Most cases you would usually need just one session; however, depending on the severity of your discoloration you might have to schedule additional treatments. Teeth whitening is not permanent, and if you avoid beverages and foods that stain your teeth, you may be able to wait one year or longer before another whitening treatment or touch-up is needed. However, if you expose your teeth to those elements that cause staining, the whiteness may start to fade in as little as one month.