Works great when done right. These trays are made from a very soft, pliable material. When immersed in water that is boiling or boiling almost instantly, the shell shrinks almost instantly, rendering it unusable. I followed the directions of several previous reviewers, which basically said: Fill a measuring glass with water and microwave for about two or three minutes, depending on your microwave's power - *remember- hot, not boiling, water. * Soak a bath in hot water for about six seconds (don't overdo it), then put it in your mouth and wrap it around your teeth, so to speak, sucking air between the bath and your teeth. If the tray doesn't get as firm as you'd like, dip it in the hot water for a few more seconds and repeat the process. This works for the top and bottom trays. To be honest, my first attempt at installing the trays wasn't great - and not terrible - but not great either, so I had to try again. The second set was perfect. When I helped my husband with his set, everything was perfect the first time. I was very happy that I had five pairs of trays - extra for practice. I've used them with Watts Power Deep Stain 36% Whitening Gel and then VitaBrites Remineralizing Gel and I'm absolutely thrilled with the results - for me and my husband. The price is great for beautiful, white, healthy teeth!
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