This document provides information about the structure of enamel in teeth. It discusses striations of Retzius, enamel rods, tufts and lamellae. It explains how variations in organic material deposition during development lead to darker and lighter banding in enamel. It also describes structures like the neonatal line, gnarled enamel, Hunter-Schreger bands, cross-striations and enamel spindles. Electron micrographs show enamel features like rods, tufts and the dentinoenamel junction in detail.

1. Enamel

2. Stria of 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 layed down
at that time so that alternating
dark (higher organic material)
and light (less organic material)
banding occurs. These bands are
called Stria of Retzius. The stria
of retzius usually intercept the
dentino-enamel junction.
Legend: A, Stria of Retzius; B, DEJ

3. Enamel - transverse ground section
Legend: A, Stria of Retzius; B, Enamel
tuft; C, Enamel lamella; D, DEJ
• 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 stria of
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 line is a dark stria
of Retzius that occurs at the time
of birth. It is due to the stress of
birth. The neonatal line is usually
the darkest and thickest stria of
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 layed down in
this pattern by ameloblasts to
make the enamel strong in this
region.
Legend: A, Gnarled enamel; B,
Neonatal line; C, Dentin; D, DEJ

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

6. 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 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 demonstates closely
positioned striations along its length
known as cross-striations or
incremental lines.
• These are thought to be formed by the
daily rhythm of the ameloblast laying
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?They are oriented perpendicular to
the length of the rod.
• Note: Not the large dark bands
projecting diagonally; these are stria of
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 ligher band 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 hydroxyapatite crystals.
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
stria of 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 ligher areas are the rod cores in which
hydroxyapatite crystals are tightly packed
in alignment with each other. The darker
areas surrounding the rod cores are the
rod sheaths in which the crystals are
loosely packed at various angles. There are
two main parts to a rod: the rod head and
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
hydroxyapatite crystals 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 Schreger bands 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-Schreger bands
• Hunter Schreger bands 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
odontoblasts projecting
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. Odontoblast process
• Odontoblast processes
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, Odontoblast process;
C, Enamel rod

22. This slide from:
Sharifa Abdulla Alhaj

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

24. ‫أ‬‫وبعدها‬ ‫المذاكره‬ ‫قبل‬ ‫دعيه‬...
‫المذاكرة‬ ‫قبل‬
‫أسرارنا‬ ‫و‬ ‫بخشٌتك‬ ‫قلوبنا‬ ‫و‬ ‫بذكرك‬ ‫عامرة‬ ‫ألسنتنا‬ ‫أجعل‬ ‫اللهم‬ ، ‫المقربٌن‬ ‫المالئكة‬ ‫و‬ ‫المرسلٌن‬ ‫حفظ‬ ‫و‬ ‫النبٌٌن‬ ‫فهم‬ ‫اسألك‬ ً‫أن‬ ‫اللهم‬
‫قدٌر‬ ‫شًء‬ ‫كل‬ ‫على‬ ‫أنك‬ ‫بطاعتك‬..‫الوكٌل‬ ‫نعم‬ ‫و‬ ‫هللا‬ ‫حسبنا‬
‫المذاكرة‬ ‫بعد‬
‫الوكٌل‬ ‫نعم‬ ‫و‬ ‫هللا‬ ‫حسبنا‬ ، ‫قدٌر‬ ‫شًء‬ ‫كل‬ ‫على‬ ‫انك‬ ‫الٌه‬ ً‫حاجت‬ ‫عند‬ ‫فرده‬ ‫تعلمت‬ ‫ما‬ ‫و‬ ‫حفظت‬ ‫ما‬ ‫و‬ ‫قرأت‬ ‫ما‬ ‫استودعتك‬ ً‫أن‬ ‫اللهم‬
‫اإلمتحان‬ ‫يوم‬
‫الٌك‬ ‫إال‬ ‫منك‬ ‫منجا‬ ‫و‬ ‫ملجأ‬ ‫ال‬ ‫الٌك‬ ‫امري‬ ‫سلمت‬ ‫و‬ ‫علٌك‬ ‫توكلت‬ ً‫أن‬ ‫اللهم‬
‫القاعة‬ ‫دخول‬
‫نصٌرا‬ ‫سلطانا‬ ‫لدنك‬ ‫من‬ ً‫ل‬ ‫أجعل‬ ‫و‬ ‫صدق‬ ‫مخرج‬ ً‫أخرجن‬ ‫و‬ ‫صدق‬ ‫مدخل‬ ً‫أدخلن‬ ‫رب‬
‫بالحل‬ ‫البدء‬ ‫قبل‬
‫الحز‬ ‫تجعل‬ ‫انت‬ ‫و‬ ‫سهال‬ ‫جعلته‬ ‫ما‬ ‫أال‬ ‫سهل‬ ‫ال‬ ‫اللهم‬ ، ‫الفتاح‬ ‫هللا‬ ‫بسم‬ ً‫قول‬ ‫ٌفقه‬ ً‫لسان‬ ‫من‬ ‫عقدة‬ ‫احلل‬ ‫و‬ ‫أمري‬ ً‫ل‬ ‫ٌسر‬ ‫و‬ ‫صدري‬ ً‫ل‬ ‫أشرح‬ ‫رب‬‫ا‬ ‫ن‬‫ذا‬
‫الراحمٌن‬ ‫ارحم‬ ‫ٌا‬ ‫سهال‬ ‫شئت‬
‫األمتحان‬ ‫أثناء‬
‫الراحمٌن‬ ‫أرحم‬ ‫أنك‬ ‫الضر‬ ً‫مسن‬ ‫ان‬ ‫رب‬ ، ‫أستغٌث‬ ‫برحمتك‬ ‫قٌوم‬ ‫ٌا‬ ً‫ح‬ ‫ٌا‬ ‫الظالمٌن‬ ‫من‬ ‫كنت‬ ً‫أن‬ ‫سبحانك‬ ‫انت‬ ‫اال‬ ‫إله‬ ‫ال‬
‫النسيان‬ ‫عند‬
ً‫ضالت‬ ‫و‬ ً‫أجمعن‬ ‫فٌه‬ ‫رٌب‬ ‫ال‬ ‫ٌوم‬ ً‫ف‬ ‫الناس‬ ‫جامع‬ ‫ٌا‬ ‫اللهم‬
‫األنتهاء‬ ‫بعد‬
‫هللا‬ ‫هدانا‬ ‫أن‬ ‫لوال‬ ‫لنهتدي‬ ‫كنا‬ ‫ما‬ ‫و‬ ‫لهذا‬ ‫هدانا‬ ‫الذي‬ ‫هلل‬ ‫الحمد‬