Bleaching gels are generally two types depending on the bleaching agent they contain - hydrogen peroxide or carbamide peroxide. Both chemicals are most commonly used in a 35% solution. Various combinations and concentrations of the above materials are commercially available in view of customers’ preferences.
Power bleaching gels containing 35% hydrogen peroxide have certain benefits before other bleaching solutions as manufacturers claim their use for in-office bleaching decreases the incidence of tooth sensitivity by reducing the tooth desiccation which is so commonly observed with the liquid and liquid/powder products. The gel contains 10-20% water which takes care of the tooth rehydration during the process of bleaching. However, the presence of water in the gel reduces its shelf-life and some of these products require mandatory refrigeration. Because the consistency of the gel allows it to stay in a close contact with the tooth, the possibility of soft tissue contact is minimized as they remain in the area where they are placed. There is scientific evidence that the viscous nature of the gels may help the better penetration of the oxidizing ions through the tooth enamel thus acting as a blanket to prevent the escape of oxidizing ions. Practically, this means that the gel allows to be evenly spread over the tooth and there will be no parts of it that will escape the bleaching procedure.
It is recommended that the bleaching gels be mixed just before the procedure starts. As the shelf-life of hydrogen peroxide is relatively short (approximately six months), it is important to check the shelf-life of the liquid prior to mixing it with the powder to form a gel. This can affect the bleaching effect of the gel. That is why a fresh solution should be mixed for every patient.