This is a very common concern. Some of the in-office systems if they use a light or laser can increase this tooth sensitivity. There is an in-office system called AcquaBrite that utilizes custom fitted trays and a special bleach that has a desensitizer mixed. This greatly reduces sensitivity both during and after the bleaching process.
The in office bleaching sessions are combined with at home bleaching in between office visits, using a bleach that is a lower concentration to decrease sensitivity. For severe sensitivity, limit your exposure time to at home bleaching. Instead of bleaching over night (usually the best way to get beautiful results), possibly try bleaching for an hour or so a day.
Be very careful purchasing over the counter systems just because they are cheaper. They can actually increase sensitivity since they are not custom fitted for each individual.
