Dental Formula
Because mammalian teeth are specialised for different functions, many mammal groups have lost teeth not needed in their adaptation. Tooth form has also undergone evolutionary modification as a result of natural selection for specialised feeding or other adaptations. Over time, different mammal groups have evolved distinct dental features, both in the number and type of teeth, and in the shape and size of the chewing surface.
The number of teeth of each type is written as a dental formula for one side of the mouth, or quadrant, with the upper and lower teeth shown on separate rows. The number of teeth in a mouth is twice that listed as there are two sides. In each set, incisors (I) are indicated first, canines (C) second, premolars (P) third, and finally molars (M), giving I:C:P:M. So for example, the formula 2.1.2.3 for upper teeth indicates 2 incisors, 1 canine, 2 premolars, and 3 molars on one side of the upper mouth.
The deciduous dental formula is notated in lowercase lettering preceded by the letter d: e.g. di:dc:dp. An animal's dentition for either deciduous or permanent teeth can thus be expressed as a dental formula, written in the form of a fraction, which can be written as, or I.C.P.M / I.C.P.M. For example, the following formulae show the deciduous and permanent dentition of all catarrhine primates, including humans:
- Deciduous: This can also be written as . (Superscript and subscript denote upper and lower jaw, i.e. do not indicate mathematical operations; the numbers are the count of the teeth of each type. The '-' in the formula are likewise not mathematical operators, but spacers. 'd' denotes deciduous, i.e. milk or baby teeth, and lower case also indicates temporary teeth. This is a redundancy.) Another annotation is, if the fact that it pertains to deciduous teeth is clearly stated, per examples found in some texts such as The Cambridge Dictionary of Human Biology and Evolution
- Permanent: This can also be written as . When the upper and lower dental formulae are the same, some texts write the formula without a fraction (in this case, 2.1.2.3), on the implicit assumption that the reader will realise it must apply to both upper and lower quadrants. This is seen for example throughout The Cambridge Dictionary of Human Biology and Evolution.
The greatest number of teeth in any known placental mammal was 48, with a formula of . However, no existing (or extant) placental mammal has this number. In extant placental mammals, the maximum dental formula is: Mammal teeth are usually symmetrical, but not always. For example, the aye-aye has a formula of, demonstrating the need for both upper and lower quadrant counts.
Read more about this topic: Dentition
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