Prior to using any whitening system (including whitening strips), you need to be checked by a dental professional for any issues needed to be addressed with the teeth. If whitening gel gets inside the tooth and the patient doesn’t know, then there it can lead to sensitivity. When you whiten in-office, there are various desensitizing liquids that we paint on the tooth structure, so there is minimal post-op sensitivity. If done incorrectly, there can be a lot of post-op sensitivity, but most of the time its transient (it goes away over the first 12 hours). However, if you have cracks or little fissures in your teeth, you can create problems along the way and later on. Whitening centers won’t tell you that. Their mission is to whiten the teeth and make a profit.