Typically, two visits to the dental office are required for professional whitening. Impressions (molds) of your teeth will be taken at the first visit to make custom, transparent plastic trays. You will try on the trays at your second visit to ensure a good fit. Based on your personal situation and goals, instructions will be given to you in order to achieve the best long term and pain free results for your teeth. When you bleach your teeth, tooth sensitivity sometimes occurs; however, it usually resolves after you cease bleaching.