Amelogenesis(Author v.mazuru)
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Transcript of Amelogenesis(Author v.mazuru)
SMPhU “Nicolae Testemitanu”
Department of Histology, Cytology and Embryology
Amelogenesis,
Structure of Enamelum,
Assistant professor
PhD:
Mazuru Vitalie
Amelogenesis
process of Enamel formation provided by Ameloblasts
During Amelogenesis ameloblasts become columnar, polarized,
secreting cell
at the moment of Eruption Ameloblasts cease their function,
decrease in volume and undergo gradually involution
Ameloblasts life cycle
1. Morphogenetic
2. Differentiation
3. Secretory
4. Maturation
5. Protective
Morphogenetic
During this stage, the cells
assume columnar shape
Develops RER
GA
Mitochondria
Differentiation
Coincide with the moment
of the beginning of enamel
secretion.
Cells elongate (columnar)
Changes the polarity
Differentiation
RER and GA are above
the nucleus => secretory
AP and non-secretory BP.
Arangement of actin
filaments forms two
terminal bars – basal and
apical.
Organizing of the
epithelium (desmosomes,
tight and gap junctions)
Secretory
Most of the enamel
formation period
↑↑↑ RER, GA, Mtch
Above the apical terminal
bar appears one elongation
– Tomes’ process
Secretory
Tomes’ process responsible
for prisms formation
Advanced secretory ameloblasts
Cells are highly polarized
Tomes’ process gives an
ruffled aspect to the enamel
surface
Maturation
Entire thickness of
Enamel has been
formed.
E is 30% mineralised
E crystals increase in
width and thickness
Water and proteins are
removed
Maturation
Tomes’ process is lost
Organelles reduced in number
Appear two types AB
Ruffle-ended (A)
Smooth-ended (B)
Alternates 6-7 times
A B
Protective (Post-maturation) stage
Enamel maturation is complete
Cells become flattened
Secrete primary E cuticle a type of
basement membrane between apical
surface and Enamelum
Are formed many hemidesmosomes
Protective (Post-maturation) stage
Other layers of
enamel organ merge
Forming Reduced
Epithelium
Enamel formation
1. Organic matrix
formation
2. Mineralisation
Dissociation of BM – TF
Mutual induction
Formation of enamel matrix
Enamel matrix produced in
RER
Enpacked in GA
Transported to the TP
Merocrine secretion
Sequential secretion (4µ/day)
Moving outward (4µ/day)
Appear incremental lines
Mineralisation
Two stages
1. Instant partial (30%)
2. Complete (4 s/stages)
Sources of Ca2+
1. Ca2+ from dentine
2. Ruffle-ended AB
3. Tuftelinum
4. AlcPh-ase of IntEE
Physical properties of the Enamel- Covers the crown
- It is the thickest over the cusps (1.3 - 2.5 mm thick), and the thinnest at cervical margins
- Is the hardest biological tissue
- Has high abrasion resistance, but low tensile strength
- Can undergo neither repair nor replacement (final structure)
- Surface enamel is harder, denser and less porous than subsurface enamel
- The translucency of enamel increases with age
Demineralised section:
Organic components remain, while
calcified are lost.
Ground section of the tooth:
Organic components are lost, while
mineral components remain.
Chemical properties
Non-organic SBST
96-98%
Calcium hydroxyapatite (88-90%)
Ca10(PO4)6(OH)2 – crystallites
Fluoride
Chloride
Sodium
Strontium
Aluminium
Magnesium
Water
Organic SBST
2-4%Proteins:
Amelogenins
Enamelins (non-Amelogenins)
Carbohydrates
Lipids
Enamel prisms (rods)
Enamel prisms cut longitudinally and running towards the surface
of the enamel.
Oblique lines – enamel stria
All 3 patterns are present in humansPattern I
Pattern IIIthe most common in humans
This pattern shows clearly “head” and “tail” regions. The
tail is placed between the heads of 2 neighbors prisms
The prisms meet the enamel surface at different angles
depending on the shape of EDJ and the thickness of enamel.
Have sinusoidal arrangement
Are organized in groups of 10-13 layers of prisms, that follow
the same direction, are blocked above and below by another
group of prisms that are oriented in different direction.
These periodic changes in prisms direction give rise to a banding
pattern – Hunter-Schreger bands.
-Size of the bands ~ 50µm.
- are visible as different bands
of prisms that reflect the light
in different directions.
- the bands of prisms cut
longitudinally – parazones
(pale)
- the bands of prisms cut
transversally – diazones (dark)
The sinusoidal direction of the
enamel prisms in alternating
sheets results in alternately
reflecting bands on the cut
surface.
Hunter-Schreger bands
A. DiazoneB. Parazone
Hunter-Schreger bands
Hunter-Schreger bands
“Gnarled” enamelum
The outer 20-100µm of enamel is prismless (aprismatic).
Incremental lines
Enamel is formed incrementally, periods of activity alternating
with periods of quiescence.
This results in structural appearances known as incremental lines.
Short period IL (cross-striation)
Long period IL (enamel striae)
Neonatal IL
Cross-striation
Are seen as lines transversing
the enamel prisms at right
angles to their long axes.
Enamel striae (Retzius lines)
Represent weekly enamel deposition
Neonatal line
Is the largest Retzius line
Specific only for deciduous teeth
Is formed at birth
Reflects the metabolic changes at
birth
The most less mineralised enamel
Surface enamel
Perikymata grooves
Perikymata ridges
Enamel caps
Enamel holes
On the lateral surface of
enamel, enamel striae
reaches the surface in a
series of fine grooves that
running circumpferentially
around the crown –
perikymata grooves.
Between them – P ridges
Enamel caps
Surface elevations 10-15 µm across
Are thought to be enamel deposition on
top of non-mineralisable debris late in
development.
Enamel holes
Surface depressions that results
from loss of caps and underlying
material.
Enamel-Dentine Junction (EDJ)
A. Enamel tufts
B. Enamel spindles
C. Enamel lamellae
Enamel spindles
Narrow, elongated tubules that extend
up to 25 nm into the enamel.
Represent hypomineralised areas
Are thought to be:
Distal edges of OB processes
Dentine collagen fibers
Remnants of dead OB
Enamel tufts
Represent hypomineralised
enamel areas.
Have the same direction and
undulate the same like prisms.
Appears at 100µm intervals
along the junctions.
Enamel lamellae
Hypomineralised enamel areas
that results from incomplete
maturation of groups of prisms.
Thereby, in these areas amount
of enamel proteins is much
higher. Are the most common
for the cervical area of the
tooth
Run through the entire
thickness of enamel.