Incisor tooth

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Serrated incisor teeth of a capybara

Incisor teeth are long, chisel-shaped, permanently growing incisors of various mammals that stand in pairs in the upper and lower jaw . They have arisen several times independently of one another and are found in rodents , rabbits , finger animals , the tillodontia , wombats and the multituberculata . In order to adapt to their diet, the front part of the dentition in these groups has developed into a gnawed bite , which, in addition to the presence of incisive teeth, is usually characterized by the absence of canine teeth . This leads to the formation of a wide, toothless gap between the gnawing and chewing bite. The upper incisor teeth form a right-angled , an obtuse or an acute angle with the skull.

Incisor teeth are usually very strong and their crown merges into the root without a neck . The permanent growth is made possible by the fact that the pulp cavity is wide open towards the tooth socket . The front of the incisor teeth is thickly coated with tooth enamel . As a result, it grinds less during use than the back side, which has missing or thin enamel. Due to the limited wear , the shear edges are automatically resharpened . A gnaw drive ensures that wear and tear is in line with growth. From a neurological point of view, this drive is not linked to the feeding behavior and can be triggered by stimulating the mediolateral thalamus .

Incisor teeth are used to gnaw hard food and, in digging animals, to loosen the soil. They can be used as tweezer-like gripping teeth and gnawing on objects is part of the exploratory behavior . The development of the incisor teeth in rodents and rabbits is probably associated with the reduction in the size of the nose , the formation of the narial pillows and the loss of rummaging, the rummaging of the ground with the snout.

Characteristics of the gnaw teeth

The gnaw bite is different in the different systematic groups :

  • From an evolutionary point of view, the rodent's incisor teeth are the second incisors of the deciduous dentition . They are only covered with enamel on the front. Other incisors and canines are missing.
  • The rabbit-like incisor teeth are also the second incisors of the deciduous teeth . They are completely covered with enamel, but the reverse side is very thin. Behind each upper incisor tooth is a small incisor that has been designed as a pin tooth . Other incisors and canines are missing. The rabbit-like teeth are never used for digging.
  • In the case of the finger animals , the four incisors, which are designed as incisor teeth, are only covered with enamel on the front side. Canine teeth are absent in adults.
  • The incisor teeth of the Tillodontia are the second incisors. There are also other incisors and canines.
  • In the wombats , the four incisors, which are designed as incisor teeth, are only covered with enamel on the front side. Canine teeth are missing.
  • The upper incisor teeth of the Multituberculata are the second incisors. Like the lower incisor teeth, they are only covered with enamel on the front side. There are also other upper incisors and, in early representatives of the group, upper canines.

Together with some extinct forms, rodents and rabbits make up the family group of the Glires and their gnaw bite is assessed as a jointly derived characteristic . The fact that such functionally important teeth as the incisor teeth cannot be replaced during ontogenesis is seen as an explanation for the lack of tooth change in the glires.

Wrong development of the incisor teeth

Abnormal growth of the incisor teeth in a dwarf rabbit with pike teeth

Various causes can lead to the incorrect development of the incisor teeth. By a misaligned teeth or by the absence of individual teeth, this abrade no longer together. As a result, the incisor teeth of the upper jaw grow spirally into the corner of the mouth, while those of the lower jaw grow like tusks forward and upward. As a result of the difficult food intake, there is a decrease in body weight .

One of the genetic causes of misaligned teeth is the pike bite , in which the lower incisor teeth stand in front of the upper ones due to a shortening of the upper jaw. Acquired misalignments can be attributed to a fracture of the upper or lower jaw that has not healed optimally , growth disorders and inflammation in the area of ​​the molar roots (retrograde growth) or to mechanical pressure such as when gnawing at the grid. The upper incisors can also fall out with age.

Badly developed incisor teeth are shortened to their functional length, ideally with a diamond disc. Correction is almost always possible without sedation or anesthesia. As a rule, regular checks and corrections are necessary for life.

literature

  • Manfred Ade: Macroscopic examinations on the Rhinarium of the Glires (Rodentia and Lagomorpha) . Science and technology, Berlin 1998, ISBN 3-89685-463-1 .
  • Markus Eickhoff: Dentistry, oral and maxillofacial medicine for small and domestic animals . Enke, Stuttgart 2005, ISBN 3-8304-1038-7 .
  • Anja Ewringmann, Barbara Glöckner: Key symptoms in hamsters, rats, mice and gerbils . Enke, Stuttgart 2008, ISBN 978-3-8304-1063-8 .
  • Meyer's Encyclopedic Lexicon in 25 volumes. Volume 16: Mei-Nat . 9th edition. Bibliographical Institute, Mannheim / Vienna / Zurich 1976.
  • Arno Hermann Müller: Textbook of paleozoology. Volume III: Vertebrates. Part 3: Mammalia . 2nd Edition. VEB Gustav Fischer Verlag, Jena 1989, ISBN 3-334-00223-3 .
  • Jochen Niethammer, Franz Krapp (Hrsg.): Handbook of mammals in Europe. Volume 1: Rodents I . Akademische Verlagsgesellschaft, Wiesbaden 1978, ISBN 3-400-00458-8 .
  • Rolf Sauermost, Doris Freudig (Ed.): Lexicon of Biology in fourteen volumes. Volume 9: Lyolysis to Nautococcus . Spektrum Akademischer Verlag, Heidelberg 2002, ISBN 3-8274-0334-0 .
  • Dietrich Starck: Textbook of Special Zoology. Volume II: Vertebrates. Part 5: Mammals . Gustav Fischer Verlag, Jena / Stuttgart / New York 1995, ISBN 3-334-60453-5 .
  • Gerhard Storch: Placentalia (Eutheria), Placentalier, Placentatiere . In: Wilfried Westheide , Reinhard Rieger (Ed.): Special Zoology. Part 2: vertebrates or skulls . Spectrum Academic Publishing House (Elsevier), Heidelberg / Berlin 2004, ISBN 3-8274-0307-3 , p. 499-504 .
  • Wilfried Westheide, Reinhard Rieger (Hrsg.): Special zoology. Part 2: vertebrates or skulls . Spectrum Academic Publishing House (Elsevier), Heidelberg / Berlin 2004, ISBN 3-8274-0307-3 .

Remarks

  1. ↑ Sauermost and joyful, 2002 (keyword "incisors")
  2. ↑ a b c Starck, 1995 (pp. 156–157)
  3. ↑ Sauermost and Freudig, 2002 (keyword "Nagegebiss")
  4. ↑ Starck, 1995 (p. 608)
  5. ^ Niethammer and Krapp, 1978 (p. 37)
  6. ↑ a b c Wolfgang Maier: Rodentia, rodents . In: Westheide and Rieger, 2004, pp. 531–547 (p. 533)
  7. ↑ Meyer's Encyclopedic Lexicon in 25 volumes, 1976 (keyword "Nagezähne")
  8. ↑ a b Ade, 1998 (pp. 131–132)
  9. ^ Renate Angermann: Lagomorpha, Hasentiere . In: Westheide and Rieger, 2004, pp. 524–531 (pp. 526–527)
  10. ↑ Starck, 1995 (p. 540)
  11. ^ Müller, 1989 (p. 602)
  12. ↑ Starck, 1995 (pp. 366-367)
  13. ↑ Müller, 1989 (p. 56 ff.)
  14. ↑ Storch, 2004 (p. 500)
  15. ↑ a b c d Ewringmann and Glöckner, 2008 (pp. 218–219)
  16. ↑ Eickhoff, 2005 (p. 229)