Embryological Development of the Face and Head Flashcards
When is the basic morphology of the face created?
Between the fourth and tenth weeks
The nasal placode invaginates to form the nasal pit. What features are derived from the nasal pit?
Lateral nasal process
Medial nasal process
How is the nasolacrimal duct formed?
It is formed by the groove between the lateral nasal process and the adjacent maxillary swelling
How is the philtrum formed?
The inferior tips of the medial nasal processes expand laterally and inferiorly and fuse to form the intermaxillary process. The intermaxillary process gives rise to the philtrum
How are the palatine shelves formed?
The medial walls of the maxillary processes produce a pair of thin medial extensions called the palatine shelves
What is the primary palate?
The floor of the nasal cavity at this stage is formed by a posterior extension of the intermaxillary process call the primary palate
What is the secondary palate
Palatine shelves grow downward parallel to the lateral surfaces of the tongue at first and then, at the end of the ninth week, they rotate rapidly upward into a horizontal position and fuse with each other and the primary palate, to form the secondary palate
How does fusion of the secondary palate happen?
First ventrally and then proceeds dorsally along the midline
What cells eventually form the bony hard palate?
Mesenchymal cells
What two processes form the nasal septum?
Ectoderm and mesoderm of the frontonasal process and the medial nasal process (they eventually fuse with the primary and secondary palate
What germ layer gives rise to the tongue?
Endoderm
Development of the tongue begins in which pharyngeal arch?
First pharyngeal arch. It is called the median tongue bud. About a week later the distal tongue buds develop
The distal tongue buds give rise to what?
Anterior two thirds of the tongue
What arch gives rise to the copula?
Second pharyngeal arch
Where does the posterior third of the tongue come from? (Hint: Copula = CONNECTS)
A midline swelling of the third and fourth arches (called the hypopharyngeal eminence) overgrows the copula to form the posterior one third of the tongue.
The motor component of the tongue is suppled by what cranial nerve?
CN XII (Except for palatoglossus which is suppled by CN X
Both the sensory and taste components of the posterior 1/3 are supplied by what cranial nerve?
CN IX
Circumvallate papillae are innervated by what CN?
Sensory branch of glossopharyngeal nerve (CN IX) supplies circumvallate papillae (located in the anterior 2/3).
If you want to be technical, what other CN (besides IX) supplies a small posterior mucosal region on the POSTERIOR tongue?
Sensory fibers of superior laryngeal branch of vagus (CN X)
The sensory component of the anterior two thirds of the tongue is supplied by what CN?
The sensory component of the anterior 2/3 is supplied by the lingual branch of the mandibular branch (V3), which comes off of the Trigeminal nerve (CN V).
The taste component of the anterior two thirds of the tongue is supplied by what CN?
The taste component of the anterior 2/3 is supplied by the chorda tympani branch of the Facial nerve (CN VII), which Innervates all taste buds except the circumvallate papillae.
Four important functions of saliva
- It has a buffering ability
- It provides a cleansing effect
- It has an antibacterial action
- And is important in the maintenance of an oral environment, which is supersaturated in calcium and phosphate.
At what pH does hydroxyapatite dissolve?
5.5
At what pH does fluorapatite dissolve?
4.5
Post eruption tooth development rely upon what two ions?
Calcium and Phosphate
Why should I care about Amorphous calcium phosphate (ACP)
ACP is a reactive and soluble calcium phosphate compound and ACP rapidly releases calcium and phosphate ions to convert to apatite and is useful to patients with impaired salivary flow to help with the remineralization of tooth structure. (It is a replacement for natural saliva)
Parotid gland devolops from what germ layer?
Ectoderm. The parotid gland develops from a groove-like invagination of ectoderm that forms in the crease between the maxillary and mandibular swellings
The submandibular and sublingual glands develop from what germ layer?
Endoderm
What are the five branches of the facial nerve?
- Temporal branch – frontalis, obicularis oculi, corrugator supercilli
- Zygomatic branch – obicularis oculi
- Buccal Branch – obicularis oris, buccinator, zygomaticus
- Marginal mandibular branch – mentalis
- Cervical branch - Platysma
What nerve supples the sensory innervation to the parotid gland?
The auriculotemporal nerve of the mandibular branch (V3) ofCN V supplies sensory to the parotid gland.
Parasympathetic innervation of the parotid gland comes from what CN?
Parasympathetic innervations to the parotid gland is through the glossopharyngeal nerve (IX).
Sympathetic innervation of the parotid gland comes from what nerve?
Superior cervical sympathetic ganglion
All glands ABOVE the level of the oral fissure are innervated by the ….
Greater petrosal branch of the facial nerve (VII).
All glands BELOW the level of the oral fissure (including the sublingual and submandibular glands) are innervated by the ….
Chorda tympani branch of the facial nerve (VII)
What is the ONLY purpose of the alveolar process?
Support the teeth. If a tooth fails to erupt, alveolar bone never forms in that area. If a tooth is extracted, the alveolus resorbs after the extraction until finally the alveolar ridge completely atrophies.
How many centers of epidermal cell proliferation exist on each dental lamina to form teeth?
10
True or False: The concentration of mesenchymal cells consists of NEURAL CREST derived cells migrating from the caudal region of the MESENCEPHALON and the cranial region of the METENCEPHALON
True
When forming the dental papilla from mesenchymal condensation, is the signal sent from the ectoderm or the mesenchymal cells?
Ectoderm. This is called the cap stage
The 20 initial tooth buds give rise to what?
Primary dentition
What is the genesis of permanent teeth?
Early in bell stage, the dental lamina superficial to each tooth bud produces a small DIVERTICULUM that migrates to the base of the primary tooth bud and becomes the bud of the permanent tooth
Where do primary and secondary molar come from?
The buds of the permanent molars that do not have a primary tooth precursor arise during POSTNATAL life from a pencil-like extension of the dental lamina that burrows back into the posterior jaw from the primary second molar tooth bud.
Where do odontoblasts come from
During bell stage the outermost cells of the dental papilla become organized into a layer just adjacent to the inner enamel epithelium and these cells differentiate into the odontoblasts. They produce predentin at the junction of the inner enamel epithelium
The inner mesenchyme of the dental papilla becomes what?
Pulp
What forms the enamel organ?
Dental lamina
What three layers eventually arise from the enamel organ in the bell stage?
– An inner enamel epithelium overlying the dental papilla
– An middle enamel reticulum of star shaped cells
– An outer enamel epithelium
Where do ameloblasts come from
As soon as mineralized dentin is formed, cells of the inner enamel epithelium differentiate into enamel-producing ameloblasts
What three stages are included in amelogenesis
– First stage: inductive stage
– Second stage: secretory stage
– Third stage: maturation stage
Inductive stage
The inner enamel epithelium has a cuboidal or low columnar appearance to form preameloblasts. No Tomes processes exist. The preameloblasts send a signal across the DEJ to stimulate deninogenesis
Secretory stage
Ameloblasts are collumnar. They produce the enamel matrix. Tomes processes are formed
Maturation stage
Cells may be striated or have a ruffled border. Enamel maturation occurs.
Ruffled border
More surface area (ruffled) indicates that the ameloblast is transporting enamel proteins to create enamel
Are enamel crystals oriented in a parallel or perpendicular orientation in the enamel rods?
Parallel
What is the length of an enamel rod?
1.5 to 3 mm in length
Rod sheath
A space that contains an increased amount of residual matrix proteins and is called the rod sheath. It
What forms the reduced enamel epithelium?
- A layer of ameloblast cells (Originate from the inner enamel epithelium)
- The adjacent layer of cuboidal cells from the outer enamel epithelium
What is another name for Hertwigs epithelial root sheath?
Epithelial root sheath
What forms the epithelial root sheath
The confluence of the inner and outer enamel epithelia elongate to form a bilayered epithelial root sheath
True or False: The epithelial root sheath cells are an unique population of epithelial cells in the periodontal ligament compartment and their functional role is not fully understood
True
True or False: the epithelial root sheath is formed from the dental papilla
False. It is formed from the enamel organ
True or False: Hertwig epithelial root sheath initiates the formation of dentin in the root of a tooth by causing the differentiation of odontoblasts from the mesenchyme of the dental papilla.
True
How do cementoblasts form?
The tooth roots are enclosed in extensions of the mesenchymal dental follicle or sac and the inner cells of the sac differentiate into cementoblasts
The outermost cells of the dental sac participate in alveolar bone formation and also form what?
PDL
Incremental lines of Salter
Cementum demonstrates relatively irregular incremental growth lines parallel to the tooth surface - these are the incremental lines of Salter
Acellular cementum
Acellular cementum forms first as the cementoblasts differentiate from dental follicular cells, which can only reach the surface of the tooth’s root once Hertwig’s Epithelial Root Sheath (HERS) has begun to deteriorate.
Cellular cementum
Cellular cementum develops after acellular cementum, and typically most cellular cementum is formed after the tooth occludes with a tooth in the opposite arch. It is usually found near the apex of the tooth
Intrinsic fibers
Collagen fibers produced by cementoblasts that are confined to the cementum
Extrinsic fibers
Collagen fibers formed by fibroblasts of the PDL form the principal fiber bundles and are partly incorporated into the cementum. Also known as Sharpy’s fibers
Do Sharpy’s fibers connect to acellular or cellular cementum?
Both
What is the most widely held eruption theory?
The most widely held current theory is that while several factors are involved in tooth eruption, root development, the periodontal ligament and the dental follicle all play primary roles in the process
Amelogenesis Imperfecta
A relatively rare group of inherited disorders characterized by abnormal enamel formation
How is amelogenesis imperfecta inherited?
An x-linked autosomal recessive or autosomal dominant condition
*Hypocalcified
Normal thickness, smooth surface, less hardness
*Hypoplastic, pitted
Normal thickness, pitted surface, normal hardness.
Hypoplastic, generalized
Reduced thickness, smooth surface, normal hardness.
Hypomaturation
Normal thickness, chipped surface, less hardness, opaque white coloration.
Dentinogenesis imperfecta
Represents a group of hereditary conditions that are characterized by abnormal dentin formation
Is dentinogenesis imperfecta an autosomal dominant or recessive disorder
Dominant
What gene is mutated in dentinogenesis imperfecta
DSPP
What proteins are mutated in amelogenesis imperfecta
AMELX, ENAM, and MMP20
What other systemic hereditary disorder can be seen with dentinogenesis imperfecta
Osteogenesis imperfecta
Osteogenesis imperfecta
Osteogenesis imperfecta is a genetic disorder characterized by bones that break, often from little or no apparent cause. It is the result of mutation in collagen producing genes COL1A1 and COL1A2
Ectodermal dysplasia
Inherited disorders, that involve defects in the hair, nails, sweat glands and teeth. Need at least two manifestations for have disorder. GENETIC DISORDER
Dental consequences of ectodermal dysplasia
- Teeth may be missing, pointed, widely spaced, or prone to cavities because of defective enamel.
- Dental treatment is almost always necessary and children may need dentures as early as two years of age.
- Multiple denture replacements are needed as the child grows, and dental implants may be an option once the child’s growth is complete.
- Orthodontic treatments may be necessary.
What trimester is most important for normal development of fetus?
First trimester
Holoprosencephaly
A birth defect of the brain, which effects the development of midline facial features. Eyes, microcephaly, cleft lip, cleft palate
Single lobed brain
Holoprosencephaly
Failure of the prosencephalon
Holoprosencephaly
Cebocephaly
Single nostril
Hypotelorism
Close set eyes
Cyclopia
One eye
Trigonocephaly
Triangular shaped skull due to premature closure (synostosis) of the suture between the frontal bones (Metopic synostosis) causing compression of the growing cerebral hemispheres
Mutation of Sonic Hedgehog protein
May cause holoprosencephaly
What teratogen is thought to be the most common cause of congenital mental retardation in the western world?
Alcohol (Preventable)
Fetal alcohol syndrome FAS
Mild form of holoprosencephaly. Slow Growth development
Embryologic manifestation of FAS
Due to deficiencies of midline tissue of the neural plate very early in embryonic development, caused by exposure to very high levels of alcohol
Characteristic facial features of FAS include
– Small eyes with drooping upper lids – Short, upturned nose – Flattened cheeks – Small jaw – Thin upper lip – Flattened philtrum
Central nervous system problems of FAS including
– Mental retardation – Hyperactivity – Delayed development of fine and gross motor skills – Impaired language development – Seizures
Neural crest cell migration problems result in what?
- Craniofacial anomalies
- Bone and muscle deficiencies in face
- Problems with the heart and great vessels
- The farther a neural crest cell has to migrate, the greater chance of deformity presents
What four drugs influence neural crest cell migration?
• Alcohol • Thalidomide (sedative) • Accutane (Cystic Acne) • Retinoic acid (is a metabolite of Vitamin A)
Treacher Collins
Altered development of neural crest cells has been implicated in Treacher Collins Syndrome or mandibulofacial dysostosis. It is characterized by a generalized lack of mesenchymal tissue in the LATERAL part of the face. Underdeveloped facial bones
Treacher Collins and infants
In severe cases, underdevelopment of the facial bones may restrict an affected infant’s airway, causing potentially life-threatening respiratory problems.
Treacher Collins manifestations include
- Eyes slant downward
- Sparse eyelashes
- Coloboma (notch by eye)
- Vision loss
- Deformed ears
- Hearing loss
- NORMAL INTELLIGENCE
Treacher Collins and dental care
- Good oral hygiene
- Fix occlusion
- Orthognathic surgery and or distraction osteogenesis
- Speech pathologist
Another name for craniofacial microsomia
Hemifacial microsomia
Craniofacial microsomia
Caused by lack of neural crest cells, during migration for unknown reasons. Characterized by a lack of development in the LATERAL facial areas. may have deformed ear and mandible/soft tissue deficiencies.
Craniosynostosis syndromes
Craniosynostosis syndromes result from early closure of the sutures between the cranial and facial bones. Occur in the final stage of facial development and in the early fetal (after 8 weeks) rather than embryologic period of prenatal life.
Define synostosis
Early closure of a suture
Cranial base is formed by what type of ossification
Endochondrial
Metopic synostosis
Results in a trigone- shaped skull with bossing (protrusion) of the parieto-occipital region
Bilateral coronal synostosis
Results in a prominent frontal bone, flattened occiput, and anterior displacement of the skull vertex
Sagittal synostosis
With a ridged, fused sagittal suture causes bitemporal narrowing, and frontal and occipital bossing
Acrocephaly
A type of craniosynostosis in which there is premature closure of the lambdoid and coronal sutures, resulting in an abnormally high, peaked, or conical cranium
Cleidocranial dysplasia is autosomal dominant or recessive
Autosomal dominant
Cleidocranial dysplasia
- Supernumerary teeth
- Short stature
- Delayed exfoliation of primary teeth
- Adult teeth develop later
- Normal intelligenc
- Abnormally large, wide-open fontanels at birth that may remain open throughout life
- Clavicular hypoplasia
- Brachydactly (shortening of fingers
Apert’s syndrome is autosomal dominant or recessive
Dominant
Apert’s syndrome results in a mutation of what gene
fibroblast growth factor receptor 2 (FGFR2) gene located on chromosome 10
Clinical features of Apert’s syndrome include
The clinical features include – mis shapen skull caused by coronal suture synostosis – wide-set eyes – symmetric syndactyly (fusion) of fingers and toes. – bone syndactyly (fusion)of hands and feet. – mid-face hypoplasia, class III occlusion – High arched palate – Intracranial anomalies – Cardiac anomalies – Delayed tooth eruption is common – Clefting of the soft palate,or bifid uvula is found in 30% of cases
Carpenter syndrome
Is an extremely rare condition affecting the skull and facial bones, as well as the bones of the hands and feet.
Carpenter syndrome is caused by what gene
RAB23 on Chromosome 6
What type of craniosynostosis is common in Carpenter’s syndrome
Acrocephaly
Clinical features of Carpenter’s syndrome include
– Extra fingers and toes – Short fingers and toes – Mental retardation – Mild obesity – Short neck – Heart disease – Syndactyly of the toes and fingers
Know differences between Aperts and Carpenters
Aperts Carpenters
Dominant Recessive
FGFR2 RAB23
Coronal Sut Lam.. and Cor.
Crouzon’s syndrome frequency
Is the most frequently occurring member of the Craniosynostosis syndromes
Crouzon’s syndrome
It is characterized by underdevelopment of the midface and eyes that seem to bulge from their sockets
Prenatally, what causes Crouzon’s syndrome
This syndrome arises because of prenatal fusion of the superior and posterior sutures of the maxilla (basal sutures) along the wall of the orbit
What type of synostosis is common in Crouzon’s syndrome
Brachycephalic head (coronal)
Clinical manifestations of Crouzon’s syndrome
- wide-set, bulging eyes and vision problems caused by shallow eye sockets
- Stenosis of the optic canal causing optic nerve atrophy
- Eyes that do not point in the same direction
(strabismus) - a beaked nose
and an underdeveloped upper jaw - Hearing loss, which is sometimes accompanied by narrow ear canals
- People with Crouzon syndrome are usually of normal intelligence
What gene is associated with Crouzon’s
FGFR2 (same as Aperts)
Is Crouzon’s autosomal dominant or recessive?
Dominant
