The trays are an exact mould of your teeth, this will ensure that the gel is kept in constant and even contact with all the crevices and contours of your teeth for a uniform whitening result. If you don’t use custom trays, the peroxide will leak onto your gums, this can result in burnt gums or irreversible recession of your gums. (Recession of gums is where the expression ‘long in the tooth’ comes from.) Peroxide is a weak acid, and even though we are using it in safe concentrations ideally, we do not want it sitting on your gums for a prolonged period of time. Our Custom trays protect your gums by holding the peroxide next to your teeth and away from your gums. The custom trays also prevent inhalation or swallowing of the gel during both night and daytime applications.