Digestive system - teeth, Biology


2398_tooth structure.png

  1. Study of teeth is odontology.
  2. Accumulation of oral bacteria & their products on teeth is plaque.
  3. Some acids are secreted by bacteria causing carries.
  4. Pyrrohea is caused by Entamoeba gingivalis. It' s transmission is possible by kissing only because encystment is absent.
  5. Teeth present in upper and lower jaw. Upper jaw is made up of premaxilla and maxilla.
  6. Lower jaw is made up of only one bone i.e. Dentany (total two bones).
  7. On jaw bones, thick mucosal folds and submusocal folds present to form gums or gingiva.
  8. Inflamation of gums is periodental disease. Teeth are partially ectodermal & partially mesodermal.
  9. True teeth is mesodermal. Teeth are partially living and partially dead. Ca contents are more.
  10. Teeth are thecodent i.e. situated in sucket or alveoli. Teeth are heteordont i.e. of different types.
  11. In Heterodont teeth are of following types -

(i) Incissor -

  1. Root less or small root i.e. Hypsodont. For cutting or gripping food.
  2. In elephant 1 pair upper incisors are modified in to tusk (In Indian elephant in male only, in African elephant in both sexes). They yield ivary. In rabbit, these are of unlimited growth.

(ii) Canine

  1. Pointed teeth. For tearing flesh. Generally well developed in carnivorous animals.
  2. Minimum changes occur in life time. In wild pig canines are of unlimited growth.
  3. In walrus upper canine (one pair) are modified into tusk & helpful in locomotion.
  4. In rabbit absent so diastema present between incisor and pre molar.

(iii) Pre molar -

  1. For chewing. 1-2 roots present.

(iv) Molars -

  1. For chewing. 2-3 roots present.
  2. Pre molar and molar collectively known as cheeck teeth.
  3. Their crown is flat and serrate so known as lophodont.
  4. In cheeak buccinator muscle present.
  5. Last molars are wisdom teeth.
  6. If crown is small teeth are brachydont.
  7. Teeth are diphyodont i.e. comes 2 times in life span. First as temporary set or deciduous second as a permanent set.
  8. In rabbit incisors are polyphyodont.
  9. In rat, mole, shrew and squirell monophyodont.
  10. In rabbit, molars are teeth are monophyodont.
  11. Osteoclast cells damage their roots so milk teeth are shed off.
  12. In man 32 teeth present.
  13.  Dental formula -
  14. 1211_dental formula.png
  15. A 17 years old boy - 2122/2122 = 28
  16. In milk teeth = 2102/2102 = 20
  17. In rabbit 28 = 2033/1023 .                               
  18. In rabbit milk teeth are 16 = 203/102 .
  19. In Dog = 3142/3143  = 42.                              
  20. In Cow = 0033/3133  = 32.
  21. In Elephant = 1003/0003  = 14.                        
  22. In Horse = 3143/3143  = 42.
  23. In oposum 50 teeth present (maximum in mammals).
  24. In each tooth there are three parts - Crown, neck and root.
  25. Crown part is present out side gum. Root present in sucket.
  26. Neck between these two parts. Cusps are square type i.e. Solenodont.
  27. If root small - Hypsodont e.g. Horse. If root large - Brachydont e.g. sheep.
  28. Cusps are pointed - Secodont e.g. lion.
  29. Crown part is covered by enemal which is dead, ectodermal, hardest part of body (5-6% H O only), made up of calcium carbonate and calcium sulphate formed by ameloblast cells. (Enemal absent in armadillows & sloth)
  30. Floride gives it strength. Inside enemel, dentine is main part having canaliculi.
  31. Tooth is hollow, having pulp cavity filled with pulp, rich in nerve & blood supply.
  32. Pulp cavity opens outside by apical foramen.
  33. If opening is wide, growth of tooth is unlimited. If opening is narrow, growth of tooth is limited.
  34. Root of pulp cavity is made up of odontoblast cells (unit of teeth, power of division present.)
  35. Tooth is fixed in gum by cement layer (formed by cementocyte cells) outside it a layer of periodontoblast cells present.
  36. Sharpen's fibres (Collagen) passes from this layer to gums & helpful in fixing.
  37. Tartar is hard deposite of calcium phosphate on tooth from saliva.
Posted Date: 10/1/2012 7:23:27 AM | Location : United States

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