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Abstract
The bonding of orthodontic brackets was concerned an important subject in orthodontics practice. In past study by using a scanning electron microscope we concluded that the result of enamel treatment with 37% phosphoric acid concentration was damaging and resulted in destruction of enamel prisms for both studied times 60 sec. and 30 sec. While 25% phosphoric acid concentration showed better results than 37%, it removed only the center of prisms. We did not find any substantial difference for various etching times. The purpose of this study was to evaluate the effect of different phosphoric acid (H 3 PO 4 ) concentrations and etching duration on the bond strength of orthodontic brackets on enamel surface. To achieve this aim, 48 extracted premolars were used. Two phosphoric acid concentrations were applied (37% and 25%) with two different times (30 sec and 60 sec). The bond strengths were measured by Testometric M350-machine. Analysis of the results revealed: Reversal relationship between the strength shear and the concentration of phosphoric acid (p 0.05). The shear bond strength with 37% phosphoric acid concentration was significantly decreased (p < 0.05) and decreased more when we delayed the application time (p < 0.05). The results of this study suggested that a 25% phosphoric acid concentration with 60 sec etching duration marked the higher bond strength.
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