The cells of the inner enamel epithelium differentiate to form ameloblast cells.
The main function of ameloblast cells is to lay down the enamel matrix and mineralization of enamel.
The cyclic changes that happen in the enamel during the life cycle of the ameloblast can be classified into the following types.
Morphogenic stage
Organizing Stages
Formative / Secretive stage
Maturative stage
Protective stage
Desmolytc stage
Morphogenic Stage
The cells of the inner enamel epithelium interact with the adjacent mesenchymal cells and determine the shape of the crown.
Cell morphology - The inner enamel epithelium cells are short columnar cells with oval nuclei.
Golgi apparatus and centrioles are present in the proximal end.
The inner enamel epithelium is separated from the dental papilla by a dental lamina and a cell-free zone.
Organizing Stage
the cells of the inner enamel epithelium interact with the adjacent dental papilla cells and initiate the differentiation of dental papilla cells into the odontoblast.
Cell morphology - Cells elongate on the distal side
Golgi apparatus and centriole migrate to the opposite side of the cell, this
of the cell, organelles is called reversal of polarity.
The inner enamel epithelium cells become polarized ie. they no longer divide.
Junctional complexes developed on both proximal and distal ends of ameloblast cells.
The growth of junctional complexes results in a reduction of cell-free zone, inner enamel epithelium comes in close contact with the tissue.
Formative / Secreative stage
Ameloblat begins the formation of the enamel matrix in this stage after a layer of dentin is laid.
Cell morphology- the ameloblast cells remain in the same size but the number of cell organelles
and secretory granules increases.
Secondary junctional complexes known as terminal bars are seen in the distal end of ameloblast these result in the compartmentalization of ameloblast into two areas.
body
tomes process (distal extension)
Two primary junctional complexes formed surround the ameloblast cells on both sides ( toward stratum intermedium and towards dentin).
Junctional complexes contain actin filament on both sides, the actin filaments control the movement of substance across the ameloblast cells.
Maturative Stage
After the entire enamel matrix is laid the ameloblasts undergoes morphological stages for maturation of enamel.
Cell morphology - The cells become shorter and attached to the enamel matrix
The maturative stages occur in two sub-stages-
Transition stage
Modulation stage
Transition stage
This stage shows changes prior to the onset of maturation.
The shortened ameloblast cells stop secretion and undergoes apoptosis ( programed cell death).
The process of removal of enamel protein begins.
Modulation stage
In this stage , Ameloblasts remove organic material form enamel and deposit inorganic material.
The ameloblast undergoes cyclic changes between ruffled end and smooth end borders.
RUFFLED ENDS - Allows incorporation of inorganic material into the matrix.
SMOOTH ENDS - Allows the exit of protein.
Protective Stage
After the enamel is completely calcified the ameloblast cells lose their columnar shape and become cuboidal.
They become indistinguishable from the outer enamel epithelium therefore the structure is called reduced enamel epithelium.
It protects the enamel surface from the connective tissue of the follicle till eruption.
Desmolytic Stage
Reduced enamel epithelium produces enzymes to destroy the overlying connective tissue by desmolysis.
It provides a pathway for the fusion of reduced enamel epithelium with the oral epithelium.
It provides a pathway for tooth eruption in the oral cavity without bleeding.
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