Firstly, This is some serious thread necromancy. (reviving a thread to make it undead) As for the OP's original point, I doubt you'll find everyone has this reaction (I don't for one) however I think you'll find it's down to how your brain has developed. Sometimes sensations can get merged together, this is why it's not common in everyone. It's possible that for some reason the brains interpretation of urinating is linked to the brains interpretation of the tooth nerves. I wouldn't know what would happen if you ever got tooth ache.