Tooth whitening is a well established procedure in cosmetic dentistry. The whitening process is effective on most discolored teeth. Darker stains, such as those caused by antibiotics may take longer to respond to treatment. The degree of whiteness will vary from patient to patient, depending on the structure of the teeth, the number of applications or the duration of time that the system is used. Some patients may need periodic re-whitening for one or two days every one to two years, especially if they continue to use staining substances like caffeine or tobacco products.