Development of Face &It's Applied Aspects

CONTENTS

1. INTRODUCTION : a) development b) growth2.CLASSIFICATION OF GROWTH3.FATE OF GERM LAYERS

4.CEPHALOCAUDIAL GRADIENT OF GROWTH

5.DEVELOPMENT OF FACE

6. DEVELOPMENT OF VARIOUS PARTS OF FACE:

A) LOWER LIP B)MANDIBLE C)UPPER LIP & MAXILLA D)EYES E)NOSE & NASAL CAVITIES F)EAR 7.APPLIED ASPECTS 8.CONCLUSION 9. REFERENCES

INTRODUCTION

Face forms an important part of the human body .It not only has functional role but also has immense psychological impact on one’s self esteem. Hence a deep understanding of the development of face & its associated anomalies is important for us as a medical professional.

Human eyes are highly sensitive in discerning minimal differences in the structure of human faces and in distinguishing persons. Discerning eyes can also detect many facial anomalies associated with systemic congenital anomalies. A classification of these facial anomalies based on embryological basis is helpful for understanding the morphogenesis of each anomaly.

The moment the human embryo is fertilized to the week of the baby’s birth is an important period for human appearance in the normally developing embryo. During preimplantation stages, differentiation occurs for precursors of embryonic. A fore-hind axis begins within the inner cell mass at the time of implantation. By the end of the eighth week of gestation, the appearance of the head, face, hands, and feet suggest the embryo’s species but is not yet definitive.

GROWTH & DEVELOPMENT

There are two aspects regarding the growth of an individual:

1. DEVELOPMENT

2. GROWTH

WHAT IS GROWTH?

“Developmental increase in mass.’’- Stewart.(1982)

“An increase in size or number.” - Profitt. (1986)

“Normal changes in amount of living substance.’’- Moyers(1988)

“Growth signifies an increase, expansion or extension of any given tissue.” - Pinkham.(1994)

WHAT IS DEVELOPMENT? There are many definitions of

development ;the commonly followed are:

“Development is a progress towards

maturity” – Todd(1931)

“Development connotes a maturational

process involving progressive

differentiation at the cellular and tissue

levels” – Enlow.

CLASSIFICATION OF GROWTH:

a. Prenatal growth

1. Period of ovum: From time of fertilization till 1 week.

2. Period of embryo: from 2nd week till 8th week

3. Period of foetus: from 9th week onwards till birth

b. Postnatal growth

c. Maturity

d .Old age

PRENATAL GROWTH The fertilized ovum,

undergoes cleavage as it moves toward the uterine cavity.

The cells formed are called blastomeres, which soon begin to rearrange themselves in order to differentiate into various groups and layers.

By the 4th day, when the zygote reaches the uterus, it is a many celled mass called a MORULA

DIVISION OF FERTILIZED OVUM

MORULA

As the cell mass divides, it enlarges and gains a fluid filled cavity termed the blastocoele(5th day).

The blastocoele separates the cell into 2 parts:

-An outer cell layer, the trophoblast, and

-An inner cell mass, the embryoblast.

BLASTOCOELE

IMPLANTATION : 6TH DAY The trophoblast

attaches to the sticky endometrial surface on the posterior wall of the body of the uterus.

The surface cells of the trophoblast produces enzymes that digest the uterine endometrial cells, which allows a deeper penetration of the cell mass.

IMPLANTATION

During the second week, the cells of the inner cell mass of the growing blastocoele differentiate into 2 cell types:

1.Columnar shaped ectodermal cells and

2.Cuboidal shaped endodermal cells adjacent to blastocele.

The amniotic cavity appears between the ectodermal cells and the overlying trophoblast.

Later in the developmental process, the amnion expands, filling the entire extra embryonic coelom .

Thus in its final form, the amnion is a free membrane enclosing a fluid-filled space around the embryo.

Again, cells grow from the trophoblast and the embryonic disc, to form a primitive yolk sac.

On day 15, a groove, called the primitive streak , appears on the surface of the midline of the dorsal aspect of the ectoderm of the embryonic disc.

By day 16, a primitive knot of cells, the Henson’s node, appears at the cephalic end of the primitive streak.

This knot gives rise to the cells that form the notochordal process.

PRIMITIVE STREAK

Cells from the primitive streak and the notochordal process migrate laterally between the ectodermal and endodermal layers of the embryonic shield.

These cells form the third germ cell layer called the mesodermal layer.

By the end of the third week, the mesoderm migrates in a lateral direction between the ectoderm and the endoderm, except at the anterior prochordal plate and posterior cloacal membrane.

PROCHORDAL PLATE

The anterior plate forms the future oropharyngeal membrane.

Finally, mesodermal cells of the embryonic disc migrate peripherally to join the extra-embryonic mesoderm on the amnion and yolk sac.

Anteriorly, mesodermal cells pass on either side of the prochordal plate to meet each other in front of this region.

FATE OF GERM LAYERS Ectodermal cells will give rise to the nervous

system; the epidermis and its appendages (hair, nails, sebaceous and sweat glands); the epithelium lining the oral cavity, nasal cavities and sinuses; a part of the intraoral glands, and the enamel of the teeth.

Endodermal cells will form the epithelial lining of the gastrointestinal tract and all associated organs.

The mesoderm will give rise to the muscles and all the structures derived from the connective tissue(e.g., bone, cartilage, blood, dentin, pulp, cementum and the periodontal ligament).

The embryonic disc will soon become altered by bends and folds necessary for further development.

CEPHALOCAUDAL GRADIENTOF GROWTH

This means that there is an axis of increased growth extending from the head towards the feet.

At about 3rd month of IU life, the head takes up 50% of total body length. By the time of birth, the proportion of head decreases to 30%.

This proportion steadily declines till in adult, the proportion of head is only 12%.

DEVELOPMENT OF FACE:The primitive

oral cavity or stomatodaeum appears late in the third prenatal week as a pit or invagination of the tissues underlying the forebrain.

STOMODEUM

This invagination appears as a result of the growth of the forebrain anteriorly and of the enlargement of the developing heart.

At the deepest end of the stomatodaeum, the oral ectoderm lies in close contact with the foregut endoderm.

The wall between the oral and pharyngeal cavity is termed the oropharyngeal membrane, as it separates the stomatodaeum from the first part of the foregut.

During the fourth week of intrauterine life, the oropharyngeal membrane disintegrates to establish continuity between the two cavities.

Soon, mesoderm covering the developing forebrain proliferates& forms a downward projection that overlaps the upper part of stomatodaeum called as FRONTO NASAL PROCESS.

PHARYNGEAL ARCHES are laid down in lateral & ventral walls of the most cranial part of the foregut.

Thus face is derived from: 1. FRONTONASAL PROCESS

2. FIRST PHARYNGEAL ARCH (MANDIBULAR ARCH OF EACH SIDE)

3.MANDIBULAR ARCH GIVES OFF A BUD FROM ITS DORSAL END WHICH IS CALLED AS MAXILLARY PROCESS(it grows ventro-medially cranial to the main part of the arch)

The mandibular arch is the first to develop. It is located just below the stomatodeum.

4.Ectoderm overlying the frontonasal process then shows bilateral localized thickenings called as NASAL PLACODES during 5th week IU(their formation is induced by underlying forebrain)

5.Placodes then sink below the surface to form NASAL PITS

6.Edges of each pit are raised above the surface forming MEDIAL NASAL PROCESS & LATERAL NASAL PROCESS during 6th week IU

On each side, the lateral nasal process is separated from the maxillary process by a groove called the nasolacrimal groove.

This groove will eventually disappear , but before it disappears, the epithelium at its depth will canalise , and form the nasolacrimal duct

PHARYNGEAL POUCHESThe endodermal epithelium of the

pharyngeal pouches differentiate into a variety of important organs.

From the 1st pouch ,the middle ear and the Eustachian tube develop.

From the 2nd, the palatine tonsils originate.

From the 3rd pouch, the inferior parathyroid and the thymus arise.

From the 4th pouch, the superior parathyroid gland forms.

From the 5th pouch, the ultimobranchial body develops.

DEVELOPMENT OF VARIOUS PARTS OF FACE: 1.LOWER LIP The mandibular process appears

initially as a partially divided bilateral structure but soon merges at the median line. This process will give rise to the mandible, the lower part of the face and the body of the tongue.

DEVELOPMENT OF MANDIBLE The mandibular

process appears initially as a partially divided bilateral structure but soon merges at the median line. This process will give rise to the mandible, the lower part of the face and the body of the tongue.

MEMERGED MANDIBL

E

Prenatal

Week 6 Intramembranous ossification centre develops lateral toMeckel's cartilage.

Week 7 -Coronoid process begins differentiating.

Week 8 -Coronoid process fuses with

main mandibular mass.

Week 10 (approx) -Both condylar and

coronoid processes are recognizable and anterior portion of Meckel's cartilage begins to ossify.

Weeks 12-14 -Secondary cartilages for the

condyle ,coronoidAnd symphysis appears

Weeks 14-16

-Deciduous tooth germs start to form

The mandible makes its structure in the sixth week of foetal life.

It is ossified in the fibrous membrane covering the outer surfaces of Meckel's cartilages ;derivative of first brachial arch

These cartilages form the cartilaginous bar of of the mandibular arch and are two in number(right & left)

Their proximal or cranial ends are connected with the ear capsules, and their distal extremities are joined to one another at the symphysis by mesodermal tissue

LINGULA is replaced by fibrous tissue,

which persists to form the sphenomandibular ligament & the perichondrium of the cartilage persists

Between the lingula and the canine tooth the cartilage disappears, while the portion of it below and behind the incisor teeth becomes ossified and incorporated with this part of the mandible.

2.DEVELOPMENT OF UPPER LIP AND MAXILLA During the 6th week, the 2 medial nasal processes merge in the midline to form the intermaxillary segment.

This will give rise to the centre of the upper lip, the primary palate, and the part of the alveolar process carrying the incisor teeth.

Each maxillary process grows medially and fuses, first with the lateral nasal processes and then with the medial nasal process.

The medial and lateral nasal processes also fuses with each other;thus closing the nasal pits to the stomatodaeum.

Thus nasal pits which are now called EXTERNAL NARES:are cut off from the stomatodaeum.

Frontonasal process becomes much narrower so that the two nares come together.

Stomatodaeum is now bounded above by upper lip which is derived from:

1.maxillary process :forms the mesodermal basis of lateral part of lip &boverlying skin derived from ectoderm

2.frontonasal process:forms the mesodermal basis of median part of lip(philtrum).ectoderm of maxillary process overgrows this mesoderm to meet the opposite in midline.

3.NOSE:Forms from FRONTONASAL PROCESS,MEDIAL PROCESS & LATERAL PROCESS.

Fronto nasal process becomes progressively narrower-its deeper part forms NASAL SEPTUM.

Mesoderm becomes heaped up in the median plane to form nasal prominence.

Groove appears between the region of the nose &the bulging forebrain.

Nose becomes prominent &external nares open downwards

4.NASAL CAVITIES Formed by the extension of nasal pits

Medial & lateral nasal process fuse & form partition between the pits & stomatodaeum called as primitive palate derived from frontonasal process.

Nasal pit deepen to form nasal sacs which expand dorsally & caudally.

Dorsal part is separated from stomatodaeum by bucconasal membrane/nasal fin which soon breaks down.

Nasal sac consists of external nares & primitive posterior nasal aperture.

Nasal cavities enlarge & intervening tissues are thinned to form NASAL SEPTUM.

Lateral wall of nose is derived from lat.nasal process & nasal conchae appear as elevations on lat.wall.

5. CHEEK:

Maxillary process & mandibular process surrounding the stomatodaeum progressively fuse to form cheeks

This fusion extends from stomatodaeum to medial angle of developing eye marked by nasoptic furrow/nasolacrymal sulcus.

A strip of ectoderm gets buried along this to form nasolacrimal duct.

6.EYE

The eyes develop during the 5th week.

The first external sign of eye development is the appearance of the lens placodes between the maxillary and frontonasal process at the lateral sides of the face. The lens placode sinks below the surface and is eventually cut off from the surface ectoderm

The earliest stage of eye development is the formation of the paired optic vesicles on either side of the forebrain. These growing diverticula expand laterally into the mesoderm of the head and develop a stalk-like connection to the main portion of the rudimentary central nervous system. In humans, this process begins at about 22 days of development; as the vesicles continue to grow, their connection to the brain becomes progressively narrower and more stalk-like. The forming stalks will eventually become the rudiments of the optic nerves.

The developing eyeball now presents as a bulge facing laterally. With the narrowing of the frontonasal process, they come to face forwards.

The eyelids are derived from folds of ectoderm that are formed above and below the eyes, and by mesoderm enclosed within the folds.

7.EXTERNAL EAR

The external ear is formed around the dorsal part of the 1st ectodermal cleft.

A series of mesodermal thickenings appear on the mandibular and hyoid arches where they adjoin this cleft.

The pinna is formed by fusion of these thickenings.

When first formed the pinna lies caudal to the developing jaw. It is pushed upwards and backwards due to later enlargement of the mandibular process

APPLIED ASPECTS

The complexity of development of face leads to many developmental anomalies or disorders. Mainly they are:

1. cleft lip :The failure of fusion of medial nasal process with the lateral nasal process leads to the formation of cleft lip.

CLEFT LIP

Cleft lip (cheiloschisis) , which can also occur together as cleft lip and palate, are variations of a type of clefting congenital deformity caused by abnormal facial development during gestation. A cleft is a fissure or opening—a gap. The failure of fusion of medial nasal process with the lateral nasal process leads to the formation of cleft lip.

Approximately 1 in 700 children born have a cleft lip and/or a cleft palate. In decades past, the condition was sometimes referred to as harelip, based on the similarity to the cleft in the lip of a hare

Lip cleft can occur as a one sided (unilateral) or two sided (bilateral). It is due to the failure of fusion of the maxillary and medial nasal processes (formation of the primary palate).

UNILATERAL COMPLETE

BILATERAL COMPLETE

A mild form of a cleft lip is a microform cleft. A microform cleft can appear as small as a little dent in the red part of the lip or look like a scar from the lip up to the nostril. In some cases muscle tissue in the lip underneath the scar is affected and might require reconstructive surgery. It is advised to have newborn infants with a microform cleft checked with a craniofacial team as soon as possible to determine the severity of the cleft.

Complications

Cleft may cause problems with feeding, ear disease, speech and socialization.

TREATMENT: Within the first 2–3 months after birth, surgery

is performed to close the cleft lip. While surgery to repair a cleft lip can be performed soon after birth, often the preferred age is at approximately 10 weeks of age, following the "rule of 10s" (the child is at least 10 weeks of age; weighs at least 10 pounds, and has at least 10g haemoglobin). If the cleft is bilateral and extensive, two surgeries may be required to close the cleft, one side first, and the second side a few weeks later.

The most common procedure to repair a cleft lip is the Millard procedure pioneered by Ralph Millard. Millard performed the first procedure at a Mobile Army Surgical Hospital (MASH) unit in Korea.

Often an incomplete cleft lip requires the same surgery as complete cleft. In order to restore the complete group a full incision must be made. To create a less obvious scar the surgeon tries to line up the scar with the natural lines in the upper lip (such as the edges of the philtrum) and tuck away stitches as far up the nose as possible. Incomplete cleft gives the surgeon more tissue to work with, creating a more supple and natural-looking upper lip.

Epidemiology

Prevalence rates reported for live births for Cleft lip with or without Cleft Palate (CL ± P) and Cleft Palate alone (CPO) varies within different ethnic groups.

The highest prevalence rates for (CL ± P) are reported for Native Americans and Asians. Africans have the lowest prevalence rates.

Incidence of CLEFT LIP in INDIANS is 1.4 per 1000 live births

2.OBLIQUE FACIAL CLEFT: non fusion of maxillary & lateral nasal process.nasolacrimal duct is not formed.

3.MICROSTOMIA: too much fusion of mandibular & maxillary process

MACROSTOMIA: inadequate fusion leading to wide mouth.

PROBOSCIS:when nose forms a cylindrical projection just below the forehead.

MANDIBULOFACIAL DYSOSTOSIS: entire first arch remains underdeveloped on one or both sides.

RETROGNATHIA: mandible is small as compared to entire face

CONGENITAL TUMOURS-leading to various facial deformities

DEVELOPMENTAL DEFECTS OF EAR:

Malleus/incus fixation

Congenital fixation of stapes (stapes anchored to oval window)

Congenital preauricular sinus

DEVELOPMENTAL DEFECTS OF EYE

CORNEAL DERMOIDS

Congenital Glaucoma

CONCLUSION

Thus development of face in brief can be summarized as:

Any defect during any stage of the development can lead to immense facial deformities

This may have marked influence on functional & psychological aspect of the individual

Development of face is a highly synchronised & intricate process leading to the formation of the most influential part of the human body “THE FACE”

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5. Persaud, Moore: The Developing Human, Clinically Oriented Embryology. 7th ed. 2003. Elsevier publications.

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THANKYOU

Dr. SWATI JAINPOST GRADUATE STUDENT(1st year)DEPT.OF PUBLIC HEALTH DENTISTRY