Craniofacial Development Embryology

Craniofacial Development

• Craniofacial development involves the formation of the face, skull, and brain
• Process begins around 3 weeks after fertilization and continues until birth
• Involves the interaction of multiple tissue layers: ectoderm, mesoderm, and endoderm
• Shh (sonic hedgehog) and other signaling pathways regulate craniofacial development

Embryology

• Week 3-4: Neural tube formation, neural crest cells migrate to form facial primordia
• Week 5-6: Facial primordia fuse to form the frontonasal prominence
• Week 7-8: Maxillary and mandibular prominences form, giving rise to upper and lower jaws
• Week 9-10: Eye and ear formation, nasal placodes invaginate to form nasal pits

Anatomy

• Cranial bones: frontal, parietal, occipital, temporal, sphenoid, and ethmoid
• Facial bones: vomer, zygoma, maxilla, lacrimal, palatine, and nasal bones
• Facial muscles: zygomaticus major, orbicularis oculi, buccinator, and mentalis
• Nerve supply: trigeminal nerve (CN V) and facial nerve (CN VII)

Facial Expression

• Facial expressions are controlled by the facial nerve (CN VII)
• 43 facial muscles work together to produce a range of emotions and movements
• Ekman's 6 basic emotions: happiness, sadness, anger, fear, surprise, and disgust
• Facial feedback hypothesis: facial expressions influence emotional experience

Oral Biology

• Development of teeth: odontogenesis, involving dental lamina and enamel organ
• Tooth structure: enamel, dentin, pulp, and cementum
• Oral mucosa: stratified squamous epithelium with underlying connective tissue
• Saliva production and function: lubrication, digestion, and immune response

Craniofacial Development

• Craniofacial development begins around 3 weeks after fertilization and continues until birth
• It involves the interaction of multiple tissue layers: ectoderm, mesoderm, and endoderm
• Shh (sonic hedgehog) and other signaling pathways regulate craniofacial development

Embryology

• Week 3-4: Neural tube formation, neural crest cells migrate to form facial primordia
• Week 5-6: Facial primordia fuse to form the frontonasal prominence
• Week 7-8: Maxillary and mandibular prominences form, giving rise to upper and lower jaws
• Week 9-10: Eye and ear formation, nasal placodes invaginate to form nasal pits

Anatomy

• Cranial bones: frontal, parietal, occipital, temporal, sphenoid, and ethmoid
• Facial bones: vomer, zygoma, maxilla, lacrimal, palatine, and nasal bones
• Facial muscles: zygomaticus major, orbicularis oculi, buccinator, and mentalis
• Nerve supply: trigeminal nerve (CN V) and facial nerve (CN VII)

Facial Expression

• Facial expressions are controlled by the facial nerve (CN VII)
• 43 facial muscles work together to produce a range of emotions and movements
• Ekman's 6 basic emotions: happiness, sadness, anger, fear, surprise, and disgust
• Facial feedback hypothesis: facial expressions influence emotional experience

Oral Biology

• Development of teeth: odontogenesis, involving dental lamina and enamel organ
• Tooth structure: enamel, dentin, pulp, and cementum
• Oral mucosa: stratified squamous epithelium with underlying connective tissue
• Saliva production and function: lubrication, digestion, and immune response

Embryonic Development (Weeks 3-4)

• The embryo is a flat disc-shaped organism made up of three layers of pluripotent cells called germ layers (endoderm, mesoderm, and ectoderm).
• By week four, the embryo takes on a more recognizable human form due to folding along the rostral-caudal and lateral axes.

Neural Tube and Germ Layers

• The neural tube expands greatly, forming the primitive forebrain and a bulge known as the frontal prominence.
• Lateral to the neural tube is the paraxial mesoderm, which partially segments rostrally to form somidomeres and fully segments caudally to form somites.

Pharyngeal Arches and Branchial Grooves

• Six pharyngeal arches sprout from the primitive pharynx.
• The pharyngeal arches are separated externally by small clefts on the pharyngeal wall called branchial grooves and internally by corresponding depressions called pharyngeal pouches.

Face Development

• Face development begins in week 4 when two patches of ectoderm on the frontal prominence start to proliferate, forming two thickenings known as the nasal placodes.

Nasal Development

• The mesodermal cells surrounding each nasal placode proliferate rapidly to form a horseshoe-shaped swelling, which further divides into the medial nasal process and the lateral nasal process.

Upper Lip and Nasal Development

• The maxillary processes start to proliferate towards the center, while remaining separated from the lateral nasal process by the naso-optic groove and the medial nasal process by the bucco-nasal groove.
• By the end of week 6, the maxillary processes fuse with the medial nasal processes on each side, forming the upper lip.

Lower Jaw and Palate Development

• The mandibular processes form the lower jaw with all its teeth and the lower lip and fuse with the maxillary processes to form the cheeks.
• The inter-maxillary segment develops into the bridge of the nose, the filtrum or center of the upper lip, middle part of the maxillary bone, and the four upper incisor teeth and the primary palate.

Palate Development

• The nasal pits burrow deeper and backwards, forming the nasal sacs behind the inter-maxillary segment.
• The oronasal membrane at the base of the nasal sac disintegrates, forming a primitive choana, which connects the nasal and oral cavities.

Primary and Secondary Palate

• A triangular plate of tissue, the primary palate, grows from the back of the inter-maxillary segment and extends till it reaches below the incisive foramen of the skull.
• The maxillary processes develop a pair of shelf-like processes called palatine shelves, which grow vertically downwards on either side of the developing tongue.
• The palatine shelves elevate into a horizontal position and then grow medially until they fuse with each other and with the primary palate in front.

Critical Period for Face and Palate Development

• The critical period for face and palate development is between month 2 and 3, or from week 6 to 12.