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ENAMEL
بسم هللا الرحمن الرحيم
Upload By : Ahmed Ali Abbas
Babylon University College of Dentistry
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PHYSICAL CHARACTERISTICS
Hard, brittle, totally acellular , highly mineralized
Secretory product of stratified squamous epithelium
Calcified tissue
Hydroxyapatite crystal arrange in prism or rods
Density:-
Decreases from the surface of enamel to the dentino-enamel junction.
Thickness:-
Thickness over the cusps of the molars where it measures 2.5 mm & incisal edges of incisors where it is 2.0 mm.
ENAMEL
1. Forms a protective covering (2 mm – knife edge).
2. Forms a resistant covering (suitable for mastication).
3. The hardest calcified tissue in human body.
4. enamel is very brittle but the underlying dentin provides some resilience
5. Acts as semipermeable membrane (selectively permeable).
6. Color: yellowish white to grayish white depends on translucency.
Enamel gains mechanical strength by interweaving HAP crystals
Enamel rod – 5-12 million/tooth
Appatite crystal is hexagonal
Enamel initially starts with a high protein content, but these are removed and the voids backfilled with HAP as the tooth matures
CHEMICAL PROPERTIES
96% inorganic - by weight
inorganic crystalline calcium phosphate –hydroxyapatite
various ions like strontium, magnesium, lead and fluoride are present at some point during enamel formation
CROSS SECTION
Cross section of enamel rod shows the key
hole pattern
Head represents the rod and key shows the
inter rod region
Head is directed towards the occlusal aspect
and tail towards the cervical region of the
tooth
CHARACTERISTICS - ENAMEL ROD/PRISM
Number: 5 – 12 millions.
Direction: Run in oblique direction and wavy
course.
Length: greater than the thickness.
Diameter average: 4 µm.
Appearance: Have a clear crystalline appearance.
Cross-section: hexagonal, round, oval, or fish
scales.
Head of enamel rod is formed by one
ameloblast and tail is formed by three
ameloblasts
Thus each rod is formed by four ameloblasts
SUBMICROSCOPIC STRUCTURE
OF ENAMEL RODS
Keyhole or paddle-shaped.
Separated by interrod substance.
About 5 µm in breadth and 9 µm in length.
The bodies are near the occlusal or incisal surface.
The tails point cervically.
The crystals; parallel to the long axis of the prism
heads.
Deviate about 65° from the tails.
ROD SHEATH
the boundary between rodand interrod is delimited bya narrow space containingorganic material – rodsheath
A thin peripheral layer.
Darker than the rod.
Relatively acid-resistant.
Less calcified and containsmore organic matter thanthe rod itself.
Electron Microscope : oftenincomplete.
ALTERNATING ROD DIRECTIONALITY
Hunter Schreger bands arealternating light and darkbands seen in a section ofenamel when cutlongitudinally and illuminatedin a special way.
•The bands are produced bythe orientation of groups ofrods.
•If the light passes throughrods cut in cross-section, theband appears light.
•If the light passes throughrods cut in longitudinally, theband appears dark.
STRIATIONS
E. rod is built-up of segments (dark lines).
Best seen in insufficient calcified E.
In a longitudinal section dark lines are seen
that shows the daily deposition of enamel
(rhythmic manner of E. matrix formation).
These lines are known as cross striation
Segment length: about 4 µm.
DIRECTION OF RODS
Near the edge or cusp tip they are oblique
At the cusp tip they are almost vertical
Run from DEJ to surface of enamel
Usually at right angles to the Dentin surface.
Follow a wavy course in clockwise and anticlockwise deviation full thickness of enamel
At the cusps or incisal edges: gnarled enamel.
At pits and fissures: rods converge in their outward course.
STRAIGHT ENAMEL RODS -LONGITUDINAL
LABIOLINGUALSECTION
The enamel rods
project in the direction
of the arrow.
Can you see the striaof
Retzius?
GNARLED ENAMEL
Enamel rods are general not straight throughout their length.
In the cuspal region, the rods are very wavy.
This is referred to as gnarled enamel.
In this section, you can see the end of an odontoblasticprocesspenetrating the enamel just past the DEJ.
This structure is called an enamel spindle.
Legend
Legend: A, Gnarled enamel; B, Enamel spindle
HUNTERSCHRAGER BANDS
Optical phenomenon seen in reflected light
Alternate light and dark bands
Seen in ground longitudinal section
Due to abrupt change in the direction of
enamel rod
Originate from the DEJ.
ENAMEL -TRANSVERSE GROUND SECTION
In a transverse section of tooth, the stria of
Retzius appear as concentric bands parallel
to the dentino-enamel junction (DEJ). In
addition to the "hypo-mineralized" dark striaof
Retzius, there also exist hypo-mineralized
areas perpendicular to the DEJ. These are
enamel lamellae(that traverse the entire
thickness of enamel) and enamel
tufts(that traverse the inner third of
enamel adjacent to the DEJ
STRAE OF RETZIUS
Incremental lines of growth
Eccentric growth rings
DEJ to outer surface of enamel
Where they end as shallow furrows known as
perikymata
NEONATAL LINE
The E. of the deciduous teeth and the 1st permanent molar (It is incremental line that is the boundary between the enamel forms before and after the birth)
The neonatal line is usually the darkest and thickest striaof Retzius.
Etiology
Due to sudden change in the environment and nutrition.
The antenatal E. is better calcified than the postnatal E.
ENAMEL LAMELLAE
Are thin, leaf like structures,
Develop in planes of tension.
Extends from E. surface towards the DEJ.
Confused with cracks caused by grinding (decalcification).
Extend in longitudinal and radial direction.
Represent site of weakness in the tooth and three types; A, B, and C.
ENAMEL LAMELLAE
In this ground cross-section of tooth, you can see enamel lamellae and enamel tufts You can also see the neonatal line.
•What do all three of these structures have in common?
Answer: They are all hypocalcified.
Legend: A, Enamel lamella; B, Enamel tuft; C, Neonatal line
Enamel tufts are less mineralized areas of enamel in the inner third of enamel adjacent to the DEJ. They resemble tufts of grass.
•They are wavy due to the waviness of the adjacent rods.
•Structures rich in organic matter (i.e. less mineralized) that project to the surface of the enamel are enamel lamellae.
Legend: A, Enamel tufts; B, Enamel lamella
ENAMEL TUFTS -TWO PLANES OF FOCUS
Enamel tufts consist of several unconnected "leaves" of hypo-calcified enamel.
•They display a wavy twisted appearance.
•Enamel spindles are the processes of odontoblastsprojectinginto the enamel.
Legend: A, Enamel spindle; B, Enamel tuft
DENTINO-ENAMEL JUNCTION
Scalloped junction – the convexities towards
D.
At this junction, the pitted D. surface fit
rounded projections of the enamel.
The outline of the junction is performed by
the arrangement of the ameloblasts and the
B. M.
ENAMEL SPINDLES
Odontoblast processesusually end at the DEJ.However, sometimes theends of the process becomeembedded in the enamel as itforms.
•These very small, usuallystraight structures that youcan see adjacent to the DEJare enamel spindles.
•They are only about onetenth the length of an enameltuft. Legend: A, Enamelspindle; B,Odontoblastprocesses indentin
C. ROD ENDS
Are concave and vary in depth and
shape.
Are shallow in the cervical regions.
Deep near the incisal or occlusal
edges.
D. CRACKS
Narrow fissure like structure.
Seen on almost all surfaces.
They are the outer edges of lamellae.
Extend for varying distance along the surface.
At right angles to CEJ.
Long cracks are thicker than the short one.
May reach the occlusal or incisal edge.
LIFE CYCLES OF THE AMELOBLASTS
According to their function, can be
divided into six stages:
1. Morphogenic stage.
2. Organizing stage.
3. Formative stage.
4. Maturative stage.
5. Protective stage.
6. Desmolytic stage.
Morphogenic stage.
React by differential growth
Produce shape of the crown
Terminal bar appears
Basal lamina separates the inner enamel epithelium and cells of the dental papilla
Pulpal layer adjacent to the basal lamina is a cell free zone
At cervical region – cell is relatively undifferentiated
Organizing stage.
Inner enamel epithelium interact with the
cells of dental papilla which differentiate into
odontoblast
Cells become elongated
Proximal part contain nuclei
Distal end is nucleus free zone
Dentin formation begins
Cell free zone disappear
As dentine is formed nutrition supply of the
inner enamel epithelium changes from dental
papilla to the capillaries that surround the
outer enamel epithelium
Reduction and gradual disappearance of the
stellate reticulum
Formative stage.
Formatve stage starts After the dentine
formation
Enamel matrix formation starts
Development of blunt cell process on the
ameloblast surface which penetrate the basal
lamina and enter the predentin
Maturative stage.
Maturation starts after most thickness of
enamel matrix formation in occlusal and
incisal area. In cervical area matrix formation
is still in progress
Ameloblast reduce in length
Cells of stratum intermedium takes spindle
shape
Protective stage.
After enamel calcification cells on ameloblast
can no longer be differentiated from stratum
intermedium and outer enamel epithelium
These layer forms reduced enamel
epithelium
Protect the enamel from connective
tissue until the tooth erupts, if it contacts
then anomalies develop enamel may be
resorbed or cementum cover may form
(afibrillar cementum)
Desmolytic stage.
Reduced enamel epithelium induces atrophy
of connective tissue separating it with oral
epithelium thus fusion of the two epithelia
can occur
Premature degeneration of the reduced
enamel epithelium may prevent the eruption
of he tooth
AMELOGENESIS
1. Organic matrix formation (follows
incremental pattern – brown striae of
Retzius).
2. Mineralization.
dpTP=distal portion of Tome’s process
ppTP=proximal portion of Tome’s process
Sg=secretory granules(E. protein)
ORGANIC MATRIX FORMATION
AMELOGENESIS
Schematic representation of
the various functional stages
in the life cycle of ameloblasts
as would occur in a human
tooth.
1, Morphogenetic stage;
2, histodifferentiation stage;
3, initial secretory stage (no
Tomes’ process);
4, secretory stage (Tomes’
process);
5, ruffle-ended ameloblast of the
maturative stage;
6, smooth-ended ameloblast of
the maturative stage;
7, protective stage.