EFFECT OF OVER THE COUNTER WHITENING ON THE SHEAR BOND STRENGTH OF ORTHODONTIC BRACKETS: AN IN-VITRO STUDY
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Introduction: The purpose of this study was to determine the effect of two over-the-counter enamel bleaching products on the shear bond strength of orthodontic brackets bonded to human premolar teeth with composite resin. Objectives: To assess: 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 2) The effects of a 7 day post-bleaching latent period on the shear bond strength of orthodontic brackets 3) The amount of bleaching that occurs and its correlation to in-vitro shear bond strength of orthodontic brackets, and 4) The differences in amount of adhesive remaining on the enamel of the unbleached and bleached groups after debdonding. Methods: Two protocols were used to test 60 human premolars. Teeth were randomly divided into two groups, I and II (n=30 per group) and then further divided into 4 subgroups A, B, C, D (n=15 per group). In the over-the-counter white strip bleaching group (n= 30), Crest® 3D WHITE™ LUXE Professional Effects Whitestrips (Proctor & Gamble, Greensboro, NC) which contains 6.5% hydrogen peroxide, was applied to the teeth daily for 14 days for 30 minutes each day. Teeth in the over-the-counter whitening dentifrice group (n=30) were treated with Crest® 3D WHITE™ BRILLIANCE 2-Step Toothpaste (Proctor & Gamble, Greensboro, NC) which contains Sodium Fluoride (Step 1) and 3% hydrogen peroxide gel (Step 2) that was brushed onto the teeth daily for 14 days for 10 seconds per tooth. After bleaching, subgroups A and C were stored in artificial saliva at 37 Co for 7 days before bonding. Subgoups B and D were stored in saliva at 37o C for 24 hours before bonding. All groups were bonded by one investigator and debonded on the same day using shear forces by another investigator. The Kruskal-Wallis test for nonparametric means was used to determine whether significant differences existed between the subgroups and an unbleached control group (n= 15). Spectrophotometric color measurements were recorded pre and post-bleaching and adhesive remnant index findings were recorded after debonding. Results: The mean ± SD shear bond strength for the control group was 9.59 ± 3.32 MPa. Means for the white strip bleaching 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 dentifrice groups were 11.01 ± 4.31 MPa and 10.83 ± 3.79 MPa for the 7-day and 24-hour delayed bonding periods, respectively. The mean spectrophotometric color change (∆E) for the control group was 4.67 ± 2.55. Means for the white strip bleaching groups were ∆E = 12.43 ± 3.81 and 11.54 ± 3.28 for the 7-day and 24-hour delayed bonding periods, respectively. Means for the whitening dentifrice groups were ∆E = 4.77 ± 2.39 and 7.41 ± 3.54 for the 7-day and 24-hour delayed bonding periods, respectively. The Kruskal-Wallis test demonstrates there are no statistically significant differences among the groups (p=0.650). The Pearson Correlation Coefficient analysis indicates there are no statistically significant correlations between color change and shear bond strength among the groups (p = 0.448). The Pearson’s Chi-squared value indicates that there are no statistically significant differences among the groups in respect to adhesive remaining on enamel (p = 0.731).