Dr. Saleem Shaikh
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Enamel is the hardest tissue of
the body
It forms the outer covering of
the crown
It varies in thickness having a
maximum thickness of 2-2.5
mm at the cusp tips of molars
and is almost as thin as a knife
edge at the cementoenamel
junction.
1.
Average knoop hardness number for enamel approximately 343.
2.
Forms a resistant covering (suitable for mastication).
3.
Brittle.
4.
Forms a protective covering
5.
Acts as semipermeable membrane.
6.
The colour of the crown appears yellowish white to grayish white,
the enamel is translucent and the colour depends on the thickness
and homogenecity of enamel.
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1.
2.
By weight:
Inorganic components (96%)
Organic and water components: 1% and 3% respectively.
Inorganic material of enamel is made up of hydroxyapatite crystals.
The chemical formula is Ca10(PO4)6 (OH4)2
The crystals are 30 nm in width, and may extends several
millimeters.
Organic components consists unique proteins and lipids. The
proteins are divided into two main groups – Amelogenin and
Nonamelogenins (Enamelin, Ameloblastin and tuftelin).
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Enamel is made up of enamel rods
(prisms).
These rods are covered by rod sheath.
The number of rods may be around 5
million in lower central incisor to 12
million in molars.
The rods start from the dentinoenamel
junction and extend upto the surface of
the tooth in a wavy (tortuous) course.
Measuring 4 μm wide to 8 μm long
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The surface of enamel also looks like
fish scale appearance.
When the rods are seen under high
magnification the rods appear to
have a ‘key hole’ pattern
appearance.
Consisting of a head and tail
When enamel is cut longitudinally it
may pass through the head of one
rod and tail of the adjacent rod.
This gives the appearance of rod and
inter rod.
The head of the rod is towards
occlusal surface and tails are
towards the cervical.
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Enamel rod sheath
A thin peripheral layer, seen
around the rod.
Darker than the rod.
Less calcified and contains
more organic matter than the
rod itself.
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Each enamel rod is made up of segments made up of dark lines –
these are known as cross striations.
In humans these segments are of 4µm width and represent daily
rythmic deposition of enamel
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More prominent when enamel is not calcified properly.
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These are different from striae of retzius.
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The rods are oriented at right angle
to the dentinoenamel junction.
They are horizontal in the center part
In the incisal and cuspal regions they
are almost vertical
In the cervical region the rods are
horizontal in deciduous and oblique
in permanent teeth.
Follow a wavy course in clockwise
and anticlockwise deviation