Hi,
As a dental hygienist, I'd have to say you need to follow the directions on the package. They only go on the front 6 teeth, and don't whitened any fillings in the front teeth, so it works if you have no fillings and if your teeth are relatively straight, as they don't get inbetween very well. It may take a couple boxes, and if you don't do it a couple nights, you'll have to start all over. Also, if you get sensitivity during treatment you should discontinue, but if bare-able.. it will go away after you are finished the treatment. Hope that helps. Thats what we suggest, but if someone likes the results.. they will get much better results with the full trays. Also we recommend not using the whitening toothpastes. I've seen the damage they can cause!
Sherri.