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This form of dentin can be easily distinguished on the surface of a tooth, and is much darker in appearance compared to primary dentin. [2] Tertiary dentin will often not be visible on the surface of a tooth, but because it is more dense it can be viewed on a Micro-CT scan of the tooth. [3] Tertiary dentin on the surface of a gorilla tooth.
There are three types of dentin, primary, secondary and tertiary. [19] Secondary dentin is a layer of dentin produced after root formation and continues to form with age. Tertiary dentin is created in response to stimulus, such as cavities and tooth wear. [20]
Tertiary dentin is deposited at specific sites in response to injury by odontoblasts or replacement odontoblasts from the pulp depending on the severity of the injury. Tertiary dentin can be divided into reactionary or reparative dentin. Reactionary dentin is formed by odontoblasts when the injury does not damage the odontoblast layer.
Dentin is best known for its occurrence in teeth, but in early vertebrates, it was an important part of the dermal skeleton that covered most of the body, [29] [30] [31] and it persists today in a few taxa such as the coelacanth. [32] Because dentin is softer than enamel, it wears away more quickly than enamel.
Dentin formation, known as dentinogenesis, is the first identifiable feature in the crown stage of tooth development. The formation of dentin must always occur before the formation of enamel. The different stages of dentin formation result in different types of dentin: mantle dentin, primary dentin, secondary dentin, and tertiary dentin. [31]
In response to dental caries, there may be production of more dentin toward the direction of the pulp. This new dentin is referred to as tertiary dentin. [82] Tertiary dentin is produced to protect the pulp for as long as possible from the advancing bacteria. As more tertiary dentin is produced, the size of the pulp decreases.
Odontoblasts also secrete tertiary dentin when irritated. Tertiary dentin secreted by odontoblasts is often due to chemical attack, either by chemicals diffusing through the dentin and insulting the odontoblasts, or by diffusion of toxic bacterial metabolites down the dentinal tubules in the instance of a carious attack with dental decay. This ...
[3] [4] Living organisms that are heterotrophic include all animals and fungi, some bacteria and protists, [5] and many parasitic plants. The term heterotroph arose in microbiology in 1946 as part of a classification of microorganisms based on their type of nutrition. [6] The term is now used in many fields, such as ecology, in describing the ...