I brushed my teeth hard a couple of times and i've got a white line in my gum line. when will it go?

White line: May be normal anatomy that you never noticed before. May be traumatic injury from over-brushing or food injury (crusty bread, for example). Can be a burn. See your Dentist to determine whether "white line" is normal or a problem, and follow his/her treatment advice. Never brush hard. Never use toothbrush bristles any harder than "soft." And don't forget to floss daily.