Whitening gel is placed around the inside, front of the bleaching tray There is no immediate need for the whitening gel to come in contact with the back side of your teeth since they are not visible to others (You may lightly bleach the rear side after completing the front side if rear stains are able to be seen through your teeth). Place the bleaching tray over your teeth.  You will notice that the whitening gel squeezes so that full coverage of all teeth is attained. There may be some additional gel that overflows out of the bleaching tray into you mouth. Simply discard this overflow gel by spitting it out.  You should wear the bleaching tray for 1 to 3 hours per whitening session. You may even chose to wear your bleaching trays overnight while you sleep. You may decrease your weartime or frequency of use if you experience sensitivities, although you whitening gel will stay active for up to 4 hours. Some people report watering of the mouth when whitening their teeth.  This is a normal reaction and tends to diminish as time goes on.  You will need to wear your mouthpieces for a total of 20 - 40 cumulative hours to complete the process. These cumulative hours of weartime can be completed in consecutive days or you may skip days if you like. It will not matter so long as you complete your 20 - 40 cumulative hours. After completion of each whitening session, wash your bleaching trays with water and store in a dry place.  Be sure to keep your whitening gel refrigerated when not in use.  There are several things you can do to make you dental whitening activities more effective and pleasurable. Take the time to read the below tips to make your dental whitening experience as easy and effective as possible.