Oral Biology

1. EEnnaammeell

2. Physical Properties
● Hardest biological tissue in human body
● Highly mineralized thus can withstand both
shearing and impact forces well
● Abrasion resistance is high , wear down slowly
● Low tensile strength
● Less elastic than dentine
● Translucent, light passes through it due to high
crystal content

3. Chemical Properties
● Principle mineral component of enamel is
Calcium Hydroxyapatite
● By volume:
- mineral : 88-90%
- water : 10%
- organic material : 2%
● By weight:
- mineral : 95-96%
-water : 3%
-organic material : less than 1%

4. Enamel Crystal
● Hydroxyapatite is in the
form of crystallites
● crystals are hexagonal in
cross section
● diameter is about 70 nm
by 25 nm
● length is unknown but
likely to be at least 1 m
● The crystallites of
dentine, bone and
cementum are much
smaller

5. Histology of Enamel : rods (prisms)
● Enamel prism or rod is the basic
structural unit of enamel
● consisting of several million
hydroxyapatite crystallites
packed into a long thing rod 5-
6m
● enamel rods run from the edj to
the surface
● Rods have a "key-hole" shape -
each one having a head and a
tail
● the heads face toward the cusp
tip and the tails toward the
cervical margin.

6. Striae of Retzius
● incremental growth lines seen in
enamel and are the result of
enamel development.
● When viewed microscopically in
cross-section, they appear as
concentric rings.
● In a longitudinal section, they
appear as a series of dark bands.
● The presence of the dark lines is
similar to the annual rings on a
tree.

7. Cross-striations
● The rods with alternating
thick and thin segments
exhibit cross-striations

8. Enamel Spindles
● Narrow spindle
shape,short, straight,
thin, dark structures
● Extensions of the
dentine tubules across
dentinoenamel junction
into enamel
● Found most commonly
beneath the cusps
● Help to make the edj
more permeable

9. Enamel tufts
● Junctional structures in the
inner third of the enamel
that in ground sections
resemble tufts of grass
● Hypomineralized and recur
at approx. 100m intervals
along the junction
● Thickened borders of rods
near edj containing
enamel proteins to
increase the amount of
organic materials

10. Enamel lamellae
● Thin sheets of enamel
proteins that run up and
down the crown of a
tooth ( from surface to
edj )
● Hypomineralized and
narrower, longer and
less common than
enamel tufts
● Contain enamel proteins
● Best seen in cross
section of enamel

11. ● A = Stria of Retzius
● B = Enamel Tuft
● C = Enamel
Lamellae
● D = DEJ

13. Perikymata
● Transverse ridges and grooves on the surface
of tooth enamel.
● indicate the termination of striae of Retzius at
the surface of enamel

14. Neonatal line
● a dark stria of Retzius that
occurs at the time of birth
● It is due to the stress of birth
● usually the darkest and thickest
stria of Retzius
● Found in decidous teeth and
cusps of permanent 1st molars
● Line on a primary tooth marking
the point at which prenatal
growth stops and postnatal
growth begins

15. Hunter-Schreger bands
● Refers to alternating light & dark
lines seen in enamel that begin at
the DEJ & end before they reach
enamel surface
● The effect is due to alternating
directions of prisms
A - Hunter-
Schreger
bands
B - D-E
junction

16. Gnarled Enamel
● Near the D-E junction (A), especially in the cuspal
regions, the enamel rods form intertwining bundles
(B)
● enamel rods are layed down in this pattern to make
the enamel strong in this region

17. Thank You