Effects of external bleaching on indentation and abrasion characteristics of human enamel in vitro.

The application of home-bleaching procedures as a means of lightening multiple teeth has become increasingly popular. Very few studies, however, have determined the effect of this treatment upon dental hard tissues. This in vitro study evaluated the effects of a 10% carbamide peroxide gel on the apparent fracture toughness, hardness, and abrasion characteristics of human enamel. The apparent fracture toughness of enamel was reduced by about 30% after bleaching for a period of 12 hours with no significant change in surface hardness. Enamel treated with the bleaching gels also exhibited a small but significant decrease in abrasion resistance. This behavior was most likely due to an alteration of the organic matrix of enamel under the chemical action of hydrogen peroxide. Further investigation of the clinical significance of this process is needed.