To minimize or remedy this problem a dentist will usually trim a person's bleaching trays in a scalloped fashion so they cover a maximum of each tooth being bleached, but rest just short of touching the gums. As a general rule, so to help reduce gum irritation, when bleaching trays are initially inserted a person should wipe away the excess whitening gel which escapes from the tray onto their gums with their finger or a toothbrush. These products contain carbamide peroxide as their active ingredient and as non-active ingredients compounds such as glycerin and flavorings. Adverse effects associated with the at home teeth bleaching process may develop when it is used inappropriately. Concerns have been postulated that teeth whiteners can possibly cause cancer in the soft tissues of the mouth.
Free radicals are capable of causing cellular damage.
One of the human body's major defenses against the adverse affects of peroxides is a compound found in saliva. This compound has been calculated to effectively neutralize about 30mg of peroxide in one minute. The typical single application of carbamide peroxide tooth whitener is only 3.52 mg. Scanning electron microscope studies of the enamel of teeth which have been bleached have typically not shown any damage either. In relative terms, studies have shown that exposure to soft drinks and fruit juices cause comparable or greater alteration of tooth enamel than tooth whiteners.