You can easily whiten your teeth with 9D Whitening Strips. [Contents] 20 sets remaining (20 for upper teeth, 20 for lower teeth) out of 21 sets, as 1 set has been used. [How to use] Apply the adhesive side of the strips to your upper and lower teeth. Leave on for about 30 minutes. Remove the strips, brush your teeth thoroughly, and then rinse your mouth well to finish. I tried using them once, but I can't stand having them on my teeth, so I'm selling them.