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tooth enamel along with dentin, cementum, and dental pulp is one of the four major tissues which make up the tooth in vertebrates. it is the hardest and most highly mineralized substance in the human body.[1] tooth enamel is also found in the dermal denticles of sharks. it is the normally visible dental tissue of a tooth because it covers the anatomical crown and must be supported by underlying dentin. ninety-six percent of enamel consists of mineral, with water and organic material composing the rest.[2] in humans, enamel varies in thickness over the surface of the tooth, often thickest at the cusp, up to 2.5 mm, and thinnest at its border with the cementum at the cementoenamel junction (cej).[3]
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 material underneath the enamel strongly affects the appearance of a tooth. the enamel on primary teeth has a more opaque crystalline form and thus appears whiter than on permanent teeth.
enamel's primary mineral is hydroxylapatite, which is a crystalline calcium phosphate.[4] the large amount of minerals in enamel accounts not only for its strength but also for its brittleness.[5] tooth enamel ranks 5 on mohs hardness scale and a young's modulus of 83 gpa[4]. dentin, less mineralized and less brittle, 3–4 in hardness, compensates for enamel and is necessary as a support.[6] on radiographs, the differences in the mineralization of different portions of the tooth and surrounding periodontium can be noted; enamel appears more radiopaque (or lighter) than either dentin and pulp since it is denser than both, both of which appear more radiolucent (or darker).[7]
enamel does not contain collagen, as found in other hard tissues such as dentin and bone, but it does contain two unique classes of proteins - amelogenins and enamelins. while the role of these proteins is not fully understood, it is believed that they aid in the development of enamel by serving as a framework for minerals to form on, among other functions.[8] once it is mature , enamel is almost totally absent of the softer organic matter. enamel is avascular and has no nerve supply within it and is not renewed, however, it is not a static tissue as it can undergo mineralization changes. [9]
contents [hide]
1 structure
2 development
3 destruction
4 oral hygiene and fluoride
5 effects of dental procedures
5.1 dental restorations
5.2 acid-etching techniques
5.3 tooth whitening
6 systemic conditions affecting enamel
7 in other mammals
8 see also
9 notes
10 references
11 external links
[edit]structure

the basic unit of enamel is called an enamel rod.[6] measuring 4–8 μm in diameter an enamel rod, formerly called an enamel prism, is a tightly packed mass of hydroxyapatite crystals in an organized pattern.[1] in cross section, it is best compared to a keyhole, with the top, or head, oriented toward the crown of the tooth, and the bottom, or tail, oriented toward the root of the tooth.
the arrangement of the crystals within each enamel rod is highly complex. both ameloblasts (the cells which initiate enamel formation) and tomes' processes affect the crystals' pattern. enamel crystals in the head of the enamel rod are oriented parallel to the long axis of the rod.[1][3] when found in the tail of the enamel rod, the crystals' orientation diverges slightly(65 degrees) from the long axis.[1]
the arrangement of enamel rods is understood more clearly than their internal structure. enamel rods are found in rows along the tooth, and within each row, the long axis of the enamel rod is generally perpendicular to the underlying dentin.[10] in permanent teeth, the enamel rods near the cementoenamel junction (cej) tilt slightly toward the root of the tooth. understanding enamel orientation is very important in restorative dentistry, because enamel unsupported by underlying dentin is prone to fracture.[10]

the area around the enamel rod is known as interrod enamel. interrod enamel has the same composition as enamel rod, however a histologic distinction is made between the two because crystal orientation is different in each.[3] the border where the crystals of enamel rods and crystals of interrod enamel meet is called the rod sheath.[11]
striae of retzius are incremental lines that appear brown in a stained section of mature enamel. these lines are composed of bands or cross striations on the enamel rods that, when combined in longitudinal sections, seem to traverse the enamel rods. [10] formed from changes in diameter of tomes’ processes, these incremental lines demonstrate the growth of enamel, similar to the annual rings on a tree on transverse sections of enamel. the exact mechanism that produces these lines is still being debated. some researchers hypothesize that the lines are a result of the diurnal, or 24 hour, metabolic rhythm of the ameloblasts producing the enamel matrix, which consists of an active secretory work period followed by an inactive rest period during tooth development. thus, each band on the enamel rod demonstrates the work/rest pattern of the ameloblasts that generally occurs over a span of a week. [12] perikymata which are associated with the striae are shallow grooves noted clinically on the nonmasticatory surfaces of some teeth in the oral cavity.[13] perikymata are usually lost through tooth wear, except on the protected cervical regions of some teeth, especially the permanent maxillary central incisors, canines, and first premolars, and may be confused as dental calculus. [14] darker than the other incremental lines, the neonatal line is a incremental line that separates enamel formed before and after birth.[15]the neonatal line marks the stress or trauma experienced by the ameloblasts during birth, again illustrating the sensitivity of the ameloblasts as they form enamel matrix. as one would expect, the neonatal line is found in all primary teeth and in the larger cusps of the permanent first molars. they contain irregular structures of enamel prisms with disordered crystal arrangements basically formed by the abrupt bending of the prisms towards the root; usually, the prisms gradually bent back again to regain their previous orientation.[16]
gnarled enamel is found at the cusps of teeth.[17] its twisted appearance results from the orientation of enamel rods and the rows in which they lie.
enamel is covered by various structures in relation to the development of tooth:
nasmyth's membrane or enamel cuticle, structure of embryological origin is composed of keratin which gives rise to the enamel organ [18][19].
acquired pellicle, structure acquired after tooth eruption is composed of food debris, calculus, dental plaque (organic film) [20].

glee
vikipedi, özgür angiblopedi
"glee" ile karıştırılmamalı.
glee

glee logosu
tür müzikal
komedi-dram
oyuncular dianna agron
chris colfer
jessalyn gilsig
jane lynch
jayma mays
kevin mchale
lea michele
cory monteith
matthew morrison
amber riley
mark salling
jenna ushkowitz
besteci james s. levine
ülke amerika birleşik devletleri
orijinal dili i̇ngilizce
sezon sayısı 1
bölüm sayısı 13 (bölüm listesi)
prodüksiyon
yönetici yapımcı ryan murphy
brad falchuk
dante di loreto
gösterim süresi 42-45 dakika
yapım şirketi 20th century fox television
yayın bilgileri
kanal fox
resim formatı 480i (sdtv)
720p (hdtv)
yayın tarihi 19 mayıs 2009 – günümüz
glee, amerikan müzikal komedi-dram dizisidir. ryan murphy, ian brennan ve brad falchuk tarafından yaratıldı ve 19 mayıs 2009'dan beri abd'de fox ekranlarında gösterilmektedir; türkiye'de ise 18 şubat 2010'dan itibaren fox life kanalında gösterilmektedir.[1]
konu başlıkları [gizle]
1 karakterler
1.1 ana karakterler
2 bölümler
3 uluslararası yayım
4 kaynakça
5 dış bağlantılar
karakterler [değiştir]

ana karakterler [değiştir]
matthew morrison : will schuester
lea michele : rachel berry
cory monteith : finn hudson
kevin mchale : artie abrams
chris colfer : kurt hummel
dianna agron : quinn fabray
amber riley : mercedes jones
jenna ushkowitz : tina cohen-chang
mark salling : noah « puck » puckerman
jayma mays : emma pillsbury
jessalyn gilsig : terri schuester
jane lynch : sue sylvester
bölümler [değiştir]

ana madde: glee bölümleri listesi
glee'in ilk sezonu 22 tane bölüm içerecektir.[2] i̇lk bölümü 19 mayıs 2009 tarihinde gösterildi.[3] dizi sonradan 9 eylül 2009'dan beri tekrar gösterime girip[4] 9 aralık 2009'a kadar her çarşamba günü saat 21:00'de gösteriliyordu. 21 eylül 2009'da fox, ilk sezon için daha çok bölüm istedi[5]; bunlar 13 nisan 2010 itibarıyla salı akşamlarında gösterilecektir.[6] 11 ocak 2010'da fox'un diziye ikinci sezonun yapılmasını ısmarladığı açıklandı.[1][7][8]
uluslararası yayım [değiştir]

glee, dünyanın birçok yerinde gösterilmektedir. kanada'da global[9], avustralya'da da network ten kanalında yayımlanmaktadır. bazı oyuncular diziyi tanıtmak için eylül 2009 galasından önce avustralya'yı ziyaret ettiler.[10] yeni zelanda'da tv3 ve c4,[11][12] latin amerika'da canal fox,[13] ve brezilya'da canal fox brasil kanalında gösterilmektedir.[14] fiji'de dizi fiji one ve sky pacific tarafından gösterilmektedir.[kaynak belirtilmeli] filipinler'de etc entertainment central ve jack tv programı yayımlamaktadır.[15] birleşik krallık'ta glee, e4 ve e4 hd kanalları,[16] i̇rlanda'da ise tv3 ve 3e kanalları tarafından gösterilir.[17][18] i̇sveç'te tv4[19], norveç'te tv2,[20] danimarka ise tv2 tarafından yayınlanmaktadır.[21] i̇talya, portekiz ve türkiye'de kendi ülkelerine ait fox life kanalları tarafından gösterilir.[22][23] gürcistan'da rustavi 2 tarafından gösterilir.[24]
kaynakça [değiştir]

^ a b "foxlife - diziler - glee". foxlife. 23 şubat 2010 tarihinde erişilmiştir.
^ schneider, michael (1 aralık 2009). "'glee' co-creator gets big fox deal" (i̇ngilizce). variety. 23 şubat 2010 tarihinde erişilmiştir.
^ "fox holds 'glee' tryouts after 'american idol' tuesday, may 19 - new one-hour musical comedy series to preview post-american idol" (i̇ngilizce). fox broadcasting company (5 mart 2009). 23 şubat 2010 tarihinde erişilmiştir.
^ mitovich, matt (28 temmuz 2009). "fox moves up two fall premieres; plus a glee video preview" (i̇ngilizce). tv guide. 23 şubat 2010 tarihinde erişilmiştir.
^ "fox sings praises of 'glee' with full-season pickup" (i̇ngilizce). the futon critic (21 eylül 2009). 23 şubat 2010 tarihinde erişilmiştir.
^ "fox announces 2009-2010 midseason schedule" (i̇ngilizce). fox broadcasting company (24 kasım 2009). 23 şubat 2010 tarihinde eri