DENTITION Arrangement of teeth in jaws in vertebrates

DENTITION � Arrangement of teeth in jaws in vertebrates � In cyclostomates , teeths are arranged on tongue and in buccal funnel � In rest of vertebrates teeth are mostly arranged on jaws.

DENTITION ON THE BASIS OF ATTACHMENT OF TEETH ACRODONT � PLEURODONT � THECODONT Ø

ACRODONT � Teeth have no roots � Attached to free surface of jaw bones � eg: sharks and amphibians � Such teeth break of easily

PLUERODONT �Teeth are attached to inner surface of jaw bone �Attached by their base as well as one side �Eg : Urodels and lizards

THECODONT � Teeth have well developed roots � Implanted in deep sockets of jaw bone � Eg: in mammals , crocodile and fossil birds like archaeopteryx

DENTITION ON THE BASIS OF SHAPE OF TEETH � HOMODONT � HETERODONT

HOMODONT � In a jaw , all teeth are of same shape this type of dentition is called homodont � Eg : vertebrates other than mammals

HETERODONT � In a jaw the teeth are of different shape and size , such type of dentition is called heterodont � These are distinguished into several types� Incisors � Canines � Pre molars � Morals

INCISORS.

CANNINE - These are present between the incisors and premolar. - There is a single such troth in each half of each jaw. - These are long conical teeth with a single root and simple, sharp pointed crown - These are present on the premaxillae bones of the upper jaw and the dentary bones of lower jaw

PREMOLAR - These follows the canines. - They have double root and compressed crown with one or two cusps. These possess grinding and crushing surfaces. Premolars are replaced once in lifetime.

MOLAR � These are next to the premolars. � They have more than two roots and cusps. � These do not have predessor and always develop in the permanent set. � Molar are used for crushing.

DENTITION ON THE BASIS OF REPLACEMENT OF TEETH � Polyphyodont-In lower vertebrates, teeth are replaced indefinite number of times during life � Diphyodontmammals develop two successive sets of teeth during life Teeth of first set are called milk or decidous teeth (these teeth after birth but bats and guinea pigs shed even before birth ) Milk teeth are replaced by permanent teeth which possessed through out the life

LOCATION OF TEETH �Generally, teeth are located in oral cavity where stomodeal ectoderm is present and where cartilage or bone to support is present �True teeth are located on – �Premaxillaries �Maxillaries and �Mandible

MODIFICATION OF CHEEK TEETH � TRICODONT- three cones are arranged in a linear fashion on the tips of teeth eg: fossil mesozoic mammals � BUNODONT-crowns have small blunt and rounded tubercles eg: man and donkey

§ LOPHODONT- cusps have several tranverse ridges called lophos eg: elephant.

DENTAL FORMULA � Mostly the number of teeths are fixed in each mammalian species. � Mammalian heterodont dentition is expressed by a DENTAL FORMULA. � The number and arrangement of teeth in each half of the upper and lower jaws is constant and identical. ++ � Teeth can be expressed by using the initials – I, C, Pm and p 4 � Number of teeth are closely related on their feeding habits. � Typical number of teeth in the mammals is 44.

RULES Numerator indicates the number of teeth on one side of upper jaw. Denominator indicates the number of teeth on one side of lower jaw. example-

SPECIAL TEETH Rootless teeth: . Do nt form root by becoming narrow at base. Pulp canal remains wide open. Continue growth throughout life e. g. Incisors of rabbit, canines of wild boar and walrus. Wearing away at cutting edges compensates continuous growth at base(incisors of rabbit). Incisors of elephant and canines ( wild boar , walrus) do nt show wearing so grow into large tusks. . Rootless teeth have high crowns called

Carnassial/Sectorial/ Shearing Teeth: The last upper premolar and first lower molar are specially large in dogs and bite on each other like a pair of scissors for citting flesh.

Importance of dentition: • Indicate their relationship • USED IN CLASSIFICATION • Mode of life of the extinct animals can be determined • Kind of contemporary vegetation can be determined from the teeth of extinct animals