Development of Orofacial Structures Flashcards
What is intramembranous ossification?
mesenchyme condenses –> osteoblasts –> osteocytes
*no cartilage in btw
*flat bones
what is endochondral ossification?
bone formation occurs in preexisting cartilagious models
long bones
primary ossification in diaphysis
What is the neurocranium?
bony case that encloses the brain
What is the viscerocranium?
bones comprising the facial skeleton
What is the cartilaginous neurocranium and its development?
endochondral ossification: several cartilages fuse –> base of cranium
occipital bone –> body of sphenoid –> ethmoid
temporal bone (petrous and mastoid parts)
What are the membranous parts of the neurocranium?
calvaria = frontal and parietal bones
(intramembranous ossification)
interconnected via sutures
What forms the cartilage of the cartilaginous neurocranium?
NCCs from midbrain
What are the structures derived from cartilaginous viscerocranium?
PA structures –>
ossicles
styloid process of temporal b
horns of hyoid
laryngeal cartilages (except epiglottis
What germ layer forms the cartilaginous viscerocranium?
NC from hindbrain
*except base of stapes = mesoderm
What is distinct about the squamous part of the temporal bone?
initially part of membranous viscerocranium –> becomes part of the neurocranium
What are the parts of the membranous viscerocranium?
squamous temporal b
maxillary b
zygomatic b
mandible (from cells of mandibular prominence, but NOT meckel’s cartilage)
What is craniosynostosis in general?
premature fusion of cranial sutures, often assoc w/ other skeletal defects
cause unclear
more common in boys
What is scaphocephaly?
premature closure of sagittal suture –> cranium becomes long, narrow, and wedge shaped
50% of cases of craniosynostosis
What is brachycephaly?
premature closure of coronal suture –> high, tower-like cranium
30% of cases of CSS
What is plagiocephaly?
early closure of coronal suture on one side –> cranium is twisted and asymmetric
What is trigonocephaly?
premature closure of the frontal (metopic) suture
deformities of frontal and orbital bones in addn to other anomalies
What do the medial nasal prominences form?
nasal septum
ethmoid bone
cribriform plate
What occurs to the face early in 4th week?
5 facial primordia appear as prominences around the stomodeum
2 MXP
2 MDP
1 FNP
What is the stomodeum?
early mouth hole
What is the oropharyngeal membrane?
bilaminar membrane over stomodeum that separates facial primordia from primordial pharynx
When does facial dev occur?
4-8 weeks
What types of germ cells are the active growth centers in the FNP, MXP, and MDPs?
NCC
from forebrain and midbrain in FNP
from midbrain and hindbrain in MXP and MDP
What are the first parts of the face to form and how does this occur?
lower jaw and lower lip
oropharyngeal membrane disintigrates –> extension and fusion of mandibular prominences at midline
*mandibular arch first to fuse*
What has occured to the face by the end of the 4th week?
nasal placodes form on inferolateral parts of FNP = thickenings of surface ectoderm that will form nasal epithelium
How do the NPs change during development?
placodal edges proliferate –> medial and lateral nasal prominences –> placodes turn into nasal pits
What is the nasolacrimal groove?
separates LNP from maxillary prominence
by end of 6th week –> MXP and LNP fuse
est continuity btw side of nose and cheek
How does the intermaxillary segment form and what does it give rise to?
MNPs merge w/ MXP and FNP btw 7th and 10th weeks = medial palatine process/intermaxillary segment
forms philtrum of upper lip
premaxillary part of maxilla (1st 2 teeth)
primary palate
What does the mesenchyme in PA2 form?
facial muscles
innervated by facial n (7)
What does the mesenchyme in PA1 form?
muscles of mastication (and others)
trigeminal N (V)
When does the mandible reach its characteristic form?
by 14 weeks
How do the orbits get a fwd-facing orientation?
as brain enlarges –> cranial cavity expands bilaterally
What is the oronasal membrane and what happens to it?
S ecto that initially separates the oral cavity and nasal sac –> ruptures at 6th week –> makes oropharynx and nasopharynx continuous
What occurs to the epithelium lining the roof of nasal cavities during dev?
specializes –> olfactory epithelium
When does palatogenesis occur?
2 stages
6th to 12th week
critical period: 6-9
What forms the median palatine process and what is it?
merging of MNPs –> median palatine process/primary palate
mesenchyme btw MXPs
forms premaxillary part of maxilla
When and how does the secondary palate form?
early in 6th week
MXP has lateral palatal shelves = mesenchyme projections –> move inferomedially and merge w/ primary palate –> keep fusing in A-P pattern
done at 7-8th week?
Why is tongue movement during development important?
Must move inferiorly and anteriorly to give the secondary palate space to grow and fuse
if it doesn’t move –> cleft palate
What is the palatine raphe?
line of fusion of lateral palatine processes
What is the incisive fossa?
remnant of nasopalatine canal in normal adults in the medial plane of the palate
What is a cleft lip?
extends from upper lip often to nose and/or maxilla
failure of MXP and MNP to fuse
What is a cleft palate?
cleft of secondary palate to incisive fossa
failure of LPPs w/ nasal septum or LPP w/ medial palatine process
When does the nasal septum fuse w/ palatine processes?
begins anteriorly at 9th week –> complete posteriorly week 12
What are the lingual swellings and what do they come from?
median lingual swelling = appears at end of 4th week; 1st part of tongue dev
lateral lingual swellings = rapidly grow, merge and overgrow median
both from PA1
What do all the tongue buds resulf from initially?
mesenchyme from PA1
what is the embryo origin of anterior 2/3 of tongue?
Posterior 1/3?
PA1
PA3
What is the terminal sulcus?
line of fusion of anterior and posterior parts of tongue
What is the hypopharyngeal/hypobranchial eminence?
initial part of tongue from PA3 and Pa4 that overgrow copula form arch 2
What is the tongue musculature derived from?
myoblasts of occipital myotomes –> CN 12 innervates them
What does the epiglottis form from?
fourth arch
What is glossoschissis?
bifid tongue
What is ankyloglossia?
tongue tied
What does innervation of vallate papilla in the ant 2/3 of tongue?
CN 9
What does the vagus n do in the tongue?
sensory of posterior tongue and pharynx
tast to epiglottis
motor to palatoglossus m
How do teeth develop initially?
from cell-cell interactions btw NC mesenchyme and overly ectoderm
What are dental laminae?
U-shaped bands of oral epithelium = 10 on top, 10 on bottom –> form tooth buds, done by 6th week
What are the parts of the cap staged tooth?
enamel organ
dental papilla = mesenchyme –< dentin and pulp
dental sac = mesenchyme surrounding all of it –> PDL and cementum
What makes up the enamel organ?
ecotdermal cells
outer layer = outer enamel epi
inner layer = inner enamel epithelium
What do dental papilla cells next to IEE form in bell stage?
odontoblasts –> predentin –> dentin
What does the IEE form in the bell stage?
ameloblasts in response to dentin production –> enamel
When does root dev occur?
after dentin and enamel formation
IEE and OEE fuse –> grows into mesenchyme and initiates root formation
odontoblasts make root dentin
What do the different cells of the dental sac form?
inner cells –> cementoblast –> cementin around roots
outer cells –> PDL = collagen L that anchors tooth to bone
What allows deciduous teeth to fall out?
as permanent teeth grow –> osteoclasts resorb deciduous root
only crown and uppermost part of root are shed
What do permanent teeth develop from?
buds from posterior extensions of the dental laminae
What is the epithelium covering the post 1/3 of the tongue derived from?
endoderm
