Editing Tooth enamel (section)

== Development ==
[[File:Toothhistology11-17-05.jpg|thumb|Histologic slide showing a developing tooth. The mouth would be in the area of space at the top of the picture.]]

Enamel formation is part of the overall process of [[Animal tooth development|tooth development]]. Under a microscope, different cellular aggregations are identifiable within the tissues of a developing tooth, including structures known as the [[enamel organ]], [[dental lamina]], and [[dental papilla]].<ref name="ross443">Ross ''et al.'', p. 443</ref> The generally recognized stages of tooth development are the bud stage, cap stage, bell stage, and crown, or calcification, stage. Enamel formation is first seen <!--under the microscope--><!--would it only be seen under the microscope?-->in the crown stage.

[[Amelogenesis]], or enamel formation, occurs after the first establishment of dentin, via cells known as ameloblasts. Human enamel forms at a rate of around 4&nbsp;μm per day, beginning at the future location of cusps, around the third or fourth month of pregnancy.<ref name="cate224" /> As in all human processes, the creation of enamel is complex, but can generally be divided into two stages.<ref name=":4" /> The first stage, called the secretory stage, involves proteins and an organic matrix forming a partially mineralized enamel. The second stage, called the maturation stage, completes enamel mineralization.

[[File:Enamelmineralization11-17-05.jpg|left|thumb|Histologic slide showing enamel formation]]
In the secretory stage, ameloblasts are polarized columnar [[cell (biology)|cells]]. 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]].<ref name="ross445">Ross ''et al.'', p. 445</ref> When this first layer is formed, the ameloblasts move away from the dentin, allowing for the development of Tomes' processes <!--what exactly are tomes processes? A clause of explanation would be helpful here -->at the apical<!--better word?--> pole of the cell. 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.<ref name=":4" /> 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 phosphate crystallites.

In the maturation stage, the ameloblasts transport substances used in the formation of enamel<!--from where to where?-->. Histologically<!--this is a high level vocabulary word, is there a better synonym?-->, the most notable aspect of this phase is that these cells become striated, or have a ruffled border.<ref name="ross445" /> 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 [[amelogenin]]s, [[ameloblastin]]s, [[enamelin]]s, and [[tuftelin]]s. How these proteins are secreted into the enamel structure is still unknown; other proteins, such as the [[Wnt signaling pathway|Wnt signaling]] components [[BCL9]] and [[PYGO2|Pygopus]], have been implicated in this process.<ref name="Cantù eaah4598">{{Cite journal|last1=Cantù|first1=Claudio|last2=Pagella|first2=Pierfrancesco|last3=Shajiei|first3=Tania D.|last4=Zimmerli|first4=Dario|last5=Valenta|first5=Tomas|last6=Hausmann|first6=George|last7=Basler|first7=Konrad|last8=Mitsiadis|first8=Thimios A.|date=2017-02-07|title=A cytoplasmic role of Wnt/β-catenin transcriptional cofactors Bcl9, Bcl9l, and Pygopus in tooth enamel formation|journal=Sci. Signal.|language=en|volume=10|issue=465|pages=eaah4598|doi=10.1126/scisignal.aah4598|issn=1945-0877|pmid=28174279|s2cid=6845295|url=http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-145418}}</ref> During this process, amelogenins and ameloblastins are removed after use, leaving enamelins and tuftelin in the enamel.<ref>Ross ''et al.'', p. 491</ref> By the end of this stage, the enamel has completed its mineralization.

At some point before the tooth erupts into the mouth, but after the maturation stage, the ameloblasts are broken down. Consequently, enamel, unlike many other tissues of the body, has no way to regenerate itself.<ref>Ross ''et al.'', p. 3</ref> After destruction of enamel from decay or injury, neither the body nor a dentist can restore the enamel tissue. Enamel can be affected further by non-pathologic processes.

Enamel is covered by various structures in relation to the development of tooth:
:* [[Robert Nasmyth|Nasmyth membrane]] or enamel cuticle, structure of embryological origin is composed of [[keratin]] which gives rise to the [[enamel organ]].<ref>{{cite journal |author=Armstrong W.G. |title=Origin and nature of the acquired pellicle |journal=Proceedings of the Royal Society of Medicine|volume=61 |issue=9|pages=923–930 |year=1968 |pmc=1902619 |last2=Pääkkö |first2=P |last3=Kerttula |first3=R |last4=Taikina-Aho |first4=O |last5=Tuuponen |first5=T |last6=Hassi |first6=J |pmid=5679017|doi=10.1177/003591576806100929 }}</ref><ref>{{cite journal |author=Darling A.I. |title=The Distribution of the Enamel Cuticle and Its Significance |journal=Proceedings of the Royal Society of Medicine|volume=36 |issue=9|pages=499–502 |year=1943 |pmc = 1998608 |last2=Pääkkö |first2=P |last3=Kerttula |first3=R |last4=Taikina-Aho |first4=O |last5=Tuuponen |first5=T |last6=Hassi |first6=J |pmid=19992694|doi=10.1177/003591574303600917 }}</ref>
:* Acquired pellicle, structure acquired after tooth eruption is composed of food debris, calculus, dental plaque (organic film).<ref>{{cite journal |author1=Bradway S.D. |author2=Bergey E.J. |author3=Scannapieco F.A. |author4=Ramasubbu N. |author5=Zawacki S. |author6=Levine M.J.  |name-list-style=amp |title=Formation of salivary-mucosal pellicle: the role of transglutaminase |journal=Biochem. J.|volume=284 |issue=2|pages=557–564 |year=1992 |pmc = 1132674 |pmid=1376115 |doi=10.1042/bj2840557}}</ref>

{| border="BORDER" style="border-collapse:collapse;padding:3px"
|+'''Progress of enamel formation for primary teeth<ref>Ash and Nelson, p. 54</ref>'''
| colspan=2 | &nbsp;
! style="background:#efefef;padding:3px" | Amount of enamel formed at birth
! style="background:#ffdead;padding:3px" | &nbsp;Enamel mineralization completed&nbsp;
|-
! style="background:#efefef;" rowspan=5 | Primary<br />maxillary<br />tooth
| style="padding:3px" | Central incisor
| 5/6
| 1.5 months after birth
|-
| style="padding:3px" | Lateral incisor
| 2/3
| 2.5 months after birth
|-
| style="padding:3px" | Canine
| 1/3
| 9 months after birth
|-
| style="padding:3px" | 1st molar
| Cusps united; occlusal completely calcified<br />and 1/2 to 3/4 crown height
| 6 months after birth
|-
| style="padding:3px" | 2nd molar
| Cusps united; occlusal incompletely calcified;<br />calcified tissue covers 1/5 to 1⁄4 crown height
| 11 months after birth
|-
! style="background:#ffdead;" rowspan=5 | Primary<br />mandibular<br />tooth
| style="padding:3px" | Central incisor
| 3/5
| 2.5 months after birth
|-
| style="padding:3px" | Lateral incisor
| 3/5
| 3 months after birth
|-
| style="padding:3px" | Canine
| 1/3
| 9 months after birth
|-
| style="padding:3px" | 1st molar
| Cusps united; occlusal<br />completely calcified
| 5.5 months after birth
|-
| style="padding:3px" | 2nd molar
| Cusps united; occlusal<br />incompletely calcified
| 10 months after birth
|}