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.