Effect of over-the-counter whitening strips and toothpaste on shear bond strength of orthodontic brackets

BACKGROUND: To investigate: 1) the effects of over-the-counter white strip enamel bleaching and 2-Step whitening toothpaste application on the shear bond strength of orthodontic brackets at 24-hours and 7-days post-bleaching latent period; and 2) the correlation between amount of bleaching and shear bond strength. MATERIAL AND METHODS: Sixty human premolar teeth were randomly assigned into two bleaching groups, white strip group treated with Crest® 3D WHITE™ LUXE Professional Effects Whitestrips (Proctor & Gamble, Greensboro, NC), and whitening toothpaste group, treated with Crest® 3D WHITE™ BRILLIANCE 2-Step Toothpaste (Proctor & Gamble, Greensboro, NC). The groups were further divided into 4 subgroups A, B, C, D (n=15 per group). Subgroups A and C were bonded 7 days after bleaching while subgoups B and D were bonded 24 hours after bleaching. Differences in shear bond strength between the subgroups and an unbleached control group (n=15) were compared using the Kruskal-Wallis test. Spectrophotometric color changes were recorded pre- and post-bleaching. RESULTS: The mean shear bond strength for the white strip groups were 10.35±3.6 MPa and 11.69±4.33 MPa for the 7-day and 24-hour delayed bonding periods, respectively. Means for the whitening toothpaste groups were 11.01±4.31 MPa and 10.83±3.79 MPa for the 7-day and 24-hour delayed bonding periods. The mean for the control group was 9.59±3.32 MPa. There were no significant differences in shear bond strength between the groups at 7-days and 24-hour (P=0.650). There was a significant difference between teeth bleached with white strips as compared to those bleached with toothpaste and controls. The correlations between color change and shear bond strength were not significant (P=0.448). CONCLUSIONS: There is a significant difference in the amount of whitening achieved by over-the-counter white strips compared to toothpaste; however, no significant effects on shear bond strength occurred after bleaching with white strips and toothpaste at 24-hours and 7-days. Key words:Bleaching, shear bond strength, orthodontics, over-the-counter.