Wow – I’ve been using the 7-day strips, and they really do show a difference after only 3 days of usage. In fact, the difference is so great, that I’m going to discontinue use until I need them again – and before my teeth are crayon white! I read somewhere that you should stop when your teeth are roughly as white as the whites of your eyes, which on most people are slightly off-white. I’m there, and satisfied. YAY!