For those who want to see instant results, whitening toothpaste might not be for you because these products tend to take more time to work. “If the patient brushes twice per day for two minutes each time, it will take two to six weeks to show an effect,” Dr. Morgano says. “The most common mistake people make is that they don’t brush long enough.” If you find you are not brushing for long enough, then Dr. Morgano recommends investing in an electric toothbrush. These devices often include a self-timer to inform the user when the two minutes for brushing are up.