There are two categories of staining as it relates to the teeth: extrinsic (external) staining and intrinsic (internal) staining.
Extrinsic stains are those that appear on the surface of the teeth as a result of exposure to dark-colored beverages, foods and tobacco, and routine “wear and tear”. Most superficial external stains can be removed with brushing and professional dental cleanings. Stubborn extrinsic stains can be removed with more involved efforts, like teeth whitening or bleaching.
Intrinsic stains are those that form on the inside of teeth. Intrinsic stains result from trauma, aging, and exposure to minerals, chemicals or antibiotics (like tetracycline) during tooth formation and/or excessive ingestion of fluoride.