This document discusses tooth structure and evolution in mammals. It describes the four main tissues that make up teeth - enamel, dentine, cementum, and pulp cavity. Teeth are either rooted, with the opening to the pulp cavity constricting, or rootless, where the opening does not constrict. There are two theories on the evolution of teeth from single-cusped reptilian teeth to multi-cusped mammalian teeth - the concrescence theory involving fusion of teeth and the Cope-Osborn theory of additional cusps forming in front of and behind the original cusp. Specializations of cheek teeth include hypsodont, brachydont, bunodont, lophodont, and selenodont structures
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
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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
9. 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.
11. 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)
12. 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
13. 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.
14. 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)
15. 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.
16. 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
17. 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
18. 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