erm ... who exactly is mother nature and what precisely are her needs?Rotting teeth might be expected if teeth just evolved. You know, as long as you live long enough to reproduce and see that your offspring survive then that's all Mother Nature needs you for. You can starve to death after that.
if you would expect a temporary world designed primarily for housing eternal living entities under the duress of pursuing temporary desires to be decked out with eternal teeth in the name of fulfilling the criteria for a perfect design brief, I think you still have aBut, just for fun, let's say some omnipotent, omnisicient being designed humans... You would think that he (or she) would've had the foresight to make teeth that don't decay.
bit more explaining to do .....