Veneers are extremely thin shells of porcelain or composite comparable to the thickness of a contact lens.  Veneers are generally placed on upper and lower front teeth that are severely discolored, poorly shaped, or slightly crooked.  Veneers may be used to lighten front teeth that are naturally yellow or have a gray cast and cannot be whitened  by bleaching.  The preperation for a veneer requires a dentist to remove a small amount of enamel  from the front and side of the tooth. Reality TV shows such as Extreme Makeover and the Swan have made porcelain veneers very popular.