It depends, but there's an issue of biocompatibility similar to any organ transplant. So no, a rock wouldn't work. The backwards tooth though is interesting - my guess is if it would fit it would stick (although it would definitely fuck up your bite).
I wouldn't be surprised if a backwards tooth could remain viable. This is the sort of error that would be noticed immediately by any conscious patient, however. A backwards tooth would mess up occlusion. Few people would ignore the fact that they can't close their mouth completely.