I've heard most of the caps don't hold. But again which tooth is it, because I think that would also make a difference. I would say personally call the Vet' if a nerve is showing rule of thumb (or so I thought) was yank the tooth. But then it will turn black and die most of the time anyways so he will figure it out. But the red area could just be a raw area, from the break, and/or cleaning. Where exactly was it red? The anibiotics are a safe place to be either way, but call the Vet on Monday. Also the teeth are most likely sore from the cleaning, I've known dogs to skip a meal or two afterwards from the pain, think how you would feel If you haven't cleaned your teeth for four years and had that Horrible Crap done!