ENAMEL
Functions of Enamel Organ
● Enamel organ determine the morphological form or the shape and size of the crown
● Inner enamel epithelial cells differentiate to form ameloblasts that deposit enamel
● Inner enamel epithelial cells helps in odontoblast differentiation
● Cervical loop of enamel organ proliferates to give rise to Hertwig’s epithelial root
sheath; the structure that determines the size, shape, type and number of roots.
● Once the formative function is completed enamel organ assumes a protective
function by forming a reduced enamel epithelial layer around the newly formed
enamel.
● Reduced enamel epithelium which is developed from enamel organ,elaborates
enzymes that have a role in eruption of tooth.
● Reduced enamel epithelium helps in establishing a dento-gingival junction.
Enamel
● Enamel is the hardest calcified tissue of the body covering the anatomic crown of
tooth.
● Enamel is a unique calcified tissue which is different from other calcified tissues of
the body.
Characteristic Features of Enamel
● Ameloblasts, the enamel forming cells are ectodermal in origin
● Enamel formation occurs only for a limited period of time till the desired thickness is
formed
● In an erupted tooth enamel is not lined by formative cells
● Enamel does not have the capacity to repair or regenerate
● Enamel is a nonliving tissue not containing cells or cellular components
● Enamel is avascular and insensitive
● Organic matrix of enamel is unique composed of enamel protein and is
non-collagenous.
AMELOGENESIS
● Amelogenesis is the process of formation of enamel.
● The cells responsible for amelogenesis are ameloblasts, which are derived from
inner enamel epithelium of enamel organ, an ectodermal component.
● Ameloblasts during their life time undergo morphological and physiological changes
that are directly related to their function.
● These Changes can be described as life cycle of ameloblasts.
● According to the functions performed, the life cycle of ameloblasts can be divided
into:
1.Pre-secretory stage
-Morphogenic stage
-Organizing/differentiating stage
2.Secretory stage
-Formative stage
3.Post-secretory stages
-Maturative
-Protective stage
-Desmolytic stage
,Morphogenic Stage
● The function of ameloblasts during this stage is determination of shape of the tooth.
● The inner enamel epithelium interacts with underlying connective tissue and through
differential growth helps to establish the dentino-enamel junction and thereby
determine the shape of the tooth to be formed.
● The ameloblasts at this stage are low columnar in shape with centrally placed
nucleus.
● Cytoplasmic organelles are not abundant, the centrioles and Golgi complex are
located at the apical part of cytoplasm and mitochondria is evenly distributed
throughout the cytoplasm.
Organizing Stage or Differentiation Stage
● During this stage, the inner enamel epithelial cells undergo differentiation to
ameloblasts as a prerequisite for enamel formation.
● This stage is also named as organizing stage because during this stage, the
ameloblasts exert organizing influence on dental papilla cells which are adjacent to
them and help in their differentiation to odontoblasts.
● In the differentiation stage, the ameloblasts increase in length to attain a length of 40
microns and also develop abundant cytoplasmic organelles necessary for protein
synthesis.
● As the cells elongate, the nucleus shifts to the apical or proximal end of cell.
● The centrioles and Golgi apparatus also move from apical cytoplasm to basal or
distal part of the cell and mitochondria becomes concentrated at the proximal end.
● This change in position of nucleus and the other organelles is called reversal of
polarity.
● This is a preparation to secretion because the organelles are moved to the secretory
end of the cell which is at the basal region.
● The cells also develop intercellular junctions the proximal and distal ends which are
termed as proximal and distal terminal bars.
● During the terminal phase of organizing stage the dentin formation begins and the
basal lamina supporting the ameloblast layer disintegrates.
● Deposition of dentin is an important event in life cycle of ameloblasts because the
ameloblasts can attain the secretory function only after a layer of dentin is deposited.
● The interdependence between ameloblasts and odontoblasts is referred to as
reciprocal induction.
● Ameloblasts also derive alternate source of nutritional supply from dental sac
because the dentin deposited blocks the nutritional supply from the dental papilla.
Formative or Secretory Stage
● In this stage, ameloblasts perform the function of secretion of enamel matrix and
partial mineralization.
● The ameloblasts which are fully differentiated starts secretory function only after a
layer of dentin is deposited.
● The secretory ameloblasts are structurally suited for synthesis and secretion of
enamel proteins.
● The cells have many mitochondria, well developed Golgi complex and extensive
cisterns of rough endoplasmic reticulum.
, ● Cytoplasm also shows many secretory granules, vacuoles, free ribosome, various
types of vesicles, microtubules, etc.
● Microtubules are involved in the movement of secretory granules to the basal plasma
membrane.
● The basal portion of cytoplasm of ameloblasts contains numerous granules packed
with enamel proteins.
● The secretory granules move towards the basal plasma membrane, fuse with it and
release the matrix protein into the extracellular space against the newly formed
dentin by a process called exocytosis.
● Secretory ameloblasts have several junctional specializations at basal and lateral cell
surfaces.
● At the proximal and distal end of cell body the adjacent cells are attached to each
other by junctional complexes.
● These intercellular junctions help to maintain organization of ameloblast layer and
also to control the metabolite diffusion along extracellular spaces.
● The proximal intercellular junctions are relatively leaky while distal ones act as a
permeability barrier to macromolecules such as enamel proteins and calcium.
● Therefore calcium is prevented from reaching the matrix throughextracellular space.
● In the initial stage of secretory phase the ameloblasts have a flat basal region.
● After a little thickness of enamel matrix is deposited, ameloblasts develop a conical
process at the base, which is called Tomes’ process.
● Tomes’ process is partially separated from cell body by an incomplete septaformed
by the microfilaments and tonofilaments extending from the distal terminal bars.
● Cytoplasm of cell body is in continuation with that of Tomes’process.
● The cytoplasm of Tomes’ process does not contain any organelles other than
secretory granules, microtubules, microfilament and a few mitochondria.
● After the Tomes’ process is formed, the secretion of enamel takes place from two
different sites and is responsible for the rod structure of enamel.
● Tomes’ process is lost before the last phase of secretory stage, before the surface
layer of enamel is deposited.
Maturative Stage
● During this stage, ameloblasts helps in the mineralization and maturation of enamel.
● Ameloblasts enter into the maturative phase only after the desired thickness of
enamel matrix is laid down.
● In this stage, ameloblasts have to introduce the inorganic material necessary for
maturation and also reabsorb proteins and water to provide space for the minerals.
● Ameloblasts performing these dual functions shows morphological alterations.
● Ameloblasts are ruffle ended when they are performing the function of introducing
inorganic components and smooth ended when they are reabsorbing proteins and
water.
● The series of repetitive morphological changes that occur in ameloblasts maturative
stage, from ruffled ended to smooth ended is referred to as ameloblast modulation.
● During this process, tight junctions and deep membrane infoldings periodically
appear (ruffle-ended), then disappear for short intervals (smooth-ended), from the
apical ends of the cells.
● Ameloblasts in maturative phase shows slight reduction in height, decrease in
volume and organelle content.
Functions of Enamel Organ
● Enamel organ determine the morphological form or the shape and size of the crown
● Inner enamel epithelial cells differentiate to form ameloblasts that deposit enamel
● Inner enamel epithelial cells helps in odontoblast differentiation
● Cervical loop of enamel organ proliferates to give rise to Hertwig’s epithelial root
sheath; the structure that determines the size, shape, type and number of roots.
● Once the formative function is completed enamel organ assumes a protective
function by forming a reduced enamel epithelial layer around the newly formed
enamel.
● Reduced enamel epithelium which is developed from enamel organ,elaborates
enzymes that have a role in eruption of tooth.
● Reduced enamel epithelium helps in establishing a dento-gingival junction.
Enamel
● Enamel is the hardest calcified tissue of the body covering the anatomic crown of
tooth.
● Enamel is a unique calcified tissue which is different from other calcified tissues of
the body.
Characteristic Features of Enamel
● Ameloblasts, the enamel forming cells are ectodermal in origin
● Enamel formation occurs only for a limited period of time till the desired thickness is
formed
● In an erupted tooth enamel is not lined by formative cells
● Enamel does not have the capacity to repair or regenerate
● Enamel is a nonliving tissue not containing cells or cellular components
● Enamel is avascular and insensitive
● Organic matrix of enamel is unique composed of enamel protein and is
non-collagenous.
AMELOGENESIS
● Amelogenesis is the process of formation of enamel.
● The cells responsible for amelogenesis are ameloblasts, which are derived from
inner enamel epithelium of enamel organ, an ectodermal component.
● Ameloblasts during their life time undergo morphological and physiological changes
that are directly related to their function.
● These Changes can be described as life cycle of ameloblasts.
● According to the functions performed, the life cycle of ameloblasts can be divided
into:
1.Pre-secretory stage
-Morphogenic stage
-Organizing/differentiating stage
2.Secretory stage
-Formative stage
3.Post-secretory stages
-Maturative
-Protective stage
-Desmolytic stage
,Morphogenic Stage
● The function of ameloblasts during this stage is determination of shape of the tooth.
● The inner enamel epithelium interacts with underlying connective tissue and through
differential growth helps to establish the dentino-enamel junction and thereby
determine the shape of the tooth to be formed.
● The ameloblasts at this stage are low columnar in shape with centrally placed
nucleus.
● Cytoplasmic organelles are not abundant, the centrioles and Golgi complex are
located at the apical part of cytoplasm and mitochondria is evenly distributed
throughout the cytoplasm.
Organizing Stage or Differentiation Stage
● During this stage, the inner enamel epithelial cells undergo differentiation to
ameloblasts as a prerequisite for enamel formation.
● This stage is also named as organizing stage because during this stage, the
ameloblasts exert organizing influence on dental papilla cells which are adjacent to
them and help in their differentiation to odontoblasts.
● In the differentiation stage, the ameloblasts increase in length to attain a length of 40
microns and also develop abundant cytoplasmic organelles necessary for protein
synthesis.
● As the cells elongate, the nucleus shifts to the apical or proximal end of cell.
● The centrioles and Golgi apparatus also move from apical cytoplasm to basal or
distal part of the cell and mitochondria becomes concentrated at the proximal end.
● This change in position of nucleus and the other organelles is called reversal of
polarity.
● This is a preparation to secretion because the organelles are moved to the secretory
end of the cell which is at the basal region.
● The cells also develop intercellular junctions the proximal and distal ends which are
termed as proximal and distal terminal bars.
● During the terminal phase of organizing stage the dentin formation begins and the
basal lamina supporting the ameloblast layer disintegrates.
● Deposition of dentin is an important event in life cycle of ameloblasts because the
ameloblasts can attain the secretory function only after a layer of dentin is deposited.
● The interdependence between ameloblasts and odontoblasts is referred to as
reciprocal induction.
● Ameloblasts also derive alternate source of nutritional supply from dental sac
because the dentin deposited blocks the nutritional supply from the dental papilla.
Formative or Secretory Stage
● In this stage, ameloblasts perform the function of secretion of enamel matrix and
partial mineralization.
● The ameloblasts which are fully differentiated starts secretory function only after a
layer of dentin is deposited.
● The secretory ameloblasts are structurally suited for synthesis and secretion of
enamel proteins.
● The cells have many mitochondria, well developed Golgi complex and extensive
cisterns of rough endoplasmic reticulum.
, ● Cytoplasm also shows many secretory granules, vacuoles, free ribosome, various
types of vesicles, microtubules, etc.
● Microtubules are involved in the movement of secretory granules to the basal plasma
membrane.
● The basal portion of cytoplasm of ameloblasts contains numerous granules packed
with enamel proteins.
● The secretory granules move towards the basal plasma membrane, fuse with it and
release the matrix protein into the extracellular space against the newly formed
dentin by a process called exocytosis.
● Secretory ameloblasts have several junctional specializations at basal and lateral cell
surfaces.
● At the proximal and distal end of cell body the adjacent cells are attached to each
other by junctional complexes.
● These intercellular junctions help to maintain organization of ameloblast layer and
also to control the metabolite diffusion along extracellular spaces.
● The proximal intercellular junctions are relatively leaky while distal ones act as a
permeability barrier to macromolecules such as enamel proteins and calcium.
● Therefore calcium is prevented from reaching the matrix throughextracellular space.
● In the initial stage of secretory phase the ameloblasts have a flat basal region.
● After a little thickness of enamel matrix is deposited, ameloblasts develop a conical
process at the base, which is called Tomes’ process.
● Tomes’ process is partially separated from cell body by an incomplete septaformed
by the microfilaments and tonofilaments extending from the distal terminal bars.
● Cytoplasm of cell body is in continuation with that of Tomes’process.
● The cytoplasm of Tomes’ process does not contain any organelles other than
secretory granules, microtubules, microfilament and a few mitochondria.
● After the Tomes’ process is formed, the secretion of enamel takes place from two
different sites and is responsible for the rod structure of enamel.
● Tomes’ process is lost before the last phase of secretory stage, before the surface
layer of enamel is deposited.
Maturative Stage
● During this stage, ameloblasts helps in the mineralization and maturation of enamel.
● Ameloblasts enter into the maturative phase only after the desired thickness of
enamel matrix is laid down.
● In this stage, ameloblasts have to introduce the inorganic material necessary for
maturation and also reabsorb proteins and water to provide space for the minerals.
● Ameloblasts performing these dual functions shows morphological alterations.
● Ameloblasts are ruffle ended when they are performing the function of introducing
inorganic components and smooth ended when they are reabsorbing proteins and
water.
● The series of repetitive morphological changes that occur in ameloblasts maturative
stage, from ruffled ended to smooth ended is referred to as ameloblast modulation.
● During this process, tight junctions and deep membrane infoldings periodically
appear (ruffle-ended), then disappear for short intervals (smooth-ended), from the
apical ends of the cells.
● Ameloblasts in maturative phase shows slight reduction in height, decrease in
volume and organelle content.
