Man, know where you are coming from having herded two boys through their early lives! My oldest did exactly the same thing - caught a sidewalk joint on skateboard, did a face-plant, sent tooth all the way through his lower lip. Kids are very durable and resilient I told him he'd live, ol' lady saw blood and freaked! It healed fine and I don't think there is any scar as far as I can see. When stuff like this happened to our rug-rats I tried to keep somewhat of a sense of humor about the whole deal and I think they sensed it and it helped their attitude about whatever incident was involved.
Good luck!