Background: Bonding is the most commonly used technique to attach brackets to tooth surfaces.
Objectives: The aim of this study was to determine the effects of time and concentration of etching with phosphoric acid on shear bond strength (SBS) of orthodontic brackets after using 10-MDP containing adhesive.
Methods: Fifty intact premolars were randomly divided into 5 groups (n = 10). They were mounted in resin blocks. In control group a gel without phosphoric acid and in-group 2, 3, 4, and 5, phosphoric acid 37% for 5 or 15 seconds and phosphoric acid 15% for 5 or 15 seconds was used respectively. Clearfil SE Bond was used as an adhesive resin for all samples. After bonding of brackets, they were put under 300 thermocycling aging regime and after that the bracket/tooth SBS was measured by universal testing machine. The adhesive remnant index (ARI) was evaluated under a stereomicroscope. Data were statistically analyzed using two-way ANOVA and Kruskal-Wallis test.
Results: The highest mean SBS belonged to the 15% phosphoric acid etching in 15 seconds while the lowest value was seen in 37% phosphoric acid etching in 5 seconds. The effect of etching time on SBS was not significant (P = 0.31) but the effect of concentration in SBS has been significant (P < 0.001). In terms of ARI, in application of 15% phosphoric acid, more than 50% of the resin remained on tooth surface. In application of 37% phosphoric acid, all the resin remained on tooth surface.
Conclusions: In using of Clearfil SE bond, containing 10-MDP, preparing enamel by 15% phosphoric acid had created strong enough SBS.