I have always had nice, whiteish teeth. Recently I went to a new dentist and since then I have started getting brown stains on my teeth!! They don't come off unless I scrape them with metal tweesers, which can't be good. The stains are only on my front teeth, inside mostly and the outside. Did he scrape off too much enamal during the cleaning? What can't I do to take care of this and prevent the stains in the future?