When is a tooth a tooth?

So Zach finally has some teeth coming in -- two on the top and one on the bottom. The ones on top are definitely further along, but I didn't notice them at first because everything I've read says that the bottom ones come in first. Of course Zach couldn't do things the normal way! I keep checking, and it looks like they might have broken through the skin, but I can't really tell. Zach won't let me pull back his lips to see, so the only way to tell is to make him laugh and look at them from underneath. I've been swinging him upside down because it accomplishes both steps that are the necessary predicates for teeth-viewing. Let me tell you, swinging around a 24 lb. baby is hard work!

So Zach may or may not have his first teeth, and I have no idea what date to officially desginate as the day he first got a tooth. Kinda like I have no idea what date to officially designate as the day he learned to crawl, since he did the wiggle worm crawl for so long.