As I wrote before, it started out as a little bump on the side of the root of my tooth when I was about 11 or 12 years old. It was fully emerged by the time I was in my late teens. Yes, it moved all of my teeth around. They used to be straight, damnit.
Anyway, now that I've got some actual photos (I couldn't find accurate depictions or names anywhere), would anyone happen to know what this is called? The "two-headed tooth" phrase is something I actually took from my dentist, so... I'm not particularly hopeful. =)