develpoment of face and tongue
TRANSCRIPT
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