Enamel 1 Flashcards
- Is enamel Acellular or cellular?
- Is it Vital or non-vital?
- is it vascular or non-vascular?
- Acellular
- Non-vital
- Non-Vascular
What is the origin of enamel?
Ectoderm
Enamel is the Hardest (most mineralized) tissue in the body T/F
True
Enamel is brittle T/F
True
What makes enamel dynamic?
It can be demineralized and remineralized
Where is enamel thickest?
At the crown, around 2.5mm
What is the primary component of enamel?
Hydroxyapatatite crystals
What is the purpose of the protein component of enamel?
Organization of crystals
How much of the enamel is organic material?
1%, distributed between the HA crystals
T/F Enamel contains collagen within the organic component
FALSE. No collagen
Where would you find major enamel proteins?
In the organic component
What are the major enamel proteins?
- Amelogenins
- Ameloblastins
- Enamelin
- Tuftelin
- Others also exist
T/F some enamel proteins are present only in developing enamel
TRUE
How much of enamel is water?
2-3%
What are the 4 mineralized tissues in the body?
- Bone
- Dentin
- Cementum
- Enamel
What is main purpose of the tooth?
survive repeated cyclical loading
How are enamel crystals arranged?
Closely packed, long, ribbon like
Many Crystals packaged together form both the ______ and ______
- Enamel rods
2. Interrod enamel
While enamel crystals are called hydrdoxyapatite, lots of enamel crystals are actually ________
Carbonatoapatite
How is carbonatoapatite different from hydroxyapatite?
CO3(2-) can substitute for PO4(3-), usually, but can also substitute for OH- sometimes
T/F enamel grows outwards, dentin is forming inwards
TRUE
Is the composition of enamel measure by weight or by volume
Weight
Hydroxyapatite can incorporate Carbonate, Magnesium, fluoride, and other ions into its structure T/F
TRUE
Where are carbonate and magnesium usually incorporated?
Inner enamel
Where is fluoride usually incorporated into enamel?
Outer enamel
T/F Outer enamel is more resilient in the face of an acid attack
TRUE
Each enamel crystal is what shape?
Hexagonal, reflective of the individual HA unit cell
What are the mature dimensions of enamel crystals?
Width: 60-70 nm
Thickness: 25-30 nm
How long is an enamel crystal?
Very long (in the mm range), it could run the entire length of the enamel layer
What happens to hexagonal symmetry as the crystals mature?
It increases, but fully mature crystals lose their shape somewhat
Enamel rods generally run perpendicular to what?
DEJ (Pulp)
What is an enamel rod?
Cylindrical accumulation of enamel crystals, lined up along the long axis of the rod
T/F Rods are straight
FALSE
**Rods are not completely straight, but curve somewhat as they progress towards the surface
Often rods are called _______
Prisms
**Technically they are not prisms because they are not that regular in terms of geometry
What is a prism?
Polyhedron with 2 polygonal bases
Rods are organized into ____ which run in alternating directions
Rows
How many ameloblasts are associated with a rod?
One ameloblast for One rod
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
What is the Rod Sheath?
A relatively protein rich area of enamel that surrounds the rods
The rod sheath runs about ___ of the way around each rod
3/4
For the most part, rod sheaths separate ___ and ______ enamel
- Rod
2. Interrod
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
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
What are the rod sheath proteins?
- Ameloblastins
2. Amelogenins
Rod sheaths are much more prominent in ______ _______
Higher mammals (not so much in rodents)
What is interrod enamel?
Same basic compositions as rods, simply different enamel crystal orientation
What doe interrod enamel do?
Fill the gaps between rods
Where is Caries though to penetrate?
Through the higher protein rod sheath areas (between rod and interrod enamel)
An enamel rod head is _________ to surface of enamel
Perpendicular
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
As enamel matures, what happens to the organic component of enamel?
It is reduced and mineralization of enamel increases
What are the 3 general phases of Ameloblast maturation?
- Pre-secretory
- Secretory
- Maturation
What is the pre-secretory phase?
Cells mature from pre-ameloblasts to ameloblasts
What happens in secretory phase?
Deposition of enamel
What is maturation phase of Ameloblasts?
Reduction of organic matrix, increase mineralization via ion transport
How do Ameloblasts deposit organic matrix?
Via secretory vesicles which exit the cell apically
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
Enamel is laid down directly in appostion to what?
Pre-dentin/mantle (first) dentin
What is Tomes’ process?
- Forms during the deposition of enamel
- Projects into the developing enamel and is the site of much secretory activity
What is holding ameloblasts together?
Junctional complexes (terminal bars)
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
What does Tomes’ process form?
Effectively it forms the Enamel rod structure
What are the distal and proximal orientations of Tomes’ process referring to?
Distal: Towards the forming enamel
Proximal: Towards the stratum intermedium
Secretion from different parts of Tomes’ process forms what?
Rods, interrod enamel
Inner enamel epithelium in tooth development become what?
Ameloblasts
Trigger for ameloblasts to make proteins for enamel is what?
Formation of first pre-dentin
What do ameloblasts do when enamel has been laid down?
The return to being a squat cell, much like a pre-ameloblast
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
How long does enamel maturation take?
Relatively slow: up to 5 years for some permanent teeth
How much of amelognesis is maturation?
roughly 2/3
What is modulation?
Process by which water and proteins are removed. Fluctuations in teh distal membrane of ameloblast layers ‘ruffing’ and ‘smoothing’
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
What are smooth cells?
Allow diffusion out of protein fragments out of enamel, which leak in between cells and laterally defuse through cell layer
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
What is the primary enamel cuticle?
A mineralized coating which is the last secretory product of the ameloblasts (Perhaps the basal lamina)
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
What does Nasmyth’s membrane refer to?
The primary and secondary enamel cuticle together
