Enamel Flashcards
(112 cards)
1
Q
What are the two stages of precipitation?
A
nucleation and crystal growth
2
Q
What are the two stages of enamel crystal growth?
A
crystal elongation and crystal maturation
3
Q
How does crystal elongation occur?
A
(prior to maturation) involves the lengthening of crystals along the C axis
4
Q
How does crystal maturation occur?
A
(after elongation) involves the deposition of ions on the sides of the crystals, increasing thickness and width
5
Q
What is the D of water?
A
80
6
Q
Why is the dielectric constant for water so high?
A
because it is polar
7
Q
Why is enamel less soluble in water?
A
Molecules or more densely packed, allowing for greater attractive forces
8
Q
What is coulomb’s law?
A
F=q1*q1/(r^2)D
9
Q
What are the “triangular” spaces between phosphate ions in enamel?
A
interstices
10
Q
What fill the interstices between phosphate ions?
A
1/3 OH-, 2/3 Ca2+
11
Q
What percentage of calcium ions are Cal?
A
40%
12
Q
What is the ratio of interstices to phosphates?
A
2:1
13
Q
What does the F- ion improve the attractive forces?
A
it is smaller than OH- and allows the structure to pack more densely, improving attractive forces
14
Q
How are the phosphate lattices layered?
A
in an A-B-A-B arrangement
15
Q
the _______ facing interstices of the A layer are aligned with the _______ facing interstices of the B layer.
A
Right : Left
16
Q
Which direction do the non-columnar interstices face in the A layer? B layer? What are they capped by? What fills them?
A
Left : Right : Phosphates : Non-columnar Ca2+ ions
17
Q
How many oxygens does a columnar Ca2+ (Cal) coordinate with?
A
9 phosphate oxygens
18
Q
How many oxygens does a non-columnar Ca2+ ion coordinate with?
A
7 (6 phosphate and 1 hydroxyl)
19
Q
What is Ksp? What do they describe?
A
solubility product constant (equilibrium of adding and loosing ions) : describe the behavior of lowly soluble ionic solids
20
Q
What is the chemical formula for Calcium Hydroxyapatite (HAP)?
A
Ca10(PO4)6(OH)2
21
Q
Give the Keq for HAP. (the formula for Keq)
A
[Ca2+]^10 x [PO4;3-]^6 x [OH-]^2 / [Ca10(PO4)6(OH)2]
22
Q
What value does the concentration of a sparingly soluble solid have in a Keq equation?
A
1
23
Q
What is Ksp when the solution is at equilibrium with the solid?
A
Ksp = Keq
24
Q
What is Qsp? What is it equal to?
A
ion product : the product of the concentrations of of the ions that make up the crystal, each raised to the power corresponding to the number of that ion in the chemical formula (basically Keq=Qsp/[S])
25
What is Keq?
equilibrium constant
26
How does the relationship of Qsp and Ksp affect mineralization of enamel?
When Qsp=Ksp there will be no net gain or loss of ions. When QspKsp the crystal grows (again, will bring back to equilibrium)
27
Explain the relationship of Qsp and Ksp. Why does it work the way it does?
Qsp is the ions in a dissociated state. When there are very few free ions (i.e. QspKsp) the solution will again push to equilibrium by growing the crystal and taking away free ions.
28
What is a solution called when its Qsp>Ksp?
Super-saturated
29
What mineral is formed when F replaces all OH? Only some of them?
Calcium Fluroapatite : Calcium Fluorhydroxyapatite
30
What does a high Ksp mean?
very soluble
31
What does carbonate (CO3;2-) substitute for in HAP?
one phosphate, or two hydroxyls
32
What affect does carbonate have on the solubility of HAP? its Ksp?
it decreases the stability of the molecule making it more soluble : higher Ksp
33
How is the charge discrepancy between carbonate and phosphate made up for when there is a substitution?
getting rid of a Cal (columnar Ca)
34
How can an enamel layer become more stable after being weekend by carbonation?
the weaker areas selectively dissolve during times of low Qsp, so it can dissolve, then remineralize (in a time of high Qsp) with HAP!
35
What positive effect can remineralization of enamel have on your teeth with age?
can make them semi resistant to caries
36
Why does acid cause demineralization?
Acids (proton donors) will give their protons to the free ions in the solution, lowering Qsp, and causing demineralization
37
What is pKa?
the pH when half the ions are protonated
38
How can an ion have more than one pKa?
If it has more than one dissociable proton. Forms with fewer hydrogens will be in higher number in basic solutions (PO4;3-<>HPO4;2-), while forms with more hydrogens will be in acidic solutions (HPO4;2-<>H2PO4-)
39
How is pKa related to pH?
pKa is a measure of an ions affinity for a hydrogen ion. High pKa means high affinity. So high pKa would be related to bases, low pKa would be acids (just like pH)
40
What two benefits does fluoride give?
it strengthens the ionic lattice, and its Qsp lowers at a slower rate, meaning it will stay in equilibrium at a lower pH
41
What is a healthy fluoride content in water?
0.7 mg/L (ppm)
42
How many protons are generated per unit cell of HAP added to enamel? Why?
11 : we need 6 PO4;2- per unit cell. we must dissociate HPO4 and H2PO4 in order to get these (at 7.2 they are roughly equal, so 3 of each nets 9 hydrogens added to solution). also, the 2 OH- that we need will come from H20, adding 2 more hydrogens. 11 total
43
What is the henderson-hasselbalch equation?
pH=pKa+log(A-/HA)
44
When is enamel crystal organization established?
during ribbon elongation
45
How is the apical and basal sides of enamel separated from the extracellular space?
apically: ameloblasts / basal: Dentin and ondontoblasts
46
What does an ameloblast control that aids in creating more enamel
it controls the ionic and organic composition of the enamel compartment. As enamel forms, it gives off H+, so ameloblasts must adjust their secretory and reabsorbative properties to maintain favorable conditions
47
Where does extension of a mineral ribbon occur primarily?
at the apical tips (mineralization fronts at distal end of cell membrane)
48
What processes are developed on an ameloblast? When?
After a uniform layer of enamel has been deposited on the dentin, Tomes' processes are formed.
49
When Tomes' processes are formed, what do the initially establish?
two partially distinct secretory zones
50
What do the two zones of the Tomes' processes secrete?
They secrete enamel proteins. Proteins secreted from the protruding portion form the enamel rods, while proteins secreted at the base of the Tomes' process, and near adjacent cells, create the interrod enamel
51
What is the difference between rods, and interrods?
mostly just the direction of the ribbon
52
How many rods does each ameloblast create?
1
53
What happens toward the end of the secretory stage?
The ameloblasts retract their Tomes' processes and and make the final extension of enamel crystallites perpendicular to the enamel surface.
54
Which side of the ameloblasts secrete enamel?
basal (as enamel grows, ameloblasts radiate away from dentin)
55
What are Hunter-Schreger bands?
an optical phenomenon caused by seeing different groups of rods extending in to the enamel
56
Where would it be typical to see rods deviating from their normal perpendicular orientation to the dentin surface?
the inner 2/3 of the enamel layer
57
How is biological control over enamel formation made possible?
By the developmental formation of an isolated compartment within the tooth organ
58
What are the three stages of forming enamel crystals?
Ribbon initiation, elongation, and maturation
59
What percentage of matured enamel is organic material/protein?
1%
60
What percentage of developing enamel is organic material/protein?
40%
61
What are the 3 "secretory stage enamel proteins"/major secretory products of ameloblasts during the secretory stage?
Amelogenin, ameloblastin, and enamelin
62
What gene family are amelogenin, ameloblastin, and enamelin a part of?
The Secretory calcium-binding phosphoprotein gene family (SCPP)
63
What is the only protease secreted by ameloblasts during the secretory stage?
Enamelysin (MMP20)
64
What is the most abundant enamel protein? How much of the organic matrix does it make up?
Amelogenin : 85-90%
65
What gene expresses Amelogenin and what chromosome is it on?
AMELX : X Chromosome
66
Where is the second AMELX gene located for males? can it make up for a defected AMELX?
on the Y chromosome (AMELY) : no, it is only expressed at marginal levels
67
How many amino acids and glycosylations does the predominant amelogenin protein have?
175
68
How can AMELX mutations be distinguished from other forms of amelogenesis imperfecta?
Its pattern of inheritance (X-linked AI) and characteristic phenotype
69
What does AMELX AI look like in females? males?
in females, enamel alternates between normal and think vertical bands of enamel. In males, who only have one copy of AMELX and is defective they will have only a very thin enamel layer.
70
What is the largest enamel protein? How abundant is it?
Enameling : low compared to amelogenin
71
How many amino acids/glycosylations make up Enameline?
1103 amino acids and multiple N-linked glycosylations
72
What type of AI do defects in ENAM cause?
Autosomal dominant amelogenesis imperfecta
73
What is the phenotype of patients with defects in ENAM?
those with a single defective ENAM allele vary from small, enamel pits to thin enamel often showing horizontal bands. Mutations on both alleles cause an absence of dental enamel (severe amelogenesis imperfecta)
74
How many amino acids/glycosylations are present on the ameloblastin protein?
421 amino acids with at least two O-linked glycosylations
75
What gene codes for ameloblastin?
AMBN
76
What do defects in AMBN contribute to?
Autosomal recessive amelognesis imperfecta (rare because both parents must carry defective allele)
77
How many offspring will show the phenotype for an autosomal recessive trait if both parents posses the defective allele?
1/4
78
What are the stages of amelogenesis?
Cells of the inner enamel epithelium differentiate into ameloblasts which progress through presecretory, secretory, transition, and maturation stages
79
What will ameloblasts look like in a sagittal section?
They will not be at the same stage of development. They will be most advanced at the cusp tip (where amelogenesis starts)
80
Where are ameloblasts found at their earliest stage of development?
nearest to the CEJ
81
What separates the inner enamel epithelium from developing odontoblasts? Containing?
the basal lamina containing type IV collagen and laminin-332
82
Junctional epidermolysis bullosa is a syndrome caused by defects in the gene encoding __________.
Laminin-332
83
Describe the process of crown formation up to the creation of the initial layer of enamel on newly mineralized dentin.
odontoblasts differentiate before ameloblasts and begin to secrete a collagen-rich predentin matrix beneath the basal lamina. The predentin accumulates in the extracellular space but does not mineralize. Presecretory ameloblasts send cytoplasmic projections through these gaps in the BL and enamel protein patches and earliest enamel crystallites appear on the irregular, recently mineralized dentin. Enamel patches grow and merge with other islands until a continuous layer of initial enamel is deposited.
84
Describe the initial layer of enamel?
it is "aprismatic" (not separately organized into rods and interrods
85
What happens to the ameloblasts after they have deposited the initial layer of enamel?
they promote to secretory ameloblasts and form Tomes' processes.
86
What is enamelysin?
MMP20 is a metalloproteinase able to cleave enamel proteins at multiple places.
87
As enamel ribbons grow longer, what happens?
the deeper enamel thickens
88
What term is given to the thickening of the enamel layer that occurs after secretion of enamel/lengthening of enamel?
appositional growth
89
What protein supports the secretory stage crystallites? What else does it do?
Nanospheres of amelogenin ~20nm in diameter.
90
What is Enamelysin responsible for?
Enamelysin (MMP20) degrades the protein matrix of amelogenin, gaining space in the deeper enamel for the crystals to widen
91
What type of AI is caused by defects in MMP20?
autosomal recessive amelogenesis imperfecta
92
What is the phenotype associated with defects in MMP20?
Without enamelysin, the enamel protein matrix is not degraded and crystal maturation (growth in width) in deeper enamel is impaired. Some organic matrix is retained, enamel is less mineralized, and the enamel tends to chip off the teeth.
93
What is the final stage of the secretory stage?
Ameloblasts anticipate the transition to maturation stage by retracting the Tomes' processes and secreting a final layer of prismatic enamel
94
What is the first step of the transition stage?
Ameloblasts become shorter and wider, and a new basal lamina is established
95
What is unique about the new basal lamina?
it contains amelotin
96
Where is amelotin expressed and what is nearby?
AMTN on chromosome 4 near ENAM and AMBN
97
T/F The basal lamina maintains a weak connection between the enamel layer and maturation stage ameloblasts.
F - strong connection
98
What do the ameloblasts secrete as they are about to enter the transition stage?
less enamel, and KLK4
99
What is KLK4?
a serine protease that degrades the remaining organic material
100
What morphologies do amelobalsts alternate between during the maturation stage?
smooth and ruffle-ended, and eventually decrease in size to the cuboidal cells of the reduced enamel epithelium
101
Why is there a "ruffled end" to ruffle ended ameloblasts?
they have membrane specialization associated with mitochondria that make a striated border (involved in endocytosis)
102
What happens to the rate of mineralization during the maturation stage? Why?
it increases. ions are adding to the sizes of the enamel crystallites (not elongating, now just mineralizing)
103
What do maturation stage ameloblasts express/secrete? Why?
express carbonic anhydrase II and secrete bicarbonate : to neutralize the acid generated by hydroxyapatite formation
104
Where are ruffle-ended ameloblasts joined to each other?
toward the enamel so that their intercellular spaces are open toward soft tissue layer
105
Where are smooth-ended ameloblasts joined to each other?
proximally with the intercellular space open to the enamel layer
106
What do the proximally located junctions on smooth ended ameloblasts allow for?
they allow the protein cleavage products to pass between ameloblasts and back toward circulation
107
What happens to enamel beneath ruffle-ended ameloblasts? the pH?
it is being rapidly mineralized causing the pH to drop
108
What happens to enamel beneath smooth-ended ameloblasts? the pH?
mineralization slows and pH rises
109
how long does the maturation stage last?
5 years
110
What happens to the levels of organic matter and enamel crystallites during the maturation phase?
organic matter drastically drops and enamel crystallites thicken (both from KLK4)
111
When is KLK4 expressed?
from the beginning of the transition stage and throughout maturation
112
What does defects in KLK4 cause?
hypo maturation autosomal recessive amelogenesis imperfecta
