Enamel 1 Flashcards
1
Q
- Is enamel Acellular or cellular?
- Is it Vital or non-vital?
- is it vascular or non-vascular?
A
- Acellular
- Non-vital
- Non-Vascular
2
Q
What is the origin of enamel?
A
Ectoderm
3
Q
Enamel is the Hardest (most mineralized) tissue in the body T/F
A
True
4
Q
Enamel is brittle T/F
A
True
5
Q
What makes enamel dynamic?
A
It can be demineralized and remineralized
6
Q
Where is enamel thickest?
A
At the crown, around 2.5mm
7
Q
What is the primary component of enamel?
A
Hydroxyapatatite crystals
8
Q
What is the purpose of the protein component of enamel?
A
Organization of crystals
9
Q
How much of the enamel is organic material?
A
1%, distributed between the HA crystals
10
Q
T/F Enamel contains collagen within the organic component
A
FALSE. No collagen
11
Q
Where would you find major enamel proteins?
A
In the organic component
12
Q
What are the major enamel proteins?
A
- Amelogenins
- Ameloblastins
- Enamelin
- Tuftelin
- Others also exist
13
Q
T/F some enamel proteins are present only in developing enamel
A
TRUE
14
Q
How much of enamel is water?
A
2-3%
15
Q
What are the 4 mineralized tissues in the body?
A
- Bone
- Dentin
- Cementum
- Enamel
16
Q
What is main purpose of the tooth?
A
survive repeated cyclical loading
17
Q
How are enamel crystals arranged?
A
Closely packed, long, ribbon like
18
Q
Many Crystals packaged together form both the ______ and ______
A
- Enamel rods
2. Interrod enamel
19
Q
While enamel crystals are called hydrdoxyapatite, lots of enamel crystals are actually ________
A
Carbonatoapatite
20
Q
How is carbonatoapatite different from hydroxyapatite?
A
CO3(2-) can substitute for PO4(3-), usually, but can also substitute for OH- sometimes
21
Q
T/F enamel grows outwards, dentin is forming inwards
A
TRUE
22
Q
Is the composition of enamel measure by weight or by volume
A
Weight
23
Q
Hydroxyapatite can incorporate Carbonate, Magnesium, fluoride, and other ions into its structure T/F
A
TRUE
24
Q
Where are carbonate and magnesium usually incorporated?
A
Inner enamel
25
Where is fluoride usually incorporated into enamel?
Outer enamel
26
T/F Outer enamel is more resilient in the face of an acid attack
TRUE
27
Each enamel crystal is what shape?
Hexagonal, reflective of the individual HA unit cell
28
What are the mature dimensions of enamel crystals?
Width: 60-70 nm
Thickness: 25-30 nm
29
How long is an enamel crystal?
Very long (in the mm range), it could run the entire length of the enamel layer
30
What happens to hexagonal symmetry as the crystals mature?
It increases, but fully mature crystals lose their shape somewhat
31
Enamel rods generally run perpendicular to what?
DEJ (Pulp)
32
What is an enamel rod?
Cylindrical accumulation of enamel crystals, lined up along the long axis of the rod
33
T/F Rods are straight
FALSE
| **Rods are not completely straight, but curve somewhat as they progress towards the surface
34
Often rods are called _______
Prisms
**Technically they are not prisms because they are not that regular in terms of geometry
35
What is a prism?
Polyhedron with 2 polygonal bases
36
Rods are organized into ____ which run in alternating directions
Rows
37
How many ameloblasts are associated with a rod?
One ameloblast for One rod
38
T/F Orientation of enamel rods is best seen with Light microscopy
FALSE, Impossible to tell from light microscopy. Rods throw off light in all directions
39
What is the Rod Sheath?
A relatively protein rich area of enamel that surrounds the rods
40
The rod sheath runs about ___ of the way around each rod
3/4
41
For the most part, rod sheaths separate ___ and ______ enamel
1. Rod
| 2. Interrod
42
What happens in the areas of the Rod that are not surrounded by a rod sheath?
The enamel crystals are continuous with interrod enamel, linking the two together
43
Where is the crystal orientation in the rod not parallel to the long axis of the rods?
In the gap areas where they become continuous with interrod enamel
44
What are the rod sheath proteins?
1. Ameloblastins
| 2. Amelogenins
45
Rod sheaths are much more prominent in ______ _______
Higher mammals (not so much in rodents)
46
What is interrod enamel?
Same basic compositions as rods, simply different enamel crystal orientation
47
What doe interrod enamel do?
Fill the gaps between rods
48
Where is Caries though to penetrate?
Through the higher protein rod sheath areas (between rod and interrod enamel)
49
An enamel rod head is _________ to surface of enamel
Perpendicular
50
What is the composition of enamel as the ameloblasts are activated and enamel begins to be deposed?
-Only around 30% mineralized, with much larger organic component
51
As enamel matures, what happens to the organic component of enamel?
It is reduced and mineralization of enamel increases
52
What are the 3 general phases of Ameloblast maturation?
1. Pre-secretory
2. Secretory
3. Maturation
53
What is the pre-secretory phase?
Cells mature from pre-ameloblasts to ameloblasts
54
What happens in secretory phase?
Deposition of enamel
55
What is maturation phase of Ameloblasts?
Reduction of organic matrix, increase mineralization via ion transport
56
How do Ameloblasts deposit organic matrix?
Via secretory vesicles which exit the cell apically
57
Initially in the deposition of enamel, what happens to the basal lamina that separates the pre-dentin and ameloblasts?
It is penetrated by cell projections and broken down
58
Enamel is laid down directly in appostion to what?
Pre-dentin/mantle (first) dentin
59
What is Tomes' process?
- Forms during the deposition of enamel
| - Projects into the developing enamel and is the site of much secretory activity
60
What is holding ameloblasts together?
Junctional complexes (terminal bars)
61
T/F Enamel has a rod arrangment even as soon as it is initially placed in appostion to dentin
FALSE, Initial enamel in apposition to dentin does not have a rod arrangement, it is uniform
62
What does Tomes' process form?
Effectively it forms the Enamel rod structure
63
What are the distal and proximal orientations of Tomes' process referring to?
Distal: Towards the forming enamel
Proximal: Towards the stratum intermedium
64
Secretion from different parts of Tomes' process forms what?
Rods, interrod enamel
65
Inner enamel epithelium in tooth development become what?
Ameloblasts
66
Trigger for ameloblasts to make proteins for enamel is what?
Formation of first pre-dentin
67
What do ameloblasts do when enamel has been laid down?
The return to being a squat cell, much like a pre-ameloblast
68
Prior to eruption what happens to enamel?
It hardens and becomes highly mineralized through the removal of water, organic material and increased HA crystal diameter
69
How long does enamel maturation take?
Relatively slow: up to 5 years for some permanent teeth
70
How much of amelognesis is maturation?
roughly 2/3
71
What is modulation?
Process by which water and proteins are removed. Fluctuations in teh distal membrane of ameloblast layers 'ruffing' and 'smoothing'
72
How do ruffles cells come to be?
- Infiltration and incorporation of calcium ions into crystals occurs during 'ruffling'
- Lowered pH perhaps favors mineralization
- Secretion of proteolytic enzymes
73
What are smooth cells?
Allow diffusion out of protein fragments out of enamel, which leak in between cells and laterally defuse through cell layer
74
What happens to the enamel organ after after enamel maturation?
The remains of the enamel orgain are attached to the tooth until eruption at which point they fuse with the oral epithelium, forming a covering over the tooth
75
What is the primary enamel cuticle?
A mineralized coating which is the last secretory product of the ameloblasts (Perhaps the basal lamina)
76
What is the secondary enamel cuticle?
- Also called 'Dental Cuticle'
- Formed from the remains of the reduced enamel epithelium merged with the oral epithelium and is removed due to mechanical forces and what not
77
What does Nasmyth's membrane refer to?
The primary and secondary enamel cuticle together
