You can use the whitening strips twice a year, but then just use a
whitening toothpaste in between this time. Your
teeth can only get
to a certain degree of white...our natural color. Some people have whiter teeth than others, so no amount of whitening strips or whitening toothpastes will make them any whiter than their natural color. Don't destroy what you have with these whitening strips, use a soft brush and never brush too hard...that also is hard on our enamel.