The purpose of this study was to compare the tensile bond strengths of orthodontic brackets bonded to enamel using conventional multi-step adhesive, self-etching primer (SEP), which combines etching and priming into a single step, and self-adhesive systems, which combine etchant, primer, and adhesive. Metal brackets were bonded to 90 extracted human premolars according to three experimental protocols: group 1, conventional multi-step adhesive system; group 2, SEP; and group 3, self-adhesive system. All specimens were debonded using an Instron universal machine and failures between the tooth surface and bracket base were observed by scanning electron microscopy (SEM). The bracket bases were then analysed by mapping of energy-dispersive X-ray (EDX) spectrometry to calculate the distributive percentages of enamel or resin. The bond strength, percentage distribution, and calcium on the debonded interface were determined and analysed by one-way analysis of variance, and means were ranked by a Tukey interval, calculated at the 95 per cent confidence level. Group 1 produced the greatest bond strength, followed by groups 2 and 3. Group 3 showed the highest debonded interface between resin and enamel or within the resin itself, followed by groups 2 and 1. Groups 1 and 2 displayed significantly more debond failures at the interface between the bracket and the resin than group 3. More calcium particles were observed on the bracket base after debonding in group 3 than in groups 2 and 1. The simplified bonding procedures caused an undesirable decrease in tensile bond strength.
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