Where the shape comes from
Two interlocking back teeth, upper and lower molars meeting — a close-up view distinct from 齒, which draws the front teeth in a row seen face-on. A plant’s first tooth-like shoot breaking the surface gives 芽, a sprout, bud; paired with 齒 itself in 牙齿, it names the teeth as a whole, the fang-shaped molar standing for the set.
汉字 filed under 牙
No published character on HSK Guide is filed under this radical yet. 汉字库.