This is the procedure of making teeth whiter and therefore more attractive and involves having impressions taken from which laboratory fabricated custom vinyl trays are made. Gel is placed in these trays and they are worn for about 3 hours, or overnight. The entire process takes 3-4 weeks of daily use. Three different strengths 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.