Development of Orofacial Structures (fellow) Flashcards
The neurocranium is derived from what embryonic tissue?
What does give rise to?
Mesenchyme
bones of the bones that enclose the brain membrane and cartilaginous components
The viscerocranium is derived from what embryological tissue?
What does it give rise to?
Mesenchyme
Bones that comprise the facial skeleton, membrane and cartilaginous components
Describe intramembranous ossification
mesenchymal origin without cartilage
neurovascularization occurs
osteoblasts come in and deposit osteoid to form bone
if it’s membranous component, it undergoes intramembranous ossification
Describe endochondral ossification
pre-existing cartilaginous model (long bones)
primary ossification center in the diaphysis
chondrocytes hypertrophy and the matrix calcifies
if it’s a cartilage component, it undergoes endochondral ossification
What bones come from the cartilaginous parts of the neurocranium?
Occipital bone
body of sphenoid bone
ethmoid bone
petrous and mastoid parts of temporal bone
What forms from the membranous parts of the neurocranium?
Calvaria (frontal and parietal bones)
What bones come from the cartilaginous part of the viscerocranium?
neural crest cells give rise to bones and CT
PA1-malleus and incus
PA2-stapes, stylpoid process, lesser horn of hyoid
PA3-greater horn of hyoid
PA4-Laryngeal cartilage
What forms from the membranous part of the viscerocranium?
Maxillary Prominence
Maxilla
Zygomatic Bone
Sqaumous part of temporal bone
What is craniosynostosis and what are the types and features?
Premature fusion of cranial structures
- scaphocephaly: sagittal suture effected, long narrow wedge shape head, most common
- brachycephaly: coronal suture, tower like head
- plagiocephaly: one side of coronal suture, twisty and asymmetric head
- trigonocephaly: frontal suture
What are the derivatives of the frontal nasal prominence
forehead and apex of nose
What are the derivatives of the lateral nasal prominence?
alae of nose
What are the derivatives of the medial nasal prominence?
nasal septum
ethmoid bone
cribiform plate
What are the derivatives of the maxillary prominence?
upper cheek/upper lip
What are the derivatives of the mandibular prominence?
chin
lower lip
cheek
Describe the facial primordium
brain development drives rate/shape of head
5 facial primordia (2 max, 2 mand, 1 frontonasal)
Appear during wk 4 and surround stomodeum
separated from pharynx by oropharyngeal membrane
ruptures around day 24
What is the first part of the face to form?
Lower jaw and lip (from mandibular prominence)
oropharyngeal membrane disintegrates and the medial ends of the mandibular prominence merge
incomplete fusion results in chin dimple/cleft
Describe the growth of the maxillary prominences
grow medially and merge laterally with mandibular prominences
give rise to upper lip, maxilla, and secondary plate
primordial lips and cheeks are invaded by mesencyme from PA 2 to give rise to facial muscles
Describe the frontonasal prominence growth
surrounds ventrolateral part of forebrain
gives rise to forehead, rostral boundary of stomodeum and nose
What are nasal placodes?
- bilateral oval thickenings of surface ectoderm on the inferolateral portion of the frontonasal prominence
- proliferation causes horse-shoe shaped elevations, forming medial and lateral nasal prominences
- these elevations result in formation of nasal pits (become nostrils)
Describe the growth of the lateral nasal prominence
shifted towards midline with medial growth of maxillary prominences
regulated by PDGFRA
fusion results in intermaxillary segment (philtrum)
Describe the lateral nasal prominence growth
separated from maxillary prominence by nasolacrimal groove
merges with maxillary prominence by end of week 6
Describe the auricular primordia
six auricular hillocks form around the PA groove 1
developing mandible pushes ears from neck to side of head at the level of the eyes
Describe the development of the nostrils
nasal placodes form nasal puts
mesenchyme from medial and lateral nasal primnences cause pits to deepen into primordial nasal sacs
nasal scas grow posterior and anterior into the forebrain
oronasal membrane seprates the sacs and ruptures at the end of wk6
What is the primordial choanae?
connection between nasophayrnx and nasal cavity
Describe primary plate palatogenesis
fusion of median nasal prominences forms median palatine process
located between maxillary prominences and forms premaxillary part of maxilla
Describe secondary plate palatogenesis
develops from lateral palatine processes (palatal shelves)
mesenchymal projections extend from internal aspects of maxillary prominences
palatogenesis occurs from wk6-12, critical period between 6-9wks
Describe the formation of the final palate
- bone extends from maxillae and palatine bones into lateral palatine processes to form the hard palate
- posterior portions do not ossify (soft palate and uvula)
- a palatine raphe is the line of fusion
- incisive foramen is remnant of nasopalatine canal
Describe the formation of the nasal septum
downward growth of internal parts of merged medial nasal prominences
fuses with lateral palatine process anterior to posterior
Cleft lip and palate
- most common malformation
- defect in fusion either bilateral or unilateral, with unilateral cleft lip being the most common
- risk factors: genetics (Shh, TGF), environment (smoking, ETOH, folate def., obesity, antiepileptics)
Choanal Atresia
- bony abnormalities of the pterygoid plates and midfacial growth abn.
- upper airway obstruction, noisy breathing, cyanosis with feeding, better with crying
- assox. with Treacher-Collins, CHARGE, Kallman, VACTERL
- can have deviated septum
Describe the development of the anterior 2/3 of the tongue
- “oral part”
- median lingual swelling appears at end of 4th wk
- two lateral swellings develop on either side of the median, induced by mesenchyme from PA1
Describe the formation of the pharyngeal part of the tongue
- a copula forms from parts of PA 2
- a hypopharyngeal eminence forms from PA 3-4
- hypopharyngeal eminence overgrows copula and the terminal sulcus forms where the fusion of the oral and pharyngeal parts meet
Describe the formation and innervation of tongue musculature
derived from myoblasts of occipital myotomes
CN XII
Describe the innervation of the anterior 2/3 of the tongue
- Mucosa:
- Taste:
- Musculature
- lingual branch of V3
- chorda tympani (CN VII)
- CN XII
What is the innervation of the posterior 1/3 of the tongue
- mucosa/taste:
- musculature
- sensation to pharynx
- palatoglossus m.
- CN IX
- CN XII
- CN X
- CN X
Development pathologies of the tongue
Glossochissis: bifid tongue
Ankyloglossia: short frenulum, issues feeding and speaking
Macroglossia: Beckwith-Wiedemann and Down Syndrome, mucopolysaccharidoses
Odontogenesis is induced by communication between what cell types?
Neural crest cels and oral epithelium
Describe dental laminae and tooth buds
Dental laminae are u-shaped bands of oral epithelium that follow the curves of the primitive jaws
tooth buds (ten in total) include anterior mandibular, anterior maxillary and posterior
Describe the Cap Stage in odontogenesis
the tooth bud becomes a cap shape when invested by mesenchyme
tooth bud consists of enamel organ, dental papilla, dental follicle/sac
What is the enamel organ?
- ectodermal cells from dental lamina form the enamel
- outer cell layer is lined by outer enamel epithelium
- inner cell later lines the papilla and is lined by inner enamel epithelium
- stellate reticulum found here
Describe the dental papilla and dental follicle/sac
dental papilla: internal part of the tooth with dentin and pulp
dental follicle/sac: mesenchyme surrounding dental papilla and enamel organ, contains cementum
Describe the bell stage of odontogenesis
enamel organ becomes bell-shaped due to differentiation of enamel
odontoblasts and ameloblasts form
What are odontoblasts?
form dental papilla cells next to inner enamel epithelim
predentin calcifies to become dentin
What are ameloblasts?
inner enamel epithelium differentiates in repsonse to dentin production
produces enamel
Describe root development and components
- epithelial root sheath from fusion of inner and outer enamel epithelium
- root dentin from odontoblasts
- pulp from central dental papilla
- cementum from cementoblasts in the inner cells of the dental sacs
- periodontal L. forms from outer cells of dental sac
How does tooth eruption occur?
root of tooth and crown erupt through oral epithelium
mandibular teeth go first
deciduous root is reabsorbed by odontoclasts (osteoclasts) and the crown and upper root are shed
(losing baby teeth)
Deciduous permanent teeth appear at
10wks and are extensions of the dental lamina, lingual to deciduous tooth buds
Nondeciduous molars develop how?
as buds from posterior extension of the dental laminae
tooth buds for permanent teeth appear at different times, including
during the fetal period and after birth (2-3rd molars)
32 permanent teeth
