Embryo Orofacial Flashcards
Intramembraneous vs. Endochondral ossification
- mesenchyme produces osseous tissue w/o cartilage formation
- bone formation occurs in preexisting cartilaginous models
Cartilaginous Neurocranium
- Several cartilages fuse, forming base of cranium (endochondral ossification)
- Defined order: occipital bone (base) → body of sphenoid → ethmoid bone
- Temporal bone (petrous & mastoid parts)
Membranous Neurocranium
• Head mesenchyme at the sides & top of the brain
• Will form calvaria (frontal & parietal bones) via
intramembraneous ossification
• Interconnected via sutures
Cartilaginous Viscerocranium
• NCCs form bones & CT of craniofacial structures
• PA1: malleus & incus
• PA2: stapes, styloid process of temporal bone;
lesser horn of the hyoid
• PA3: greater horns of the hyoid bone.
• PA4: cartilages fuse → laryngeal cartilages
(except epiglottis)
What is the temporal unique?
formed from two parts
neuro cranial: petrous & mastoid parts
viscerocranial - styloid process
Membranous Viscerocranium
- Intramembranous ossification w/in maxillary prominence: squamous temporal**, maxillary, & zygomatic bones
- Cells of mandibular prominence form the mandible
Craniosynostosis
- Premature fusion of cranial sutures, often associated with other skeletal defects
- Cause is unclear
- More common in boys
Scaphocephaly
premature closure of sagittal suture → cranium becomes long, narrow, & wedge shaped
• Accounts for 50% of cases
Brachycephaly
premature closure of the coronal suture → a high, tower-like cranium
• Accounts for 30% of cases
Plagiocephaly
premature closure of the coronal suture on one side → cranium is twisted & asymmetric
Trigoncephaly
premature closure of the frontal (metopic) suture
• Deformities of frontal & orbital bones in addition to other anomalies
What does the facial development depend on?
inductive interactions of forebrain, frontonasal region, and developing eye
When do the five facial primordia appear? and where?
4th week - prominences around stomodeum
- Maxillary prominences (2)
- Mandibular prominences (2)
- Frontonasal prominence (1)
maxillary and mandibular fuse at front
What separates the facial primordial from the primordial pharynx?
bilaminar membrane, oropharyngeal membrane
When does facial development occur? where are the growth factors?
- week 4-8
- mesenchyme
What forms from the frontonasal prominence?
- Frontal portion will form the forehead
- Nasal portion forms rostral boundary of stomodeum & nose
- NCC from fore brain & midbrain
What are the first parts of the face to form?
lower jaw and lower lip
• Oropharyngeal membrane disintegrates
• Extension & fusion of mandibular prominences toward/at the
midline
When/where doe the nasal placodes form? what are they?
- week 4
- inferolateral parts of FNP
- Bilateral oval thickenings of the surface ectoderm that are primordia of the nasal epithelium
What fuses first: maxillary or mandibular?
mandibular
What do NP’s edges form?
- medial and lateral nasal prominences as the placode invaginate
- leaves the nasal pits of the placodes, which form the nostrils and nasal cavities
- lateral nasal prominences form the alae (sides) of the nose
What does the nasolacrimal groove separate?
Lateral nasal prominence from maxillary prominence
*by end of 6th week though they merge at the nasolacrimal groove
When does the medial nasal prominences merge with the maxillary and lateral nasal prominences?
b/t weeks 7-10
*results in the continuity of the upper jaw and lip, and separation of nasal pits form the stomodeum
How do we get the inter maxillary segment?
Medial nasal prominences form it when they merge
- Forms deep portion of philtrum of upper lip
- Premaxillary part of maxilla
- Primary palate
Where does most of the upper lip, maxilla, and secondary palate come from?
maxillary prominences
*will merge laterally with mandibular prominences
How do we get primordial nasal sacs? what separates it from the oral cavity?
- expansion of MNP and LNP mesenchyme causes nasal pits to deepen
- oronasal membrane (ruptures end of 6 week connecting cavities - why you can water come out of your nose)
When does palatogenesis begin?
6th week (done by 12)
critical period: 6-9
What is included in palatogenesis?
Merging of the MNP forms the median palatine process (primary palate)
• Wedge-shaped mass of mesenchyme
• Between the maxillary prominences
• Forms premaxillary part of the maxilla
How do we get the second palate?
- early 6th week from lateral palatine processs (palatine shelves)
- mesenchymal projections project inferomedially on each side of tongue
- as the jaw elongates it pulls tongue away from its root and moves inferiorly in the mouth
- processes assume horizon position above tongue in weeks 7-8
What does the primary palate contribute to? secondary?
- hard
2. soft and hard
If the tongue doesn’t get out of the way what happens?
palatel shelves can’t merge
How do we get the hard plate? soft palate?
- bone extends from maxillae and palatine bones into lateral palatine processes
- posterior portions don’t ossify –> extend posteriorly and fuse –> form soft palate and uvula
Cleft lip
• Often clefting of the nose and/or maxilla
• Maxillary prominence(s) & median nasal
prominence(s)
Cleft Palate
clefts of secondary palate to incisive fossa
• May involve uvula and/or hard & soft palates
• Lateral palatine processes w/nasal septum
• Lateral palatine processes w/medial palatine process
What is the basic reason for cleft?
primordia don’t fuse properly
How do we get the nasal septum?
- Down growth from internal parts of merged medial nasal prominences
- Fusion of nasal septum & palatine processes begins anteriorly (9th week) & is completed posteriorly (12th week)
What is the first indication of tongue development?
- Median lingual swelling appears end of 4th week
- triangular elevation in floor of primordial pharynx
What grows on the sides of the medial lingual swelling?
- lateral lingual swellings (distal tongue buds)
- rapidly proliferate, merge, and overgrow median swelling
Where do tongue buds come from?
proliferation of mesenchyme in venttomedal parts of PA1
What forms the oral part of tongue (ant 2/3)? posterior 1/3?
- merged lateral lingual swellings
- hypo pharyngeal eminence overgrows copula
*where they fuse is terminal sulcus; where circumvalle papilla taste buds form
How do we form the pharyngeal part of the tongue?
• Ventromedial parts of PA2 fuse, forming the copula
• Ventromedial parts of PA3 & PA4 develop the
hypopharyngeal eminence
Where does the muscle of the tongue come from?
myoblasts of occipital metopes (XII to innervate)
NOT NC
Glossoschissis
bifid tongue
*lateral lingual swellings don’t fuse completely
Ankyloglossia
tongue tied; connection b/t floor of mouth and tongue is too long, and limits tongue movements
Macroglossia
tongue is too big for mouth
Odontogenesis
development of teeth
*Teeth develop from reciprocal inductions between neural crest– induced mesenchyme & overlying oral epithelium (ectoderm)
What are dental laminae? tooth buds?
- U-shaped bands of oral epithelium that follow the curves of the primitive jaw
- form in each dental laminae during “bud stage”
*anterior mandibular –> anteriorly maxillary –> posteriorly (6th week)
Cap Stage
- Tooth bud is invested by mesenchyme & becomes ‘cap shaped’
- Consists of the enamel organ, dental papilla, & dental sac
Enamel organ
ectodermal cells from dental lamina → produces enamel
• Outer cell layer = outer enamel epithelium (OEE)
• Inner cell layer lining the papilla = inner enamel epithelium (IEE)
• Stellate reticulum
Dental Papilla
internal part of each tooth (mesenchyme)→ forms dentin & pulp
Dental Follicle/sac
mesenchyme surrounding dental papilla & enamel organ → forms the PDL &
cementum (anchors tooth in jaw)
Bell Stage
- Differentiation of enamel organ results in a bell shape
- Dental papilla cells adjacent to IEE form odontoblasts
Produce predentin → calcifies & become dentin
• Inner enamel epithelium → differentiates into ameloblasts in response to dentin production → produce enamel
• Enamel & dentin formation begins at the cusps & progresses toward the future root
What is the epithelial root sheath?
• Fusion of IEE & OEE • Grows into mesenchyme & initiates root formation • Odontoblasts produce root dentin
What forms the pulp of the tooth? inner cells of the dental sac? outer cells of the dental sac?
- central dental papilla
- Cementoblasts (they product cementum around roots)
- PDL (collagen ligament that anchors tooth to bone)
Tooth Eruption
Emergence of the tooth from the dental follicle in the jaw & its functional position in the mouth
•Root of the tooth grows & crown gradually erupts through oral epithelium
Mandibular teeth usually erupt before maxillary teeth Gingiva: part of the oral mucosa around the erupted crown
As a permanent tooth grows, the deciduous root is resorbed by osteoclasts (odontoclasts)
• Only crown and uppermost part of the root are shed Permanent teeth usually begin to erupt at 6yrs
Permanent Tooth Development
- Permanent dentition consists of 32 teeth • Stages are similar to deciduous teeth
- Deciduous permanent teeth appear at ~10 weeks
- Extensions of the dental lamina, lingual to deciduous tooth buds
- Nondeciduous molars develop as buds from posterior extensions of the dental laminae
- Tooth buds for permanent teeth appear at different times
- Mostly during the fetal period
- Buds for 2nd/3rd permanent molars develop after birth
