This is a repaired and slightly modified version of "human tooth model" by Svenergy. The model is watertight and a 2 manifold.

I've been told by someone with deep knowledge about human teeth that a tooth like this does not usually exist. It is the top of a a certain tooth and the bottom / root of another.

That's likely the reason why the original model by Svenergy was broken broken in the first place. In the process of merging the seams probably became corrupted.