There are two types of stains on teeth - superficial and inherent. Superficial stains caused by what we eat, drink and expose our teeth to. This stain is usually yellowish in nature, and yields the best teeth whitening system results. Inherent stains are caused by minerals, fluoride and various antibiotics such as tetracycline, our bodies absorb. Ingested at key developmental phases in life certain of these substances can permanently discolor teeth, and no teeth whitening system will be the cure. In such circumstances people may choose to whiten their teeth with veneers, which corrects the stains, and tooth "look" (length & shape).