Crest White Strips and other whitening trays have never worked for me, so I decided to use professional whitening. My dentist gives patients the option to use nitrous oxide during uncomfortable or painful procedures at no additional charge. Using nitrous oxide makes the process extremely comfortable and much more bearable. I don't think I would do it without it. I'm very satisfied with the results. You aren't supposed to drink any foods associated with staining 24 hours after finishing Zoom. I had this done 2 years ago, and it lasted for about a year and half. I'm sure it would have lasted longer, but I drink coffee in the morning. I'm going to do it again in a few weeks. It does work, and it is painful. I really suggest using nitrous oxide if the dentist gives you the option, even if it is an additional charge.