1 Introduction

Development of an analysis method to determine peroxides in or released from tooth-whitening/dental-bleaching products.

Peroxides in different chemical forms are present in almost all products for whitening teeth, either alone or in combination. Tooth-whitening products can contain free hydrogen peroxide or peroxides bonded to other substances (releasers), which are released during the treatment as free H₂O₂ (1). Urea peroxide, perborates and percarbonates are examples of H₂O₂ releasers present in tooth-whitening products. The peroxides exist in a dissolved state in different matrices, depending on whether the tooth-whitening products are applied as a gel or are painted or sprayed onto the teeth.

In order to regulate retail sales of tooth-whitening agents, analytical routines are required to control the content of peroxides in products. Different chemical methods for measuring peroxides exist today. These include redox titration e.g. with iodine or permanganate salts (2,3). Since all substances that can be oxidised will be titrated in a redox titration with iodine or permanganate, this method can only be used to determine H₂O₂ in tooth-whitening products, if no other oxidative substances are present in the product. Interference from such substances could possibly be avoided by measuring free H₂O₂ using spectrophotometric methods (4). The concentration of free H₂O₂can also be measured with biosensors. Biosensors containing the H₂O₂-degrading catalase enzyme have been used for the determination of H₂O₂ in antiseptics and in cosmetics, including tooth-whitening agents (5-7).

Tooth-whitening products that contain H₂O₂ releasers (e.g. urea peroxide) release H₂O₂ slowly. Therefore, the total content of bound H₂O₂ in these products can only be determined either by theoretical calculation, by measuring the H₂O₂ releaser directly, or by measuring the total H₂O₂ released. This report gives a short overview of the different peroxides which have been reported to be present in tooth-whitening agents. The products tested were either bought in a shop or over the internet. All the products contained either free hydrogen peroxide or urea peroxide. The other peroxides mentioned and tested in pure state are found in products prescribed by dentists. This report describes a new protocol for the measurement of peroxides in tooth-whitening products, whether these are added as free H₂O₂ or as one or more releasers, possibly in combination. The protocol uses a catalase bioassay, which converts the free hydrogen peroxide to oxygen and water continuously, while the changes in oxygen concentrations are used to calculate the overall amount of peroxide in the product. The accuracy and applicability of the method are compared to chemical methods to determine peroxides.