Well, first of all, unless the zombie came from a human with recently, and professionally, cleaned teeth they would never be pearly white.

Secondly, just look at the manner in which their teeth cause wounds! Huge chunks of flesh ripped off, people torn asunder. And have you ever in a zombie movie seen a tooth left behind in the bite wound of an unfortunate victim, or torn out and discarded, ala sharks?

I think the evidence already speaks for itself.