Enamel Flashcards
What is enamel and what is the precursor cell?
Specialized covering over teeth developed from mandibular epithelium.
The precursor cell is called an ameloblast.
During tooth eruption, ______ are removed.
Ameloblast
Enamel is what color?
Translucent/ light yellow to gray-white
from 2.5 mm to very thin
Enamel is thinnest at the _______ and thickest at the ________.
Gingival line (CEJ), Crown cusp
Enamel is highly mineralized. True or false?
True
What are the 3 main components of enamel ?
How does the ratio of these components contribute to the physical properties of enamel?
96% mineral
3% Water
1% Organic Material
Makes enamel hard and BRITTLE
Where does the ___ % of organic material in enamel come from?
1% ; It is a proteins of pre-enamel left behind after mineralization of the other 96% has occurred
This 1% contains TRAP (tyrosine-rich amelogenin) and nonamelogenin proteins where are a family of SECRETORY proteins that form the matrix that then will become mineralized to become mature enamel.
What is the ____% of inorganic material in enamel made of?
Crystalline calcium or carbonated phosphate
hydroxyapatite
______ is a necessary base or enamel fracture.
Dentin
How can enamel fracture?
Caries or improper cavity preparation
Enamel and dentin are separated layers.
NO! They are confluent.
The basic unit of the enamel is the _______. Surround it is the ________.
Rod, Inter-Rod Region
Rods are cylinders surrounded by inter-rod enamel wrapping around them
Enamel rod and interrod are both made of _____________ that can be ____ wide and ____ long.
Long crystals made of hydroxyapatite
60-70 nm (0.06-0.07 micrometer)
>100 micrometer
What is the difference between rods and interrods?
The direction they run! Rods run parallel. Interrods go at an angle leaning onto the rods as they wrap them
How are enamel crystals formed?
They form from the first layer of pre-enamel (proteins) that can be mineralized by calcium.
As enamel grows, the crystals become hexagonal due to the structure of calcium phosphate.
In the most mature state that enamel crystals are pushed together. They become organized as rod or inter-rod enamel depending on where they are secreted.
NO NEED TO KNOW CALCIUM PHOSPHATE CHEMISTRY
Aside from 96% _________, 3%______ and 1%________, what else can be found in enamel?
Hydroxyapatite crystals
Water
Protein from pre-enamel left behind
Ions: Flouride, Mg, Strontium, Lead
Acid can dissolve enamel crystals.
What is the major enemy of enamel?
Acid
Enamel starts out as organic material and becomes inorganic when it gets _______.
Mineralized
What is a rod sheath and what is it made of?
The region between the rod and interrod region.
More organic material in rod sheath (water and amelogenin pre-enamel matrix protein)
Rod and interrod are continuous with each other; they are not completley different structures
At the end of enamel maturation, organic material is removed and the remnants are present mostly in the _________.
Rod Sheath
What are the 3 steps of amelogenesis ?
- Presecretory - Inner Enamel Epithelium
Cells differentiate and become protein secreting ameloblasts.
- Secretory
Ameloblasts make and organize enamel
- Maturation
Remove organic material and transport ions for mineral deposition
Which stage of amelogenesis determines tooth morphology via the production of rods and interrods ?
Secretory
From the secretary stage to late maturation, water content_________, mineral content_________ and protein content________.
(Increases/decreases)
Decreases
Increases (29% to 95%)
Decreases (66% to 4%)
Amelogenesis requires _______ which is involved with _________ induction.
Describe this process.
Dentin ; Reciprocal
Inner Enamel Epithelium stimulates dental papilla to become odontoblasts which form dentin. Dentin production then stimulates inner enamel epithelium (presecretory ameloblasts) to become secretory ameloblasts
During what stage of tooth development is amelogenesis happening?
Apposition Stage
There will always be more dentin than enamel because __________
dentin forms first.
Dentin and enamel content will be higher at the __________ during tooth development.
Tooth cusp/ bud tip
7 Steps of Ameloblast Differentiation and Morphogenesis.
- Cuboidal non-secretory cells with central nuceli
- Histodifferentiation - Columnar nuclear migration
- Initial secretory Stage
- Secretory Stage via Tomes Processes
- Maturation stage - Ruffle ended
- Maturation Stage- Smooth ended
Water and organic content DECREASES - Protective Stage
Until tooth is ready for eruption
What factor of amelogenesis is important for rod formation? Does this factor form interrod too?
Tomes Process
NO
What happens to the outer enamel epithelium, stellate reticulum and stratum intermedium during amelogenesis?
They fuse together to form the papillary layer which holds blood vessels that supply nutrients to ameloblasts for enamel formation.
OEE IS KEY HERE!!!!
Odontoblasts which produce ____ are induced by mature ameloblasts.
dentin
FLASE
Pre-secretory ameloblasts induce odontoblasts
What do ameloblasts look like at this stage?
Nuclei shift towards SI (away from odontoblasts)
Golgi prominent in center of cell
Abundant RER
Junctional complexes at both ends
Terminal web seen
When does induction of the ameloblast occur?
When the basal laminal breaks down !
How is the DEJ formed?
We know that Tome’s processes make rods.
However, the first layer of enamel is NOT laid by Tomes process and is rather a softer ECM that fuses with Dentin to make the DEJ
Tomes processes are for life. True or false
True
Amelogenins are hydro_______. They are found on chromosomes ___________ and contain ___ exons. It is associated with 2 extracellular processing proteins called _________.
How do amelogenins regulated enamel growth?
phobic
X and Y (heterogenous)
7
TRAP and LRAP
They self-aggregate to form nanospheres which is a key factor in controlling the growth of hydroxyapatite crystals during enamel mineralization.
What are the 3 nonamelogenins?
- Ameloblastin - Promotes mineralization
- Enamelin - Crystal nucleation and growth
- Tuftelin - Not specific to enamel; function uncler
Ameloblastin and amelogenin proteins are secreted in their own vesicles. True or False?
FALSE
They are secreted together.
In immunogold staining, small ameloblastin dots and large amelogenin dots are seen traveling together in the same vesicle
Tome’s Processes
When enamel is laid down, there is only the ______ portion of Tomes process which leads to formation of the ________.
As ameloblasts move away from the dentin, the _________ form and secrete _________ while ___________ Tome’s process secrete interrod enamel
Proximal
non-rod enamel; the enamel that will make up DEJ
distal Tomes processes, rod
interrod, proximal tomes
The distal Tomes process is ________ of the projection.
fingertip
1 rod :1 Ameloblast. True or False
True
When enough enamel has been produced, what do ameloblasts do next?
This results in rods being ________ between _______ of _______ and _________ enamel.
They go back to secreting the structure less enamel as they lose their Tome’s processes
sandwiched between two layers of initial and final
During the maturation stage, what happens to ameloblasts?
- Ameloblasts get shorter, get rid of some RER and Golgi
- Ameloblasts have two morphologies
- Ruffled Cell Border : Adding inorganic material
- Smooth Ended Border : Removal of water and organic material
Ruffled Cell border of the _____ stage of _____ does what?
maturation stage of enamel
Adds inorganic material
Produces bicarbonate ions
Alkalizes enamel fluids to prevent reverse demineralization
Maintains pH for degrading matrix
RESTABLISHES BASAL LAMINA to separate enamel from cells
*Strong tight junctions**
Smooth Cell border of the _____ stage of _____ does what?
maturation stage of enamel
Removes water and organic material
LATERAL borders of cell
Decreased tight junctions to allow for fluid and its content to move between the cells
What happens to the ameloblast after maturtion?
Apoptosis
What is the protective stage?
The ruffled border secretes basal lamina and hemidesmosomes form between ameloblasts.
Rods run _____ to surface of dentin and _________ long axis of tooth.
They are not in a ________.
Inner part of enamel rods _______.
perpendicular, circumferentially around
straight line
intertwine
What is the Striae of Retzius?
Incremental lines of growth that ends at the surface of the enamel called perikymata
This is because enamel growth is cycles of 6-11 days by ameloblasts.
(Start stop Start stop kind of production)
Looks like tree trucks
What are cross striations in enamel?
Alternating white and dark portions in rod.
Enamel is laid down at 4 micrometers per day. So each cross striation shows a days formation of de
What are Hunter-Schrager Bands?
Can be seen with reflected light
Optical pattern of gray and white areas resulting from changes in rod direction as it curves into tooth
In the cuspal region of a crown, enamel rods _____ forming _____.
Twist, Gnarled enamel
Enamel will look splotchy
DEJ will be _____ shaped.
Scalloped
Enamel Tufts
Abrupt changes in enamel rods at the DEJ
LESS mineralization in this region (more protein)
Enamel Spindles
Odontoblast processes caught between enamel formed by adjacent ameloblast. They penetrate from the dentin into the enamel via DEJ.
Similar to tufts but much shorter.
Enamel Lamella are located on the _______ and contain_______.
Enamel, water and protein
Large black lines
What can affect enamel helath?
Excess acid (coke, beer, coffee)
Bulimia (stomach acid)
TETRACYCLIN- enamel discoloration and brittle
Excess Flouride- Staining
