Design Principles for Oxidative Tooth Whitening: Factors Affecting Soft Tissue Tolerability
As mentioned, hydrogen peroxide (along with carbamide peroxide which produces hydrogen peroxide) is the most used oxidative tooth whitener. One of the reasons for this is the excellent patient tolerability for the use of this ingredient. After all, oxidation from any source can affect human tissues in numerous negative ways.32-35 We are all familiar with the use of nutritional supplements “antioxidants” to help fight damage caused by oxidative processes in respiration.36-37 So we come to the question: why is hydrogen peroxide safe for the soft tissues? The surprising answer is that hydrogen peroxide is created naturally by the human body’s own immune systems as part of our protection against pathogens.
In the human body, immune system cells such as macrophages create hydrogen peroxide to help kill pathogens such as bacteria and viruses. If the body produces too much peroxide, Mother Nature has found a fascinating manner to deal with this – enzymes, for example catalase.38
Catalase converts unused hydrogen peroxide into water and oxygen. The production of and elimination of hydrogen peroxide in our bodies is a normal function of our immune system. In fact, protection against too much peroxide reactivity is a priority for our health. We can see catalase in action when we use peroxides in wound cleaning; it is the catalase in our blood plasma which causes oxygen generation and foaming when it is applied at the sites of cuts and scrapes. Likewise, it is catalase that can protect the soft tissues from damage when we are using tooth whiteners containing hydrogen peroxide. However, even though catalase is ubiquitously expressed in our body, the local quantities are naturally finite, particularly on our soft tissues.
Design principles for the management of peroxide tolerability to soft tissues include formulation features including pH and control of quantity of hydrogen peroxide on the tissues of the gingival during bleaching procedures, which is a function of applied concentration and dose to tissues. For conventional whitening gels, delivery of ~2.0 mg/cm,2 enables concentrations as high as 15% to be used provided that the applied layer is thin and consistent.