If it was the same dentist as the one I usually see, he will certainly have mentioned flossing if he thought that a lack of it was at all a problem. And would have recommended the little interdental brushes rather than floss, 'cos (a) they're better and (b) go in from the side, so you don't have the horrible sliding-down thing (I've got very wedge-shaped teeth, and this is a big thing for me). Actually, I think the latter would have applied whoever you saw at that practice.