Teeth whitening helps to restore a smile tainted by discoloration. In-office teeth whitening produces the fastest results and is the safest form of teeth whitening. How it works: Significant color change in a short period of time is the major benefit of in-office whitening. This protocol involves the carefully controlled use of a relatively high-concentration peroxide gel, applied to the teeth by the dentist or trained technician after the gums have been protected with a paint-on rubber dam. Generally, the peroxide remains on the teeth for up to an hour at most. Those with particularly stubborn staining may be advised to return for one or more additional bleaching sessions, or may be asked to continue with a home-use system.