Teeth Whitening is a bleaching process that lightens discolorations of tooth enamel. Dental bleaching systems use an effective whitening solution retained in a custom-fitted mould that is worn over your teeth for 1-4 hours per day, or even overnight. Many people notice an immediate whitening of their teeth within a few hours of bleaching, but it usually takes between 20 - 40 hours of cumulative bleaching time to complete the whitening process (This is true for all at-home dental bleaching systems, no matter who the manufacturer). You can break your hours into just a few days (for people who are in a hurry) or a few months (for people who are not). Professional strength whitening gel formulated with carbamide peroxide is the most widely used and most desirable active ingredient in effective dental bleaches.