I've used Crest White Strips before (2 times actually) and I wasn't impressed at all. I saw a very
minimal difference in the whiteness of my teeth. I didn't have yellow teeth, but I'm a big coffee drinker so there was definitely improvement to be made.
After that didn't work out, I went to my dentist and asked him what I could do. He made me custom molds for my teeth (I paid $150, maybe more; I can't remember exactly), and I bought the bleaching gel from from him as well for $60. I just had to put some gel in the trays and wear them for about 30-45 minutes a day for 2 weeks. (Because of tooth sensitivity I was experiencing, my doctor later instructed my to switch that to every other day.)
It works AMAZING! The first time I bleached and took the trays out, I was literally shocked! My teeth were sooooooo white after only one use! Such a huge difference, and I didn't even think my teeth were bad before!
Anyway, I later found a website that sells the same EXACT whitening gels I was buying from my dentist for much, much cheaper. For the past 2 years, I've been ordering it from there instead. Now I just whiten every once in a while for maintenance when I need it.
My friend then decided that she wanted to whiten her teeth as well, but didn't want to pay for custom molds from her dentist, so she ordered the "Boil & Bite" kit that they offer. Basically, it's cheaper molds that you make yourself. (Put them in boiling water for about 5 seconds, put them in your mouth and bite down to mold them to your teeth. Then they're ready to be used!) She had amazing results with these.....the only thing is that she had to do was trim the molds down with a scissor so that the molds weren't covering any parts of her gums.
Wow, this turned into a reeeeaally long post.
You can get all of this stuff I'm talking about at Dental Care | Dental Health | Dentistry products at Dentist.net
You can get the Boil & Bite kit here from $30-$39 (depending on the strength of the peroxide purchased):BOIL and BITE BLEACHING TRAYS | Whitening Trays for use with Bleaching Gel by Dentist.net
They also have the custom molds available, just like the ones I got in my dentists office for $79:PROFESSIONAL WHITENING TRAYS | Bleaching Kits | Nite White, Day White, Opalescence, Zoom, Generic
Hope that helps!
You will really be amazed at how well this works!