In vitro evaluation of toothbrushing abrasion of differently bleached bovine enamel

Purpose: To evaluate in vitro, the effect of different external bleaching agents on the susceptibility of enamel against toothbrushing abrasion. Methods: 96 bovine enamel specimens were embedded in acrylic resin, polished and covered with tape except for a 1.4 x 10 mm window. The samples were divided into eight groups (A-H), 12 specimens each (A-G) were treated with seven different home-bleaching (A: Whitestrips, B: Rapid White, C: Opalescence 10%, D: Opalescence PF 15%) and in-office-bleaching agents (E: Opalescence Extra, F: Opalescence Quick, G: Opalescence Extra Boost) according to manufacturers' instructions. Before and after each individual bleaching treatment the samples were brushed 40 times in an automatic brushing machine using a slurry containing artificial saliva and fluoridated toothpaste. The control group (Group H) was not bleached, but also brushed. After each cycle the specimens were stored in artificial saliva for 24 hours. Results: After 20 cycles loss of enamel was determined by profilometry, resulting in the following values (mean standard deviation) which were statistically analyzed: Group A: (0.169 mum +/- 0.035), Group B (11.108 mum +/- 0.655), Group C (0.207 mum +/- 0.042), Group D (0.154 mum +/- 0.028), Group E (0.081 mum +/- 0.015), Group F (0.084 mum +/- 0.018), Group G (0.087 mum +/- 0.014), Group H (0.076 mum +/- 0.012). Group B differed significantly from the other groups (r= 0.001). Samples of Groups C, D and A showed a significant difference compared to the control H (r= 0.001). Statistical analysis revealed no significant difference between enamel loss of Groups E, F, G and the Control H. It could be proven that toothbrushing abrasion of bleached enamel may be increased depending on the bleaching agent and application form used. Nevertheless, with the exception of bleaching treatment with Rapid White, toothbrushing abrasion of bleached enamel seems to be clinically less relevant.