ToothStructureandEvolution.ppt

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)
 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
 http://animaldiversit
y.ummz.umich.edu/a
nat/tooth_introducti
on.html

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
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
 Dental Lamina
 Enamel Organ
 Dermal Papilla
 Ameloblasts
 Odontoblasts

Types of Teeth
 Incisors
 Canines
 Premolars
 Molars

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)
 Primitive Marsupial Dental Formula
 I 5/4, C 1/1, P 3/3, M 4/4

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
 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)
 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
 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
 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
 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
 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)
 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

ToothStructureandEvolution.ppt

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