We whiten teeth every day for patients. It’s a really popular treatment and we routinely carry out this treatment for our patients when we are happy that it is going to work. A top up kit once a year is usually all that is required to stay white and fresh. The cost for these (typically around €70) is much lower that the price for the initial whitening so its a nice affordable option to stay white for life.
If we don’t think it will work for you we won’t get your hopes up by promising something that we don’t believe will actually happen and there are other options for this case anyway. As with most things we’ll find a way to get you there.