There is a complete aisle of over-the-counter whitening products out there. For the most part, they contain a much lower concentration of product, which means you will likely have to use the product for much longer than you would a custom, dentist-administered system. Other things to consider when assessing the effectiveness of over-the-counter whitening systems is how long it is in contact with your teeth. If the solution is in contact with saliva, it will quickly be washed away. If it is only in contact with your teeth while brushing, it is going to take a very long time to see any difference. A tray-based system holds the solution against the teeth, preventing the saliva from diluting it, making it much more efficient and effective. With the over-the-counter whitening strips, you are restricted with a generic length and width. If you have a broad smile, the whitening strip may not cover the ‘corners’ of your smile, making your smile look like an uneven color from the side profile. If your teeth are larger than average, you will not be able to consistently whiten the teeth, leaving your teeth with stripes of different colors. Another concern with the whitening strips, especially if teeth are crowded or overlapped, is that if the strip is not carefully contoured into the crevices between the teeth, you will end up with dark areas between the teeth. The strip may also extend onto the gum tissue, which can lead to sensitivity, tenderness, and temporary discolouration of the gum tissue. Generally over-the-counter whitening products are safe, but using them without first having a dental consultation could result in issues like sensitivity, if cavities or root exposure are present. There are things that can be done in conjunction with whitening to help reduce any sensitivity. As well, it is important to realize that existing fillings and crowns will not change colour when you whiten your natural teeth. If your fillings currently match your tooth colour and you lighten your teeth, your filling is then going to appear darker and you will be looking at the additional cost of replacing or polishing it.