Last while playing football my son got hit on the face and unfortunately he was wearing dental braces. So he injured the inner part of his top lips at 3 places and after 2 days it developed into canker sores. Its has been very painful, we tried salt water mouth washing and it did no good. Its been a week today with no much improvement yesterday we went to the dentist and he prescribed a gel. The problem now is that when he applies the gel, the canker sore turns red and there are blood stain on the cotton used to apply the gel .is this normal? The gel is chlorhexidine gluconate ,metronidazole and lignocaine hydrochloride gel