Development of Orofacial structures Flashcards
Neurocranium:
Derived from mesenchyme
Gives rise to bones that enclose brain
Has cartilagenous and membranous components
Viscerocranium:
Derived from mesenchyme
Gives rise to bones of the facial skeleton
Has cartilagenous and membranous components
Intramembranous ossification:
Mesenchymal origin, does not involve cartilage
Neovascularization occurs
Osteoblasts produce the osteoid and produces bone and osteocytes
Endochondral ossification:
Uses preexisting cartilage model (e.g. long bones)
Diaphysis has the primary ossification centers
Chondrocytes undergo hypertrophy and matrix will calcify
Cartilagenous part of the neurocranium:
Occipital bone
Body of sphenoid
Ethmoid
Petrous and mastoid parts of the temporal bone
Membranous part of the neurocranium:
Frontal and parietal bones
Cartilagenous parts of the viscerocranium:
Malleus and Incus (PA1)
Stapes, styloid process and lesser horn (PA2)
Greater horn (PA3)
Laryngeal cartilage (PA4)
Derived from neural crest
Membranous parts of the viscerocranium:
Maxillary prominence
Squamous part of temporal bone
Maxilla
Zygomatic bone
Craniosynostosis:
Premature fusion of cranial sutures
Scaphocephaly
Brachycephaly
Plagiocephaly
Trigonocephaly
Involves sagittal suture, wedge shaped cranium (from superior view)
Involves entire coronal suture. Tower like cranium
Involves one side of the coronal suture, twisted and asymmetric cranium
Involves the frontal suture
What drives the shape/rate of growth of the head?
Brain development
What is the precursor structure for head development?
Appears?
Separated by? When does this rupture?
Facial primordia
Appears during week 4 and surround the stomodeum
Separated from the primordial pharynx by oropharyngeal membrane (ruptures at day 26)
Parts of the facial primordia:
2 maxillary prominences
2 mandibular prominences
1 frontonasal promince
Identify the parts of the facial primordia
Refer to drawings
Mandibular prominence
Derivatives:
Chin, lower lip and cheek
Incomplete fusion of mandibular prominence results in …
Chin dimple
Draw the development of the facial primordia
Refer to drawings
Maxillary prominence:
Derivatives:
Upper lip, maxilla and secondary palate
Grows medially and merges laterally with mandibular prominence
PA2 mesenchyme invade primordial lips and cheeks and give rise to facial muscles
Frontonasal prominence:
Derivatives:
Forehead, dorsal nose
Will go and surround the ventrolateral part of the forebrain
Nasal placodes and development:
Bilateral oval thickenings of surface ectoderm on inferolateral portion of frontonasal prominence
Proliferation forms horse shoe shaped elevations that form the medial and lateral nasal prominences, nasal pits and primordial nares
Medial Nasal prominence is regulated by?
What happen to it?
Regulated by PDGFRA
Shifted towards midline and fuses together to form the intermaxillary segment (philtrum)
Lateral nasal prominence is separated from the maxillary prominence by?
Fuses with what by week?
Nasolacrimal groove separates it from maxillary prominence but merges with the prominence by end of wk 6
Auricular primordia:
Six auricular hillocks will form around the first pharyngeal groove
Mandible development will push the ear from neck to side of head at the level of the eyes
What signaling molecule is responsible for apoptosis of cells in the mandibular process (and webbings of hand and feet)
BMP
Examples of proportion and position changes during development
nose is initially flat and mandible is underdeveloped. Reaches form at 14 weeks.
As brain develops, the cranial cavity expands and orbits move from lateral to anterior positions
Nasal cavity development:
Nasal placodes form the nasal pits > mesenchyme form medial and lateral nasal prominence induce pits to be deeper and form primordial nasal sacs > sacs grow and oronasal membrane separates it from the oral cavity (this ruptures at wk 6)
Primordial choanae:
Nasal conchae
Olfactory epithelium:
Connection between nasopharynx and nasal cavity
Forms superior, middle and inferior turbinates, inflamed with rhinitis
Specializes into the olfactory nerve, loss of smell sign of Parkinson’s
Timing of palatogenesis
Development between wk 6 - wk 12. Critical period wk 6 - start of wk 9
Primary palate:
Fusion of median nasal prominence to form the median palatine process
Secondary palate:
Develops from the fusion of the lateral palatine process (via mesenchymal projections). Basically replaces the oronasal membrane
How is the hard palate formed?
Bone extends from the maxillae and palatine bones to the lateral palatine processes to form the hard palate
Posterior portions do not ossify (soft palate and uvula)
Palatine raphe is formed (line of fusion)
What is the incisive fossa?
Foramen thing at the frontal palate. Remnant of the nasopalatine canal
How is the nasal septum formed?
Downward growth from internal parts of medial nasal prominences and fuses with lateral palatine process (anterior to posterior)
Cleft lip and palate:
Defects in fusion of palatine bones
Most common form: unilateral left cleft lip
Choanal Atresia:
Associated with bony abnormalities of pterygoid plates and midface growth abnormalities. Deviated septum
Upper airway obstruction, noisy breathing, canosis that worsens with feeding and Improves with crying
How does the Anterior 2/3 of the tongue develop?
When does it start to develop?
Week 4: median lingual swelling (median tongue bud) appears
Lateral tongue swellings (distal tongue buds) then develop on either side of the median swelling. Induced by mesenchyme from PA1
How does the pharyngeal (posterior 1/3) part of the tongue develop?
Copula comes from ventromedial parts of PA 2
Hypopharyngeal eminence comes from ventromedial parts of PA 3 and 4.
HPE overgrows the Copula
Terminal sulcus
Fusion of oral and pharyngeal parts occur here
Tongue musculature is derived from …
Innervated by ….
Myoblasts of occipital myotomes
CN XII
Tongue innervation:
Anterior 2/3
Mucosa: Lingual N.
Taste: CN VII (via chorda tympani)
Taste buds: CN IX
Musculature: CN XII
Tongue innervation:
Posterior 1/3
Mucosa: Glossopharyngeal
Musculature: Hypoglossal
Sensation to pharynx: Vagus
Palatoglossus M: Vagus
Glossoschissis
Ankyglossia
Macroglossia
- Bifid tongue (two point ends)
- Short frenulum, problems with breastfeeding/speaking
- large tongue (associated with Beckwith-Wiedemann and Down syndromes)
How do teeth develop?
Neural crest and epithelium on the jawbone communicate and induce the dental laminae (oral epithelium that follow curves of primitive jaws)
Tooth buds develop
Cap stage of tooth development:
Tooth bud becomes cap shaped when invested with mesenchyme
Tooth bud composition:
Enamel (ectoderm)
Dental papilla (inner part of the tooth with dentin and pulp)
Dental follicle/sac (mesenchyme from mesoderm, surrounds the dental papilla and enamel organ
Bell stage of tooth development:
Enamel differentiates and causes enamel organ to become bell shaped
Odontoblasts
Ameloblasts
- Form the dental papilla cells next to inner enamel epithelium. Predentin will calcify to form dentin
- Produces enamel. Inner enamel epithelium differentiates in response to dentin production
How do these root components develop? Epithelial root sheath Pulp Cementum Periodontal ligament
Epithelial root sheath forms from the fusion of inner and outer enamel epithelium
Pulp forms from central dental papilla
Inner cells of the dental sac form cementoblasts
Outer cells of the dental sac form PDL
Tooth eruption:
Root of tooth and crown will erupt through the oral epithelium
Mandibular teeth erupt first
Deciduous root is reabsorbed by odontoclasts (teeth osteoclasts) while crown and upper root are shed
Decidious and permanent teeth development
Wk 10: decidious teeth appear as extensions of the dental lamina
Nondeciduous molars form as buds from posterior part of the dental lamina. Tooth buds appear at different times (most during fetal period, but buds for 2nd and 3rd molars develop after birth)
What induces the formation of the dental papilla?
Mesenchyme cells interacting with ectoderm cells
