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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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tooth anatomy
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.
anatomy continued
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
diagram of tooth structure
Diagram of Tooth Structure
rooted versus rootless teeth
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.
examples of rootless teeth
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

development of teeth
Development of Teeth
  • Dental Lamina
  • Enamel Organ
  • Dermal Papilla
  • Ameloblasts
  • Odontoblasts
types of teeth
Types of Teeth
  • Incisors
  • Canines
  • Premolars
  • Molars
dental formulas
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.

dental formulas continued
Dental Formulas (Continued)
  • Primitive Marsupial Dental Formula
    • I 5/4, C 1/1, P 3/3, M 4/4
how to distinguish types of teeth
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)
sets of teeth
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
sets of teeth continued
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.
evolution of teeth
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)

conscrescent theory
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.
cope osborn theory
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
specialization of cheek teeth
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
specializations continued
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