How i remove black lines naturally from my teeth?

Black lines?: It depends on whether they are just extrinsic stains or intrinsic (caused by other reasons, such as antibiotics ). A simple staining cause by food or beverages can be removed by cleaning and or bleaching. Intrinsic stains however cannot be fixed without placing veneers or crowns on the teeth.

Depends: It really depends on what the black lines are from. If they are organic stains, any whitening agent can remove them, or a hygienist with some mild pumice. Your local natural food/product store will have things on the shelf you can use. If they are areas of decay, you should have the decay removed and the tooth filled. Check with your dentist to make sure you know what the lines are from.