A Study on Vital Tooth Bleaching : Enamel Surface Morphology, Acid Resistance and Effect of Fluoride Application

Abstract

Recently, requests to improve mild discoloration of teeth have been increasing, and bleaching treatment, which is less invasive while still achieving an esthetic improvement, has thus become increasingly popular. Current bleaching methods for vital teeth are classified broadly into two categories-namely, in-office bleaching in which dentists perform bleaching treatment at dental offices, and at-home bleaching in which patients perform such treatment at home. However, the effects of such bleaching treatments on healthy enamel have not yet been fully evaluated. Therefore, in order to elucidate the effects of vital tooth bleaching on the surface of the enamel, we observed the microstructure changes of the tooth surface by means of confocal laser scanning microscopy before and after bleaching using an in-office and an at-home bleaching agent (Hi Lite® and Nite White Excel®, respectively) in freshly extracted human teeth (young group from 20- to 30-year-old and elderly group from 60-year-old or older patients). Shade changes in the teeth were also scored. In addition, application of fluoride (Fluorident Gel; 9,000 ppmF) was also performed to improve the acid resistance of the enamel on the bleached surface, and calcium ion release from the tooth surface was measured. The following results were obtained: 1. The application of both Hi Lite and Nite White Excel to the tooth surface caused demineralization and an increase of surface roughness of the enamel. In addition, the surface roughness was improved by polishing the tooth surface. 2. The values of demineralization and surface roughness were higher in the young group than in the elderly group. 3. As for color change, both bleaching agents were effective, but in comparison to the elderly group, the shade score appeared to be more improved in the young group. 4. The topical application of fluoride to the bleached and polished tooth surface significantly decreased the calcium ion release from the enamel. No major microstructure changes of the enamel surface were found and no effects on tooth color were recognized. These findings indicated that not only polishing the tooth surface but also the application of fluoride, in an attempt to improve the acid resistance of the tooth structure, were together considered to be effective follow-up modalities after bleaching.