The teeth whitening industry is one that continues
If you are new to teeth whitening, you may automatically assume that the trays that are included with these products are made to fit everyone's teeth. However that is not the case. You generally have to mould them yourself to fit your own teeth because everyone's teeth are different shapes and sizes, and they are not always perfectly straight. This can be easily done because you just have to expose them to hot water, at which point they will become more pliable and can be fitted to your teeth to create your trays for the upper and lower teeth. It is very important that you take your time doing this because the results of your teeth whitening could be impaired if the trays are not fitted properly. You need to make sure that they are quite a tight fit and are not too loose. The dangers of using trays that are too loose or ill-fitting are fairly obvious, and it will soon become apparent if this is the case because the whitening gel that you place inside the trays will start leaking into your mouth. This can lead to irritation and possible bleeding around the gums, and you may even end up swallowing some of the gel. Of course you may find that you have done everything correctly, and still get some leakage. In which case it's probably down to a poor quality product. Although most home whitening treatments provide you with custom trays, they are not all made the same and they can differ in quality. So you may well find that you have found a product that offers whitening gel that actively whitens your teeth, but the trays don't enable you to do so effectively. In which case your best bet is to get some trays professionally fitted by your dentist. I personally used the plastic retainers that I received from my orthodontist after I got my teeth straightened with braces many years ago, and they seemed to do the job really well. They were a tight fit and there was never any leakage (other than the first occasion when I happened to put too much gel into each of the trays). Anyway the point is that if you go to the trouble of buying a home whitening kit, ready to whiten your teeth for a few weeks, you have to mould the trays so that they fit your teeth perfectly. If you don't then you could damage your gums because some of the gel will leak into your mouth, and you may find that some teeth are not whitened as much as others. So this is something to bear in mind whenever you use tray based teeth whitening kits.