From frontonasal processFrom median nasal process

Lips : 1. Upper lip : As the maxillary, lateral and nasal processes fuse and the nares come close to each other the upper lip forms from the -- Maxillary process -- Frontanasal process

The mesodermal basis of lateral part

Maxillary process The mesodermal basis of median part Frontonasal process

The ectoderm of the max. process overgrow the philtrum to meet the opposite side.

Therefore the skin of the entire upper lip is formed by the maxillary process, and innervated by the maxillary nerves.

Cheeks : After the formation of the lips the maxillary and mandibular processes undergo progressive fusion to form the cheeks.

Tongue : Ant 2/3rd : -- Median triangular elevation in the floor of the primitive pharynx ant. to foramen caecum termed as Median tongue bed. ( Tuberculum Impar) -- Mesenchyme of the 1st arch give rise to 2 distal tongue beds on either side of median tongue bed.

Median and distal tongue beds rapidly increase in size and fuse together to form the ant.2/3rd of the tongue.

2 elevations copula and the hypobranchial eminence form the posterior 1/3rd of the tongue.

REFERENCESContemporary orthodontics- PROFFIT

Principles and practice of orthodontics GRABER

Essentials of facial growth- ENLOW

Craniofacial embryology- SPERBER

oral histology and embryology- TENCATE