Development of the Face

Development of Face

• The face develops from 5 processes around the primitive mouth (stomodeum)
• Stomodeum, a shallow depression, forms by longitudinal folding of the early embryo
• In the 4th week, the 3 germ layers differentiate, and the embryo folds
  • Ectoderm provides protection
  • Endoderm provides nutrition
  • Mesoderm forms skeletal tissues, muscles, and the blood vascular system
• By the end of the 2nd month, the embryo has a distinct human appearance

Mesenchymal Prominences

• At the 4th week, there are 5 prominences
• The frontonasal prominence is a slight round elevation cranial to the stomodeum forming the middle part
• The maxillary prominence is the dorsal portion of the 1st arch, lateral to the stomodeum
• The mandibular prominence is caudal to the stomodeum
• The nasal/olfactory placode is a thickening of the surface ectoderm on either side of the frontonasal prominence

Nasal Placodes & Processes

• Nasal placodes appear in the 4th week
• Nasal placodes invaginate to form nasal pits in the 5th week
• Mesenchyme around the nasal pits proliferates, forming a horseshoe-shaped elevation
• Elevations of the nasal pits form the medial (half) and lateral (half) nasal processes
• Nasomedial processes grow and fuse with the maxillary processes completing the upper jaw arch
• Nasomedial tissues give rise to the philtrum of the lip
• Nasal placodes are the primordia of the nose and nasal cavities

Nasolacrimal Groove & Nasal Sacs

• The nasolacrimal groove exists between the lateral nasal prominence and the maxillary swelling
• Nasal pits deepen to form nasal sacs by the end of the 6th week
• Nasal sacs become separated from the oral cavity by the oronasal membrane
• The oronasal membrane ruptures communicating the primitive nasal cavities with the oral cavity
• These communications are called the primitive choana
• The primitive choana is located posterior to the primary palate

Development of Palate

• The primary palate is formed by medial frontonasal processes
• The primary palate is a transient structure from which the upper lip and premaxillary palate form
• The secondary palate (roof of the oral cavity) develops from the maxillary processes
• After development of the secondary palate, the choana change position
• The definitive choana is located at the junction of the nasal cavity and the pharynx

Development of Nose

• The external nose develops from:
  • The frontonasal process, forming the bridge of the nose
  • Two fused medial nasal processes, forming the dorsum and tip (apex) of the nose
  • Two lateral nasal processes, forming the sides and alae of the nose
• The intermaxillary segment forms when two medial nasal processes fuse
  • Labial component becomes the philtrum of the upper lip
  • The upper jaw (alveolar process) carries 4 incisor teeth
  • The palatal component forms the triangular primary palate (premaxilla)

Development of Nasal Cavity & Septum

• The nasal cavity develops from:
  • Nasal pits that deepen to form the nasal sac
  • This sac grows and forms the primitive nasal cavity
  • The dorsal end of this cavity is separated from the oral cavity by the oronasal membrane
  • The external opening of nasal pits persist as external nares
  • Superior, middle, and inferior conchae develop as curved elevations from the lateral wall
  • Ectoderm forms the olfactory epithelium (olfactory nerves)
• Nasal septum formation
  • The nasal septum develops from a downgrowth of the frontonasal process
  • It joins the superior aspect of the anterior three-fourths of the hard palate in the midline

Formation of Facial Components

• Nasal pit grow deeper to form nasal cavities
• The median nasal process thins to form the primitive nasal septum
• Maxillary processes fuse with lateral nasal processes to form the lateral parts of the upper lip and upper cheek
• Two mandibular processes form the lower lip and lower part of the cheek
• The opening of the stomodeum forms the oral fissure
• The lens placode is the site of eye development

Facial Derivatives

• The Frontonasal process forms the forehead, external nose, nasal cavity, nasal septum, and philtrum of the upper lip
• The maxillary process forms the lateral parts of the upper lip and upper parts of the cheek
• The mandibular process forms the chin, lower lip, and lower part of the cheek

Facial Anomalies

• Facial clefts result from the failure of fusion of embryonic facial prominences
• Clefts can be unilateral or bilateral and involve:
  • Lips only (cleft lip)
  • Palate only (cleft palate)
  • Lip and palate (cleft lip and palate)
  • Region of the nasolacrimal groove (facial clefts)
• Breathing, feeding, sucking, swallowing & speech can be difficult

Specific Cleft Types

• Median cleft lip: medial nasal prominences fail to merge
• Unilateral cleft lip: maxillary prominence fails to merge with the medial nasal prominence
• Bilateral cleft lip: maxillary prominences fail to meet and unite with the medial nasal prominences on both sides
• Oblique facial cleft: failure of the maxillary prominence to fuse with the lateral nasal prominence
• Cleft palate: nasal and oral cavities connected