molly, a couple thoughts. first, i sucked my thumb, and my little brother sucked his thumb, until four or five years old (we both stopped once we hit school age). my teeth are perfectly straight, my little brother needed braces - but not because of sucking his thumb. i got my mom's straight teeth, my brother got my dad's crooked ones. it was pure genetics. now my son is sucking his thumb, and personally i have no problem with it. you have to remember it's a self soothing thing, and if you take the binky away, immediately he will latch onto the thumb. but the way i see it, if you give a binky the first year or two, then take it away, likely the same thing will happen. i kind of wished my son had taken a paci (he NEVER wanted it, from day one), because it seems to me it'd be a lot easier habit to break - you can't take away his thumb! but we got a thumb sucker, and i don't think there's much you can do about it. plus it's awful cute :) anyway, rest easy. i have heard a lot of conflicting information about teeth and thumb sucking, but when it comes down to it you can't force a kid not to. and i don't buy the whole "messing up the teeth" thing. just my experience. good luck and congrats on your new gift :)