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Teeth

Teeth. A unique vertebrate structure. Tooth Anatomy. Enamel ~96% hydroxyapatite (inorganic); very hard but brittle Dentin ~70% hydroxyapatite; similar to bone Cementum ~50% hydroxyapatite Pulp – connective tissue, blood vessesls , nerves, odontoblasts

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Teeth

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  1. Teeth A unique vertebrate structure

  2. Tooth Anatomy • Enamel ~96% hydroxyapatite (inorganic); very hard but brittle • Dentin ~70% hydroxyapatite; similar to bone • Cementum ~50% hydroxyapatite • Pulp – connective tissue, blood vessesls, nerves, odontoblasts • Periodontal ligament – collagenous; connects cementum to bone of socket

  3. Tooth Anatomy Above gum-line = Made by cementoblasts Within socket = Covered by cementum Apical foramen – entrance in root for blood vessels and nerves

  4. Dentition • Homodont – all teeth similar • Heterodont – teeth differ in appearance • Polyphyodont – teeth continuously replaced • Diphyodont – two sets of teeth • Deciduous dentition = first set • Permanent dentition = second and final set • Monophyodont– one set of teeth

  5. Tooth Development • Epidermis produces enamel organ • Neural crest cells in dermis form dermal papilla • Ameloblastsin enamel organ produce enamel • Odontoblasts in dermal papilla produce dentin • Crown, then root, then cementum and periodontal ligament – sit within dermal bone

  6. Tooth Development From neural crest cells Permanent tooth primordium forms before deciduous tooth lost Fig. 13.8

  7. Tooth Support • Thecodont = set in socket with periodontal ligament; mammals, some reptiles • Acrodont = attached to top of bone or in shallow sockets; some bony fishes, some reptiles • Pleurodont = set in shelf on inner side of jawbone; some bony fishes, amphibians, some reptiles Fig. 13.10

  8. Bony Fish • Some have no teeth • Most with polyphyodont, homodont teeth • Variety of shapes according to diet • Some have pharyngeal teeth that are not homologous to teeth of other vertebrates

  9. Cartilaginous Fish • Polyphyodont, homodont teeth • Lack dermal bones, so develop in a whorl within skin • Some sharks shed > 35,000 teeth in a lifetime!

  10. Cartilaginous Fish • Placoid scales in skin are just small teeth!

  11. Amphibians • Polyphyodont, homodont teeth • Pedicellate teeth – crown and base separated by layer of uncalcified dentin

  12. Amphibians • Frogs have only upper jaw teeth, except one species (Gastrothecaguentheri) • “Fanged frogs” have dentary protrusions • Some amphibians have no teeth Gastrothecaguentheri Limnonectesmacrocephalus

  13. Tetrapods • Birds and turtles do not have teeth • Reptiles – polyphyodont, homodont teeth – variation due to diet

  14. Mammals • Most heterodont, diphyodont • Lots of specializations and variation due to diet • Incisors of rodents and lagomorphs continually grow Grow at roots while crown wears away

  15. Specialized Teeth in Mammals • Incisors – cutting, clipping • Canines – puncturing, holding • Premolars – crushing, grinding • Molars – crushing, grinding • Dental formula explains what teeth present: • I 3/3, C 1/1, PM 4/4, M 2/3 • 3-1-4-2/3-1-4-3 Coyote

  16. Specialized Teeth in Mammals • Mule deer dental formula: 0-0-3-3/3-1-3-3 No upper incisors or canines

  17. Specialized Teeth in Mammals • Cheek teeth = molariform teeth = premolars and molars Fig. 13.15 Notice how wear exposes dentin Can classify based on crown height Low crowns = = High crowns

  18. Specialized Teeth in Mammals • Cusps = raised ridges or peaks on occlusal surfaces (contacts opposing surface) = Cusps in crescent-shaped ridges; artiodactlys = Cusps drawn out into straight ridges; perissodactlys, rodents = Cusps form rounded peaks; omnivores

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