I have used Crest 3D whitening strips for years, 9 to be exact! They work fantastic for stains, yellowing and any day to day touch up you may need. They give you 14 days worth, I personally used them every day for 14 days the very first time I purchased them. After those were up, I bought another box that lasted me months! I only needed to use one every couple of weeks. They leave my teeth glistening white and I’m always getting compliments about them. Do not overuse as they will make your teeth sensitive. Definitely consult with a dentist or purchase the sensitivity kind if usage becomes uncomfortable.