round teeth
A common depiction of a wide, open-mouthed smile where the front upper teeth are drawn as a single round semicircle. Often, it is reserved for depictions of youthfulness, playful personality, and innocence, and is very often a recurring physical trait in certain characters (as with Mizuno Kaede and Aoi Sora). However, it is common enough that it might show up without any qualifiers. K-On! loves this tag.
Differs from buck teeth in that buck teeth describes only the two upper front teeth, or a something that resembles just those two front teeth, while round teeth describes the entire row of front upper teeth.