Exam 3 - Amelogenesis Davenport Flashcards
Hallmark of bell stage
- form of the tooth is determined
- hard tissues start being produced
When does the primary epithelial band form?
37 days
What is the primary epithelial band
continuous band of thickened epithelium forms around the mouth in the presumptive upper/lower jaws
____ corresponds to the future dental arches
Primary epithelial band
Two subdivisions of the primary epithelial band
- vestibular lamina
- dental lamina
Dental lamina gives rise to
Teeth
Teeth will be ____ to the vestibular lamina
Lingual
Stages of tooth development
- bud
- cap
- bell
- early crown
- crown
- late crown formation
- root formation and eruption
- function
In what stage of tooth development does dentinogenesis occur?
Early crown stage
In what stage of tooth development does amelogenesis occur?
Crown stage (after dentinogenesis)
_____ is marked by histodifferentiation and morphodiferentiation
Bell stage
Enamel organ consists of:
- inner enamel epithelium
- outer enamel epithelium
- stellate reticulum
- stratum intermedium
Enamel is secreted as ____ and does not contain ____
Partially mineralized substance; fibers
Cells of the inner enamel epithelium are ____ in nature. The nuclei are ___ located
Cuboidal; centrally to basally (sitting on basement membrane where future DEJ is)
To begin dentinogenesis, the cells of the ______ begin to line up along the basement membrane, and these cells will begin to ____. Then they eventually produce ____
Dental papilla; elongate; predentin
What is the signal for amelogenesis to begin?
When predentin mineralizes and forms dentin
How does amelogenesis begin? (describe changes in cells involved)
- cells of inner enamel epithelium undergo transformation of polarity; become columnar
- nucleus goes to proximal side of cell, cell machinery between nucleus and basement membrane
- distal face becomes secretory
What is the process that extends from the secretory face of the odontoblast to the DEJ?
Tome’s fiber
Initial layer of enamel after dentin mineralizes
Aprismatic enamel
Aprismatic enamel does not contain:
Enamel rods
Ameloblast projection on distal face is called:
Tome’s process
Tome’s process secretes:
Enamel rods
Unit structure of enamel is called
Enamel rod
What is perpendicular to the DEJ?
Haversian systems
As you go up the contour of the tooth, what changes?
Angle of the rods are different
Enamel maturation occurs after:
The full width of enamel has been deposited
Influx of mineral makes crystals larger, increases thickness and width
When is enamel maturation fully completed?
When tooth is erupted and comes into contact with oral fluids (saliva)
3 stages of amelogenesis
- presecretory
- secretory
- maturation
Stage prior to production of enamel
Presecretory stage
Aprismatic enamel and Tome’s process is formed during the:
Secretory stage
What covers the crown of the tooth until it is ready to erupt?
Reduced enamel epithelium
When does Tome’s process retract?
Maturation phase
What happens during presecretory stage of amelogenesis?
- phenotype differentiation
- polarity change
- develop secretory machinery (ER, golgi, mitochondria)
- prepare to secrete enamel
Ameloblasts carry out multiple activities during their:
Life cycle
Ameloblasts may _____ depending on developmental requirements
Upregulate or downregulate
Differentiation of IEE and OEE begins at what parts of the tooth?
Cusps or incisal edge (enamel knot is unique structure to this area)
Amelogenesis progresses in what direction?
Cervically
Blood supply changes during what stage?
Amelogenesis
True or false: the initial layer of enamel contains enamel rods
False - aprismatic enamel
What part of the enamel organ needs to be present in order to form enamel?
Stratum intermedium
After enamel rod formation, there is a ____ transition and formation of ____ layer. Then, the ____ forms to protect the crown of the tooth
Postsecretory; papillary; Reduced enamel epithelium
The ___ is a potential space
DEJ
Is the DEJ a smooth interface?
No, it is intercalated to tighten the fit of the enamel over the dentin
In general, is there any mixing of the enamel and dentin?
No, as long as dentin is produced before enamel. Enamel spindles can form however
During mantle dentin formation, what happens to the basement membrane?
Perforates and degenerates
presecretory stage in amelogenesis
During the early secretory stage of amelogenesis, the cells have a ____ face. During the active secretory stage, _____ develops
smooth face (aprismatic enamel); Tomes’ process
Secretion is ____ during the secretory phase of amelogenesis
Constitutive
continuous; no storage of secretory granules
The secretory phase of amelogenesis is described as having:
Intense synthetic and secretory activity
Is there a lag phase in initiation of mineralization during amelogenesis?
No
True or false: enamel crystals interdigitate with those with dentin
True
surface of dentin is scalloped and enamel fits in the edges
Interrod substance is also known as
Junctional complexes
Face of Tome’s process secretes:
Enamel rod
What is the “rule of 4”?
Takes 4 ameloblasts to produce one rod, and 1 ameloblast contributes to 4 rods
Dentin is produced at a rate of:
4 microns a day
Enamel rod is _____ to the DEJ
Perpendicular
however forms more of sinusoidal curve
Maximum thickness of enamel
2.5mm
Are enamel rods in phase with one another? Why is this significant to enamel structure?
No; contributes to strength of the enamel as long as there is support from the dentin underneath
What happens during the maturation phase of amelogenesis?
- Transitional phase: morphology changes, reduced by half
- Maturation Proper: modulation produces smooth end/ruffle-ended ameloblasts to transport calcium, secretion of covering basal lamina (enamel cuticle); collapse of enamel organ leads to reduced enamel epithelium
What is the modulation cycle in ameloblasts?
Goes between smooth end and ruffle ended
Maturation requires a gradient in order to:
Deposit enamel that goes from the DEJ to the surface of the tooth - otherwise center will be gooey
Ameloblast secretory products
- amelogenins
- enamelin and ameloblastin
- tuftelin
- Proteases
non-collagenous proteins (enamel proteins and enzymes)
____ make up 90% of ameloblast secretory proteins
Amelogenins
____ make up 10% of non-amelogenin proteins
Enamelin and ameloblastin
Amelogenins are controlled by:
Genes on both X and Y chromosome (sexual heterogeneity)
Amelogenins undergo what kind of processing?
- short and long term extracellular processing by proteolytic enzymes into tyrosine rich amelogenin polypeptide (TRAP)
- has to be broken down in order for mineralization and maturation to occur
True or false: amelogenins directly nucleate, shape, or orient crystal ribbons
False - they do not
Amelogenins function
- separates and supports ribbons
- expands matrix to accommodate ribbon elongation
- regulates growth in thickness/width, prevents them from fusing during formation
- must be removed to prevent subsequent enlargement of crystals during maturation
When does amelogenin expression stop?
When enamel reaches full thickness
Amelogenins inhibit:
lateral growth of HA crystals
What happens if there is a loss of function of amelogenins?
thin hypoplastic enamel layer is formed that lacks enamel rods
Amelogenins are a ____ group of proteins
Heterogenous (5-45 kDa)
Non-amelogenin proteins are _____ proteins
65 kDa sulfated proteins
Both amelogenin and non-amelogenin proteins undergo:
Extracellular processing
Function of non-amelogenin proteins
Promote and guide formation of enamel crystals
Ameloblastin is mostly found in:
Newly formed enamel matrix
Ameloblastin has what binding properties?
Calcium
Mutant ameloblastin causes:
- aborting enamel formation
- enamel organ regresses and becomes cystic
Largest and least abundant of enamel matrix proteins?
Enamelin
Where is enamelin present?
Only at growing enamel surface, not detected inside forming enamel
Enamelin is ____ to crystal growth but ____ crystal elongation
Inhibitory; promotes
Loss of function of enamelin
no defined enamel layer
Proteinases function
Have to do with Ca/phosphate binding
Inner enamel epithelium - Functional stages
- Morphogenetic
- Histodifferentiation
- Initial secretory (no Tomes’ process)
- Secretory (Tomes’ process)
- Maturative (ruffled end)
- Maturative (smooth end)
- Protective/desmolytic
During which stage does change in polarity of ameloblasts occur?
Histodifferentiation (presecretory)
Between what 2 stages is there a modulation of activity?
Maturative stage - ruffled end and smooth end
What happens during the protective/desmolytic stage?
After enamel completion, enamel organs collapse and form reduced enamel epithelium over the surface of the tooth
