"I can't believe how white my teeth are now. Wow!"If you want to whiten your teeth, the best place to start is with a healthy mouth. Tooth decay, sensitive or cracked teeth, infections or periodontal (gum) problems should be diagnosed and treated before any tooth whitening procedure. Otherwise, you could experience discomfort. The whitening process may aggravate existing problems, or the whitening process simply may not be right for you.