The aims of this in vitro study were to evaluate the effect of enamel fluorosis on the shear bond strength (SBS) of orthodontic brackets and to determine whether adhesion promoter, Enhance LC, increases the bond strength of brackets to fluorosed enamel.Forty-five (30 fluorosed and 15 non-fluorosed) non-carious fresh human premolar teeth, extracted for orthodontic reasons and without any caries or visible defects, were used in this study. The fluorosed teeth were selected according to the modified Thylstrup and Fejerskov index, which is based on the clinical changes in fluorosed teeth. In groups 1 (fluorosed teeth) and 3 (control), the brackets were bonded with Light Bond composite resin and cured with a halogen light. In group 2, Enhance LC was applied to fluorosed enamel before bonding. After bonding, the SBS of the brackets was tested with a universal testing machine. One-way analysis of variance and Tukey multiple comparison tests were used to compare the SBS of the groups. Any adhesive remaining after debonding was assessed and scored according to the modified adhesive remnant index.The results showed that while fluorosis significantly reduced the bond strengths of the orthodontic brackets (mean 13.94 ± 3.24 MPa; P < 0.01), Enhance LC significantly increased bond strength on fluorosed enamel (mean 18.22 ± 5.97 Mpa; P < 0.05). Groups 1 and 3 had greater bond failures at the composite-bracket interface, whereas group 2 showed bond failure primarily at the enamel-composite interface.
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