LEIPZIG, Germany: New research has shown that human teeth can lose some enamel hardness following the application of teeth whitening products used in the home. According to lead author Shereen Azer, Assistant Professor of Restorative and Prosthetic Dentistry at Ohio State University in the US, the average loss of enamel ranged from 1.2 to 2 nanometres on the treated teeth.

Tooth bleaching products contain solutions of varying strengths of either hydrogen peroxide or carbamide peroxide, which produce free radicals that attack pigment molecules in the organic parts of enamel, to provide the whitening effect.

Several studies have sought to determine the effect of tooth whitening on tooth enamel hardness but results have been inconclusive, Azer said. He added that previous studies measured the loss of enamel hardness in microns, or millionths of a metre, while he used a nanometre scale in his study. In his research, he used whitening strips and trays filled with whitening gel on extracted molars, as well as an atomic force microscope to observe the tiny nanometre-scale effects on the teeth. The reduction in hardness and elastic modulus amongst the different products was largely similar. However, there was a significant difference between one strip treatment method and one tray method, with the tray method reducing enamel hardness more significantly than the strip treatment.

Although the study did not address methods of restoring hardness to bleached teeth, Azer noted that extensive research has indicated that fluoride treatments, including the use of fluoride toothpaste, can promote enamel remineralisation. He suggested that, based on the study, future generations of teeth whitening products be reformulated in an effort to reduce these side effects.