A few thoughts on this product and teeth-whitening in general:* Peroxide gels like this and the in-office dental equivalent are, far and way, the preferred method of teeth whitening. In my experience, whitening toothpaste is for maintenance only, whitening strips are worthless, and no drugstore kit gives results worth mentioning. The latter two simply don't merit your time.* You'll want custom-molded trays to use peroxide this strong. They'll cost $300 to have done on-site with a dentist or around $50 as a send-away kit with molding material. Cheap heat-and-wear mouthpieces won't fit properly nor provide gum shielding, and are therefore not good enough. Custom trays will last for years. They're absolutely worth the expense and I wouldn't buy this product, or any serious gel, without them.* There's enough gel in this kit to last at least ten whitening sessions. If kept in a refrigerator, the gel will expire in about two years. Bleaching sessions can be for any duration from 30 minutes to multiple hours. The gel neutralizes itself over time, so most of the bleaching effect occurs in the first hour or two. Wearing overnight is not advisable; I wouldn't go higher than 15% solution for that.* This is a powerful, but not overpowering gel. With my custom trays, I had no trouble with two back-to-back bleaching sessions, each for 90 minutes. The only irritation was where a small amount of gel had touched my gums. My teeth are not ordinarily prone to cold or heat sensitivity. I noticed mild cold sensitivity that lasted an hour or two after bleaching. The remineralization gel in this kit was not necessary, but I have used it in the past and it's worth having if you've never bleached before and haven't discovered your tolerance.* My results were very good from this single session starting from an average shade for a non-smoker, though not Hollywood white. That would probably take two more sessions. Changes become less dramatic with additional sessions. If you take no special care to avoid dark beverages (soda, wine, coffee), the results will last about six months. If you do avoid those beverages, particularly in the first few days after bleaching, your teeth may maintain the new shade for a year or more.* The shade chart in this product won't be useful if your teeth are already fairly white. The gradients on the brighter side of the scale are too far apart, so even a visible shift may not register a new tone. The brightest tone won't be bright enough for some.All considered, a product I would buy again.