Amelogenesis
Encyclopedia
Amelogenesis is the formation of enamel
on teeth
and occurs during the crown stage of tooth development after dentinogenesis
, which is the formation of dentine. Although dentine must be present for enamel to be formed, it is also true that ameloblasts must be present in order for dentinogenesis to continue. A message is sent from the newly differentiated odontoblasts to the inner enamel epithelium
(IEE), causing the epithelial
cells to further differentiate into active secretory ameloblasts. Dentinogenesis is in turn dependent on signals from the differentiating IEE in order for the process to continue. This prerequisite is an example of the biological concept known as reciprocal induction, in this instance between mesenchymal
and epithelial cells.
Amelogenesis is considered to have two stages. The first stage is known as the secretory phase, and the second stage is known as the maturation stage. Proteins and an organic matrix form a partially mineralized enamel in the secretory stage. The maturation stage completes enamel mineralization.
differentiation is initiated by the presence of predentin. IEE cells elongate and become preameloblasts.
Preameloblasts elongate and become postmitotic, polarized, secretory ameloblasts.
No tomes' process yet.
It is at this stage that a signal is sent from the newly differentiated ameloblasts back across the dentino-enamel junction (DEJ) to stimulate dentinogenesis.
Ameloblasts secrete organic matrix: enamel proteins and enzymes.
. In the rough endoplasmic reticulum of these cells, enamel proteins are released into the surrounding area and contribute to what is known as the enamel matrix, which is then partially mineralized by the enzyme alkaline phosphatase
. When this first layer is formed, the ameloblasts move away from the dentin, allowing for the development of Tomes’ processes at the end of the cell which is in contact with the DEJ. Tomes' process is the term given to the end of the cell which lays down the crystals of the enamel matrix. The Tomes' processes are angled, which introduces differences in crystallite orientation, and hence structure. Enamel formation continues around the adjoining ameloblasts, resulting in a walled area, or pit, that houses a Tomes’ process, and also around the end of each Tomes’ process, resulting in a deposition of enamel matrix inside of each pit. The matrix within the pit will eventually become an enamel rod, and the walls will eventually become interrod enamel. The only distinguishing factor between the two is the orientation of the calcium crystals.
s, ameloblastin
s, enamelin
s, and tuftelin
s. During this process, amelogenins and ameloblastins are removed after use, leaving enamelins and tuftelin in the enamel. By the end of this stage, the enamel has completed its mineralization.
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
on teeth
Tooth
Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...
and occurs during the crown stage of tooth development after dentinogenesis
Dentinogenesis
Dentinogenesis is the formation of dentin, a substance that forms the majority of teeth. Dentinogenesis is performed by odontoblasts, which are a special type of biological cells on the outside of dental pulps, and it begins at the late bell stage of a developing tooth...
, which is the formation of dentine. Although dentine must be present for enamel to be formed, it is also true that ameloblasts must be present in order for dentinogenesis to continue. A message is sent from the newly differentiated odontoblasts to the inner enamel epithelium
Inner enamel epithelium
The inner enamel epithelium, also known as the internal enamel epithelium, is a layer of cells located on the rim nearest the dental papilla of the enamel organ in a developing tooth. This layer is first seen during the bell stage....
(IEE), causing the epithelial
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
cells to further differentiate into active secretory ameloblasts. Dentinogenesis is in turn dependent on signals from the differentiating IEE in order for the process to continue. This prerequisite is an example of the biological concept known as reciprocal induction, in this instance between mesenchymal
Mesenchyme
Mesenchyme, or mesenchymal connective tissue, is a type of undifferentiated loose connective tissue that is derived mostly from mesoderm, although some are derived from other germ layers; e.g. some mesenchyme is derived from neural crest cells and thus originates from the ectoderm...
and epithelial cells.
Amelogenesis is considered to have two stages. The first stage is known as the secretory phase, and the second stage is known as the maturation stage. Proteins and an organic matrix form a partially mineralized enamel in the secretory stage. The maturation stage completes enamel mineralization.
Inductive stage
AmeloblastAmeloblast
Ameloblasts are cells, present only during tooth development, that deposit tooth enamel, the hard outermost layer of the tooth that forms the chewing surface....
differentiation is initiated by the presence of predentin. IEE cells elongate and become preameloblasts.
Initial Secretory stage
A shift in polarity occurs.Preameloblasts elongate and become postmitotic, polarized, secretory ameloblasts.
No tomes' process yet.
It is at this stage that a signal is sent from the newly differentiated ameloblasts back across the dentino-enamel junction (DEJ) to stimulate dentinogenesis.
Secretory ameloblasts
Secretory stage ameloblasts are polarized, elongated cells with the cytoplasm full of organelles.Ameloblasts secrete organic matrix: enamel proteins and enzymes.
Secretory stage
In the secretory stage, ameloblasts are polarized columnar cellsCell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
. In the rough endoplasmic reticulum of these cells, enamel proteins are released into the surrounding area and contribute to what is known as the enamel matrix, which is then partially mineralized by the enzyme alkaline phosphatase
Alkaline phosphatase
Alkaline phosphatase is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides, proteins, and alkaloids. The process of removing the phosphate group is called dephosphorylation...
. When this first layer is formed, the ameloblasts move away from the dentin, allowing for the development of Tomes’ processes at the end of the cell which is in contact with the DEJ. Tomes' process is the term given to the end of the cell which lays down the crystals of the enamel matrix. The Tomes' processes are angled, which introduces differences in crystallite orientation, and hence structure. Enamel formation continues around the adjoining ameloblasts, resulting in a walled area, or pit, that houses a Tomes’ process, and also around the end of each Tomes’ process, resulting in a deposition of enamel matrix inside of each pit. The matrix within the pit will eventually become an enamel rod, and the walls will eventually become interrod enamel. The only distinguishing factor between the two is the orientation of the calcium crystals.
Maturation stage
In the maturation stage, the ameloblasts transport substances used in the formation of enamel. Microscopically, the most notable aspect of this phase is that these cells become striated, or have a ruffled border. These signs demonstrate that the ameloblasts have changed their function from production, as in the secretory stage, to transportation. Proteins used for the final mineralization process compose most of the transported material. The noteworthy proteins involved are amelogeninAmelogenin
Amelogenin is a protein found in developing tooth enamel, and it belongs to a family of extracellular matrix proteins. Developing enamel contains about 30% protein, and 90% of this is amelogenins...
s, ameloblastin
Ameloblastin
Ameloblastin, also known as amelin, is a gene-specific protein found in tooth enamel. Although less than 5% of enamel consists of protein, ameloblastins comprise 5%-10% of all enamel protein. This protein is formed by ameloblasts during the early secretory to late maturation stages of amelogenesis...
s, enamelin
Enamelin
Enamelin was described in older literature as an EDTA soluble enamel protein. It accounts for the organic portion of enamel, which represents 4% of enamel's mass. It turned out in recent research to be albumin derived from blood contamination....
s, and tuftelin
Tuftelin
Tuftelin is an acidic phosphorylated glycoprotein found in tooth enamel. In humans, the Tuftelin protein is encoded by the TUFT1 gene.- Function :This protein is formed for a short time during amelogenesis...
s. During this process, amelogenins and ameloblastins are removed after use, leaving enamelins and tuftelin in the enamel. By the end of this stage, the enamel has completed its mineralization.