• Enamel is an Epithelially derived hard, protective
covering of teeth
• Fully formed enamel is the most highly mineralized extracellular
• It is highly brittle yet exhibits certain degree of resistance to
• Enamel is the hardest substance of the body, its hardness is
comparable to mild steel.
• Average knoop hardness number for enamel is approximately 343
• Surface of enamel is more mineralized and hard than deeper enamel.
• Unlike other calcified structures in the body enamel is unique as it
is totally acellular.
Composition of enamel
Enamel consists of approximately 96% of inorganic material and 4% of
organic material and water by weight.
The organic component forms the matrix and the inorganic component
comprises of various minerals.
Percentage of dental tissue components by weight
The organic matrix of enamel is made from non-collagenous proteins
Of the enamel proteins 90% are amelogenins and 10% are nonamelogenins.
The different types of nonamelogenins associated with formation of
enamel are ameloblastin, enamelin and tuftelin.
The primary function of the organic material is to direct the growth of
The inorganic component
Enamel hydroxyapetite crystals are the largest hydroxyapetite crystals of all the
calcified tissues in the body.
In addition to hydroxyapetite crystals enamel also contains carbonates and trace
These crystals are susceptible to dissolution by acids and hence provides the
basis for dental caries.
Enamel is translucent and varies in colour from light yellow to
It varies in thickness, with maximum over cusps (2.5 mm) to a
feather edge at the cervical line
Thickness of enamel in primary teeth is nearly half than
that in permanent teeth
Although enamel is an extremely hard tissue it is partially permeable
to some fluids, bacteria and other products of the oral cavity
The permeability of enamel is due to the presence of cracks and
microscopic spaces on the surface of enamel which allows
penetration of fluids
The permeability of enamel decreases and hardness
increases with age
Structure of enamel
Rod and interrod enamel
The fundamental units of enamel are rods and interrod enamel.
The rod and interrod enamel is built from closely packed and long ribbon
like hydroxyapetite crystals.
The rod is shaped like a cylinder with a wide head portion, a neck and a
thinner tail portion .
Each rod is formed by four ameloblasts.
Rods are formed nearly perpendicular to DEJ and curve slightly towards the cusp tip
The follow a wavy course as the traverse from the DEJ to the surface of the crown
The length of most rods is much longer than the thickness of enamel
The diameter of the rod at the outer surface is double the diameter at DEJ
Crystals that surround each rod are called interrod enamel
Rod and interrod enamel is formed from the Tomes process of Ameloblasts
Features of enamel
Enamel spindles originate from the DEJ
Before enamel forms, some developing odontoblasts process extend into
the ameloblast layer, and when enamel formation begins become trapped to
form enamel spindles.
Enamel tufts also originate from the DEJ, run a short distance in the
enamel or sometimes to one half of the thickness.
They represent protein (enamelin) rich areas in the enamel matrix that
fail to mature.
They are formed during the formative stages of enamel.
Enamel lamellae extend from the surface to varying depths of the enamel
• They are faults that develop as a result of failure of maturation process.
• They are filled with organic material and water.
Cross striations are periodic bands that appear along the full length of
enamel rod (appears like a ladder).
They appear at regular intervals that is in agreement with the rate of
enamel deposition (which is approximately 4μm per day).
Striae of Retzuis
Striae of Retzuis also represent incremental growth.
In ground cross sections they appear like concentric growth rings similar to
those found in trees.
In ground longitudinal sections they appear to be dark line extending from
the DEJ to the tooth surface.
where they end in shallow furrows know as perikymata (or imbrication lines)
Ageing and changes in enamel
• Worn out because of masticatory attrition.
• Decrease in the permeability of enamel.
• Discoloration and a change in the surface layer.
Enamel attrition and discoloration
Defects of enamel formation
Generally three conditions effect enamel during its formative stages
• Defects caused by febrile disease.
• Defects caused by tetracycline.
• Finally defects caused by excess fluoride.
Dental Fluorosis (mottled enamel)
If fluoride ion is incorporated into the hydroxyapetite crystals then it
becomes more resistant to acid dissolution.
The amount of fluoride must be controlled because high fluoride can cause
mottled enamel (in excess of 5ppm).
Treated with sodium fluoride solution
Acid etching of enamel is a very important technique for conditioning enamel for many
Acid etching is used when doing fissure sealants, restoration, orthodontic bracket etc.
It is carried out by using a mild acid like orthophosphoric acid on the enamel surface for a
controlled period of time.
Enamel before acid etching
Enamel after acid etching
SEM images of specimen conditioned with 37% phosphoric acid
Acidic Soft Drinks Effects
The demineralization areas of enamel surface in the in
vitro Coca-Cola group (1000X magnification).
The demineralization areas in enamel surface in the in
vitro Sprite group (500X magnification).
Evaluation of the bleached human enamel by Scanning Electron
Evaluation of the bleached
human enamel by Scanning
• Scanning electron microscopic observation of morphological modifications
produced by Fluorostom on enamel surface CRISTINA NICOLAE, MIHAELA
HÎNCU, C. AMARIEI Faculty of Dental Medicine, “Ovidius”
University, ConstantaRom J Morphol Embryol 2011, 52(4):1255–1259