Editing Human tooth (section)

==Parts==
===Enamel===
{{Main|Tooth enamel}}

Enamel is the hardest and most highly [[mineralized tissues|mineralized substance]] of the body. It has its origin from oral [[ectoderm]]. It is one of the four major tissues which make up the tooth, along with [[dentin]], [[cementum]], and [[dental pulp]].<ref>{{harvnb|Ross|2002|page=441}}</ref> It is normally visible and must be supported by underlying dentin. 96% of enamel consists of mineral, with water and organic material comprising the rest.<ref>{{harvnb|Cate|1998|page=1}}</ref> The normal color of enamel varies from light yellow to grayish white. At the edges of teeth where there is no dentin underlying the enamel, the color sometimes has a slightly blue tone. Since enamel is semitranslucent, the color of dentin and any restorative dental material underneath the enamel strongly affects the appearance of a tooth. Enamel varies in thickness over the surface of the tooth and is often thickest at the [[Cusp (dentistry)|cusp]], up to 2.5mm, and thinnest at its border, which is seen clinically as the CEJ.<ref name="Cate, A. R 1998 p. 219">{{harvnb|Cate|1998|page=219}}</ref> The wear rate of enamel, called attrition, is 8 micrometers a year from normal factors.<ref>{{Cite web | url=http://www.dd-database.org/dental/tooth-enamel.html | title=Tooth enamel &#124; Drug Discrimination Database}}</ref>

Enamel's primary [[mineral]] is [[hydroxyapatite]], which is a [[crystal]]line [[calcium phosphate]].<ref name = "biology"/> The large amount of minerals in enamel accounts not only for its strength but also for its brittleness.<ref name="Cate, A. R 1998 p. 219"/> Dentin, which is less mineralized and less brittle, compensates for enamel and is necessary as a support.<ref name="biology">Johnson, Clarke (1998). "[http://www.uic.edu/classes/orla/orla312/BHDTwo.html Biology of the Human Dentition] {{webarchive|url=https://web.archive.org/web/20151030052831/http://www.uic.edu/classes/orla/orla312/BHDTwo.html |date=2015-10-30 }}". uic.edu.</ref> Unlike dentin and [[bone]], enamel does not contain [[collagen]]. [[Protein]]s of note in the [[tooth enamel#Development|development]] of enamel are [[ameloblastin]]s, [[amelogenin]]s, [[enamelin]]s and [[tuftelin]]s. It is believed that they aid in the development of enamel by serving as framework support, among other functions.<ref>{{harvnb|Cate|1998|page=198}}</ref> In rare circumstances enamel can fail to form, leaving the underlying dentine exposed on the surface.<ref>{{Cite web|url=https://www.researchgate.net/publication/319987728|title=Severe Plane-Form Enamel Hypoplasia in a Dentition from Roman Britain|website=ResearchGate|language=en|access-date=2019-01-09}}</ref>

===Dentin===
{{Main|Dentin}}

Dentin is the substance between enamel or cementum and the pulp chamber. It is secreted by the [[odontoblast]]s of the dental pulp.<ref name = "ross448"/> The formation of dentin is known as [[dentinogenesis]]. The porous, yellow-hued material is made up of 70% inorganic materials, 20% organic materials, and 10% water by weight.<ref name = "Cate150"/> Because it is softer than enamel, it decays more rapidly and is subject to severe cavities if not properly treated, but dentin still acts as a protective layer and supports the crown of the tooth.

Dentin is a mineralized [[connective tissue]] with an organic matrix of collagenous proteins. Dentin has microscopic channels, called dentinal tubules, which radiate outward through the dentin from the pulp cavity to the exterior cementum or enamel border.<ref name="ross450">{{harvnb|Ross|2002|page=450}}</ref> The diameter of these tubules range from 2.5 μm near the pulp, to 1.2 μm in the midportion, and 900&nbsp;nm near the dentino-enamel junction.<ref name="Cate152">{{harvnb|Cate|1998|page=152}}</ref> Although they may have tiny side-branches, the tubules do not intersect with each other. Their length is dictated by the radius of the tooth. The three dimensional configuration of the dentinal tubules is genetically determined.

There are three types of dentin, primary, secondary and tertiary.<ref>{{Cite journal |title=Sex- and Age-related Differences in Primary and Secondary Dentin Formation |journal = Advances in Dental Research |volume = 15 |pages = 42–45 |doi=10.1177/08959374010150011101 |pmid = 12640738 |year = 2001 |last1 = Zilberman |first1 = U. |last2 = Smith |first2 = P. |citeseerx = 10.1.1.535.5123|s2cid = 4798656 }}</ref> 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 [[Tooth decay|cavities]] and [[tooth wear]].<ref>{{Cite web|url=https://www.researchgate.net/publication/331906742|title=Tertiary Dentine Frequencies in Extant Great Apes and Fossil Hominins|website=ResearchGate|language=en|access-date=2019-03-28}}</ref>

===Cementum===
{{Main|Cementum}}

Cementum is a specialized bone like substance covering the root of a tooth.<ref name = "ross448"/> It is approximately 45% inorganic material (mainly [[hydroxyapatite]]), 33% organic material (mainly [[collagen]]) and 22% water. Cementum is excreted by [[cementoblast]]s within the root of the tooth and is thickest at the [[Root apex (dental)|root apex]]. Its coloration is yellowish and it is softer than dentin and enamel. The principal role of cementum is to serve as a medium by which the [[periodontal ligament]]s can attach to the tooth for stability. At the cement to enamel junction, the cementum is acellular due to its lack of cellular components, and this acellular type covers at least {{frac|2|3}} of the root.<ref name="Cate236">{{harvnb|Cate|1998|page=236}}</ref> The more permeable form of cementum, cellular cementum, covers about {{frac|1|3}} of the root apex.<ref name="Cate241">{{harvnb|Cate|1998|page=241}}</ref>

=== Dental pulp ===
{{Main|Pulp (tooth)}}
The dental pulp is the central part of the tooth filled with soft connective tissue.<ref name = "Cate150"/> This tissue contains blood vessels and nerves that enter the tooth from a hole at the apex of the root.<ref name="Ross451">{{harvnb|Ross|2002|page=451}}</ref> Along the border between the dentin and the pulp are odontoblasts, which initiate the formation of dentin.<ref name="Cate150">{{harvnb|Cate|1998|page=150}}</ref> Other cells in the pulp include fibroblasts, preodontoblasts, [[macrophage]]s and [[T cells|T lymphocytes]].<ref name="Walton11thru13">Walton, Richard E. and Mahmoud Torabinejad. ''Principles and Practice of Endodontics.'' 3rd ed. 2002. pp. 11–13. {{ISBN|0-7216-9160-9}}.</ref> The pulp is commonly called "the nerve" of the tooth.