Densaugeo

From UnknowableWiki

Densaugeo is a spell that Draco Malfoy attempts to cast on Harry Potter; he misses, and hits Hermione Granger instead. The incantation causes her teeth to grow at an alarming rate, and, terrified, she runs to the hospital wing to get them fixed (GF18).

Ron and Harry later remark that she allowed Madam Pomfrey to shrink her teeth more than they ought to have been, and that Hermione is no longer slightly bucktoothed (GF22).