I just got this, so I'll try to remember to update this review after I've had it a while. I didn't have any problems fitting it. I heated it slightly less time than the instructions say, since I didn't want it to squish up too much around my teeth. I've read a lot of the negative reviews on here, and I think people need to remember that there is a lot of variation in mouths and teeth, so it's totally possible for something to work for some people but not others. (The negative reviews that question the integrity of the positive reviewers are, IMO, uncalled for.) I wanted to address some of the other criticisms I see in the negative reviews, from my personal perspective: 1. People complaining that it doesn't properly cover the front teeth. -- No, it doesn't. This clearly an intentional part of the design, not a flaw. (Whether that design element works for you or not is personal variation, but it isn't a 'this isn't working as it should' situation.) 2. It's too big/too small. -- Again, people vary wildly, and this is a one-size-fits-all product. Of course it's not going to fit everyone. I would say I'm fairly average-sized, which might be why I didn't seem to have an issue. 3. The instructions are confusing. -- Are they? I found them to be extremely straightforward and clear. 4. It falls out. -- I think this is another thing that comes down to your own personal mouth/teeth shape. I haven't had any problems with it falling out. (So far. I've only used it once as of this writing.) 5. My lips can't close easily over it. -- Are they supposed to? It doesn't strike me as something we should reasonably expect from something like a mouth guard to be able to fully close our mouths over it, but the only other one I've used was from the dentist. One other thing I want to point out is that I used these on my lower teeth instead of the upper. I get headaches/migraines from the clenching, and when I had an upper guard from my dentist, the pressure from my guard squeezing my teeth kind of contributed to the pressure feeling in my head. My theory is that if it's on my lower teeth, that won't be as much of a problem. I'll see how it goes. This might also help with the 'falling out' problem that some people have mentioned, but I think that might also be more of an 'individual mouth shape' thing. I actually quite liked that it really clung only to the side teeth and not the front ones, so there was less squeezing pressure. ETA May 2022: These are still working pretty well, but I've discovered that they need to be replaced every couple months or so. Also need to make sure that when you're molding them, you do things exactly as instructed so you can get a good mold. (One time, I waited just a few seconds too long before putting it in my mouth, and I wasn't able to bite down hard enough to get a firm mold, so that one was always too thick for what I needed.) If you're looking at cost-effectiveness of these vs. a permanent one, I'd say plan on needing to buy a new one every 2 months.
