Dr Dip Mukherjee Assistant Professor of Zoology SBS Government College Hili Delivered on 04012020 Introduction D entition is the arrangement of teeth in the upper and lower jaws mainly on the premaxilla maxilla and dentary bones ID: 934889
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DENTITION IN MAMMALS
B.Sc. (H), SEM II: ZOOL-H-DC4-TDr. Dip MukherjeeAssistant Professor of ZoologyS.B.S. Government College, HiliDelivered on: 04.01.2020
Slide2Introduction
Dentition is the arrangement of teeth in the upper and lower jaws, mainly on the premaxilla, maxilla and dentary bones.Adult platypus
(Ornithorhynchus
sp.), spiny anteater (Echidna
sp.)-
No true teeth.Absence of teeth: Myrmecophaga sp., Balaena sp., Balaenoptera sp. etc.
Slide3Origin and structure
Origin: Denticles, near the margins of mouth as ossification in the integument.Two parts: Crown
(exposed part, above root) and Root
(hidden part, anchored to alveolus of jaw bone).
Central pulp cavity
(blood vessels, nerves, connective tissue), junction of crown and root is
neck.Enamel (thin, hard, shiny) covers crown (hardest and heaviest tissue); Dentine (hard, dermal, bony layer); Cement (acellular, non-vascular, covers root); pulp cavity lined by bone cells called odontoblasts.
Slide4Types of Dentition
Acc. to: shape
& size
Homodont/
Isodont
similar shape and size, eg.-toothed
whales
Heterodont
different shape,
size, function, eg.-mammal like
reptiles
:mode of attachment
Thecodont
lodged in alveoli,
eg.- mammals, crocodiles
Acrodont
fused to surface of underlying jaw bone, eg.- fishes, amphibians, some reptiles
Pleurodont
attached
to inner side of jaw bone, no roots,
eg.-
Necturus
sp., some reptiles
:succession/replacement
Monophyodont
only one set in life time, eg.-marsupials, toothed whales, squirrels etc.
Diphyodont
2 sets of teeth develop (temporary & permanent), eg.- humans
Polyphyodont
teeth
replaced continuously throughout life, eg.-dogfish, snakes
Slide5Types of teeth
Incisors:
conical, single root,
monocuspid; cutting & cropping; chisel-shaped, open rooted, grows continuously through life (rodents, lagomorphs)
Canines:
large pointed, long crowned, single root; -
nt in rodents (gap b/w i & pm: diastema)Premolars: bicuspid, 2 roots; grindingMolars: 2/more roots, several cusps; crushing;
pm+m
=cheek teeth;
fissipeds: last upper pm & 1st m in lower jaw with chisel-shaped cusps called as carnassial teeth; last molar of humans: wisdom tooth.
Slide6Cusp patterns of cheek teeth
Pattern
No. &
shape of cusps
Triconodont
Molars: 3 cones; arranged
anteroposteriorly
; eg.-
Triconodon
Trituberculate
Molars: 3 cones; arranged triangularly; eg.-
Spalacotherium
Bunodont
Cheek teeth cusps separate, rounded,
eg.- Human, omnivores
Lophodont
Cusps
joined to form ridges,
enamel+dentine
folds, eg.-Elephant
Secodont
Cheek
teeth with sharp cutting crowns; tearing flesh, eg.- terrestrial carnivores
Selenodont
Cheek teeth with crescent shaped cusps, eg.- ruminants,
horses
Brachydont
Cheek teeth with low
crown+long
root, eg.- Human
Hypsodont
High
crown, short, open tooth, eg.- horse, incisor of elephant
Slide7Slide8Dental Formula
Equation to express number of teeth.
Number of each type of tooth in each half of
upper & lower jaw.
Upper jaw
(numerator),
lower jaw (denominator); separated by horizontal line.
Indicated by letters i(incisors), c(canines), pm(premolars), m(molars).
Slide9Unusual specialised teeth
Elephant’s tusk:
2
nd
pair of incisors in th
e upper jaw. Pig’s tusk: Upper canines. Male Barking deer’s tusk
: Enlarged canines.
Walrus’s tusk:
Modified upper canines.
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