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Hunter-Schreger band

Hunter-Schreger bands, commonly abbreviated as HSB, are features of the enamel of the teeth in mammals, mostly placentals.[1] In HSB, enamel prisms are arranged in layers of varying thickness at about right angles to each other. HSB strengthen the enamel and prevent cracks from propagating through the tooth.[2]

HSB are first observed in early Paleocene mammals, but at this time the HSB occupy only a small portion of the incisor and the angle between the bands is low. By the late Paleocene, HSB is seen to extend throughout the enamel and the bands are located at nearly right angles to each other.[1]
Under oblique reflected light HSB can be seen as dark and light strips of variable width.

Among Glires, the group containing rodents, lagomorphs, and their primitive relatives, the absence of HSB from the incisors has been considered primitive.[3] Some early representatives, including Eurymylus, lack HSB, but others, including Matutinia[4] and some mimotonids, have double-layered incisor enamel with HSB in the inner portion (portio interna, PI). Other mimotonids have single-layered enamel with HSB. All leporids studied also exhibit this pattern, except for an early Eocene, indeterminate leporid with HSB only in the PI.[5] Ochotonids also have HSB in the PI only.[6]

In rodents, HSB are usually present in the PI. Three types of HSB can be separated—pauciserial, uniserial, and multiserial. Pauciserial HSB, present in some primitive Paleogene rodents, are usually three to six prisms thick and have inter-prismatic matrix (IPM) surrounding the prisms, which have irregular cross-sections. Uniserial HSB, present in most living rodents, consist of a single layer of prisms. Multiserial HSB, three to seven prisms thick, characterize the living Hystricognathi and the gundis (Ctenodactylidae) and springhares (Pedetes).[2] There are three subtypes on the basis of the orientation of the IPM. In the first, the IPM runs mostly parallel to the HSB, but does not surround it as in pauciserial enamel; in the second, the IPM makes an angle of about 45° with the HSB; and in the third, the two are located at right angles to each other. The last type serves to further strengthen the enamel and is characteristic of the Octodontoidea.[7]

Among carnivorans, the hyenas exhibit specialized HSB, which form a complex, three-dimensional zigzag pattern, a specialization for bone-eating.[8]

In humans, their average width is 50 micrometers.[citation needed]

References Edit

  1. ^ a b Line and Bergqvist, 2005, p. 924
  2. ^ a b Martin, 1994, p. 121
  3. ^ Martin, 2004, p. 411
  4. ^ Martin, 2004, p. 417
  5. ^ Martin, 2004, p. 418
  6. ^ Martin, 2004, p. 419
  7. ^ Martin, 1994, pp. 121–122
  8. ^ Barycka, 2007, p. 276

Literature cited Edit

  • Barycka, E. 2007. Evolution and systematics of the feliform Carnivora (subscription required). Mammalian Biology 72(5):257–282.
  • Line, S.R.P. & Bergqvist, L.P. 2005. Enamel structure of Paleocene mammals of the São José de Itaboraí Basin, Brazil. 'Condylarthra', Litopterna, Notoungulata, Xenungulata, and Astrapotheria (subscription required). Journal of Vertebrate Paleontology 25(4):924–928.
  • Martin, T. 1994. On the systematic position of Chaetomys subspinosus (Rodentia: Caviomorpha) based on evidence from the incisor enamel microstructure (subscription required). Journal of Mammalian Evolution 2(2):117–131.
  • Martin, T. 2004. Evolution of incisor enamel microstructure in Lagomorpha (subscription required). Journal of Vertebrate Paleontology 24(2):411–426.\

hunter, schreger, band, commonly, abbreviated, features, enamel, teeth, mammals, mostly, placentals, enamel, prisms, arranged, layers, varying, thickness, about, right, angles, each, other, strengthen, enamel, prevent, cracks, from, propagating, through, tooth. Hunter Schreger bands commonly abbreviated as HSB are features of the enamel of the teeth in mammals mostly placentals 1 In HSB enamel prisms are arranged in layers of varying thickness at about right angles to each other HSB strengthen the enamel and prevent cracks from propagating through the tooth 2 HSB are first observed in early Paleocene mammals but at this time the HSB occupy only a small portion of the incisor and the angle between the bands is low By the late Paleocene HSB is seen to extend throughout the enamel and the bands are located at nearly right angles to each other 1 Under oblique reflected light HSB can be seen as dark and light strips of variable width Among Glires the group containing rodents lagomorphs and their primitive relatives the absence of HSB from the incisors has been considered primitive 3 Some early representatives including Eurymylus lack HSB but others including Matutinia 4 and some mimotonids have double layered incisor enamel with HSB in the inner portion portio interna PI Other mimotonids have single layered enamel with HSB All leporids studied also exhibit this pattern except for an early Eocene indeterminate leporid with HSB only in the PI 5 Ochotonids also have HSB in the PI only 6 In rodents HSB are usually present in the PI Three types of HSB can be separated pauciserial uniserial and multiserial Pauciserial HSB present in some primitive Paleogene rodents are usually three to six prisms thick and have inter prismatic matrix IPM surrounding the prisms which have irregular cross sections Uniserial HSB present in most living rodents consist of a single layer of prisms Multiserial HSB three to seven prisms thick characterize the living Hystricognathi and the gundis Ctenodactylidae and springhares Pedetes 2 There are three subtypes on the basis of the orientation of the IPM In the first the IPM runs mostly parallel to the HSB but does not surround it as in pauciserial enamel in the second the IPM makes an angle of about 45 with the HSB and in the third the two are located at right angles to each other The last type serves to further strengthen the enamel and is characteristic of the Octodontoidea 7 Among carnivorans the hyenas exhibit specialized HSB which form a complex three dimensional zigzag pattern a specialization for bone eating 8 In humans their average width is 50 micrometers citation needed References Edit a b Line and Bergqvist 2005 p 924 a b Martin 1994 p 121 Martin 2004 p 411 Martin 2004 p 417 Martin 2004 p 418 Martin 2004 p 419 Martin 1994 pp 121 122 Barycka 2007 p 276Literature cited EditBarycka E 2007 Evolution and systematics of the feliform Carnivora subscription required Mammalian Biology 72 5 257 282 Line S R P amp Bergqvist L P 2005 Enamel structure of Paleocene mammals of the Sao Jose de Itaborai Basin Brazil Condylarthra Litopterna Notoungulata Xenungulata and Astrapotheria subscription required Journal of Vertebrate Paleontology 25 4 924 928 Martin T 1994 On the systematic position of Chaetomys subspinosus Rodentia Caviomorpha based on evidence from the incisor enamel microstructure subscription required Journal of Mammalian Evolution 2 2 117 131 Martin T 2004 Evolution of incisor enamel microstructure in Lagomorpha subscription required Journal of Vertebrate Paleontology 24 2 411 426 Retrieved from https en wikipedia org w index php title Hunter Schreger band amp oldid 1160613317, wikipedia, wiki, book, books, library,

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