This is the procedure of making teeth whiter, and therefore more attractive.  Our office uses several methods:  passive tray whitening, and professional strength white strips.
The tray method involves having impressions taken from which laboratory fabricated custom vinyl trays are made.  A carbamide peroxide gel is placed in these trays and the trays with gel  are worn for about 3 hours, or overnight.  The entire process takes 3-4 weeks of daily use.  Two different strength of gel may be used, however the higher the strength the greater the likelihood of reactions or tooth sensitivity.  The tray method is recommended for badly stained teeth, such as tetracycline staining, and it may take several months of use to see significant color improvement.  For maintenance of whitened teeth the trays should be used every several months.
Additional whitening information can be found at Webmd.com.