Lecture 8: Orofacial Development Flashcards
What is formed by the neurocranium versus viscerocranium?
- Neurocranium = brain case
- Viscerocranium = face, jaw and larynx
Which neurocranium bones of the skull arise from paraxial mesoderm and undergo endochondral ossification?
- Occipital
- Body of sphenoid
- Petrous and mastoid parts of temporal
Which viscerocranium bones of the skull arise from neural crest cells and undergo endochondral ossification?
Ossicles of the ear (malleus, Incus, Stapes)
Which neurocranium bones of the skull arise from neural crest cells and undergo endochondral ossification?
Ethmoid
Which neurocranium bones of the skull undergo intramembranous ossification?
- Flat bones of the skull (i.e., Frontal and Parietal)
Which viscerocranium bones arise from neural crest cells and undergo intramembranous ossification?
- Squamous temporal
- Maxillary
- Zygomatic
What is Scaphocephaly?
Premature closure of sagittal suture —> cranium becomes long, narrow, and wedge shaped
What is Plagiocephaly?
- Premature closure of the coronal and lamboid suture on one side –> cranium is twisted and asymmetric
What is Oxycephaly or Brachycephaly?
Premature closure of the coronal suture —> a high, tower-like cranium
When do the 5 facial primordia arise, what are they and where are they found?
- Appear early in 4th week as prominences around the stomodeum
- Frontonasal prominence
- Paired maxillary prominence
- Paired mandibular prominence
The facial primordia are separated from cavity of primordial pharynx by what bilaminar membrane; what ‘derm layer (s)?
- Oropharyngeal membrane (buccopharyngeal membrane)
- Surface ectoderm
- Foregut endoderm
What are the 4 steps in formation of the face?
Step 1 : growth and migration of the maxillary and mandibular prominences
Step 2: differentiation of frontonasal prominence into: nasal placode, medial/lateral nasal prominence, nasolacrimal groove
Step 3: migration of nasal prominences to midline
Step 4: fusion of medial nasal prominences w/ each other and fusion of medial and lateral nasal prominces w/ maxillary prominence
What are the derivatives of the face from the maxillary and mandibular prominences?
Maxillary = sides of face, lateral palatal shelves, upper lip
Mandibular = lower jaw
What are the derivatives of the medial nasal prominence?
- Intermaxillary segment: Philtrum of lip and Primary Palate
- Nasal septum
What 2 structures form the nasal lacrimal groove?
Where lateral nasal prominence and maxillary prominence come together
What are the characteristics and embryological mechanism to account for Frontonasal Dysplasia?
- Hypertelorism (wide-set eyes), Widow’s Peak, Cramium Bifidum Occultim (cleft skull), and a median cleft of the upper lip and palate
- A lack of migration and fusion of the medial nasal prominences, part of the frontal nasal prominence
Embryologically how can we account for the facial clefts in A-F?
A) Incomplete fusion of medial nasal prominence
B) Incomplete fusion of mandibular prominences
C) Nasolacrimal duct did not form AND maxillary prominence did not fuse with the intermaxillary segment or lateral nasal prominence
D) Maxillary and Mandibular prominences did not fuse enough
E) Overfusion of the maxillary and mandibular for the small mouth. The one nostril is a result of overfusion of medial nasal prominence
F) Medial nasal prominence did not completely fuse
When does development of the palate begin and what is the critical period?
- From the 6th to 12th week
- Critical period = 6th - 9th week
What does the seconary palate give rise to and where does it develop from?
- Gives rise to most of hard and ALL of soft palate
- From lateral palantine processes (shelves) = NC
What is the importance of the nasal septum migrating down to the palantine shelves?
Provides reinforcement by fusing with the lateral palantine shelves
Where is the primary palate derived from and explain how it forms the completed palate?
- From the intermaxillary segement (NC)
- Primary palate fuses w/ lateral palantine shelves and produces the top 4 front teeth
- Where it fuses w/ the hard palate is called the incisive papilla (fossa)
What are the embryological mechanisms that can account for cleft palate?
- Failure of fusion of lateral palatine shelves from one or both sides + nasal septum
- May involve uvula and/or hard and soft palates
What are the embryological mechanisms that can account for cleft lips?
- Often clefting of the nose and/or maxilla
- Failure of fusion of Maxillary prominence(s) and Intermaxillary prominences
- Primary palate did not fuse w/ one or both palatine shelves
What abnormality is this and how can we account for this embryologically?
- Bilateral cleft lip
- Intermaxillary segment did not fuse w/ maxillary prominences on either side
Explain the embryologic development of the nose starting from nasal placodes to definitive choana?
- Nasal placodes become depressed, forming nasal pits –> nasal sacs
- Nasal cavity is separated by an oronasal membrane which ruptures
- Once ruptured there is formation of the primitive choana = opening from the nasal cavity into pharynx
- Secondary palate forms and we form the definitive choana
Embryologically what is the significance of olfactory nerve fibers (CN I)?
- Olfactory nerve is from surface ectoderm
- Can regenerate!
What is the ectodermally lined primitive mouth?
Stomodeum
How does the 1st pharyngeal arch play a role in the development of the tongue?
- Lateral lingual swellings (distal tongue bud) migrate towards midline and grow over our median lingual swelling (tongue bud)
- This forms the anterior 2/3 of tongue; oral portion
How does the 3rd and 4th pharyngeal arch play a role in the development of the tongue and epiglottis (key players)?
- 3rd pharyngeal arch gives rise to the hypobranchial eminence going over arches 3 and 4.
- Portion of 3rd arch migrates up and fuses w/ ectoderm of 1st arch = formation of posterior 1/3 of tongue
- Caudal portion of hypobranchial eminence in arch 4 becomes the epiglottis
Embryologically where do they muscles of the tongue develop from; innervated by what CN?
- Occipital somites (mesoderm)
- Innervated by CN XII
Embryologically where do the blood vessels and CT of the tongue arise from?
Neural crest cells
Embryologically where do the papillae and taste buds of the tongue arise from?
Ectoderm
What structure on the tongue demarcates the area where the 1st and 2nd pharyngeal arches meet?
Sulcus Terminalis
What specific branches provide the sensory, taste, motor, and the exception for innervation to the anterior 2/3 of tongue?
Sensory: the lingual branch of V3 (CN V)
Taste: chorda tympani branch of facial nerve (CN VII)
Motor: the hypoglossal nerve (CN XII)
Exception: the vallate papillae innervated by glossopharyngeal (CN IX)
What specific branches provide the sensory, taste, motor to the posterior 1/3 of tongue?
Sensory: the glossopharyngeal nerve (CN IX)
Taste: the glossopharyngeal nerve (CN IX)
Motor: the hypoglossal nerve (CN XII)
What abnormality is this and how do we account for this embryologically?
- Glossoschisis (bifid or cleft tongue)
- Lateral lingual swellings did not finish migrating toward the midline
Macroglossia (large tongue), fissuring of the tongue, and hypertrophy of the lingual papillae are charateristics often seen in infants with what disorder?
Down Syndrome
What abnormality is this and how do we account for this embryologically?
- Ankyloglossia
- Frenulum of tongue is too close to the anterior 2/3; coming from the 1st pharyngeal arch
What week do teeth begin development and what occurs first?
- Week 6
- Dental lamina thickening of surface ectoderm migrates into mesenchyme and forms a tooth bud.
- Tooth bud will give rise to deciduous (baby teeth) and adult teeth
What occurs during the cap stage of teeth development (main players)?
- Mesenchyme and neural crest (mainly) migrating into tooth bud and forming dental papilla (neural crest)
- Tooth bud is now the enamel organ consisting of: outer and inner dental epithelium
- Also have formation from neural crest cells of the dental sac (cementum, peridontal lig.)
Where do ameloblast and stellate reticulum form from and their role in tooth development; what stage specifically?
- The Bell stage
- Internal enamel epithelium gives rise to Ameloblast cells, which produce enamel (from surface ectoderm)
- Outer enamel epithelium gives rise to the Stellate reticulum, a mesh work allowing enamel to grow and be produced
What forms within the dental papilla during the Bell stage of tooth development and how/where do we get our vasculature and innervation?
- In dental papillae (NC) we have the Odontoblasts, secreting dentin (2nd strongest substance in body to enamel)
- The dental pulp (mesoderm/NC) mix becomes the root of the tooth and is where our vasculature and nerves come in
What induces root formation of the teeth and describe this process?
- Enamel epithelium (ectoderm) induces root formation
- Odontoblasts start to secrete more dentin and root continues to grow and cover all of the dental pulp (papilla)
How do we get anchoring of the tooth in the socket (key players)?
- The dental sac (NC) produces cementoblasts which secrete cementum, which adheres tooth to bone
- Dental sac also form the peridontal ligament, which assists in anchoring of tooth to bone
- All coming from NEURAL CREST
What abnormality is this and how do we account for this embryologically?
- Ameloblast imperfect
- Enamel of the teeth is misformed
- Teeth are hypoplastic, hypomature, and/or hypocalcified
What causes this and why is this clinically significant?
- Tetracycline
- Given anytime from week 14 after fertilization until month 10 after birth
