He'll be ok without that tooth. I got alot of dogs without tooth because of biting the chain, kennel cages and they are still ok. Let me just ask you a question? Could it be that they collide nose first running towards each other? That's why the tooth got loose? You would hear a bonelike sound snapping when that happens. When I hear that sound I always looks at the floor.. it happens most of the times on scratches.