It’s talking about growing a third set of teeth so it is regrowth
some newspaper translator had to figure out how to translate the novel(ish?) phrase 歯生え薬. what do you want? it's not like this is FDA-approved marketing materials for something that's actually available.
It's not exactly difficult:
歯 - tooth
生え - grow
薬 - medicine
Doesn't say anything about "regrowth" though.
That has a fascinating answer but requires R, no TL;DR from me :)