Enamel is the hardest tissue in the body and is derived from the inner enamel epithelium. It is composed mainly of hydroxyapatite crystals and proteins. Enamel is thickest at the incisal edges and cusp tips and thins cervically. Healthy thick enamel appears bluish white while thin enamel near the dentin looks more yellow. Enamel prisms (rods) vary in number between teeth and their twisted structure in cuspal areas adds strength. The rods are surrounded by interprismatic substance and have transverse striations. Enamel is selectively permeable but not impermeable to ions.

1. Enamel

2. 1-enamel is ectodermal in origins
2-it is derived from inner enamel
epithelium of enamel organ.
3-mature enamel is completely
non cellular
Ameloblasts are derived from outer enamel epithelium)
Mature enamel is completely acellular (True or false )

3. Physical characters
1-Thickness
2-Color
3- Hardness
4- Tensile strength
5-Permeability
6-Solubility

4. thickness
It is thick at the incisal edge and cusp tip of molars and
premolars (2-2.5 mm) and ends cervically as knife edge
The thickest part of the enamel is present in---------, and………….

5. color
Thick enamel---------------------- bluish white
Decrease in thickness-----------------------yellow due
to the underlying dentin
Healthy thick enamel is -------- in color, while thin enamel is …………in color

6. hardness
Enamel is the hardest calcified tissue in the body
Because of its high content of minerals.
Enamel can withstand load of mastication and
resist wear process.
------- is the hardest calcified tissue in the body.
Enamel is the hardest calcified tissue in the body (give a reason)

7. Tensile strength
Although it is hard , enamel is extremely
brittle and depends on the strength of
the underlying dentin.
Tensile strength of enamel is greater than that of dentin ( true or false)

8. permeability
Enamel is selectively
permeable, permitting partial or
complete passage of ions due to the
presence of microscopic pores.
Enamel is completely impermeable to ions
(False or true)

9. solubility
Enamel dissolves in acid media. Its
surface is less soluble than deep
enamel.

10. Chemical composition
Mature enamel consists of:
Mainly(96%)
inorganic substance
Small (3%)
amount of organic substance
& 1%)
water

11. Inorganic component
Mainly calcium phosphate crystals
(hydroxyapatite crystals)

12. organic component
Mainly non collagenous proteins:
A- amelogenins
B- non-amelogenins

13. Microscopic structure
1-Rods (prism).
2- Rod sheath.
3-Inter rodal cement substance

14. Ground section Decalcified section
the organic the inorganic
substance is burnt substance is dissolved
and the inorganic and the organic
substance remain substance remain

15. Enamel rods
1- Course.
2- Number.
3- Transverse striation.
4- Direction.
5- Gnarled enamel.

16. Course: the enamel rod starts straight
at dentino-enamel junction (D.E.J.)
for about 30 µ then has a wavy
course till near the outer surface of
enamel where it become straight
once more.

17. The number
of the enamel rods varies from 5 millions in
lower lateral incisor to 12 millions in the
upper first perm.The number of the rods
equals the number of the ameloblasts.
anent molar.
At the tooth surface there are about 20000-
30000 enamel rods in 1 mm2
The density of the rods is at the DEJ about 10%
higher than at the enamel surface.
The total number of enamel rods varies from------- to ---------

18. transmission electron microscope

20. Scanning electron microscope

21. Transverse striation of rods

22. Direction of rods
permanent tooth Deciduous tooth

23. Gnarled enamel
Twisted
Gnarled course of
enamel enamel rods
D
Gnarled enamel is twisted and intertwined rode
structure associated with increase strength of the
enamel ,Present mainly in the incisal edges and tip
of the cusps. (enamel rods develop in planes of
tension).
Give short account on gnarled enamel

24. Gnarled enamel

25. Rod sheath
L.M. distinct thin layer peripheral to the rods
Different refractive index, darker and more
acid resistant, and less calcified and more
organic.
E.M. not distinct layer, but organically rich inter-
rod space devoid of crystals.

26. Inter rod substance
L.M. distinct cement substance with higher
refractive index.
E.M.tail of the adjacent rod with different
direction of the crystals

27. INCREMENTAL LINES OF
RETZIUS

28. NEONATAL LINE
Prenatal enamel
Neonatal line
Postnatal enamel

29. PERIKYMATA
The external manifestation of the
incremental lines of Retzius represented
as transverse wave like grooves on the
surface of the enamel are known as
perikymata.

30. HUNTER SCHREGER
BANDS
The dark bands (Diazones) absorb the •
light where the light bands (Parazones)
reflect the light.

31. ENAMEL TUFTAND
ENAMEL LAMELLAE

32. ENAMEL SPINDLE
It makes the area hypersensitive to pain
Enamel spindles are :
A- odontoblastic processes cross the dentinoenamel junction.
B- remnants of ameloblasts.
C- enamel rods develop in planes of tension.

33. Surface structure
It is relatively structure-less layer covers the cervical
region of the teeth. 30um in thickness in 70% of
People, and it is hyper-mineralized.

34. ENAMEL CUTICLE
Primary cuticle secondary cuticle
It is delicate membrane covers It is non cellular keratinized layer
the crown of the newly formed by reduced enamel
Erupted tooth. It has epithelium after tooth eruption,
the same Structure as After removal of the primary one
basement membrane by wear and brushing

35. ENAMEL pellicle
It is a glycoprotein of saliva that covers the tooth
immediately after eruption. It reforms within hours
after removal.
ENAMEL plaque
Within a day or two after the pellicle has formed it
colonized With microorganisms to form bacterial
Plaque.