Tooth whitening (termed tooth bleaching when utilising bleach), is either the restoration of a natural tooth shade or whitening beyond the natural shade.
Restoration of the underlying natural tooth shade is possible by simply removing surface stains caused by extrinsic factors, stainers such as tea, coffee, red wine and tobacco. The buildup of calculus and tartar can also influence the staining of teeth. This restoration of the natural tooth shade is achieved by having the teeth cleaned by a dental professional (commonly termed "scaling and polishing"), or at home by various oral hygiene methods. Calculus and tartar are difficult to remove without a professional clean.Wikipedia