All mammals except the monotremes, the edentates, the pangolins, and the cetaceans have up to four distinct types of teeth, with a maximum number for each. These are the incisor, the canine, the premolar, and the molar. Mammals that have distinct types of teeth are heterodont; others are homodont. The number of teeth of each type is written as a dental formula. The human dental formula is
2 1 2 3
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2 1 2 3
Of cats it is
3 1 3 1
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3 1 2 1
The last upper premolar and first lower molar of the cat, since it is a carnivore, are called carnassials and are used to slice meat and skin. The armadillo, being homodont, has a dental formula that is simply 7/7. The maximum dental formula for heterodont mammals is
5 1 4 4
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4 1 4 4
which is approached most nearly by the opossum, which has 3/3 premolars.
In many mammals the children have a set of teeth that fall out and are replaced by adult teeth. These are called deciduous teeth or milk teeth. Animals that have two sets of teeth, one followed by the other, are said to be diphyodont. Normally the formula for milk teeth is the same as for adult teeth except that the molars are missing. The milk tooth formula for humans is
2 1 2 0
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2 1 2 0
The kitten has 26 teeth.
Teeth are numbered starting at 1 in each group, except the premolars which end at 4. This means that the carnassials are always the fourth upper premolar and the first lower molar. Thus the human teeth are I1, I2, C1, P3, P4, M1, M2, and M3.