The mode of action of the most effective over-the-counter teeth whiteners is founded on the science of peroxide chemistry. While peroxide compounds have been utilized in dentistry for many decades as teeth whiteners, to date dental research has yet to provide a definitive explanation about their mode of action. This is at least in part due to the fact that dental science has yet to definitively describe the mechanism that imparts a tooth with its color.
A detailed study into the makeup of a tooth's structure will reveal that its enamel covering is a highly mineralized tissue. In fact, a tooth's enamel is over 95% mineral in content. Under even closer inspection, one undertaken at a microscopic level, one would find that interspersed between the mineral content of the enamel is a framework (a matrix) that is composed of organic matter. It is assumed that the cause of a tooth's staining (either inherent or acquired) is related to the presence of various organic compounds in this matrix.
Researchers have found that within just a matter of minutes after application of a whitener peroxide has the ability to penetrate into the inner aspect of teeth. The general assumption is that the peroxide (by way of releasing free radicals) oxidizes the stain producing organic compounds that reside in the enamel's matrix. When these compounds have been oxidized (cleaved into smaller derivative compounds) the residual molecules are colorless (at least to the extent that these molecules do not produce the same staining effect on the tooth that their parent compound did). The net result of this oxidation process is a tooth whitening effect.
As a possible confirmation of this theory, there is a phenomenon that takes place with teeth whitening where a tooth will lighten to a certain degree and then no further. This would suggested that peroxide whitener had reached a point where it had oxidized essentially all of the stain producing organic compounds residing in the enamel matrix and therefore can offer no more whitening effect.
Some of you reading may know that tooth dentin is somewhat similar in nature to dental enamel in the sense that it has a high mineral content (although less so than enamel) and also has an organic matrix. Peroxide teeth whiteners are not known for producing a lightening effect on dentin. We do not have an explanation to provide you with regarding this apparent paradox.