CRANIOFACIAL DEVELOPMENT: FACE DEVELOPMENT

early in development, the face is

small in comparison with the neurocranium

smaller appearance of face is caused by

absence of the paranasal air sinuses

small sizes of the bones, particularly the jaws

with the appearance of teeth and development of the air sinuses,

the face loses its babyish characteristics

facial development occurs mainly

between weeks 4-8

1st pharyngeal arch on each side with its max and mand prominences plays an

important role in facial development

the face develops around the primitive mouth or AKA

stomodeum

stomodeum

ectodermal depression on the surface of the primitive face

stomodeum forms the

primitive oral cavity, lined by ectodermally derived oral mucosa

stomodeum is separated from the pharynx (endodermal foregut) by

oropharyngeal membrane

the oropharyngeal membrane rupture by week 4, bringing the

pharynx and foregut in communication with the amniotic cavity

5 facial primordia appear as prominences around the stomodeum including

1 frontal prominence

paired max prominences (from pharyngeal arch 1)

paired mand prominences (from pharyngeal arch 1)

the frontonasal prominence forms the

forehead

upper boundary of the stomodeum (mouth)

bridge and dorsum of the nose

the maxillary prominences form the

lateral boundaries of the stomodeum (mouth)

the mandibular prominences constitute the

caudal boundary of the stomodeum (mouth)

the lower jaw and lower lip are the

1st parts of the face to form

during weeks 4-5, the mand prominence gradually

enlarge and merge in the midline

between weeks 5-8, NCCs of the 1st pharyngeal arch give rise to the

L & R cartilaginous rods called meckel cartilage

meckel cartilage form the

cores around which the bone of the lower jaw develops

the mandibular prominences form the

lower lip

lower jaw

lower cheek regions

the mentum or genu of the mandible marks the site where the

2 mandibular processes merge in the midline

the mentum or genu contains the line of fusion of the

2 separate halves of the mandible (mental symphysis)

the line of the fusion of the mentum or genu divides inferiorly to

enclose a triangular area called the mental protuberance

a partial or incomplete merger of the mand processes forms the

common midline chin dimple or cleft

failure of the R and L mand prominences to meet results in a

midline cleft of mandible and/or lower lip

partial midline cleft

may only affect the lower lip

complete midline cleft

both sides move independently

until the end of the 6th week, the primordial jaws comprise only

masses of mesenchymal tissue with no differentiation of the lips and gingivae

at the end of week 6, a curvy thickening of ectoderm, the labio-gingival lamina,

grows into the underlying mesenchyme

most of the labio-gingival lamina degenerates creating a

labio gingival groove or sulcus between the lips and gingivae

a small midline remnant of the labio-gingival lamina persists as the

frenulum of the lower lip

later in the 6th week, a second lamina, the dental lamina arises in the

more buccal region of the developing gingiva of both jaws

the dental lamina eventually will give rise to

tooth buds that penetrate the mesenchyme of both jaws and will form the deciduous and permanent teeth

proliferation of the max prominences

makes them enlarge and grow medially toward each other

also results their fusion with mand prominence to create the lateral boundaries of the oral cavity

macrostomia (lateral facial cleft)

failure of the max processes to merge with the mand processes laterally / hypoplasia of the max processes

macrostomia results in a

large mouth on one or both sides which can extend almost to the ears in several cases

macrostomia can occur in

isolation or as part of a sequence / with other congenital differences

the max prominences will also grow and meet

extensions of the frontonasal prominence to form the upper lip

by the end of week 4, nasal placodes

develop on each side of the frontonasal prominence

the margins of the placodes proliferate

producing horseshoe-shaped elevations, the medial and lateral nasal prominences

as a result, the nasal placodes lie in depressions,

the nasal pits (which become anterior nares / nostrils), nasal cavities, and the lateral nasal prominences form the alae (sides) of the nose

frontonasal dysplasia

excessive tissue in the frontonasal prominence

frontonasal dysplasia results in a spectrum of nasal differences, but

typically includes a broad nasal bridge and hypertelorism

in severe cases of frontonasal dysplasia,

2 external nares are separated with a midline groove

merging the medial nasal and max prominences results in continuity of the

upper jaw and lip and separation of the nasal pits from the stomodeum

unilateral or bilateral cleft upper lip occurs when

max prominence fails to fuse with medial nasal prominence on one or both sides

as medial nasal prominences merge,

they form an intermaxillary segment

the intermaxillary segment forms the

middle part of the lip (philtrum), the premaxillary part of the maxilla and its associated gingiva (gum) and the primary palate

median cleft upper lip occurs when

medial nasal processes fail to fuse in midline to form the intermaxillary segment

each lateral nasal prominence is initially separated from the max prominence by a

cleft, the nasolacrimal groove

by the end of the 6th week, each max prominence has begun to merge with the

lateral nasal prominence along the line of the nasolacrimal groove

this establishes continuity between the sides of the nose which is formed by lateral nasal prominence and cheek region formed by max prominence

the nasolacrimal duct develops in the

floor of the nasolacrimal groove

the superior end of the nasolacrimal duct expands to

form the lacrimal sac

by the late fetal period, the nasolacrimal duct drains into the

inferior meatus in the lateral wall of the nasal cavity

part of the nasolacrimal duct may fail to canalize resulting in

congenital atresia (lack of an opening) of the nasolacrimal duct

oblique facial cleft occurs when

max prominence fails to fuse with lateral and medial nasal prominences

the medial nasal process forms the

lower nose and philtrum

medial nasal processes also contribute to

palate development (primary palate)

the lateral nasal processes form the

sides and alae of the nose

the maxillary processes form the

upper cheek regions and most of the upper lip

maxilla

zygoma

the maxillary processes also contribute to

palate (secondary palate)

the mandibular processes form the

chin

lower lip

lower cheek regions

mandible

by the end of the 5th week, the primordia of the auricles (external ears)

have begun to develop

6 auricular hillocks (3 swellings on each side; 1-6) form around the

1st pharygneal groove, the primordia of the auricle, and the external acoustic meatus respectively

initially, the external ears are located

in the neck region

as the mandible develops, where do ears become located?

on the side of the head at the level of the eyes

when the auricular hillocks fail to fuse completely,

a preauricular pit or cyst may result

preauricular pit

small hole or cyst just in front of your ear above your ear canal

does not connect to the skin

extra ectodermal folds may also be created during

formation of the auricle from 6 auricular hillocks