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236 Cards in this Set
- Front
- Back
What is the Stomatodeum bounded by?
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the cardiac plate and the neural plate
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What separates the stomatodeum from the foregut?
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the buccopharyngeal membrane
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What is the first step in the development of the face? When does it happen?
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The disintegration of the buccopharyngeal membrane allowing the stomadeum to deepen
4th week |
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When does the stomadeum appear?
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day 26
|
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What germ layer is the stomadeum in?
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embryonic surface ectoderm
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Describe the tissue that the stomadaeum gives rise to.
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Primitive 2-3 cell thick layer of oral epithelium that covers embryonic connective tissue
Some of this develops into Dental Lamina |
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When does odontogenesis start?
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week 6
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What are the 3 phases of odonotogenesis
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initiation, morphogenesis, and differentiation
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What two types of tissue are required for odontogenesis?
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ectomesenchyme
oral epithelium (dental lamina) |
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What are the mineralized tissues formed during odontogenesis?
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enamel, dentin, cementum
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What are the soft tissues formed during odonotogenesis?
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pulp, PDL
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When do primary teeth begin to form?
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month 4
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When do permanent teeth begin to form?
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birth
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When does tooth formation begin and end?
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6 weeks after conception and as much as 30 years after birth
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Define mesenchyme.
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undifferentiated loose connective tissue derived from mesoderm
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Define ectomesenchyme.
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undifferentiated loose connective tissue and neural crest cells that have migrated into pharyngeal arch 1.
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What are the migration, proliferation, and differentiation of cells into oral structures directed by?
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genes and their protein products
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What is an example of epithelial-mesenchymal interactions?
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Dental Lamina secretes growth factor that induces the production of transcription factors that lead to the differentiation of the ectomesenchyme.
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What transcription factors are expressed by ectomesenchyme early in tooth formation?
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Msx-1 and Pax-9
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What does knocking out Msx-1 and Pax-9 do?
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arrested tooth development in mice
tooth agenesis in humans |
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Which dentition is affected more frequently by tooth agenesis?
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permanent
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What does the phrase "variable expressivities" mean in relation to tooth agenesis?
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tooth agenesis is variable, suggesting other genetic and environmental factors are involved in tooth agenesis.
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What is Pax-9 associated with?
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tooth agenesis in posterior teeth
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What is Msx-1 associated with?
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human nonsyndromic premolar
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What does a missense mutation result in?
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Different protein
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What does a silent mutation result in?
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same protein
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What causes a nonsense mutation?
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premature protein chain termination
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What is the equation for tooth germs?
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placodes (dental lamina) + ectomesenchyme = tooth germs
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When does thickened epithelium appear in the presumptive upper and lower jaws and where is it derived from?
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6th-7th week
ectoderm |
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Describe the formation of the dental lamina.
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the thickened epithelium around the mouth undergoes mitotic activity and forms a horseshoe shaped band.
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Describe the structures surrounding the dental lamina.
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surrounded by ectomesenchyme of the mandibular and maxillary arches but separated from it by basal lamina.
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Compare the time of appearance and the relative positions of the dental lamina and vestibular lamina.
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Dental forms first.
Vestibular forms just in front dental lamina. |
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What signifies the start of odontogenesis?
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The appearance of the dental lamina.
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Define andontia and tell what it is freq. associated with.
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congenital absence of all teeth
assoc. with ectodermal dysplasia |
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define ectodermal dysplasia
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a defect in the development of all ectoderm-derived tissues of the body
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Define hypodontia.
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1-5 teeth missing
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Define oligodontia.
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> 6 teeth missing
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What causes oligodontia? (does anyone know if this causes hypodontia too?)
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tooth germs not developed due to developmental disturbance with dental lamina formation
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Give multiple names for hyperdontia, how is it most commonly manifested, and what causes it.
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polydontia, supernumerary teeth
most common in the permanent dentition most common is the mesioden caused by developmental disturbance in dental lamina leading to formation of extra tooth germ |
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Define mesioden.
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extra tooth between the central incisors
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What initiates odontogenesis?
What is the driving force after it's initiated and on what day does it take over? |
factors resident in the first arch epthelium that influence the ectomesenchyme. After day 12, ectomesenchyme takes over
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What are the determinants of odontogenesis? i.e. what is are teeth formed from?
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combination of neural crest cells and oral (mandibular) epithelium
NOT limb bud epith. |
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What are two theories of tooth type determination?
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clone model and field model
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When is the earliest histological indication of tooth development?
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day 11
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What are the earliest mesenchymal markers of tooth development and when do they come?
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Lhx-6 and Lhx-7 detected on day 9.
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What is Pax-9 and what is its significance?
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a homeobox gene that codes for an important signaling protein in tooth dev.
A mutation in just one copy of human Pax-9 can result in molar hypodontia. |
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Can a permanent succedaneous tooth come in if its deciduous predecessor was missing?
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No.
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What is Cbfa-1 (Runx-2) and what is its significance?
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gene that codes for an important signaling protein in tooth dev.
A mutation in just one copy results in Cleidocranial displasia |
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What is Cleidocranial Displasia characterized by?
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a failure of teeth eruption due to:
supernumerary teeth heavy fibrous gingiva defective primary tooth and bone resorption |
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Describe the field model of tooth type determination.
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factors that determine tooth shape reside in the ectomesenchyme in distinct graded and overlapping fields for each tooth family.
These fields express different combos of homeobox genes. Redundancy of genes reflects the importance of their expression. |
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Describe the clone model of tooth type determination.
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Epithelium programs ectomesenchymal cells to form certain tooth classes. Each class is derived from clones of these ectomesenchymal cells.
The molar clone ectomesenchyme induces the dental lamina to begin development. Then it proceeds posteriorly. |
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What is the functional difference between dental lamina and vestibular lamina?
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Dental gives teeth and vestibular gives rise to other structures
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What are 6 stages of tooth dev.?
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initiation
bud cap bell aposition maturation (other possibilities: root formation and eruption) |
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What is the main event of the bud stage?
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differentiation of the dental lamina.
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How is the tooth bud formed?
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the first incursion of the dental lamina into the ectomesenchyme of the jaw
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What are the shapes of the epithelial cells during the bud stage?
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core cells are stellate (star-shaped)
peripheral cells are cuboidal |
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What supports the tooth bud?
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ectomesenchymal cells condense to pack closely beneath and around it. They are separated from the bud by a basement membrane.
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How are the buds for deciduous teeth formed?
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The dental lamina interacts with the dental papilla (ectomesenchyme) to form placodes into the ectomesenchyme.
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Is tooth bud formation synchronous or asynchronous?
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they develop asynchronously according to emergence.
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What is the order of where tooth germs are formed?
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first anterior mandible, then ant. max. then in an anterior to posterior order.
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What are two abnormalities that arise from the bud stage?
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Micro- and Macrodontia
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What teeth are usually affected by microdontia?
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Max. lateral incisors and third molars
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Can macrodontia happen to just one tooth?
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yes, but it is uncommon and usually associated with hemifacial hypertrophy.
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What signifies the transition from bud to cap stage?
And what do OEE, SR, and IEE stand for? |
the appearance of the enamel organ made up of the Outer Enamel Epith., Stellate Reticulum, and Inner Enamel Epith.
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What marks the onset of morphologic differences in tooth germs that give rise to different types of teeth?
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the transition from bud to cap stages.
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Why is the cap stage called the "cap" stage?
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The tooth bud proliferates into the ectomesenchyme (pulling the dental lamina with it) and forms a cap over the dental papilla.
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Define Lateral Lamina.
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An extension of the dental lamina that keeps the developing tooth tethered to the dental lamina during the cap stage.
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What does the papilla ultimately form?
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pulp and dentin
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What makes up the tooth germ?
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the enamel organ, the dental papilla, and the dental follicle.
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When do "important developmental changes" in the tooth germ occur?
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late in the cap stage and during the transition from cap to bell.
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What does the enamel organ do?
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Gives rise to distinct cell layers during the cap and bell stages.
Elaborates enamel. Signals the cell of the dental papilla to form dentin. |
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What cells of the tooth germ produce proteoglycans and why?
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the core cells of the enamel organ to maintain its morphology.
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How is the stellate reticulum formed?
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cells that are held together by desmosomes are squished by the viscosity of the extracellular fluid.
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Define cervical loop.
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Where the OEE and IEE meet
will become the cervix of the tooth |
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What types of cells make up the OEE?
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simple squamous to low cuboidal
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What types of cells make up the IEE?
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simple cuboidal to low columnar
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The enamel organ differentiates into what 4 main types of cells?
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OEE
SR SI IEE |
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What is the Stellate Intermedium (SI) good for?
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SI plays a role in the formation and differentiation of ameloblasts.
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What do IEE cells become?
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ameloblasts
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Which cells are responsible for dentinogenesis?
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the peripheral-most cells of the dental papilla (those bordering the basement membrane between papilla and enamel organ)
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What cells will form the pulp?
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the inner cells of the dental papilla
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Compare the components of pulp and follicle.
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The follicle is more fibrous (more collagen fibrils) and less cellular than the pulp, both are made from ectomesenchyme.
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What separates the enamel organ from the follicle?
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a basement membrane
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What cells produce cementum?
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the inner cells of the dental follicle become cementocytes, which produce cementum.
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What do the outer cells of the dental follicle form?
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the PDL and some alveolar bone
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How are succession tooth germs formed?
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the Dental Lamina proliferates more during cap stage of primary germ), forming a bud at its deepest extremity (dormant for some time).
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What are the only permanent teeth whose germs form facially to their primary germ counterparts?
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max. canines
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What are accessional teeth and where do they arise from?
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non-succedaneous teeth (permanent molars) arise from posterior extensions of max and mand. Dental Laminae
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When do the posterior extensions of the dental laminae begin to form?
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5th month of gestation
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When the dental lamina extends posteriorly, where does it go in relation to other tissues?
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underneath the epith. of oral mucosa and into the ectomesenchyme.
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What complication can formation of the posterior extension of the mand. dental lamina cause?
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molars forming in the ramus
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What is the fate of the vestibular lamina and what are formed from it?
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the cells of the vestibular lamina undergo apoptosis to form the vestibule,
minor labial and buccal salivary glands, and the internal lining of the lips, cheeks, alveolar mucosa and gingiva. |
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Describe the Enamel Knot and give another name for it.
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Ahren's Knot
A transient structure made of a cluster of nondividing Stellate Reticulum cells within the enamel organ near the Dental Papilla during the Cap stage |
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What controls the folding of the inner enamel epithelium during the cap stage?
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the ectomesenchymal cells of the dental papilla induce the cells of the Enamel Knot to express signaling molecules to control folding of the IEE.
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What are Enamel Knots good for?
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They play a role in Crown Pattern Formation
Via signaling molecules they induce other cells to proliferate, causing the formation of crowns as well individual cusps. |
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What two molecules does the Enamel Knot need in order to fulfill its function?
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Epidermal Growth Factor (EGF)
Fibroblast Growth Factor-4 (FGF-4) |
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Describe Dens in Dente and give another name for it.
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Dens Invaginalis
The Enamel Organ over-expands and invaginates into the dental papilla causing a tooth within a tooth. |
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What are 3 abnormalities that can occur during the Cap Stage?
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Dens in Dente
Fusion Germination |
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Describe fusion.
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two tooth germs join and develop as one tooth. Decreases number of teeth in mouth. results in extra wide crown with one pulp cavity.
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Describe Germination.
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One tooth germ attempts to divide into two (incomplete twinning) giving an extra wide crown and conserving the number of teeth in the mouth.
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What histodifferentiation happens at the start of the Bell Stage?
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Peripheral epith. cells differentiate into IEE and OEE.
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What do GAGs have to do with the start of the Bell Stage and what is another name for these specific GAGs?
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Perlecan
Synthesized and secreted by cells in the center of the enamel organ. They are hydrophylic, so they draw water, increasing the volume of the enamel organ. They force apart the desmosomal contacts causing the SR cells to become more star shaped. They transport nutrients and calciuum from outlying blood vessels to future ameloblasts. |
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What comprises the periodontium?
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free and attached gingiva
periodontal ligament (PDL) cementum alveolar bone |
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What periodontal development occurs at week 10?
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ectomesenchyme is attracted to the tooth germ and forms around it creating "woven bone" which will become alveolar bone.
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What 3 cells does the dental follicle differentiate into to make periodontal structures?
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cementoblasts (cementum)
osteoblasts (alveolar bone) fibroblasts (periodontal membrane) |
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What has to happen before cementum can be formed?
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dentin must be formed first
then the cells nearest the dentin differentiate into cementoblasts and produce cementum |
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What has to happen before the periodontal membrane can be formed?
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cementum must be formed
then the cells nearest cementum differentiate into fibroblasts to make the PDM |
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What does HERS stand for?
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Hertwig's Epithelial Root Sheath
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What is the connection between Hertwig's Epithelial Root Sheath and the Epithelial rests of Malassez?
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The disintegration of HERS forms the rests of Malassez
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What type of collagen makes the PDL?
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type 1 collagen
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How are teeth connected to the PDL?
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As the root grows, the collagen of the PDL is incorporated into the cementum
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What does the pulp develop from?
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ectomesenchymal cells derived from neural crest cells
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Which comes first, enamel or dentin? Explain.
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dentin comes first
odontoblasts must first lay down predentin so the ameloblast can be stimulated to form enamel |
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What's the percent makeup of enamel?
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94% large calcium hydroxyapatite crystals covered in 4% organic material (enamelins and tuftleins (heavy glycoproteins))
|
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What are the 5 major functions of Enamel?
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1. Induction (induces dentin formation which induces enamel formation)
2.Formation (formation of primary, secondary, and tertiary dentin) 3. Nutrition (via blood supply) 4. Defense (laying down tertiary dentin) 5. Sensation (innervation via A deltas, A betas, and C fibers) |
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What is the difference between morphodifferentiation and histodifferentiation?
When do these take place in the developing tooth? |
morpho gives the shape of the tooth (incisiform, caniniform, etc.) and histo gives different types of cells (odontoblasts and ameloblasts).
They take place at the beginning of the bell stage. |
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Describe the stratum intermedium.
|
SI
at the beginning of the Bell Stage cells from the inner enamel epith. and the stellate reticulum form it. flattened layer of cells with gap junctions transports phosphate from blood to enamel organ via alkaline phosphatase works with IEE to form enamel |
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How are roots formed?
|
Once the crown is formed, Hertwig's Epith. Root Sheath takes over.
It stimulates continued production of dentin (mantle dentin) Eventually cementum is bound to the dentin |
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Differentiate between Lateral, Accessory, and Furcation Canals.
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Lateral Canal: canal through the side of the root that conncts pulp with PDL.
Accessory Canals: random maze of canals near the apical thrid of the root Furcation Canals: canals found at the furca if a tooth has bifurcated roots |
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Describe the diameter of the dentinal tubules.
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Smaller towards the enamel, larger towards the pulp
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Define "dead tract".
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When an odontoblast dies, it leaves an empty tubule called dead-tract tubule.
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Describe dentinogenesis.
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Odontoblasts produce a matrix of collagen fibers and proteoglycans that is then mineralized to form dentin.
|
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What does it mean that odontoblasts are post mitotic end cells?
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it does not undergo mitosis any longer
|
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What are the two main parts of an odontoblast?
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cell body and cell process
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What organelles are important for dentin produciton?
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RER, Golgi, mitochondria
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When does dentinogenesis occur?
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as long as the pulp is alive.
more rapid in early stages of tooth development. when odontoblasts are restimulated by trauma or irritation |
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What types of collagen are in the pulp?
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I and II
|
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What's the most common cell type in the pulp?
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fibroblast (more numerous coronally)
|
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What is the function of fibroblasts in the pulp?
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produce and maintain collagen and pulpal ground substance.
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What is in the pulpal ground substance?
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GAGs
Glycoporteins Water |
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Where are Undifferentiated Multipotential Cells found and what do they do?
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Found in the pulp (most concentrated in cell rich zone)
replace dead odontoblasts and fibroblasts and produce collagen and ground substance |
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What's the difference in structure between regular dentin and tertiary dentin?
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tertiary dentin does not have the tubular form
|
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What are the two main sensory fibers of the pulp and what are their characteristics?
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A deltas
-mylenated -sharp pain -react quickly -associated with odonotoblasts C fibers -nonmylenated -prolonged pain -associated with tissue damage |
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What are the 3 theories of dentin pain reception?
|
Direct Innervation
Odontoblastic Receptors Hydrodynamic Theory of Pulpal Pain |
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What are a tooth's responses to injury?
|
Pain
Nerve Sprouting Neurogenic Inflammation Immune System Response Dentinogenesis |
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What does neurogenic inflammation of the tooth entail?
|
C fibers release neuropeptides causing vasodilation and increased vascular permeablilty
early and localized reaction since teeth are noncompliant |
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What are 2 important events of the Bell Stage?
|
Disintegration of the Lateral Lamina
Folding of the Inner Enamel Epith. to determine crown Pattern and number of cusps |
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What is a consequence of the disintegration of the Lateral Lamina during the Bell Stage and how does the mouth cope with it?
|
the tooth germ is separated from the oral epith.
Later, the tooth reconnects with the oral epith. when junctional epith is formed. |
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What causes folding of the Inner Enamel Epith. during the Bell stage?
|
intrinsic growth due to differential rates of mitotic division in the IEE.
|
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What are side effects of the disintegration of the Lateral Lamina during the Bell Stage?
|
Fragments of it form clumps of epith. cells surrounded by connective tissue called Rests of Serres
Some are phagocytosed by macrophages Some form Eruption Cysts, Odontomes, or supernumerary teeth. |
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What does the Dental Sac differentiate into?
|
the periodontium
|
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What's the order of the 3 precursors to enamel?
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IEE->preameloblasts->ameloblasts
|
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What tooth structures are derived from neural crest cells?
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All except enamel
|
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What controls the afferent circulation to the pulp?
|
smooth muscle
|
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What is responsible for decreased rate of blood flow in the pulpal arterioles?
|
decreased smooth muscle
|
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What is the order of the afferent vessels in the pulp?
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arterioles, metarterioles, precapillaries, capillary bed
|
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What is the pulpal Shunt system called and when is it most active?
|
Arteriovenous Shunt (AV shunt)
most active during inflammation |
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What is the relationship between circulation and inflammation in the pulp?
|
inflammation -> vasodilation and vessel permeability-> tissue pressure exceeds venule pressure ->stasis of blood flow -> local tissue damage -> pulp necrosis spreading from coronal to apical
|
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What is the importance of lymphatics where the pulp is concerned?
|
It reduces fluid pressure in the pulp
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What are the 2 ways fluid pressure is reduced in the pulp?
|
venules
lymphatics |
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What are 4 cells in the pulp that play a role in immune response?
|
macrophage
dendritic lymphocytes (T) Mast |
|
What is a dendritic cell?
|
accessory immune cell
found in lymph and connective tissue antigen presenter |
|
What are Mast Cells?
|
release histamine
found in inflamed pulp |
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What is peri-radicular disease?
|
a defense response to microbial invasion of the root
|
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What does PMN stand for, what do they do, and what's their negative side?
|
Polymorphonuclear Leukocytes (Neutrophils)
phagocytoses microbes and kills them with free radicals or enzymes can cause damage to host tissue dead neutrophil build-up can cause tissue break-down in acute phase of apical periodontitis |
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What are opsonins?
|
antibodies that cover microbes to enhance phagocytosis of the microbes
|
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What do B-lymphocytes do?
|
produce antibodies
|
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Which cells respond to acute inflammation and which cells respond to chronic inflammation?
|
PMN's to acute
Macrophages to chronic |
|
Which Apical Periodontitis is acute?
|
Symptomatic Apical Periodontitis
|
|
What are branchial arches?
|
the same as pharyngeal arches. branchial refers to gills.
|
|
When do the pharyngeal arches begin to form?
|
week 4
|
|
What pharyngeal arches are visible by the end of week 4?
|
arches 1-4 are visible externally
|
|
What are the components of the pharyngeal arches?
|
ectoderm outside, endoderm inside
mesenchyme in the middle (made from mesoderm during the 3rd week, made from neural crest cells during the fourth week) |
|
What is the truncus arteriosus?
|
the common arterial trunk from the heart
|
|
What is another name for the first pharyngeal arch?
|
mandibular arch
|
|
What is another name for the second pharyngeal arch?
|
hyoid arch
|
|
What subdivisions come from the 1st pharyngeal arches?
|
mandibular prominence
maxillary prominence |
|
What does the dorsal end of the first arch cartilage become?
|
meckel cartilage which ossifies to become the malleus and the incus
|
|
What does the middle of the first arch cartilage become?
|
the anterior ligament of malleus and sphenomandibular ligament
|
|
What does the ventral end of the first arch cartilage become?
|
primordium of the mandible
|
|
What does the dorsal end of the second arch cartilage become?
|
Reichert Cartilage ossifies to become stapes and styloid process of temporal bone
|
|
What does the middle of the second arch cartilage become?
|
part of the Hyoid bone (lesser cornu and superior part of the body)
|
|
What does the perichondrium of the second arch cartilage become?
|
the stylohyoid ligament
|
|
What does the third arch cartilage become?
|
part of the Hyoid bone (greater cornu and inferior part of the body)
|
|
What do the 4th and 6th arch cartilages form?
|
the laryngeal cartilages:
cricoid cuneiform corniculate thyroid cartilage |
|
What muscles does the second pharyngeal arch form?
|
stapedius, stylohyoid, posterior belly of digastric, auricular and muscles of facial expression
|
|
What muscles does the fourth pharyngeal arch form?
|
the cricothyroid, levator veli palatini, constrictors of the pharynx
|
|
What is a highly microbicidal agent?
|
hypochlorous acid (HOCl)
|
|
Describe Symptomatic Apical Periodontitis
|
Acute Response
Neutrophil Dominated Lesion Intense Response of short duration Caused by microbes, trauma, or endodontic material Bone not yet affected |
|
What are the symptoms of Symptomatic Apical Periodontitis?
|
Intense Response of short duration
-Pain -Tooth elevation due to edema of PDL -Tenderness to pressure |
|
Describe Asymptomatic Apical Periodontitis
|
Chronic
Macrophage, Lymphocyte, and plasma cell dominated lesion Encapsulated in collagenous connective tissue |
|
What is a true cyst?
|
cyst completely enclosed in epithelial lining
|
|
What is a Bay Cyst/Pocket Cyst?
|
Cyst lined with epith. yet open to the root canal
|
|
What are the 4 main components of an apical true cyst?
|
cavity
epith. wall collagenous capsule extraepith. tissue |
|
What is the Vermillion Zone?
|
The part of the lips that are darker.
|
|
When does the upper face form and what is one of the first events in it's formation?
|
week 4
nasal and lense placodes form on the frontonasal prominence |
|
What are two major events of the formation of the upper face?
|
-formation of the medial and lateral nasal processes that encircle the nasal pits
-fusion of the medial nasal processes forming the premaxillary process |
|
Which forms faster: your upper face or your lower face?
When do they stop growing? |
upper face
puberty |
|
What results in bulges of the frontal eminence and a horseshoe shaped ridge around each olfactory placode and what do these ridges become?
|
proliferation of the underlying mesenchymal cells
the ridges become the medial and lateral nasal processes |
|
What is between the medial nasal processes?
|
the place where the nose develops known as the frontonasal prominence
|
|
What do the medial nasal processes and the frontonasal prominence give rise to? (4 things)
|
middle of the nose
middle of upper lip front of maxilla primary palate |
|
What are the facial events of Day 24?
|
frontal prominence grows to cover expanding brain
mand. and max. processes begin to form from the 1st arch defined boundaries of the stomatodeum results |
|
What are the facial events of Day 26?
|
well formed max. and mand. prominences
|
|
What are the facial events of Day 27?
|
appearance of the nasal placode and odontogenic epith.
|
|
What are the facial events of Day 28?
|
localized thickenings develop within the nasal prominence (olfactory placodes)
|
|
What forms the upper lip and when?
|
the medial nasal processes
fusion of the maxillary processes 4th week |
|
What is the middle of the upper lip called?
|
philtrum
|
|
What is the nasolacrimal groove and what forms it?
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groove extending from median corner of eye to nasal cavity
formed by the fusion of the max. processes to the lateral nasal processes. |
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What forms the primary palate and secondary palate?
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primary is formed by premaxillary process
secondary is formed by palatine shelves |
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What 2 structures are formed in part by the palatine shelves?
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hard and soft palate
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What are "internal projections of the max. processes"?
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the palatine shelves
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What is in the oronasal cavity before it is divided into the nasal and the oral cavities by the palate?
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the primary palate and the developing tongue
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What is *likely* involved in the closure of the secondary palate?
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hardening of the palatine shelves
vacation of the tongue |
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When do the 3 palatal processes completely fuse?
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week 12
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What forms the nasal pits?
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rapid proliferation of underlying mesenchyme around the olfactory placodes causing the frontal eminence to bulge forward
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Describe the lining of the nasal cavity.
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pseudostaritified ciliated columnar epith. with goblet cells on the basement membrane
vascular lamina propria (warm the air) roof has the olfactory epith. |
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What are the 4 paranasal sinuses?
What is their purpose? |
frontal
sphenoid ethmoid maxillary provide mucus for nasal sinus |
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Compare the lining of the paranasal sinuses with the lining of the nasal sinus.
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it is the same "respiratory mucosa" but is thinner and with fewer goblet cells.
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How do paranasal sinuses form and which are present at birth?
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as outgrowths of the wall of the nasal cavity
Maxillary and Ethmoid |
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When does the lower face form and how does it start?
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week 4
starts as 2 bulges inferior to the stomadeum |
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What event in the development of the lower face occurs in the 6th week?
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Meckel's Cartilage forms a rod in a fibrocellular capsule
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When does intramembranous ossification of the mandible begin?
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week 7
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How are the left and right sides of the mandible connected?
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they are not fused until shortly after birth
but are connected by mandibular symphysis made of Meckel's cartilage. |
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What are the 3 secondary growth cartilages that influence the growth of the mandible?
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Condylar
Coronoid Symphyseal |
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When does the condylar growth cartilage appear, what does it form, and does it persist after birth?
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week 12
forms ramus via interchondral ossification persists on head of condyle |
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When does the coronoid growth cartilage appear and does it persist after birth?
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4 months
no |
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Where does the symphyseal growth cartilage appear and does it persist after birth?
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in the connective tissue at the ends of the Meckel's cartilage
persists for 1 year after birth |
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When does the tongue begin to develop?
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week 4
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What is the first step in formation of the tongue?
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proliferation of mesenchyme forms several swellings in the floor of the oral chamber
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What is the oral part of the tongue and what is it formed from?
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the anterior 2/3 of the tongue
forms from the fusion of the lateral lingual swellings and median tongue bud |
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What are two other names for the posterior 1/3 of the tongue and what does it develop from?
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pharyngeal part or root of the tongue
formed from the fusion of the copula and the hypobranchial eminence (comes from arches 2, 3, and 4) |
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What parts of the tongue come from occipital somites?
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myoblasts which become the muscles of the tongue
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What parts of the tongue come from pharyngeal arch #1?
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the lateral lingual swellings (which become the mucosa of the ant. 2/3)
and the median tongue bud |
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What parts of the tongue are formed by the pharyngeal arch #2?
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the copula (no adult structures)
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What parts of the tongue come from pharyngeal arch #3?
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ventral part of hypopharyngeal eminence which becomes the mucosa of the posterior 1/3 of tongue
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What parts of the tongue come from pharyngeal arch #4?
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dorsal part of hypopharyngeal eminence which becomes the mucosa of the dorsal part of the posterior 1/3 of tongue
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What parts of the tongue come from the head mesoderm?
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myoblasts which become the
palatoglossus muscle |
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What is the primordial pharynx derived from?
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the foregut
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What does the first pharyngeal pouch turn into?
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an elongate tubotympanic recess
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What does the tubotympanic recess give rise to?
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the tympanic cavity and the mastoid antrum
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What does the second pharyngeal pouch become?
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palatine tonsils
tonsillar sinus/fossa tonsillar crypts 20 weeks->pouch mesenchyme->lymphoid tissue->lymphatic nodules |
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When does the epith. of the 3rd and 4th pouches begin to proliferate to form the parathyroid glands?
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week 5
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Describe the events of the histiogenesis of the parathyroid glands that involve the 3rd and 4th pouches.
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nodules are formed on the dorsal ends of the pouches
vascular mesenchyme grows into the nodules forming a capillary network chief cells are differentiated in utero oxiphil cells are differentiated 5-7years after birth |
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Describe the histiogenesis of the ultimobranchial body and tell what its cells do.
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elongated ventral part of fourth pouches form ultimobranchial body
its cells disseminate into the thyroid creating "C" cells that come from neural crest cells and produce calcitonin |
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When does the thyroid gland first appear?
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late in the 4th week
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Describe the thyroid gland primordia during the fourth week.
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a mass of endoderm that proliferates from the apex of the foramen cecum of the primitive tongue
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