Dr. Saleem Shaikh
Introduction
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The development of tooth is divided into stages –
bud, cap, early bell and advanced bell stage
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Enamel organ consists of 4 layers – outer enamel
epithelium, inner enamel epithelium, stratum
intermedium, stellate reticulum.

The cells of the inner enamel epithelium become
more columnar and convert into ameloblasts, which
produce enamel.
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Enamel formation begins in the advanced bell stage.
Life cycle of Ameloblasts
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Divided into six stages:
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Morphogenic stage
Organizing stage
Formative stage
Maturative stage
Protective stage
Desmolytic stage
Amelogenesis occurs during formative and maturative stage.
Ameloblasts start differentiating from the tips of cusps or
incisal region and progresses towards the cervical region.
Morphogenic stage

This is the first stage

The cells are short and columnar with nucleus
which fills up almost the entire cell body
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The golgi apparatus and centrioles are located
in the proximal end – near stratum
intermedium

Mitochondria are present throughout the
cytoplasm
Organizing stage

Ameloblasts interact with the adjacent connective tissue.
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Odontoblast form in the dental papilla

Ameloblasts become longer and reversal of functional
polarity takes place; nucleus moves towards the top part
(proximal) and centrioles – golgi apparatus moves
towards the lower part (distal end).

During the last phase of organizing phase dentin
formation is seen
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Reversal of nutrition of ameloblasts
Formative stage

This stage begins after formation of 1st layer of dentin –
reciprocal induction

Ameloblasts develop a blunt process at their end which is
known as tomes process

Enamel matrix is laid down durng this stage, but the
enamel matrix is rich in organic constituents and is later
modified to reach its final form.

Tomes process contain secretory granules as well as
rough endoplasmic reticulum.

The tomes process appear to be separate from the rest of
the cell by a structure known as DISTAL TERMINAL BAR.
Maturative stage

During this stage ameloblasts are slightly reduced in
length and are closely attached to the enamel surface.

The cells absorb organic material from the matrix and
infuse inorganic elements into the matrix.

Two phases of ameloblasts seen in this stage
 Smooth end
 Ruffled border (microvilli)
Calcium is actively pumped during ruffel ended phase and
passively during smooth ended phase
Proteases are secreted by ameloblasts which degrades the enamel
proteins and these are absorbed by the ruffle ended
ameloblasts.
More than 90% of the initially secreted protein is lost during enamel
maturation.
Protective stage

When enamel is completely calcified the ameloblasts
become small and fuse with the other layers of enamel
organ. i.e. outer enamel epithelium, stellate reticulum and
stratum intermedium.

All these layers together form a covering over the enamel
and this is known as REDUCED ENAMEL EPITHELIUM

Its function is to prevent the mature enamel from coming
in contact with the connective tissue (dental follicle).

If enamel comes in contact with the dental follicle then
cementum may deposit on top of enamel.
Desmolytic stage

During eruption the reduced enamel epithelium
releases enzymes which tend to cause the atrophy
of the connective tissue so that the tooth can erupt
through the oral mucosa.

The reduced enamel epithelium fuses with the oral
epithelium and this helps in the tooth eruption
without any bleeding.

Premature degeneration of the reduced enamel
epithelium may prevent the eruption of the tooth.
Amelogenesis

This process is divided into two parts
 Formation of enamel matrix
 Mineralization and maturation of enamel matrix
Enamel matrix: enamel matrix is initially deposited as small islands
and then it forms a continous layer
Amelogenin is the major component of enamel matrix proteins. It
maintains the space between enamel crystals. Absence of this
protein results in hypoplastic teeth.
Ameloblastin and enamelin are other important proteins of enamel.
These help in growth of crystals.
Tuftelin is another protein which is seen only near the
dentinoenamel junction.

Mineralization of enamel matrix takes place in
two stages.
 Immediate partial mineralization
 Maturation
Nucleation is initiated when enamel matrix comes in
contact of the crystals of dentin.
Maturation is completed by gradually by removing
organic and deposition of inorganic material
The process of matrix formation, mineralisation and
maturation starts from the cusp tips and progresses
towards the cervical region. It also starts from the
dentinoenamel junction and proceeds towards the
surface.