It is best to brush your teeth lightly before any whitening treatment and leave about 30 to 60 minutes before each whitening procedure. It is best to use desensitizing toothpaste that contains about 5% potassium nitrate and fluoride to treat tooth sensitivity and also strengthen tooth enamel. Rinsing and flossing before a whitening procedure. However it is best to avoid rinsing with acidic liquids that could lead to weakening of tooth enamel. In addition flossing lightly helps remove built up bacteria, but make sure you do it at least 30 minutes before you start the whitening procedure.