211. The "Tooth" Radical: 歯

The "tooth" radical 歯 looks identical to this Joyo kanji:

歯 (290: tooth; cog)

And just as this kanji carries the Joyo kun-yomi は, the Japanese primarily call the radical は. The name はへん works if 歯 slides to the left side of a character, as it does here:

齢 (1925: age)

Now you've seen the only two Joyo kanji featuring an on-duty 歯 radical.

The Shapes of the "Tooth" Radical

In both China and Japan, the traditional form of this radical is the 15-stroke 齒, but that has become the variant shape in Japan, whereas the 12-stroke 歯 serves as the main rendering. Essentially, the four people (人) in the box have been replaced with rice (米)! 

Nelson treats 齒 as the parent shape and 歯 as the variant, which seems ill advised; in the Joyo world, 歯 is the shape that matters. Nowadays, we find 齒 only in non-Joyo kanji such as 齔 (child; losing baby teeth), and it's not as if all non-Joyo kanji contain that variant; 噛 (to bite) includes the Joyo shape of our radical. 

Photo Credit: Corey Linstrom

What an artistic depiction of 歯科 (しか: dentistry). I'm sure the aesthetics soothe nervous patients.

Two Etymologies

Henshall provides these etymologies in his newer edition:

歯 (290: tooth; cog)

An early form (not 齒) depicted a mouth, including teeth. In the bronze era, the phonetic 止 (stop) appeared as the top component, providing the associated sense "be lined up" or "stay, stop" (depending on which scholar you consult). One expert believes the whole character represents "teeth 'stay in place' while chewing." Well, I should hope so! Henshall says nothing about the role of 米 (rice), unfortunately.

齢 (1925: age)

This character combines the 歯 radical with the phonetic 令 (order, rule). Etymology experts are split in their analyses. If the 令 phonetically suggests "count," says one group, then 齢 represents "count teeth and determine age." That sense later narrowed to just "age." This is logical, according to one specialist, because people can ascertain the age of cattle by checking their teeth. If instead the 歯 represents "age, years" (presumably as an extended sense, says Henshall) and if the phonetic conveys the associated sense "pass, elapse," then 齢 means "age" overall. 

Photo Credit: Eve Kushner

We again find 歯科 here, but someone has playfully replaced the interior 米 with the name of the dental practice, とねしか. The とね must be the dentist's surname, one usually rendered as 利根.