Enamel

1. Enamel

2. Striaof Retzius
•During development of enamel,
variations in the metabolism of
the organism cause variations in
the amount of organic material
deposited in the enamel. This
causes changes in the coloration
of the enamel that is layeddown
at that time so that alternating
dark (higher organic material)
and light (less organic material)
banding occurs. These bands are
called Striaof Retzius. The stria
of retziususually intercept the
dentino-enamel junction.
Legend: A, Striaof Retzius; B, DEJ

3. Enamel -transverse ground section
Legend: A, Striaof Retzius; B, Enamel
tuft; C, Enamel lamella; D, DEJ
•In a transverse section of tooth,
the striaof Retziusappear 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.

4. Neonatal line
•The neonatal lineis a dark stria
of Retziusthat occurs at the time
of birth. It is due to the stress of
birth. The neonatal line is usually
the darkest and thickest striaof
Retzius. The enamel at the cusp
of the tooth generally exhibits a
wavy pattern. This enamel is
called gnarled enamel. This is
NOT hypo-mineralized. The
enamel rods are layeddown in
this pattern by ameloblaststo
make the enamel strong in this
region.
Legend: A, Gnarled enamel; B,
Neonatal line; C, Dentin; D, DEJ

5. Straight enamel rods -longitudinal
labiolingualsection
•The enamel
rods project in
the direction of
the arrow.
•Can you see the
striaof Retzius?

6. Gnarled enamel
•Enamel rods are general not
straight throughout their
length.
•In the cuspalregion, the rods
are very wavy.
•This is referred to as gnarled
enamel.
•In this section, you can see
the end of an odontoblastic
process penetrating the
enamel just past the DEJ.
•This structure is called an
enamel spindle.
Legend: A, Gnarled
enamel; B, Enamel spindle

7. Cross-striations
•Each enamel rod demonstatesclosely
positioned striations along its length
known as cross-striationsor
incremental lines.
•These are thought to be formed by the
daily rhythm of the ameloblastlaying
down more and less mineralized
enamel.
•The striations are approximately 5 µm
apart. This distance represents one day
of enamel deposition. In this
micrograph rods project in the
direction of the arrow.
•Can you see the striations on each
rod?Theyare oriented perpendicular to
the length of the rod.
•Note: Not the large dark bands
projecting diagonally; these are striaof
Retzius.

8. Enamel cut
•In enamel cut in perfect
cross-section the shape of
the enamel rod exhibits a
"keyhole"-shaped pattern.
However, in a normal cross-
section of enamel, as seen
here, most rods are cut
obliquely.
•This is because they do not
travel in a straight line.
•The micrograph on the left
is produced by differential
interference microscopy
while the micrograph on the
right is from transmitted
light microscopy.

9. Enamel rods sectioned longitudinally
•In this electron micrograph enamel rods
are cut longitudinally (in parallel with their
long axis). The ligherband represents the
inner part of the rod or rod core, while the
darker part represents the outer covering
or rod sheath. This difference in
appearance is caused by the packing
density of the rod hydroxyapatitecrystals.
In the core the crystals are packed in
parallel with one another and tightly
together (very mineralized), whereas in
the rod sheath, the crystals are lossly
packed and are oriented at variable angles
to one another with organic material
interspersed (less mineralized). In this
particular section, the cores are narrow
and the sheaths wide, signifying that this
area is taken from a dark cross-striation or
striaof Retzius.
•Note that the rod sheaths are shared by
two adjacent rods.
Legend: A, Rod sheath; B, Rod core

10. Enamel rods sectioned in cross-
section
•In this electron micrograph enamel rods
are cut perpendicular to their long axis.
The ligherareas are the rod coresin which
hydroxyapatitecrystals are tightly packed
in alignment with each other. The darker
areas surrounding the rod cores are the
rod sheathsin which the crystals are
loosely packed at various angles. There are
two main parts to a rod: the rod headand
rod tail. The head has the central core
(light area), and is sometimes referred to
as the "rod". The tail is made of the rod
sheath (less mineralized enamel). During
development, one ameloblast(in position
1 in the inset diagram) makes the rod core
for the rod at position 1, while three other
ameloblasts(in positions 2, 3 and 4)
produce the rod tail of rod 1. The tail is
located between 2 and 3 and above 4.
Legend:A, Rod core; B, Rod
sheath; C, Rod tail; D, Rod head

11. Box diagram of human enamel
•This diagram represents a 25 X 25 X
25 µm of enamel.
•It demonstrates the arrangements of
hydroxyapatitecrystals in the enamel
rods in three planes of section.
•One rod is highlighted in blue to
demonstrate the typical human rod
shape.
•In the rod core, hydroxyapatite
crystals are aligned with the long axis
of the rod.
•In the tail the crystals are aligned
diagonally or perpendicularly to the
long axis of the rod.

12. Alternating rod directionality
•Hunter Schregerbands are
alternating light and dark
bands seen in a section of
enamel when cut
longitudinally and illuminated
in a special way.
•The bands are produced by
the orientation of groups of
rods.
•If the light passes through
rods cut in cross-section, the
band appears light.
•If the light passes through
rods cut in longitudinally, the
band appears dark.
Legend: A, Rods cut longitudinally;
B, Rods cut cross-sectionally

13. Hunter-Schregerbands
•Hunter Schregerbands are
seen here with special
illumination in longitudinal
ground sections of enamel
as light and dark bands.
•The red arrows indicate
three light bands.

14. Enamel tufts
•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

15. 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
odontoblastsprojecting
into the enamel.
Legend: A, Enamel spindle;
B, Enamel tuft

16. Enamel tufts aligned in rows
•Enamel tufts are
aligned in rows.
•They may
represent planes of
tension during
development.
Legend: A, Enamel tufts; B, DEJ;
C, Dentin

17. 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

18. Decalcified tooth
•In a decalcified
section of tooth,
only the organic
material is left
behind.
•In this micrograph
you can see an
enamel lamella
and enamel tufts.
Legend: A, Enamel lamella; B, Enamel tuft

19. Odontoblastprocess
•Odontoblastprocesses
usually end at the DEJ.
However, sometimes the
ends of the process
become embedded in
the enamel as it forms.
•These very small, usually
straight structures that
you can see adjacent to
the DEJ are enamel
spindles.
•They are only about one
tenth the length of an
enamel tuft.
Legend: A, Enamel spindle; B, Odontoblast
processes in dentin

20. Enamel spindles
•In this high
magnification of the
DEJ you can clearly
see the bifurcation
of the ends of some
of the odontoblast
processes as well as
enamel spindles.
Legend: A, Enamel spindle; B, Odontoblastprocess;
C, Enamel rod

22. This slide from:
Sharifa Abdulla Alhaj

23. Good
Luck
All
Done by: Bedour Al-Arfaj.

24. أاهدعبو هركاذملا لبق هيعد...
ةركاذملا لبق
انرارسأ و كتٌشخب انبولق و كركذب ةرماع انتنسلأ لعجأ مهللا ، نٌبرقملا ةكئلاملا و نٌلسرملا ظفح و نٌٌبنلا مهف كلأسا ًنأ مهللا
رٌدق ءًش لك ىلع كنأ كتعاطب .. لٌكولا معن و الله انبسح
ةركاذملا دعب
لٌكولا معن و الله انبسح ، رٌدق ءًش لك ىلع كنا هٌلا ًتجاح دنع هدرف تملعت ام و تظفح ام و تأرق ام كتعدوتسا ًنأ مهللا
ناحتملإا موي
كٌلا لاإ كنم اجنم و أجلم لا كٌلا يرما تملس و كٌلع تلكوت ًنأ مهللا
ةعاقلا لوخد
ارٌصن اناطلس كندل نم ًل لعجأ و قدص جرخم ًنجرخأ و قدص لخدم ًنلخدأ بر
لحلاب ءدبلا لبق
زحلا لعجت تنا و لاهس هتلعج ام لاأ لهس لا مهللا ، حاتفلا الله مسب ًلوق هقفٌ ًناسل نم ةدقع للحا و يرمأ ًل رسٌ و يردص ًل حرشأ برا ن اذ
نٌمحارلا محرا اٌ لاهس تئش
ناحتملأا ءانثأ
نٌمحارلا محرأ كنأ رضلا ًنسم نا بر ، ثٌغتسأ كتمحرب موٌق اٌ ًح اٌ نٌملاظلا نم تنك ًنأ كناحبس تنا لاا هلإ لا
نايسنلا دنع
ًتلاض و ًنعمجأ هٌف بٌر لا موٌ ًف سانلا عماج اٌ مهللا
ءاهتنلأا دعب
الله اناده نأ لاول يدتهنل انك ام و اذهل اناده يذلا لله دمحلا