3213: Dental Formulas

Dental Formulas

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Title text: I mean, half of these are undefined. And your multiplication dots are too low; they look like decimal points.

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Explanation

This is one of 70 incomplete explanations: This page was created recently. Don't remove this notice too soon. If you can fix this issue, edit the page!

A dental formula specifies the number of teeth of each type on each side of the jaw, with dots separating the numbers. There are two rows, representing the upper and lower jaw, separated by a horizontal line. The number of incisors is indicated first, canines second, premolars third, and finally molars, so the formula in the comic would represent 3 incisors, 1 canine, 3 premolars, and 1 molar on each side of the upper jaw, and equal numbers in the lower jaw except only 2 premolars. This is the dental formula for the cat family. The adult human dental formula is 2.1.2.3 for both the upper and lower jaw.

Cueball is (wrongly) treating a dental formula as an arithmetic expression, with the line indicating division and the dots indicating multiplication. In the title text his statement that "half the formulae are undefined" refers to animals that lack one of the four types of teeth in the lower jaw, leading to a zero in the "denominator" of the dental formula and an undefined division expression. He also notes that the "dots are too low", as in fact the dots in a dental formula are period or decimal point characters and aren't meant to imply multiplication.

'Mammologists' is also misused; the correct term is mammalogists. Mammologists study human breasts specifically, usually in a medical context. This may be a deliberate nod towards Cueball not understanding what he's looking at, or may simply be a mistake.

Transcript

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[ Cueball and Megan are standing in front of a whiteboard, on which is written

3.1.3.1
3.1.2.1

along with some other scribbles.

Underneath the panel is the caption, "Mathematicians encounter dental formulas".]

Cueball: Do mammologists think these are hard?

Cueball: I mean this one just evaluates to 3/2.

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Discussion

First!AmethystSky14 (talk) 21:43, 27 February 2026 (UTC)

The top left drawing is a tooth. Xkdvd (talk) 22:04, 27 February 2026 (UTC)

This confused me for a long time (partly due to the mammal/mammol thing) - I took them to be dentists. I'm now inferring that the counts are typical of a species rather than descriptive of an individual patient. Maybe the write up could make that more clear in case someone else as dumb as me passes by 2A00:23EE:10C8:110F:D992:D45:1C7A:DF02 guest

"in case someone as dumb as me passes by" - that would be everyone, see Explain xkcd: It's 'cause you're dumb. 64.201.132.210 22:21, 27 February 2026 (UTC)

Because I'm sure someone else will be wondering, based on a very cursory search, the formula on the board appears to be permanent teeth for felines. At the very least, Wikipedia's entry on Dentition lists this formula for cats, lions, and tigers. Perhaps an actual expert will come along and shed further light on this. 97.116.61.145 22:52, 27 February 2026 (UTC)
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