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Tooth Structure and Evolution

Tooth Structure and Evolution. Tooth Anatomy. Enamel – Composed of crystals of hydroxyapatite [3(Ca 3 PO 4 ) 3 * Ca(OH) 2 ] Enamel is the hardest tissue in the body

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Tooth Structure and Evolution

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  1. Tooth Structure and Evolution

  2. Tooth Anatomy • Enamel – Composed of crystals of hydroxyapatite [3(Ca3PO4)3 * Ca(OH)2] Enamel is the hardest tissue in the body • Dentine – Softer than enamel. The inorganic salt composition is the same as enamel but the content of organic fibers is approx. 30% compared to 3% for enamel.

  3. Anatomy (Continued) • Cementum – Cementum is a nonvascular bone that is usually acellular. Cementum is rich in collagen fibers and is softer than dentine. • Pulp Cavity – Blood vessels and nerves pass into the pulp cavity

  4. Diagram of Tooth Structure • http://animaldiversity.ummz.umich.edu/anat/tooth_introduction.html

  5. Rooted versus Rootless Teeth • Rooted Teeth – In most mammals the opening to the pulp cavity constricts reducing the blood supply to the tooth and growth stops. • Rootless Teeth – In other mammals the opening to the pulp cavity does not constrict and the tooth continues to grow throughout the life of the mammal.

  6. Examples of Rootless Teeth Incisors of rodents Cheek teeth of some rodents All teeth of rabbits except 2nd pair of incisors Upper incisors of elephants – all dentine tusks Upper canines of the walrus Left incisor of male narwhal

  7. Development of Teeth • Dental Lamina • Enamel Organ • Dermal Papilla • Ameloblasts • Odontoblasts

  8. Embryological Tooth Development - Diagram

  9. Developing Tooth - Picture

  10. Developing Tooth – Picture 2

  11. Developing Tooth – Picture 3

  12. Types of Teeth • Incisors • Canines • Premolars • Molars

  13. Types of Teeth - Picture

  14. Dental Formulas • Primitive Placental Dental Formula • I 3/3, C 1/1, P 4/4, M 3/3 = 44 Reductions in this number are common. Increases are rare. The giant armadillo, African bat eared fox, most toothed whales have more than 44 teeth.

  15. Dental Formulas (Continued) • Primitive Marsupial Dental Formula • I 5/4, C 1/1, P 3/3, M 4/4

  16. How to Distinguish Types of Teeth • Incisors in upper jaw are in premaxilla bone • In most mammals you cannot distinguish premolars from molars • Unless the animal is a carnivorous member of the Placental Order Carnivora and has a Carnassial Pair of teeth (fourth upper premolar and first lower molar)

  17. Types of Teeth - Picture

  18. Sets of Teeth • Most mammals have two (2) sets of teeth • Toothed whales and a few other mammals have only one set of teeth • Diphyodont, Deciduous milk teeth and a permanent second set of teeth • Monophyodont, this is a secondary condition

  19. Sets of Teeth (Continued) • In Diphyodont mammals the Incisors, Canines, and Premolars have deciduous precursors. The molars do not have deciduous precursors. • Some people consider the molars to be the first set of teeth retarded in their development.

  20. Evolution of Teeth • Problem – to go from a single cusped reptilian tooth to a multicusped mammalian tooth. Two Theories: Concrescence Theory Differentiation Theory (Cope-Osborn Theory)

  21. Conscrescent Theory • States that a multicusped mammalian molar is formed by the fusion of a number of simple conical teeth. • Greatest support came from Multituberculates in which molars had distinct cusps. Assumed that each cusp represented a reptilian tooth. • Later Multituberculaltes had more cusps than older species.

  22. Cope-Osborn Theory • Even the most complex mammalian molar originated from a single cusped reptilian tooth. • Formation of additional cusps in front of and behind the original cusp • Accessory cusps change position relative to the main cusp to form a triangle. • A heel is added to triangle in lower jaw

  23. Specialization of Cheek Teeth • Hypsodont = high crown • Brachydont = low crown • Bunodont = usually brachydont with 4 major rounded cusps, omnivores • Lophodont = usually hypsodont with a fusion of cusps to form elongated ridges termed lophs, herbivores

  24. Specializations (Continued) • Selenodont = usually hypsodont with each ridge formed by the elongation of a single cusp, ridges are crescent shaped, herbivores • Secodont or Carnassial = scissor action of upper and lower teeth, carnivores of the Order Carnivora

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