The procedure involves taking an impression at your first appointment and custom-made trays are made.  The trays fit into your mouth like a very thin gum shield.  On your second visit to the dentist, the trays are fitted and you will be given the whitening gel and instructions on how to apply the product.  You will be advised to wear your trays, usually through the night for a period of about one to two weeks.  It is also strongly recommended that you have a hygiene appointment before starting the bleaching.  The whitening process differs from person to person, but usually a noticeable difference can be seen after about 14 days.  Your progress is assessed by comparing the original shade of your teeth to a shade guide scale.  Typically we would expect an improvement of between eight to ten shades lighter after a course of treatment.