Does anyone else have issues with tartar building up on their DC's teeth? DS (16) seems to get a ribbon of yellow along the front and back of his lower teeth despite consistent brushing. He's not flossing though; maybe that would help? Every time we go to the dentist (NHS) she comments on the buildup saying he needs to brush better but never removes it. He's only had a few fillings so his brushing can't be that bad...