The first step in professional at-home whitening is to have your dentist take an impression of your teeth. Using this impression, your dentist will create custom bleaching trays that fit perfectly over your teeth. Next, prior to placing the trays in your mouth, the whitening gel is placed inside the trays. Because the trays are designed to fit perfectly on your teeth the gel coats your teeth but stays off of the gum tissue. Depending on the type of whitening and the recommendations of the dentist trays can be worn over night, at night or during short periods of time during the day. The length of treatment can range from 7 to 14 days but is really dependent on the desired results and the dentists recommendation. If sensitivity does occur, over the counter toothpastes can help alleviate the symptoms.