The strips are designed to be used on either upper or lower teeth, and have a notch cut out in them showing you how to place them on your teeth. The way the strips are cut is in a straight rectangle. So if you are one of those lucky people who have been blessed with straight teeth that are all the same height, then these strips would probably work wonderfully for you. For the rest of us who grind our teeth or for some other reason have teeth that aren't the same height, the strips are problematic ... at least they were for me. There seemed to be more strip on my gums than my teeth in some areas, and the whitening agents irritated my gums.
The strips are supposed to dissolve in 5-10 minutes with no need to brush or spit afterwards. That was not the case for me. It felt like I had plastic on my teeth for about 30 minutes and even tried brushing it off, but that didn't work.
Bottom line: Try to get a free sample of these before you spend your money on them. While they do whiten your teeth, I found there are many other hurdles and drawbacks to using them and do not believe they live up to the promises of the manufacturer.