Dentition in Mammals

DENTITION IN MAMMALS
The study of arrangement structure and number of types of teeth collectively is called as dentition. Teeth are present in the foetal as well as in adults of mammals, based on the presence of teeth Mammals are two types.
Edentata : In some animals teeth are absent hence called as edentate. e.g., Echidna or spiny ant-eater (Tachyglossus) the teeth are absent in all stages of life.
Dentata : Teeth are present in all mammals though a secon¬dary toothless condition is found in some mammals. Modern turtles and birds lack teeth. The adult platypus (Ornithorhynchus) bears epidermal teeth but no true teeth are present. In platypus embryonic teeth are replaced by horny epidermal teeth in adult.
Classification According to the Shape and Size of the Teeth:
Homodont:
Homodont or Isodont type of teeth is a condition where the teeth are all alike in their shape and size in the toothed whales e.g., Pinnipedians. Fishes, amphibians, reptiles and in the extinct toothed birds.
Heterodont
Heterodont condition is the usual feature in mammals, i.e. the teeth are distinguished according to their shape, size and function. The function is also different at different parts of the tooth row.
According to the Mode of Attachment of Teeth:
Thecodont : The teeth are lodged in bony sockets or alveoli of the jaw bone and capillaries and nerves enter the pulp cavity through the open tips of the hollow roots e.g., mammals, crocodiles and in some fishes.
Acrodont: The teeth are fused to the surface of the underlying jawbone. They have no roots and are attached to the edge of the jawbone by fibrous membrane e.g., fishes, amphibians and some reptiles.

Pleurodont:

The teeth are attached to the inner-side of the jawbone. The tooth touches the bone only with the outer surface of its root. In acrodont and pleurodont types of dentition, there are no roots, and nerves and blood vessels do not enter the pulp cavity at the base, e.g., Necturus (Amphibia) and some reptiles.
According to the Succession or Replace¬ment of Teeth:

1. DENTITION IN MAMMALS Dr D Prasanna Assistant Professor of Zoology

2. The study and arrangement, structure and number of types of teeth collectively called as dentition. Teeth are the hard pointed structures attached to the jaw bones. There are two types of teeth in animals I) Epidermal teeth II) True teeth

3. Epidermal teeth – These are the horny projection of the stratum corneum Ex: Cyclostomes, beak of turtles and birds. True teeth – The teeth evolved from bony scales & composed of crown, neck & root. Ex : vertebrates

4. Types of teeth based on the attachment to the jaw bone

5. Types of teeth based on structure, teeth are two types 1) Homodont : The teeth with similar size and structure Ex: Dolphins, Seals. 2) Heterodont : Teeth are of different size, shape and function. Ex: All Mammals

6. Heterodont dentition

7. Types of teeth based on the replacement in life time classified into three types. 1) Monophyodont : only one set of teeth develops in their life time. Ex: Marsupials 2) Diphyodont : Two sets of teeth develops Ex: Eutherians a) Deciduous or milk teeth b) Permanent teeth 3) Polyphodont the teeth are replaced continuously. Ex: Fishes and snakes

8. Teeth in mammals

9. Dental formula

10. Structure of tooth L.S OF (INCISOR) TOOTH L.S OF (MOLAR) TOOTH

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