Effect of different force application during placement of orthodontic brackets on shear bond strength in three adhesive systems

Abstract

Bond strength of brackets is affected by many factors. Different force magnitudes on brackets during bonding could result in different adhesive thicknesses and may have an influence on the bond strength. Aim: The purpose of this study was to evaluate the effect of different force magnitudes during placement of brackets on shear bond strength. Methods and materials: a total of 420 brackets were placed on the bovine teeth, using three types of adhesives, Concise, Unite, and Transbond XT, with the application of seven force magnitudes of 50, 100, 200, 300, 400, 600 and 1000 g in twenty-one groups of twenty samples each. Shear bond strength means (using two-way ANOVA with Tukey post-hoc test) and adhesive remnant index were compared between these twenty-one groups. Results: Shear bond strength increased with an increase in force. No increase in Transbond XT shear bond happened after 400 g. In addition, Transbond XT had the lowest bond strength among three adhesives. Adhesive remnant index result also indicated a shift in the failure mode from bracket-adhesive interface to adhesive-enamel interface, as the bonding force got heavier. Conclusion: The force applied on bracket during bonding influences the shear bond strength. In order to have a higher bond strength, application of heavy force would be advisable. It is also recommended that constant forces be applied for bracket bonding in future studies.